THE SAUDI BUILDING CODE for STEEL
STRUCTURES
SBC 306 - CR
Code Requirements
2018
The Saudi Building Code for
STEEL STRUCTURES
(SBC 306-CR)
Key List of the Saudi Codes: Designations and brief titles
Code Req.1
Code & Com.2
Arabic Prov. 3
The General Building Code
SBC 201-CR
SBC 201-CC
SBC 201-AR
Structural – Loading and Forces
SBC 301-CR
SBC 301-CC
SBC 301-AR
Structural – Construction
SBC 302- CR
Structural – Soil and Foundations
SBC 303- CR
SBC 303-CC
SBC 303-AR
Structural – Concrete Structures
SBC 304- CR
SBC 304-CC
SBC 304-AR
Structural – Masonry Structures
SBC 305- CR
SBC 305-CC
SBC 305-AR
Structural – Steel Structures
SBC 306-CR
SBC 306-CC
SBC 306-AR
Electrical Code
SBC 401- CR
Mechanical Code
SBC 501-CR
SBC 501-CC
SBC 501-AR
Energy Conservation- Nonresidential
SBC 601- CR
SBC 601- CC
SBC 601- AR
Energy Conservation-Residential
SBC 602- CR
SBC 602- CC
SBC 602- AR
Plumbing Code
SBC 701- CR
SBC 701-CC
SBC 701-AR
Private sewage Code
SBC 702- CR
Fire Code
SBC 801- CR
SBC 801-CC
SBC 801-AR
Existing Buildings Code
SBC 901- CR
SBC 901-CC
SBC 901-AR
Green Construction Code
SBC 1001- CR
SBC 1001-CC
SBC 1001-AR
Residential Building Code-V1
Arch. Planning and Structural Reqs.
SBC 1101- CR
SBC 1101-CC
SBC 1101-AR
Residential Building Code-V2
MEP, Gas and Energy Requirements
SBC 1102- CR
SBC 1102-CC
SBC 1102-AR
Title
1.
2.
CR: Code Requirements without Commentary
CC: Code Requirements with Commentary
3.
AR: Arabic Code Provisions
SBC 306-CR-18
SBC 302-AR
SBC 401-AR
SBC 702-AR
i
The Saudi Building Code for
STEEL STRUCTURES
(SBC 306-CR)
COPYRIGHT © 2018
by
The Saudi Building Code National Committee (SBCNC).
(Edition 200923)
ALL RIGHTS RESERVED. All intellectual property rights of this Saudi Code are owned by the National
Committee of Saudi Building Code as per the Saudi laws of the intellectual property. No part of this code may
be reproduced, distributed or leased in any form or by any means, including but not limited to publishing on
cloud sites, computer networks or any electronic means of communication, without prior written permission
from the National Committee of the Saudi Building Code. The purchase of an electronic or a paper copy does
not exempt the individual or entity from complying with the above limitations.
SBC 306-CR-18
i
THE TECHNICAL COMMITTEE
(SBC 306-CR)
The Saudi Building Code for
STEEL STRUCTURES
1 Dr. Saleh Ibrahim Aldeghaither
Chairman
2
3
4
5
Member
Member
Member
Member
Dr. Shehab Eldin M. Mourad
Dr. Mohamed Nour Eldin Fayed
Dr. Abdelrahim Badawy Abdelrahim
Dr. Sherif Mohamed Ibrahim
REVIEW COMMITTEE
THE SAUDI BUILDING CODE NATIONAL
COMMITTEE (SBCNC)
1 H. E. Dr. Saad O. AlKasabi
2 Dr. Naif M. Alabbadi
3 Dr. Abdulrahman G. Al-Enizi
4 Engr. Saeed K. Kadasah
5 Dr. Hassan S. Alhazmi
6 Engr. Badr S. AL-maayoof
7 Engr. Fayez A. Alghamdi
8 Engr. Mohammed A. Alwaily
9 Dr. Bandar S. Alkahlan
10 Engr. Ahmad N. Hassan
11 Engr. Abdulnasser S. Alabdullatif
12 Dr. Hani M. Zahran
13 Engr. Khalifa S. Alyahyai
14 Dr. Khaled M. Aljammaz
15 Dr. Ibrahim O. Habiballah
16 Dr. Saeed A. Asiri
17 Dr. Abdallah M. Al-Shehri
18 Engr. Saad S. Shuail
Chairman
Vice Chairman
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
1
2
3
4
5
Dr. Naif M. Alabbadi
Dr. Khaled M. Aljammaz
Dr. Abdulrahman G. Al-enizi
Eng. Saeed K. Kadasah
Eng. Tawifik I. Aljrayed
Chairman
Member
Member
Member
Member
REVIEWERS
Prof. Mostafa Morsi Elshami
RCJY team
EDITORIAL COMMITTEE
1 Prof. Ahmed B. Shuraim
2 Dr. Abdallah M. Al-Shehri
3 Eng. Tawifik I. Aljrayed
Chairman
Member
Member
EDITORIAL SUPPORT
THE ADVISORY COMMITTEE
1 Dr. Khaled M. Aljammaz
2 Eng. Khalifa S. Alyahyai
3 Dr. Hani M. Zahran
4 Prof. Ali A. Shash
5 Prof. Ahmed B. Shuraim
6 Dr. Khalid M. Wazira
7 Dr. Abdulhameed A. Al Ohaly
8 Dr. Hamza A. Ghulman
9 Engr. Hakam A. Al-Aqily
10 Prof. Saleh F. Magram
11 Engr. Nasser M. Al-Dossari
12 Dr. Waleed H. Khushefati
13 Dr. Waleed M. Abanomi
14 Dr. Fahad S. Al-Lahaim
Chairman
Vice Chairman
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
Member
SBC 306-CR-18
ii
PREFACE
PREFACE
The Saudi Building Code for Steel Structures (SBC 306) provides minimum requirements for the
structural design and construction of structural steel system or systems with structural steel acting
compositely with reinforced concrete. The first edition of SBC 306 was published in the year of 2007.
SBC 306-18 is the second edition of SBC 306. The current edition of the Code has been substantially
reorganized and reformatted relative to its 2007 version. The code is reorganized into 16 chapters and
six appendices. The reorganization was in response to past requests concerning the difficulty in finding
provisions. The new layout is more user-friendly and will better facilitate the use of the design
provisions.
ANSI/AISC 360-10 is the base code in the development of this Code. Saudi Building Code National
Committee (SBCNC) has made an agreement with the American Institute of Steel Construction (AISC)
to use their materials and modify them as per the local construction needs and regulatory requirements
of Saudi Arabia. AISC is not responsible for any modifications or changes the SBCNC has made to
accommodate local conditions.
The writing process of SBC 306-18 followed the methodology approved by the Saudi Building Code
National Committee. Many changes and modifications were made in its base code (ANSI/AISC 36010) to meet the local weather, materials, construction and regulatory requirements.
The committees responsible for SBC 306 Code and Commentary have taken all precautions to avoid
ambiguities, omissions, and errors in the document. Despite these efforts, the users of SBC 306 may
find information or requirements that may be subject to more than one interpretation or may be
incomplete. The SBCNC alone possesses the authority and responsibility for updating, modifying and
interpreting the Code.
It is a common assumption that engineering knowledge is a prerequisite in understanding code
provisions and requirements; thus, the code is oriented towards individuals who possess the
background knowledge to evaluate the significance and limitations of its content and
recommendations. They shall be able to determine the applicability of all regulatory limitations before
applying the Code and must comply with all applicable laws and regulations.
The requirements related to administration and enforcement of this Code are advisory only. SBCNC
and governmental organizations, in charge of enforcing this Code, possess the authority to modify
these administrative requirements.
SBC 306-CR-18
iii
TABLE OF CONTENTS
Table of Contents
CHAPTER 1 —GENERAL PROVISIONS......................................................................................................... 29
1.1 —SCOPE ........................................................................................................................................................................ 29
1.2 —REFERENCED SPECIFICATIONS, CODES AND STANDARDS ....................................................................................... 30
1.3 —MATERIAL .................................................................................................................................................................. 32
1.4 —STRUCTURAL DESIGN DRAWINGS AND SPECIFICATIONS ........................................................................................ 34
CHAPTER 2 —DESIGN REQUIREMENTS ...................................................................................................... 36
2.1 —GENERAL PROVISIONS ............................................................................................................................................... 36
2.2 —LOADS AND LOAD COMBINATIONS........................................................................................................................... 36
2.3 —DESIGN BASIS ............................................................................................................................................................ 36
2.4 —MEMBER PROPERTIES ............................................................................................................................................... 38
2.5 —MEMBER LENGTHS .................................................................................................................................................... 39
2.6 —FABRICATION AND ERECTION ................................................................................................................................... 39
2.7 —QUALITY CONTROL AND QUALITY ASSURANCE ........................................................................................................ 39
2.8 —EVALUATION OF EXISTING STRUCTURES................................................................................................................... 39
CHAPTER 3 —DESIGN FOR STABILITY........................................................................................................ 43
3.1 —GENERAL STABILITY REQUIREMENTS........................................................................................................................ 43
3.2 —CALCULATION O F REQUIRED STRENGTHS .............................................................................................................. 43
3.3 CALCULATION OF DESIGN STRENGTHS ......................................................................................................................... 46
CHAPTER 4 —DESIGN OF MEMBERS FOR TENSION................................................................................. 48
4.1 —SLENDERNESS LIMITATIONS ...................................................................................................................................... 48
4.2 —DESIGN TENSILE STRENGTH ...................................................................................................................................... 48
4.3 —EFFECTIVE NET AREA ................................................................................................................................................. 48
4.4 —BUILT-UP MEMBERS ................................................................................................................................................. 48
4.5 —PIN-CONNECTED MEMBERS ...................................................................................................................................... 49
4.6 —EYEBARS .................................................................................................................................................................... 49
CHAPTER 5 —DESIGN FOR COMPRESSION ............................................................................................... 52
5.1 —GENERAL PROVISIONS ............................................................................................................................................... 52
5.2 —EFFECTIVE LENGTH .................................................................................................................................................... 52
5.3 —FLEXURAL BUCKLING OF MEMBERS WITHOUT SLENDER ELEMENTS ....................................................................... 52
5.4 —TORSIONAL AND FLEXURAL-TORSIONAL BUCKLING OF MEMBERS WITHOUT SLENDER ELEMENTS ........................ 53
5.5 —SINGLE ANGLE COMPRESSION MEMBERS................................................................................................................. 54
5.6 —BUILT-UP MEMBERS .................................................................................................................................................. 54
5.7 —MEMBERS WITH SLENDER ELEMENTS ...................................................................................................................... 56
CHAPTER 6 —DESIGN OF MEMBERS FOR FLEXURE ................................................................................ 61
6.1 —GENERAL PROVISIONS ............................................................................................................................................... 61
6.2 —DOUBLY SYMMETRIC COMPACT I-SHAPED MEMBERS AND CHANNELS BENT ABOUT THEIR MAJOR AXIS ............ 62
6.3 —DOUBLY SYMMETRIC I-SHAPED MEMBERS WITH COMPECT WEBS AND NONCOMPECT OR SLENDER FLANGES
BENT ABOUT THEIR MAJOR AXIS ....................................................................................................................................... 63
6.4 —OTHER I-SHAPED MEMBERS WITH COMPACT OR NONCOMPACT WEBS BENT ABOUT THEIR MAJOR AXIS ......... 63
6.5 —DOUBLY SYMMECTRIC AND SINGLY SYMMETRIC I-SHAPED MEMBERS WITH SLENDER WEBS BENT ABOUT THEIR
MAJOUT AXIS ...................................................................................................................................................................... 65
6.6 —I-SHAPED MEMBERS AND CHANNELS BENT ABOUT THEIR MINOR AXIS ................................................................ 66
6.7 —SQUARE AND RECTANGULAR HSS AND BOX-SHAPED MEMBERS ............................................................................ 67
6.8 —ROUND HSS ............................................................................................................................................................... 67
6.9 —TEES AND DOUBLE ANGLES LOADED IN THE PLANE O F SYMMETRY ..................................................................... 68
6.10 —SINGLE ANGLES ....................................................................................................................................................... 69
6.11 —RECTANGULAR BARS AND ROUNDS....................................................................................................................... 70
6.12 —UNSYMMETRICAL SHAPES ...................................................................................................................................... 70
SBC 306-CR-18
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TABLE OF CONTENTS
6.13 —PROPORTIONS OF BEAMS AND GIRDERS .............................................................................................................. 71
CHAPTER 7 —DESIGN OF MEMBERS FOR SHEAR .................................................................................... 75
7.1 —GENERAL PROVISIONS .............................................................................................................................................. 75
7.2 —MEMBERS WITH UNSTIFFENED OR STIFFENED WEBS ........................................................................................... 75
7.3 —TENSION FIELD ACTION ............................................................................................................................................. 76
7.4 —SINGLE ANGLES ......................................................................................................................................................... 77
7.5 —RECTANGULAR HSS AND BOX-SHAPED MEMBERS................................................................................................... 77
7.6 —ROUND HSS ............................................................................................................................................................... 77
7.7 —WEAK AXIS SHEAR IN DOUBLY SYMMETRIC AND SINGLY SYMMETRIC SHAPES ..................................................... 78
7.8 —BEAMS AND GIRDERS WITH WEB OPENINGS .......................................................................................................... 78
CHAPTER 8 —DESIGN OF MEMBERS FOR COMBINED FORCES AND TORSION .................................. 80
8.1 —DOUBLY AND SINGLY SYMMETRIC MEMBERS SUBJECT TO FLEXURE AND AXIAL FORCE ......................................... 80
8.2 —UNSYMMETRIC AND OTHER MEMBERS SUBJECT TO FLEXURE A N D AXIAL FORCE .............................................. 81
8.3 —MEMBERS SUBJECT TO TORSION AND COMBINED TORSION, FLEXURE, SHEAR AND/OR AXIAL FORCE ................ 81
8.4 RUPTURE OF FLANGES WITH HOLES SUBJECT TO TENSION ......................................................................................... 83
CHAPTER 9 —DESIGN OF COMPOSITE MEMBERS .................................................................................... 85
9.1 —GENERAL PROVISIONS ............................................................................................................................................... 85
9.2 —AXIAL FORCE ............................................................................................................................................................. 86
9.3 —FLEXURE .................................................................................................................................................................... 88
9.4 —SHEAR ........................................................................................................................................................................ 90
9.5 —COMBINED FLEXURE AND AXIAL FORCE .................................................................................................................. 91
9.6 —LOAD TRANSFER........................................................................................................................................................ 91
9.7 —COMPOSITE DIAPHRAGMS AND COLLECTOR BEAMS .............................................................................................. 93
9.8 —STEEL ANCHORS ........................................................................................................................................................ 93
9.9 —SPECIAL CASES .......................................................................................................................................................... 97
CHAPTER 10 —DESIGN OF CONNECTIONS .............................................................................................. 100
10.1 —GENERAL PROVISIONS ........................................................................................................................................... 100
10.2 —WELDS ................................................................................................................................................................... 102
10.3 —BOLTS AND THREADED PARTS .............................................................................................................................. 105
10.4 —AFFECTED ELEMENTS OF MEMBERS AND CONNECTING ELEMENTS ................................................................. 109
10.5 —FILLERS .................................................................................................................................................................. 110
10.6 —SPLICES .................................................................................................................................................................. 110
10.7 —BEARING STRENGTH .............................................................................................................................................. 110
10.8 —COLUMN BASES AND BEARING ON CONCRETE ................................................................................................... 111
10.9 —ANCHOR RODS AND EMBEDMENTS..................................................................................................................... 111
10.10 —FLANGES AND WEBS WITH CONCENTRATED FORCES ....................................................................................... 111
CHAPTER 11 —DESIGN OF HSS AND BOX MEMBER CONNECTIONS ................................................... 122
11.1 —CONCENTRATED FORCES ON HSS ........................................................................................................................ 122
11.2 —HSS-TO-HSS TRUSS CONNECTIONS ....................................................................................................................... 122
11.3 —HSS-TO-HSS MOMENT CONNECTIONS .................................................................................................................. 124
11.4 —WELDS OF PLATES AND BRANCHES TO RECTANGULAR HSS ............................................................................... 125
CHAPTER 12 —SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS ................................... 143
12.1 —GENERAL REQUIREMENTS..................................................................................................................................... 143
12.2 —GENERAL SEISMIC DESIGN REQUIREMENTS .......................................................................................................... 146
12.3 —MOMENT-FRAME AND BRACED-FRAME SYSTEMS ............................................................................................... 155
12.4 —COMPOSITE MOMENT-FRAME AND BRACED-FRAME SYSTEMS ........................................................................... 165
12.5 —FABRICATION AND ERECTION ............................................................................................................................... 167
12.6 —QUALITY CONTROL AND QUALITY ASSURANCE .................................................................................................... 169
12.7 —PREQUALIFICATION AND CYCLIC QUALIFICATION TESTING PROVISIONS ............................................................. 169
CHAPTER 13 —DESIGN FOR SERVICEABLILITY ...................................................................................... 181
SBC 306-CR-18
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TABLE OF CONTENTS
13.1 —GENERAL PROVISIONS ........................................................................................................................................... 181
13.2 —CAMBER................................................................................................................................................................. 181
13.3 —DEFLECTION........................................................................................................................................................... 181
13.4 —DRIFT ..................................................................................................................................................................... 181
13.5 —VIBRATION............................................................................................................................................................. 181
13.6 —WIND-INDUCED MOTION ...................................................................................................................................... 181
13.7 —EXPANSION AND CONTRACTION........................................................................................................................... 181
13.8 —CONNECTION SLIP ................................................................................................................................................. 182
CHAPTER 14 —FABRICATION AND ERECTION ........................................................................................ 184
14.1 —SHOP AND ERECTION DRAWINGS......................................................................................................................... 184
14.2 —FABRICATION......................................................................................................................................................... 184
14.3 —SHOP PAINTING ..................................................................................................................................................... 186
14.4 —ERECTION .............................................................................................................................................................. 186
CHAPTER 15 —QUALITY CONTROL AND QUALITY ASSURANCE ......................................................... 188
15.1 —SCOPE .................................................................................................................................................................... 188
15.2 —FABRICATOR AND ERECTOR QUALITY CONTROL PROGRAM ................................................................................ 188
15.3 —FABRICATOR AND ERECTOR DOCUMENTS ........................................................................................................... 189
15.4 —INSPECTION AND NONDESTRECTIVE TESTING PERSONNEL ................................................................................. 190
15.5 —MINIMUM REQUIREMENTS F O R INSPECTION O F STRUCTURAL STEEL BULIDINGS .......................................... 191
15.6 —MINIMUM REQUIREMENTS FOR INSPECTION OF COMPOSITE CONSTRUCTION.................................................. 195
15.7 —APPROVED FABRICATORS AND ERECTORS ............................................................................................................ 195
15.8 —NONCONFORMING MATERIAL AND WORKMANSHIP ............................................................................................ 196
CHAPTER 16 —EVALUATION OF EXISTING STRUCTURES .................................................................... 204
16.1 —GENERAL PROVISIONS ........................................................................................................................................... 204
16.2 —MATERIAL PROPERTIES ......................................................................................................................................... 204
16.3 —EVALUATION B Y STRUCTURAL ANALYSIS ............................................................................................................ 205
16.4 —EVALUATION BY LOAD TESTS............................................................................................................................... 205
16.5 —EVALUATION REPORT ........................................................................................................................................... 205
APPENDIX A —DESIGN BY INELASTIC ANALYSIS ................................................................................... 207
A.1 — GENERAL REQUIREMENTS ..................................................................................................................................... 207
A.2 — DUCTILITY REQUIREMENTS. ................................................................................................................................... 207
A.3 — ANALYSIS REQUIREMENTS. ................................................................................................................................... 209
APPENDIX B —DESIGN FOR PONDING ...................................................................................................... 211
B.1 —SIMPLIFIED DESIGN FOR PONDING ........................................................................................................................ 211
B.2 — IMPROVED DESIGN FOR PONDING ......................................................................................................................... 211
APPENDIX C —DESIGN FOR FATIGUE ....................................................................................................... 216
C.1 — GENERAL PROVISIONS ........................................................................................................................................... 216
C.2 — CALCULATION OF MAXIMUM STRESSES AND STRESS RANGES ............................................................................. 216
C.3 — DESIGN STRESS RANGE........................................................................................................................................... 217
C.4 — SPECIAL FABRICATION AND ERECTION REQUIREMENTS........................................................................................ 218
APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS ............................................................. 237
D.1 — GENERAL PROVISIONS ........................................................................................................................................... 237
D.2 — STRUCTURAL DESIGN FOR FIRE CONDITIONS BY ANALYSIS ................................................................................... 237
D.3 — DESIGN BY QUALIFICATION TESTING ..................................................................................................................... 240
APPENDIX E —STABILITY BRACING FOR COLUMNS AND BEAMS ....................................................... 246
E.1 — GENERAL PROVISIONS ............................................................................................................................................ 246
E.2 — COLUMN BRACING ................................................................................................................................................. 246
E.3 — BEAM BRACING ...................................................................................................................................................... 247
E.4 — BEAM-COLUMN BRACING ...................................................................................................................................... 248
SBC 306-CR-18
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TABLE OF CONTENTS
APPENDIX F —ALTERNATIVE METHODS OF DESIGN FOR STABILITY............................................. 250
F.1 — GENERAL STABILITY REQUIREMENTS...................................................................................................................... 250
F.2 — EFFECTIVE LENGTH METHOD ................................................................................................................................ 250
F.3 — FIRST-ORDER ANALYSIS METHOD ........................................................................................................................... 251
APPENDIX G —APPROXIMATE SECOND-ORDER ANALYSIS ................................................................. 254
G.1 — LIMITATIONS .......................................................................................................................................................... 254
G.2 — CALCULATION PROCEDURE.................................................................................................................................... 254
SBC 306-CR-18
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LIST OF SYMBOLS
List of Symbols
Some definitions in the list below have been simplified in the interest of brevity. In all cases, the definitions
given in the body of the Code govern. Symbols without text definitions, used only in one location and defined
at that location are omitted in some cases. The section or table number in the right-hand column refers to the
Section where the symbol is first used.
Symbol
Definition ............................................................................................ Section
ABM
Ab
Abi
Abj
Ac
Ac
Ae
Ae
Cross-sectional area of the base metal, mm2 ........................................ 10.2.4
Nominal unthreaded body area of bolt or threaded part, mm2 ............. 10.3.6
Cross-sectional area of the overlapping branch, mm2 .......................... 11.2.3
Cross-sectional area of the overlapped branch, mm2 ........................... 11.2.3
Area of concrete, mm2 ......................................................................... 9.2.1.2
Area of concrete slab within effective width, mm2 ............................... 9.3.2.3
Effective net area, mm2 .............................................................................. 4.2
Summation of the effective areas of the cross section based on the reduced
effective width, be, mm2 ............................................................................. 5.7
Area of compression flange, mm2 .......................................................... 7.3.1
Gross area of tension flange, mm2 ..................................................... 6.13.1
Net area of tension flange, mm2 ......................................................... 6.13.1
Area of tension flange, mm2 .................................................................... 7.3.1
Gross cross-sectional area of member, mm2 .......................................... 2.3.6
Gross area of composite member, mm2 ................................................. 9.2.1
Gross area subject to shear, mm2 ........................................................ 10.4.3
Net area of member, mm2 ....................................................................... 2.4.3
Area of the directly connected elements, mm2................................ Table 4-1
Net area subject to tension, mm2 .......................................................... 10.4.3
Net area subject to shear, mm2 ............................................................. 10.4.3
Projected area in bearing, mm2 ............................................................... 10.7
Cross-sectional area of steel section, mm2 .......................................... 9.2.1.2
Cross-sectional area of the structural steel core, mm2 .................. 12.2.5.4 .2
Cross-sectional area of steel headed stud anchor, mm2....................... 9.8.2.1
Area on the shear failure path, mm2........................................................ 4.5.1
Minimum area of tie reinforcement, mm2 ...................................... 12.2.5.4 .2
Area of continuous reinforcing bars, mm2 .............................................. 9.2.1
Area of adequately developed longitudinal reinforcing steel within the
effective width of the concrete slab, mm2 ............................................. 9.3.2.4
Net area in tension, mm2 ................................................................. App. C.3.2
Area of web, the overall depth times the web thickness, dtw, mm2 ............... 7.2.1
Afc
Afg
Afn
Aft
Ag
Ag
Agv
An
An
Ant
Anv
Apb
As
As
Asa
Asf
Ash
Asr
Asr
At
Aw
SBC 306-CR-18
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LIST OF SYMBOLS
Bbi
Bbj
Effective area of the weld, mm2 ............................................................. 10.2.4
Effective area of weld throat of any ith weld element, mm2 .................. 10.2.4
Loaded area of concrete, mm2 ............................................................. 9.6.3.1
Area of steel concentrically bearing on a concrete support, mm2 ........... 10.8
Maximum area of the portion of the supporting surface that is geometrically
similar to and concentric with the loaded area, mm2 ............................... 10.8
Overall width of rectangular HSS member, measured 90 to the plane of the
connection, mm ...............................................................................Table 4-1
Overall width of rectangular steel section along face transferring load, mm
.............................................................................................................. 9.6.3.1
Overall width of rectangular HSS branch member, measured 90to the plane
of the connection, mm ......................................................................... 11.2.1
Overall width of the overlapping branch, mm ..................................... 11.2.3
Overall width of the overlapped branch, mm ..................................... 11.2.3
Bp
Width of plate, measured 90 to the plane of the connection, mm....... 11.1.1
B1
Multiplier to account for P-effects ................................................... App.G.2
B2
C
Ca
Cb
Multiplier to account for P-Δeffects ................................................ App.G.2
HSS torsional constant............................................................................ 8.3.1
Ratio of required strength to design strength ............................. TABLE 12-2
Lateral-torsional buckling modification factor for nonuniform moment
diagrams ................................................................................................... 6.1
Coefficient relating relative brace stiffness and curvature............. 12.2.5.2.1
Coefficient accounting for increased required bracing stiffness at inflection
point ............................................................................................... App. E.3.1
Constant from Table A-3.1 for the fatigue category ....................... App.C.3.1
Coefficient accounting for nonuniform moment ............................ App. G.2.1
Ponding flexibility coefficient for primary member in a flat roof .. App. B.1
Coefficient for web sidesway buckling ................................................ 10.10.4
Ponding flexibility coefficient for secondary member in a flat roof . App. B.1
Web shear coefficient ............................................................................. 7.2.1
Warping constant, mm6 ............................................................................. 5.4
Edge distance increment .......................................................TABLE 10-10
Outside diameter of round HSS, mm ............................................ Table 2-1
Outside diameter of round HSS main member, mm ............................ 11.2.1
Nominal dead load, N ................................................................................ App. B.2
Dead load due to the weight of the structural elements and permanent
features on the building, N ............................................................. 12.2.5.4 .2
Outside diameter of round HSS branch member, mm ......................... 11.2.1
In slip-critical connections, a multiplier that reflects the ratio of the mean
installed bolt pretension to the specified minimum bolt pretension ..... 10.3.8
Modulus of elasticity of steel 200 000 MPa...................................Table 2-1
Awe
Awei
A1
A1
A2
B
B
Bb
Cd
Cd
Cf
Cm
Cp
Cr
Cs
Cv
Cw
C2
D
D
D
D
Db
Du
E
SBC 306-CR-18
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LIST OF SYMBOLS
Ec
Ec (T)
Emh
Es
E (T)
EIeff
Fc
Fca
Fcbw , Fcbz
Fcr
Fcre
Fcry
Fcrz
Fe
Fe (T)
Fex
FEXX
Fey
Fez
Fin
FL
Fn
Fn
FnBM
Fnt
F nt
Fnv
Fnw
Fnw
Fnwi
Fnwix
Fnwiy
Fp (T)
Modulus of elasticity of concrete, MPa ............................................... 9.2.1.2
Modulus of elasticity of concrete at elevated temperature, MPa App. D2.3.2
Horizontal seismic load ffect including overstrength factor, N ............ 12.2.1
Modulus of elasticity of steel 200 000 MPa ..................................... 9.2.1.2
Elastic modulus of elasticity of steel at elevated temperature, MPa ...............
................................................................................................................... App. D2.4.3
Effective stiffness of composite section, N-mm2 .................................. 9.2.1.2
Design stress, MPa ............................................................................... 11.1.1
Design axial stress at the point of consideration, MPa .......................... 8.2
Design flexural stress at the point of consideration, MPa ....................... 8.2
Critical stress, MPa ................................................................................... 5.3
Critical stress calculated from Specification Chapter E using expected yield
stress, MPa......................................................................................... 12.3.4.6
Critical stress about the y-axis of symmetry, MPa ..................................... 5.4
Critical torsional buckling stress, MPa ..................................................... 5.4
Elastic buckling stress, MPa ................................................................... 5.3
Critical elastic buckling stress with the elastic modulus E (T ) at elevated
temperature, MPa ........................................................................ App. D2.4.3
Flexural elastic buckling stress about the major principal axis, MPa ...... 5.4
Filler metal classification strength, MPa ........................................... 10.2.4
Flexural elastic buckling stress about the minor principal axis, MPa ...... 5.4
Torsional elastic buckling stress, MPa ................................................... 5.4
Nominal bond stress, 0.40 MPa ........................................................ 9.6.3.3
Magnitude of flexural stress in compression flange at which flange local
buckling or lateral-torsional buckling is influenced by yielding, MPa . Table
2-2
Nominal stress, MPa ............................................................................... 8.3.3
Nominal tensile stress, Fnt, or shear stress, Fnv, from TABLE 10-7, MPa10.3.6
Nominal stress of the base metal, MPa ................................................. 10.2.4
Nominal tensile stress from TABLE 10-7, MPa .................................... 10.3.7
Nominal tensile stress modified to include the effects of shear stress, MPa
............................................................................................................... 10.3.7
Nominal shear stress from TABLE 10-7, MPa ...................................... 10.3.7
Nominal stress of the weld metal, MPa ................................................. 10.2.4
Nominal stress of the weld metal Chapter 10 with no increase in strength due
to directionality of load, MPa .................................................................. 11.4
Nominal stress in ith weld element, MPa ............................................... 10.2.4
x component of nominal stress, Fnwi, MPa ........................................... 10.2.4
y component of nominal stress, Fnwi, MPa ............................................ 10.2.4
Proportional limit at elevated temperatures, MPa ......................... App. D2.3.2
SBC 306-CR-18
4
LIST OF SYMBOLS
FSR
FTH
Fu
Fu (T)
Fy
Fyb
Fybi
Fybj
Fyf
Fyp
Fysr
Fyst
Fy (T)
Fyw
Fysr
G
G (T)
H
H
H
H
Hb
Hbi
I
Ic
Id
Ip
Allowable stress range, MPa..................................................................... App. C.3
Threshold allowable stress range, maximum stress range for indefinite design
life from TABLE C-1, MPa ........................................................................ App. C.1
Specified minimum tensile strength, MPa .................................................. 4.2
Minimum tensile strength at elevated temperature, MPa....................................
................................................................................................................... App. D2.3.2
Specified minimum yield stress, MPa. As used in this Code, “yield stress”
denotes either the specified minimum yield point for those steels that have a
yield point or specified yield strength (for those steel that do not have a yield
point) ....................................................................................................... 2.3.6
Specified minimum yield stress of HSS branch member material, MPa .........
............................................................................................................... 11.2.1
Specified minimum yield stress of the overlapping branch material, MPa ....
.............................................................................................................. 11.2.3
Specified minimum yield stress of the overlapped branch material, MPa11.2.3
Specified minimum yield stress of the flange, MPa ........................... 10.10.1
Specified minimum yield stress of plate, MPa ...................................... 11.1.1
Specified minimum yield stress of reinforcing bars, MPa ................... 9.2.1.2
Specified minimum yield stress of the stiffener material, MPa ............. 7.3.3
Yield stress at elevated temperature, MPa ....................................... App. D2.4.3
Specified minimum yield stress of the web material, MPa ................... 7.3.3
Specified minimum yield stress of the ties, MPa ............................ 12.2.5.4 .2
Shear modulus of elasticity of steel 77 200 MPa ................................... 5.4
Shear modulus of elasticity of steel at elevated temperature, MPa ................
...................................................................................................... App. D2.3.2
Flexural constant ....................................................................................... 5.4
Story shear, in the direction of translation being considered, produced by the
lateral forces used to compute ΔH, N........................................ App. G.2.2
Overall height of rectangular HSS member, measured in the plane of the
connection, mm ..............................................................................Table 4-1
Height of story, which is permitted to be taken as the distance between the
centerline of floor framing at each of the levels above and below, or the
distance between the top of floor slabs at each of the levels above and below,
mm ................................................................................................... 12.2.6.4.3
Overall height of rectangular HSS branch member, measured in the plane of
the connection, mm ............................................................................. 11.2.1
Overall depth of the overlapping branch, mm ..................................... 11.2.3
Moment of inertia in the plane of bending, mm4 ............................. App. G.2.1
Moment of inertia of the concrete section about the elastic neutral axis of the
composite section, mm4 ..................................................................9.2.1.2
Moment of inertia of the steel deck supported on secondary members, mm4
......................................................................................................................... App. B.1
Moment of inertia of primary members, mm4 ........................................ App. B.1
SBC 306-CR-18
5
LIST OF SYMBOLS
Is
Is
Isr
Ist
Ist1
Ist2
Ix, Iy
Iy
Iyc
Iz
J
K
Kx
Ky
Kz
K1
L
L
L
L
L
L
L
L
Lb
Lb
Lb
Lm
Lp
Lp
Moment of inertia of secondary members, mm4 ............................... App. B.1
Moment of inertia of steel shape about the elastic neutral axis of the
composite section, mm4 ........................................................................ 9.2.1.2
Moment of inertia of reinforcing bars about the elastic neutral axis of the
composite section, mm4 ......................................................................... 9.2.1.2
Moment of inertia of transverse stiffeners about an axis in the web center for
stiffener pairs, or about the face in contact with the web plate for single
stiffeners, mm4 ......................................................................................... 7.3.3
Minimum moment of inertia of transverse stiffeners required for development
of the web shear buckling resistance in Section 7.3.3 , mm4 ................... 7.3.3
Minimum moment of inertia of transverse stiffeners required for development
of the full web shear buckling plus the web tension field resistance, Vr Vc2,
mm4 ......................................................................................................... 7.3.3
Moment of inertia about the principal axes, mm4 ...................................... 5.4
Out-of-plane moment of inertia, mm4 ........................................... App. E3.2.1
Moment of inertia the compression flange about the y-axis, mm4 .......... 6.4.2
Minor principal axis moment of inertia, mm4 ....................................... 6.10.2
Torsional constant, mm4............................................................................. 5.4
Effective length factor ......................................................................... 3.3, 5.2
Effective length factor for flexural buckling about x-axis.......................... 5.4
Effective length factor for flexural buckling about y-axis.......................... 5.4
Effective length factor for torsional buckling ............................................ 5.4
Effective length factor in the plane of bending, calculated based on the
assumption of no lateral translation at the member ends, set equal to 1.0
unless analysis justifies a smaller value ............................................. App. G.2.1
Height of story, mm .................................................................................. App. F.3.2
Length of member, mm ............................................................................ 8.3.1
Nominal occupancy live load ......................................................... App. D.1.4
Laterally unbraced length of member, mm .............................................. 5.2
Length of span, mm ...................................................................... App. E3.2.1
Length of member between work points at truss chord centerlines, mm . 5.5
Live load due to occupancy and moveable equipment, N .............. 12.2.5.4 .2
Length of brace, mm .......................................................................... 12.3.4.5
Length between points that are either braced against lateral displacement of
compression flange or braced against twist of the cross section, mm .... 6.2.2
Distance between braces, mm ................................................................... App. E.2
Largest laterally unbraced length along either flange at the point of load, mm
............................................................................................................. 10.10.4
Limiting laterally unbraced length for eligibility for moment redistribution in
beams according to Section 2.3.7 ........................................................ 6.13.5
Limiting laterally unbraced length for the limit state of yielding, mm .. 6.2.2
Length of primary members, mm ...................................................... App. B.1
SBC 306-CR-18
6
LIST OF SYMBOLS
Lpd
Lr
Ls
Lv
MA
MB
MC
Mcx , Mcy
Mcx
Mcx
Me
Mlt
Mmax
Mmid
Mn
Mn,PR
Mnt
Mp
Mp
Mp
Mpc
Mp,exp
Mr
Mr
Mrb
Mr-ip
Mr-op
Mrx,Mry
Mrx
Mu
My
Limiting laterally unbraced length for plastic analysis, mm ......... App. A.2.3
Limiting laterally unbraced length for the limit state of inelastic lateraltorsional buckling, mm............................................................................ 6.2.2
Length of secondary members, m..................................................... App. B.1
Distance from maximum to zero shear force, mm ..................................... 7.6
Absolute value of moment at quarter point of the unbraced segment, N-mm6.1
Absolute value of moment at centerline of the unbraced segment, N-mm . 6.1
Absolute value of moment at three-quarter point of the unbraced segment, Nmm .............................................................................................................. 6.1
Design flexural strength determined in accordance with Chapter 6, N-mm
................................................................................................................. 8.1.1
Design lateral-torsional strength for strong axis flexure determined in
Accordance with Chapter 6 using Cb = 1.0, N-mm .............................. 8.1.3
Design flexural strength about the x-axis for the limit state of tensile rupture
of the flange, N-mm .................................................................................. 8.4
Elastic lateral-torsional buckling moment, N-mm .............................. 6.10.2
First-order moment, due to lateral translation of the structure only, N-mm
.........................................................................................................................App. G.2
Absolute value of maximum moment in the unbraced segment, N-mm ...... 6.1
Moment at the middle of the unbraced length, N-mm .................... App. A.2.3
Nominal flexural strength, N-mm ............................................................... 6.1
Nominal flexural strength of PR connection at a rotation of 0.02 rad, N-mm
......................................................................................................... 12.3.1.6.3
First-order moment, with the structure restrained against lateral translation,
N-mm ...........................................................................................................App. G.2
Plastic bending moment, N-mm ................................. Table 2-1, Table 2-2
Moment corresponding to plastic stress distribution over the composite cross
section, N-mm ...................................................................................... 9.3.4.2
Nominal plastic flexural strength, N-mm ........................................ 12.3.1.6.2
Nominal plastic flexural strength of the column, N-mm .................... 12.2.6.4
Expected flexural strength, N-mm................................................... 12.2.5.2.3
Required second-order flexural strength, N-mm ...................................App. G.2
Required flexural strength, N-mm ........................................................... 8.1.1
Required bracing moment, N-mm ......................................................... App. E.3.2
Required in-plane flexural strength in branch, N-mm .......................... 11.3.2
Required out-of-plane flexural strength in branch, N-mm ................... 11.3.2
Required flexural strength, N-mm........................................................... 8.1.1
Required flexural strength at the location of the bolt holes; positive for
tension in the flange under consideration, negative for compression, N-mm8.4
Required flexural strength, N-mm ....................................................... 10.10.4
Moment at yielding of the extreme fiber, N-mm ............................ Table 2-2
SBC 306-CR-18
7
LIST OF SYMBOLS
My
Myc
Myt
Yield moment about the axis of bending, N-mm .................................. 6.10.1
Moment at yielding of the extreme fiber in the compression flange, N-mm6.4.2
Moment at yielding of the extreme fiber in the tension flange, N-mm .... 6.4.4
M1
Effective moment at the end of the unbraced length opposite from M2, N-mm
...................................................................................................................... App. A.2.3
Smaller moment at end of unbraced length, N-mm ......... 6.13.5 , App. A.2.3
Larger moment at end of unbraced length, N-mm ............ 6.13.5 , App. A.2.3
Notional load applied at level i, N ....................................................... 3.2.2.2
Additional lateral load, N .......................................................................... App. F.3
Overlap connection coefficient ............................................................ 11.2.2
Design axial strength, N ......................................................................... 8.1.1
Design compressive strength out of the plane of bending, N .................. 8.1.3
Elastic critical buckling load determined in accordance with Chapter 3 or
Appendix F, N ...................................................................................... 9.2.1.2
Elastic critical buckling strength for the story in the direction of translation
being considered, N .................................................................................. App G.2.2
Elastic critical buckling load for buckling about the weak axis, N ....... 8.1.2
Elastic critical buckling strength of the member in the plane of bending, N
..................................................................................................................... App. G.2.1
First-order axial force, due to lateral translation of the structure only, NApp.
G.2
Total vertical load in columns in the story that are part of moment frames, if
any, in the direction of translation being considered, N ................ App. G.2.2
Nominal axial strength, N .......................................................................... 4.2
Nominal compressive strength, N .............................................................. 5.1
Nominal compressive strength of the composite column calculated in
accordance with the Code, N ............................................................. 12.2.5.4
Nominal compressive strength of zero length, doubly symmetric, axially
loaded composite member, N ..................................................................... 9.2
First-order axial force, with the structure restrained against lateral
translation, N ................................................................................................App. G.2
Nominal bearing strength, N .................................................................... 10.8
Required second-order axial strength, N ................................................App. G.2
Required axial compressive strength, N ................................................. 3.2.3
Required axial strength, N ...................................................................... 8.1.1
Required axial strength of the member at the location of the bolt holes;
positive in tension, negative in compression, N ......................................... 8.4
Required external force applied to the composite member, N ............. 9.6.2.1
Required brace strength, N ........................................................................ App. E.2
Total vertical load supported by the story, including loads in columns that are
not part of the lateral force resisting system, N ................................ App. G.2.2
M1
M2
Ni
Ni
Ov
Pc
Pcy
Pe
Pe story
Pey
Pe1
Plt
Pmf
Pn
Pn
Pn
Pno
Pnt
Pp
Pr
Pr
Pr
Pr
Pr
Prb
Pstory
SBC 306-CR-18
8
LIST OF SYMBOLS
Pu
Pu
Pu
Py
Q
Qa
Qct
Qcv
Qf
Qn
Qnt
Qnv
Qrt
Qrv
Qs
R
R
R
RFIL
Rg
RM
Rn
Rn
Rn
Rnwl
Rnwt
Rnx
Rny
Rp
Rpc
Rpg
RPJP
Rpt
Rt
Required axial strength in chord, N ............................................ TABLE 11-1
Required axial strength in compression, N ......................................... App. A.2.2
Required axial strength using LRFD load combinations,N ........ TABLE 12-2
Axial yield strength, N............................................................................. 3.2.3
Net reduction factor accounting for all slender compression elements .... 5.7
Reduction factor for slender stiffened elements ......................................... 5.7
Design tensile strength, N ....................................................................... 9.8.3
Design shear strength, N...................................................................... 9.8.3.3
Chord-stress interaction parameter ................................................... 11.2.2
Nominal strength of one steel headed stud or steel channel anchor, N .. 9.3.2
Nominal tensile strength of steel headed stud anchor, N .................... 9.8.3.2
Nominal shear strength of steel headed stud anchor, N .................... 9.8.3.1
Required tensile strength, N ................................................................. 9.8.3.3
Required shear strength, N .................................................................. 9.8.3.3
Reduction factor for slender unstiffened elements ..................................... 5.7
Radius of joint surface, mm .......................................................... TABLE 10-2
Nominal load due to rainwater, exclusive of the ponding contribution, MPa
......................................................................................................................... App. B.2
Seismic response modification coefficient .............................................. 1.1.1
Reduction factor for joints a pair of transverse fillet welds only ... App. C.3
Coefficient to account for group effect................................................. 9.8.2.1
Coefficient to account for influence of P- on P-ΔApp. G.2.2
Nominal strength, specified in Chapters 2 through 11 .......................... 2.3.3
Nominal slip resistance, N .................................................................... 10.3.8
Nominal strength of the applicable force transfer mechanism, N .......... 9.6.3
Total nominal strength of longitudinally loaded fillet welds, as determined in
accordance with TABLE 10-5, N .......................................................... 10.2.4
Total nominal strength of transversely loaded fillet welds, as determined in
accordance with TABLE 10-5 without the alternate in Section 10.2.4 a, N
............................................................................................................... 10.2.4
Horizontal component of the nominal strength of a weld group, N ..... 10.2.4
Vertical component of the nominal strength of a weld group, N .......... 10.2.4
Position effect factor for shear studs.................................................... 9.8.2.1
Web plastification factor ......................................................................... 6.4.1
Bending strength reduction factor .......................................................... 6.5.2
Reduction factor for reinforced or nonreinforced transverse partial-jointpenetration PJP groove welds............................................................ App. C.3
Web plastification factor corresponding to the tension flange yielding limit
state ........................................................................................................ 6.4.4
Ratio of the expected tensile strength to the specified minimum tensile strength
Fu, as related to overstrength in material yield stress, Ry ................ 12.1.2.2
SBC 306-CR-18
9
LIST OF SYMBOLS
Ru
Ry
S
S
Sc
Se
Sip
Smin
Sop
Sxc, Sxt
Sx
Sy
T
Tb
Tc
Tn
Tr
Tu
U
U
Ubs
Up
Us
V
Vc
Vc1
Vc2
Vn
Vr
Vr
Vr
Required strength ................................................................................... 2.3.3
Ratio of the expected yield stress to the specified minimum yield stress, Fy
............................................................................................................ 12.1.2.2
Elastic section modulus, mm3 ................................................................. 6.8.2
Spacing of secondary members, m ................................................... App. B.1
Elastic section modulus to the toe in compression relative to the axis of
bending, mm3 ........................................................................................ 6.10.3
Effective section modulus about major axis, mm3 ................................. 6.7.2
Effective elastic section modulus of welds for in-plane bending TABLE 11-13,
mm3 .......................................................................................................... 11.4
Lowest elastic section modulus relative to the axis of bending, mm3 ...... 6.12
Effective elastic section modulus of welds for out-of-plane bending TABLE
11-13, mm3 ........................................................................................ 11.4
Elastic section modulus referred to compression and tension flanges,
respectively, mm3 ...............................................................................Table 2-2
Elastic section modulus taken about the x-axis, mm3 ............................. 6.2.2
Elastic section modulus taken about the y-axis. For a channel, the minimum
section modulus, mm3 ............................................................................. 6.6.2
Nominal forces and deformations due to the design-basis fire defined in
Appendix Section D.2.1 .................................................................. App. D.1.4
Minimum fastener tension given in TABLE 10-6, N ............................. 10.3.8
Design torsional strength, N-mm ............................................................ 8.3.2
Nominal torsional strength, N-mm........................................................... 8.3.1
Required torsional strength, N-mm .......................................................... 8.3.2
Required tension force, N .................................................................... 10.3.9
Shear lag factor.......................................................................................... 4.3
Utilization ratio ..................................................................................... 11.2.2
Reduction coefficient, used in calculating block shear rupture strength 10.4.3
Stress index for primary members .................................................... App. B.2
Stress index for secondary members ................................................. App. B.2
Nominal shear force between the steel beam and the concrete slab transferred
by steel anchors, N ............................................................................... 9.3.2.3
Design shear strength, N ......................................................................... 8.3.2
Smaller of the design shear strengths in the adjacent web panels with Vn as
defined in Section 7.2.1 , N ..................................................................... 7.3.3
Smaller of the design shear strengths in the adjacent web panels with Vn as
defined in Section 7.3.2 , N .................................................................... 7.3.3
Nominal shear strength, N ......................................................................... 7.1
Larger of the required shear strengths in the adjacent web panels, N ... 7.3.3
Required shear strength, N ..................................................................... 8.3.2
Required longitudinal shear force to be transferred to the steel or concrete, N
................................................................................................................. 9.6.2
SBC 306-CR-18
10
LIST OF SYMBOLS
Yi
Z
Zb
Zx
Zy
a
a
a
a
a
aw
b
b
b
b
b
b
bcf
be
be
beoi
beov
bf
bfc
bft
bl
bs
bs
d
d
d
d
d
Gravity load applied at level i from the LRFD load combination, N, 3.2.2.2 ,
App. F.3.2
Plastic section modulus about the axis of bending, mm3 ..................... 6.7.1
Plastic section modulus of branch about the axis of bending, mm3 ...... 11.3.1
Plastic section modulus about the x-axis, mm3 .................................... 6.2.1
Plastic section modulus about the y-axis, mm3 ....................................... 6.6.1
Clear distance between transverse stiffeners, mm ................................ 6.13.2
Distance between connectors, mm ............................................................. 5.6
Shortest distance from edge of pin hole to edge of member measured parallel
to the direction of force, mm ................................................................... 4.5.1
Half the length of the non-welded root face in the direction of the thickness of
the tension-loaded plate, mm ............................................................ App. C.3
Weld length along both edges of the cover plate termination to the beam or
girder, mm ............................................................................................. 6.13.3
Ratio of two times the web area in compression due to application of major
axis bending moment alone to the area of the compression flange components
................................................................................................................. 6.4.2
Full width of leg in compression, mm ................................................... 6.10.3
For flanges of I-shaped members, half the full-flange width, bf ; for flanges of
channels, the full nominal dimension of the flange, mm ......................... 6.6.2
Full width of longest leg, mm ..................................................................... 5.7
Width of unstiffened compression element; width of stiffened compression
element, mm ............................................................................................ 2.4.1
Width of the leg resisting the shear force, mm ........................................... 7.4
Inside width of a box section, mm ................................................... 12.4.3.5.2
Width of column flange, mm ............................................................... 10.10.6
Reduced effective width, mm ...................................................................... 5.7
Effective edge distance for calculation of tensile rupture strength of pinconnected member, mm ........................................................................... 4.5.1
Effective width of the branch face welded to the chord, mm................. 11.2.3
Effective width of the branch face welded to the overlapped brace, mm11.2.3
Width of flange, mm ................................................................................ 2.4.1
Width of compression flange, mm ........................................................... 6.4.2
Width of tension flange, mm.................................................................... 7.3.1
Length of longer leg of angle, mm ............................................................. 5.5
Length of shorter leg of angle, mm ............................................................ 5.5
Stiffener width for one-sided stiffeners, mm ................................... App. E.3.2
Nominal fastener diameter, mm ............................................................ 10.3.3
Nominal bolt diameter, mm ................................................................. 10.3.10
Full nominal depth of the section, mm .................................. 2.4.1 , 10.10.3
Depth of rectangular bar, mm ............................................................... 6.11.2
Diameter, mm ........................................................................................... 10.7
SBC 306-CR-18
11
LIST OF SYMBOLS
d
d
db
db
dc
e
emid-ht
fc
fc(T)
fo
fra
frbw, frbz
frv
g
g
h
h
h
hc
hcc
ho
hp
hr
k
kc
ksc
kv
l
Diameter of pin, mm ............................................................................... 4.5.1
Overall beam depth, mm ............................................................. TABLE 12-2
Depth of beam, mm ............................................................................. 10.10.6
Nominal diameter (body or shank diameter), mm ............................ App. C.4
Depth of column, mm .......................................................................... 10.10.6
Eccentricity in a truss connection, positive being away from the branches, mm
............................................................................................................... 11.2.1
Distance from the edge of steel headed stud anchor shank to the steel deck
web, mm ............................................................................................... 9.8.2.1
Specified compressive strength of concrete, MPa ............................... 9.2.1.2
Compressive strength of concrete at elevated temperature, MPa ...............
........................................................................................................App. D2.3.2
Stress due to D R (D nominal dead load, R nominal load due to
rainwater exclusive of the ponding contribution), MPa ......................... App.
B.2
Required axial stress at the point of consideration, MPa .......................... 8.2
Required flexural stress at the point of consideration, MPa...................... 8.2
Required shear stress, MPa .................................................................. 10.3.7
Transverse center-to-center spacing (gage) between fastener gage lines, mm
................................................................................................................. 2.4.3
Gap between toes of branch members in a gapped K-connection, neglecting
the welds, mm ........................................................................................ 11.2.1
Width of stiffened compression element, mm .......................................... 2.4.1
Height of shear element, mm................................................................ 7.2.1 b
Clear distance between flanges less the fillet or corner radius for rolled
shapes; distance between adjacent lines of fasteners or the clear distance
between flanges when welds are used for built-up shapes, mm.......... 10.10.4
Twice the distance from the center of gravity to the following: the inside face
of the compression flange less the fillet or corner radius, for rolled shapes;
the nearest line of fasteners at the compression flange or the inside faces of
the compression flange when welds are used, for built-up sections, mm 2.4.1
Cross-sectional dimension of the confined core region in composite columns
measured center-to-center of the transverse reinforcement, mm ...... 12.2.5.4
Distance between the flange centroids, mm............................................ 6.2.2
Twice the distance from the plastic neutral axis to the nearest line of fasteners
at the compression flange or the inside face of the compression flange when
welds are used, mm ................................................................................. 2.4.1
Nominal height of rib, mm ................................................................... 9.8.2.1
Distance from outer face of flange to the web toe of fillet, mm .......... 10.10.2
Coefficient for slender unstiffened element ......................................Table 2-2
Slip-critical combined tension and shear coefficient............................ 10.3.9
Web plate shear buckling coefficient ...................................................... 7.2.1
Actual length of end-loaded weld, mm .................................................. 10.2.2
SBC 306-CR-18
12
LIST OF SYMBOLS
l
lb
lc
la
le
lov
lp
n
nb
ns
nSR
p
pi
r
rcr
ri
ri
𝑟̄0
rt
rts
rx
rx
ry
rz
s
t
t
t
t
t
t
t
t
Length of connection, mm ................................................................Table 4-1
Length of bearing, mm ............................................................................. 10.7
Clear distance, in the direction of the force, between the edge of thehole and
the edge of the adjacent hole or edge of the material, mm ................. 10.3.10
Length of channel anchor, mm ............................................................. 9.8.2.2
Total effective weld length of groove and fillet welds to rectangular HSS for
weld strength calculations, mm ................................................................. 11.4
Overlap length measured along the connecting face of the chord beneath the
two branches, mm ................................................................................. 11.2.1
Projected length of the overlapping branch on the chord, mm ............ 11.2.1
Number of nodal braced points within the span ............................... App. E.3
Number of bolts carrying the applied tension....................................... 10.3.9
Number of slip planes required to permit the connection to slip.......... 10.3.8
Number of stress range fluctuations in design life ............................ App. C.3
Pitch, mm per thread...................................................................... App. C.3.2
Ratio of element i deformation to its deformation at maximum Stress . 10.2.4
Radius of gyration, mm .............................................................................. 5.2
Distance from instantaneous center of rotation to weld element with minimum
u/ri ratio, mm ..................................................................................... 10.2.4
Minimum radius of gyration of individual component, mm....................... 5.6
Distance from instantaneous center of rotation to ith weld element, mm10.2.4
Polar radius of gyration about the shear center, mm ................................ 5.4
Radius of gyration of the flange components in flexural compression plus onethird of the web area in compression due to Application of major axis bending
moment alone, mm .................................................................................. 6.4.2
Effective radius of gyration, mm ............................................................. 6.2.2
Radius of gyration about the x-axis, mm ................................................... 5.4
Radius of gyration about the geometric axis parallel to the connected leg, mm
.................................................................................................................... 5.5
Radius of gyration about y-axis, mm ......................................................... 5.4
Radius of gyration about the minor principal axis, mm ............................ 5.5
Longitudinal center-to-center spacing (pitch) of any two consecutive holes,
mm ........................................................................................................... 2.4.3
Thickness of element, mm .......................................................................... 5.7
Thickness of wall, mm ................................................................................ 5.7
Thickness of angle leg, mm ................................................................... 6.10.2
Width of rectangular bar parallel to axis of bending, mm ................... 6.11.2
Thickness of connected material, mm ................................................. 10.3.10
Thickness of plate, mm ............................................................................ 4.5.1
Total thickness of fillers, mm ................................................................ 10.5.2
Design wall thickness of HSS member, mm ............................... 2.4.1 , 11.1.1
SBC 306-CR-18
13
LIST OF SYMBOLS
tb
tbi
tbj
tcf
tf
tf
tf
tfc
tp
tp
tst
tw
tw
tw
w
w
w
w
w
wc
wr
x
xi
xo, yo
x–
y
yi
z
Ωo
T
br
eff
eop
sec
Design wall thickness of HSS branch member, mm .............................. 11.2.1
Thickness of overlapping branch, mm .................................................. 11.2.3
Thickness of overlapped branch, mm ................................................... 11.2.3
Thickness of column flange, mm ......................................................... 10.10.6
Thickness of flange, mm .......................................................................... 6.6.2
Thickness of loaded flange, mm .......................................................... 10.10.1
Thickness of flange of channel anchor, mm ......................................... 9.8.2.2
Thickness of compression flange, mm .................................................... 6.4.2
Thickness of plate, mm .......................................................................... 11.1.1
Thickness of tension loaded plate, mm ............................................. App. C.3
Thickness of web stiffener, mm..................................................... App. E3.2.1
Thickness of web, mm ......................................................................Table 2-1
Smallest effective weld throat thickness around the perimeter of branch or
plate, mm .................................................................................................. 11.4
Thickness of channel anchor web, mm ................................................ 9.8.2.2
Width of cover plate, mm ...................................................................... 6.13.3
Size of weld leg, mm .............................................................................. 10.2.2
Subscript relating symbol to major principal axis bending ....................... 8.2
Width of plate, mm ...........................................................................Table 4-1
Leg size of the reinforcing or contouring fillet, if any, in the direction of the
thickness of the tension-loaded plate, mm ........................................ App. C.3
Weight of concrete per unit volume (1500 wc 2500 kg/m3) .............. 9.2.1
Average width of concrete rib or haunch, mm ........................................ 9.3.2
Subscript relating symbol to strong axis bending ................................... 8.1.1
x component of ri .................................................................................. 10.2.4
Coordinates of the shear center with respect to the centroid, mm............. 5.4
Eccentricity of connection, mm........................................................Table 4-1
Subscript relating symbol to weak axis bending ..................................... 8.1.1
y component of ri ................................................................................... 10.2.4
Subscript relating symbol to minor principal axis bending ....................... 8.2
System overstrength factor .................................................................... 12.2.1
Reduction factor given by Eq. (10-1) ..................................................... 10.2.2
Width ratio; the ratio of branch diameter to chord diameter for round HSS;
the ratio of overall branch width to chord width for rectangular HSS . 11.2.1
Overall brace system stiffness, N-mm/rad ..................................... App. E3.2.1
Required brace stiffness, N/mm ..................................................... App. E.2.1
Effective width ratio; the sum of the perimeters of the two branch members in
a K-connection divided by eight times the chord width ........................ 11.2.1
Effective outside punching parameter................................................... 11.2.3
Web distortional stiffness, including the effect of web transversestiffeners, if
SBC 306-CR-18
14
LIST OF SYMBOLS
Tb
w
H
i
mi
ui
cu(T)
p
pd
pf
pw
r
rf
rw
B
b
c
c
T
t
t
v
any, N-mm/rad.............................................................................. App. E3.2.1
Required torsional stiffness for nodal bracing, N-mm/rad .......... App. E3.2.1
Section property for unequal leg angles, positive for short legs in compression
and negative for long legs in compression ........................................... 6.10.2
First-order interstory drift combinations, mm .............................. App. F.3.2
First-order interstory drift due to lateral forces, mm ................. App.G.2.2
Deformation of weld elements at intermediate stress levels, linearly
proportioned to the critical deformation based on distance from the
instantaneous center of rotation, ri, mm........................................... 10.2.4
Deformation of weld element at maximum stress, mm ...................... 10.2.4
Deformation of weld element at ultimate stress (rupture), usually in element
furthest from instantaneous center of rotation, mm .............................. 10.2.4
Maximum concrete strain at elevated temperature, % ................ App. D2.3.2
Chord slenderness ratio; the ratio of one-half the diameter to the wall
thickness for round HSS; the ratio of one-half the width to wall thickness for
rectangular HSS ..................................................................................... 11.2.1
Gap ratio; the ratio of the gap between the branches of a gapped Kconnection to the width of the chord for rectangular HSS .................... 11.2.1
Load length parameter, applicable only to rectangular HSS; the ratio of the
length of contact of the branch with the chord in the plane of the connection
to the chord width ................................................................................... 11.2.1
Slenderness parameter ............................................................................ 6.3.2
Limiting slenderness parameter for compact element ............................... 2.4
Limiting slenderness parameter for plastic design ........................... App. A.2
Limiting slenderness parameter for compact flange .............................. 6.3.2
Limiting slenderness parameter for compact web ...................................... 6.4
Limiting slenderness parameter for noncompact element ......................... 2.4
Limiting slenderness parameter for noncompact flange ........................ 6.3.2
Limiting slenderness parameter for noncompact web............................. 6.4.2
Mean slip coefficient for Class A or B surfaces, as applicable, or as
established by tests................................................................................ 10.3.8
Resistance factor, specified in Chapters 2 through 11 ........................... 2.3.3
Resistance factor for bearing on concrete ........................................... 9.6.3.1
Resistance factor for flexure ...................................................................... 6.1
Resistance factor for compression .......................................................... 2.3.6
Resistance factor for axially loaded composite columns ..................... 9.2.1.2
Resistance factor for torsion ................................................................... 8.3.1
Resistance factor for tension...................................................................... 4.2
Resistance factor for steel headed stud anchor in tension ................... 9.8.3.2
Resistance factor for shear ........................................................................ 7.1
SBC 306-CR-18
15
LIST OF SYMBOLS
v
sr
st
i
b
Resistance factor for steel headed stud anchor in shear ...................... 9.8.3.1
Minimum reinforcement ratio for longitudinal reinforcing .................... 9.2.1
The larger of Fyw /Fyst and 1.0 ................................................................. 7.3.3
Angle of loading measured from the weld longitudinal axis, degrees .. 10.2.4
Acute angle between the branch and chord, degrees ........................... 11.2.1
ngle of loading measured from the longitudinal axis of ith weld element,
degrees .................................................................................................. 10.2.4
Stiffness reduction parameter ................................................................. 3.2.3
COMMENTARY SYMBOLS
Symbol
Definition ............................................................................................ Section
A
Cf
Fys
H
Ig
ILB
Ipos
Ineg
Is
Itr
Iy Top
Iy
Ks
MCL
MS
MT
Mo
N
Qm
Rcap
Rm
Sr
Ss
Angle cross-sectional area, mm2 ............................................................... 7.4
Compression force in concrete slab for fully composite beam; smaller of Fy As
and 0.85fcAc, N ........................................................................................ 9.3.2
Static yield stress, MPa ......................................................................... 16.2.2
Height of anchor, mm ............................................................................. 9.8.2
Moment of inertia of gross concrete section about centroidal axis, neglecting
reinforcement, mm4 ................................................................................. 9.2.1
Lower bound moment of inertia, mm4 ..................................................... 9.3.2
Effective moment of inertia for positive moment, mm4 ........................... 9.3.2
Effective moment of inertia for negative moment, mm4 .......................... 9.3.2
Moment of inertia for the structural steel section,mm4........................... 9.3.2
Moment of inertia for the fully composite uncracked transformed section,mm4
.........................................................................................................................
................................................................................................................. 9.3.2
Moment of inertia of the top flange about an axis through the web, mm4 6.1
Moment of inertia of the entire section about an axis through the web, mm4
… ................................................................................................................ 6.1
Secant stiffness, MPa .............................................................................. 2.3.5
Moment at the middle of the unbraced length, N-mm ................................ 6.1
Moment at service loads, N-mm.............................................................. 2.3.5
Torsional moment, N-mm........................................................................... 7.4
Maximum first-order moment within the member due to the transverse
loading, N-mm.......................................................................................... G.2
Number of cycles to failure ....................................................................... C.3
Mean value of the load effect Q .............................................................. 2.3.3
Minimum rotation capacity .....................................................................A.2.2
Mean value of the resistance R ............................................................... 2.3.3
Stress range............................................................................................... C.3
Section modulus for the structural steel section, referred to the tension flange,
mm3 ......................................................................................................... 9.3.2
SBC 306-CR-18
16
LIST OF SYMBOLS
Str
VQ
VR
Vb
acr
ap
ay
fv
k
𝛽
𝛽act
𝛿𝑜
𝜈
𝜃𝑆
Section modulus for the fully composite uncracked transformed section,
referred to the tension flange of the steel section mm3 ........................... 9.3.2
Coefficient of variation of the load effect Q............................................ 2.3.3
Coefficient of variation of the resistance R............................................. 2.3.3
Component of the shear force parallel to the angle leg with width b and
thickness t, N .............................................................................................. 7.4
Distance from the compression face to the neutral axis for a slender section,
mm .............................................................................................................. 9.3
Distance from the compression face to the neutral axis for a compact section,
mm .............................................................................................................. 9.3
Distance from the compression face to the neutral axis for a noncompact
section, mm ................................................................................................ 9.3
Shear stress in angle, MPa ........................................................................ 7.4
Plate buckling coefficient characteristic of the type of plate edge-restraint5.7
Reliability index ...................................................................................... 2.3.3
Actual bracing stiffness provided...............................................................E.1
Maximum deflection due to transverse loading, mm ................................ G.2
Poisson’s ratio .......................................................................................... 5.7
Rotation at service loads, rad ................................................................. 2.3.5
SBC 306-CR-18
17
GLOSSARY
Glossary
Terms defined in this Glossary are italicized in the
Glossary and where they first appear within a section
or long paragraph throughout the code.
Notes:
(1) Terms designated with * are usually qualified
by the type of load effect; for example,
nominal tensile strength, design compressive
strength, and design flexural strength.
(2) Terms designated with ** are usually qualified by
the type of component; for example, web local
buckling and flange local bending.
Active fire protection. Building materials and systems
that are activated by a fire to mitigate adverse effects
or to notify people to take some action to mitigate
adverse effects.
Amplified seismic load. Seismic load effect including
overstrength factor.
Applicable building code. Building code under which
the structure is designed.
Authority having jurisdiction (AHJ). Organization,
political subdivision, office or individual charged
with the responsibility of administering and enforcing
the provisions of the applicable building code.
Average rib width. In a formed steel deck, average
width of the rib of a corrugation.
Block shear rupture. In a connection, limit state of
tension rupture along one path and shear yielding or
shear rupture along another path.
Boundary member. Portion along wall or diaphragm
edge strengthened with structural steel sections
and/or longitudinal steel reinforcement and
transverse reinforcement.
Braced frame. Essentially vertical truss system that
provides resistance to lateral forces and provides
stability for the structural system.
Bracing. Member or system that provides stiffness
and strength to limit the out-of-plane movement of
another member at a brace point.
Branch member. In an HSS connection, member that
terminates at a chord member or main member.
Buckling. Limit state of sudden change in the
geometry of a structure or any of its elements under a
critical loading condition.
Buckling strength. Strength for instability limit
states.
Buckling-restrained brace. A prefabricated, or
manufactured, brace element consisting of a steel
core and a buckling-restraining system as described
in Section 12.4 and qualified by testing.
Buckling-restrained braced frame (BRBF). A
diagonally braced frame employing buckling
restrained braces.
Batten plate. Plate rigidly connected to two parallel
components of a built-up column or beam designed
to transmit shear between the components.
Built-up member, cross section, section, shape.
Member, cross section, section or shape fabricated
from structural steel elements that are welded or
bolted together.
Beam. Nominally horizontal structural member that
has the primary function of resisting bending
moments.
Camber. Curvature fabricated into a beam or truss so
as to compensate for deflection induced by loads.
Beam-column. Structural member that resists both
axial force and bending moment.
Charpy V-notch impact test. Standard dynamic test
measuring notch toughness of a specimen.
Bearing. In a connection, limit state of shear forces
transmitted by the mechanical fastener to the
connection elements.
Chord member. In an HSS connection, primary
member that extends through a truss connection.
Bearing (local compressive yielding). Limit state of
local compressive yielding due to the action of a
member bearing against another member or surface.
Cold-formed steel structural member. Shape
manufactured by press-braking blanks sheared from
sheets, cut lengths of coils or plates, or by roll
forming cold- or hot-rolled coils or sheets; both
forming operations being performed at ambient room
temperature, that is, without manifest addition of heat
such as would be required for hot forming.
Bearing-type connection. Bolted connection where
shear forces are transmitted by the bolt bearing
against the connection elements.
Cladding. Exterior covering of structure.
SBC 306-CR-18
18
GLOSSARY
Collector. Also known as drag strut; member that
serves to transfer loads between floor diaphragms
and the members of the lateral force resisting system.
Column. Nominally vertical structural member that
has the primary function of resisting axial
compressive force.
Column base. Assemblage of structural shapes,
plates, connectors, bolts and rods at the base of a
column used to transmit forces between the steel
superstructure and the foundation.
Composite slab. Reinforced concrete slab supported
on and bonded to a formed steel deck that acts as a
diaphragm to transfer load to and between elements
of the seismic force resisting system.
Concrete breakout surface. The surface delineating a
volume of concrete surrounding a steel headed stud
anchor that separates from the remaining concrete.
Concrete crushing. Limit state of compressive
failure in concrete having reached the ultimate
strain.
Compact section. Section capable of developing a
fully plastic stress distribution and pos- sessing a
rotation capacity of approximately three before the
onset of local buckling.
Concrete haunch. In a composite floor system
constructed using a formed steel deck, the section of
solid concrete that results from stopping the deck on
each side of the girder.
Compartmentation. Enclosure of a building space
with elements that have a specific fire endurance.
Concrete-encased beam. Beam totally encased in
concrete cast integrally with the slab.
Complete-joint-penetration (CJP) groove weld.
Groove weld in which weld metal extends through
the joint thickness, except as permitted for HSS
connections.
Concrete-encased shapes. Structural steel sections
encased in concrete.
Composite. Condition in which steel and concrete
elements and members work as a unit in the
distribution of internal forces.
Composite beam. Structural steel beam in contact
with and acting compositely with a rein- forced
concrete slab.
Composite component. Member, connecting element
or assemblage in which steel and concrete elements
work as a unit in the distribution of internal forces,
with the exception of the special case of composite
beams where steel anchors are embedded in a solid
concrete slab or in a slab cast on formed steel deck.
Composite brace. Concrete-encased structural steel
section (rolled or built-up) or concrete filled steel
section used as a diagonal brace.
Composite column. Concrete-encased structural steel
section (rolled or built-up) or concrete-filled steel
section used as a column.
Composite intermediate moment frame (C-IMF).
Composite moment frame meeting the requirements
of Section 12.4.2 .
Connection. Combination of structural elements and
joints used to transmit forces between two or more
members.
Construction
specifications,
drawings.
documents. Design drawings,
shop drawings and erection
Continuity plates. Column stiffeners at the top and
bottom of the panel zone; also known as transverse
stiffeners.
Cope. Cutout made in a structural member to remove
a flange and conform to the shape of an intersecting
member.
Coupling beam. Structural steel or composite beam
connecting adjacent reinforced concrete wall
elements so that they act together to resist lateral
loads. Demand critical weld. Weld so designated by
these Provisions.
Cover plate. Plate welded or bolted to the flange of
a member to increase cross-sectional area, section
modulus or moment of inertia.
Composite ordinary braced frame (C-OBF).
Composite braced frame meeting the requirements of
Section 12.4.3 .
Cross connection. HSS connection in which forces
in branch members or connecting elements
transverse to the main member are primarily
equilibrated by forces in other branch members or
connecting elements on the opposite side of the main
member.
Composite ordinary moment frame (C-OMF).
Composite moment frame meeting the requirements
of Section 12.4.1 .
Design-basis fire. Set of conditions that define the
development of a fire and the spread of combustion
products throughout a building or portion thereof.
SBC 306-CR-18
19
GLOSSARY
Design drawings. Graphic and pictorial documents
showing the design, location and dimensions of the
work. These documents generally include plans,
elevations, sections, details, schedules, diagrams and
notes.
Design load. Applied load determined in accordance
with either LRFD load combinations.
Design strength*. Resistance factor multiplied by the
nominal strength, Rn.
Design wall thickness. HSS wall thickness assumed in
the determination of section properties.
Design earthquake. The earthquake represented by
the design response spectrum as specified in the
applicable building code.
Design story drift. Calculated story drift, including
the effect of expected inelastic action, due to design
level earthquake forces as determined by the
applicable building code.
Diagonal brace. Inclined structural member carrying
primarily axial force in a braced frame.
Diagonal stiffener. Web stiffener at column panel
zone oriented diagonally to the flanges, on one or
both sides of the web.
Diaphragm. Roof, floor or other membrane or bracing
system that transfers in-plane forces to the lateral
force resisting system.
Diaphragm plate. Plate possessing in-plane shear
stiffness and strength, used to transfer forces to the
supporting elements.
Direct analysis method. Design method for stability
that captures the effects of residual stresses and
initial out-of-plumbness of frames by reducing
stiffness and applying notional loads in a secondorder analysis.
Direct bond interaction. In a composite section,
mechanism by which force is transferred between
steel and concrete by bond stress.
Distortional failure. Limit state of an HSS truss
connection based on distortion of a rectangular HSS
chord member into a rhomboidal shape.
Distortional stiffness. Out-of-plane flexural stiffness
of web.
Double curvature. Deformed shape of a beam with one
or more inflection points within the span.
Double-concentrated forces. Two equal and
opposite forces applied normal to the same flange,
forming a couple.
Doubler. Plate added to, and parallel with, a beam
or column web to increase strength at locations of
concentrated forces.
Drift. Lateral deflection of structure.
Eccentrically braced frame (EBF). Diagonally
braced frame meeting the requirements of Section
12.4.3 that has at least one end of each diagonal brace
connected to a beam with a defined eccentricity from
another beam-to-brace connection or a beam-tocolumn connection.
Effective length. Length of an otherwise identical
column with the same strength when analyzed with
pinned end conditions.
Effective length factor, K. Ratio between the effective
length and the unbraced length of the member.
Effective net area. Net area modified to account for
the effect of shear lag.
Effective section modulus. Section modulus
reduced to account for buckling of slender
compression elements.
Effective width. Reduced width of a plate or slab
with an assumed uniform stress distribution which
produces the same effect on the behavior of a
structural member as the actual plate or slab width
with its nonuniform stress distribution.
Elastic analysis. Structural analysis based on the
assumption that the structure returns to its original
geometry on removal of the load.
Elevated
temperatures.
Heating
conditions
experienced by building elements or structures as a
result of fire which are in excess of the anticipated
ambient conditions.
Encased composite member. Composite member
consisting of a structural concrete member and one or
more embedded steel shapes.
Encased composite beam. Composite
completely enclosed in reinforced concrete.
beam
Encased composite column. Structural steel column
completely encased in reinforced concrete.
End panel. Web panel with an adjacent panel on one
side only.
End return. Length of fillet weld that continues
around a corner in the same plane.
Engineer of record. Licensed professional
responsible for sealing the design drawings and
specifications.
SBC 306-CR-18
20
GLOSSARY
Engineer of record. Licensed professional
responsible for sealing the contract documents.
Expansion rocker. Support with curved surface on
which a member bears that can tilt to accommodate
expansion.
Expansion roller. Round steel bar on which a
member bears that can roll to accommodate
expansion.
Expected tensile strength*. Tensile strength of a
member, equal to the specified minimum tensile
strength, Fu, multiplied by Rt.
Expected yield strength. Yield strength in tension of
a member, equal to the expected yield stress
multiplied by Ag.
Expected yield stress. Yield stress of the material,
equal to the specified minimum yield stress, F y,
multiplied by R y.
Eyebar. Pin-connected tension member of uniform
thickness, with forged or thermally cut head of
greater width than the body, proportioned to provide
approximately equal strength in the head and body.
Face bearing plates. Stiffeners attached to structural
steel beams that are embedded in reinforced concrete
walls or columns. The plates are located at the face of
the reinforced concrete to provide confinement and to
transfer loads to the concrete through direct bearing.
Finished surface. Surfaces fabricated with a
roughness height value measured in accordance with
ANSI/ASME B46.1 that is equal to or less than 500.
Fire. Destructive burning, as manifested by any or
all of the following: light, flame, heat or smoke.
Fire barrier. Element of construction formed of fireresisting materials and tested in accordance with an
approved standard fire resistance test, to demonstrate
compliance with the applicable building code.
Fire resistance. Property of assemblies that prevents
or retards the passage of excessive heat, hot gases or
flames under conditions of use and enables them to
continue to perform a stipulated function.
First-order analysis. Structural analysis in which
equilibrium conditions are formulated on the
undeformed structure; second-order effects are
neglected.
Fitted bearing stiffener. Stiffener used at a support
or concentrated load that fits tightly against one or
both flanges of a beam so as to transmit load through
bearing.
Flare bevel groove weld. Weld in a groove formed
by a member with a curved surface in contact with
a planar member.
Flare V-groove weld. Weld in a groove formed by two
members with curved surfaces.
Factored load. Product of a load factor and the
nominal load. Fastener. Generic term for bolts, rivets
or other connecting devices.
Flashover. Transition to a state of total surface
involvement in a fire of combustible materials within
an enclosure.
Fatigue. Limit state of crack initiation and growth
resulting from repeated application of live loads.
Flat width. Nominal width of rectangular HSS minus
twice the outside corner radius. In the absence of
knowledge of the corner radius, the flat width may
be taken as the total section width minus three times
the thickness.
Faying surface. Contact surface of connection
elements transmitting a shear force.
Filled composite member. Composite member
consisting of a shell of HSS filled with structural
concrete.
Filled composite column. HSS filled with structural
concrete.
Flexural buckling. Buckling mode in which a
compression member deflects laterally with- out
twist or change in cross-sectional shape.
Filler. Plate used to build up the thickness of one
component.
Flexural-torsional buckling. Buckling mode in
which a compression member bends and twists
simultaneously without change in cross-sectional
shape.
Filler metal. Metal or alloy added in making a
welded joint.
Force. Resultant of distribution of stress over a
prescribed area.
Fillet weld. Weld of generally triangular cross
section made between intersecting surfaces of
elements.
Formed section. See cold-formed steel structural
member.
Fillet weld reinforcement. Fillet welds added to
groove welds.
Formed steel deck. In composite construction, steel
cold formed into a decking profile used as a
permanent concrete form.
SBC 306-CR-18
21
GLOSSARY
Fully composite beam. Composite beam that has a
sufficient number of steel headed stud anchors to
develop the nominal plastic flexural strength of the
composite section.
Fully restrained moment connection. Connection
capable of transferring moment with negligible
rotation between connected members.
Gage. Transverse
fasteners.
center-to-center
spacing
of
Inelastic analysis. Structural analysis that takes into
account inelastic material behavior, including plastic
analysis.
In-plane instability. Limit state involving buckling in
the plane of the frame or the member.
Instability. Limit state reached in the loading of a
structural component, frame or structure in which a
slight disturbance in the loads or geometry produces
large displacements.
Gapped connection. HSS truss connection with a
gap or space on the chord face between intersecting
branch members.
Intermediate moment frame (IMF). Moment frame
system that meets the requirements of Section 12.3.2
.
Geometric axis. Axis parallel to web, flange or angle
leg.
Introduction length. In an encased composite
column, the length along which the column force is
assumed to be transferred into or out of the steel
shape.
Girder. See Beam.
Girder filler. In a composite floor system
constructed using a formed steel deck, narrow piece
of sheet steel used as a fill between the edge of a
deck sheet and the flange of a girder.
Gouge. Relatively smooth surface groove or cavity
resulting from plastic deformation or removal of
material.
Gravity load. Load acting in the downward direction,
such as dead and live loads.
Grip (of bolt). Thickness of material through which a
bolt passes.
Groove weld. Weld in a groove between connection
elements. See also AWS D1.1/D1.1M.
Gusset plate. Plate element connecting truss
members or a strut or brace to a beam or column.
Heat flux. Radiant energy per unit surface area.
Heat release rate. Rate at which thermal energy is
generated by a burning material.
High-strength bolt. Fastener in compliance with
ASTM A325, A325M, A490, A490M, F1852,
F2280 or an alternate fastener as permitted in Section
10.3.1 .
Highly ductile member. A member expected to
undergo significant plastic rotation (more than 0.02
rad) from either flexure or flexural buckling under the
design earthquake.
Horizontal shear. In a composite beam, force at the
interface between steel and concrete surfaces.
HSS. Square, rectangular or round hollow structural
steel section produced in accordance with a pipe or
tubing product specification.
Inverted-V-braced frame. See V-braced frame.
Joint. Area where two or more ends, surfaces or
edges are attached. Categorized by type of fastener
or weld used and method of force transfer.
Joint eccentricity. In an HSS truss connection,
perpendicular distance from chord member center of
gravity to intersection of branch member work points.
k-area. The region of the web that extends from the
tangent point of the web and the flange- web fillet a
distance 38 mm into the web beyond the k
dimension.
K-braced frame. A braced-frame configuration in
which braces connect to a column at a location with
no out-of-plane support.
K-connection. HSS connection in which forces in
branch members or connecting elements transverse
to the main member are primarily equilibriated by
forces in other branch members or connecting
elements on the same side of the main member.
Lacing. Plate, angle or other steel shape, in a lattice
configuration, that connects two steel shapes
together.
Lap joint. Joint between two overlapping connection
elements in parallel planes.
Lateral bracing. Member or system that is designed
to inhibit lateral buckling or lateral- torsional
buckling of structural members.
Lateral force resisting system. Structural system
designed to resist lateral loads and provide stability
for the structure as a whole.
Lateral load. Load acting in a lateral direction, such
as wind or earthquake effects.
SBC 306-CR-18
22
GLOSSARY
Lateral-torsional buckling. Buckling mode of a
flexural member involving deflection out of the
plane of bending occurring simultaneously with twist
about the shear center of the cross section.
Leaning column. Column designed to carry gravity
loads only, with connections that are not intended to
provide resistance to lateral loads.
Length effects. Consideration of the reduction in
strength of a member based on its unbraced length.
Lightweight concrete. Structural concrete with an
equilibrium density of 1840 kg/m3 or less as
determined by ASTM C567.
Limit state. Condition in which a structure or
component becomes unfit for service and is judged
either to be no longer useful for its intended function
(serviceability limit state) or to have reached its
ultimate load-carrying capacity (strength limit state).
Link. In EBF, the segment of a beam that is located
between the ends of the connections of two diagonal
braces or between the end of a diagonal brace and a
column. The length of the link is defined as the clear
distance between the ends of two diagonal braces or
between the diagonal brace and the column face.
Link intermediate web stiffeners. Vertical web
stiffeners placed within the link in EBF.
Local yielding**. Yielding that occurs in a local area
of an element.
Lowest anticipated service temperature (LAST). The
lowest 1-hour average temperature with a 100-year
mean recurrence interval.
LRFD (load and resistance factor design). Method of
proportioning structural components such that the
design strength equals or exceeds the required
strength of the component under the action of the
LRFD load combinations.
LRFD load combination. Load combination in the
applicable building code intended for strength design
(load and resistance factor design).
Main member. In an HSS connection, chord member,
column or other HSS member to which branch
members or other connecting elements are attached.
Mechanism. Structural system that includes a
sufficient number of real hinges, plastic hinges or
both, so as to be able to articulate in one or more rigid
body modes.
Member brace. Member that provides stiffness and
strength to control movement of another member outof-the plane of the frame at the braced points.
Mill scale. Oxide surface coating on steel formed by
the hot rolling process.
Link rotation angle. Inelastic angle between the link
and the beam outside of the link when the total story
drift is equal to the design story drift.
Moment connection. Connection that transmits
bending moment between connected members.
Load-carrying reinforcement. Reinforcement in
composite members designed and detailed to resist
the required loads.
Moderately ductile member. A member expected to
undergo moderate plastic rotation (0.02rad or less)
from either flexure or flexural buckling under the
design earthquake.
Load. Force or other action that results from the
weight of building materials, occupants and their
possessions, environmental effects, differential
movement or restrained dimensional changes.
Load effect. Forces, stresses and deformations
produced in a structural component by the applied
loads.
Load factor. Factor that accounts for deviations of
the nominal load from the actual load, for
uncertainties in the analysis that transforms the load
into a load effect and for the prob- ability that more
than one extreme load will occur simultaneously.
Local bending**. Limit state of large deformation of
a flange under a concentrated transverse force.
Local buckling**. Limit state of buckling of a
compression element within a cross section.
Moment frame. Framing system that provides
resistance to lateral loads and provides stability to the
structural system, primarily by shear and flexure of the
framing members and their connections.
Negative flexural strength. Flexural strength of a
composite beam in regions with tension due to
flexure on the top surface.
Net area. Gross area reduced to account for removed
material.
Nodal brace. Brace that prevents lateral movement or
twist independently of other braces at adjacent brace
points (see relative brace).
Nominal dimension. Designated or theoretical
dimension, as in tables of section properties.
Nominal load. Magnitude of the load specified by the
applicable building code.
SBC 306-CR-18
23
GLOSSARY
Nominal rib height. In a formed steel deck, height of
deck measured from the underside of the lowest
point to the top of the highest point.
Nominal strength*. Strength of a structure or
component (without the resistance factor or safety
factor applied) to resist load effects, as determined in
accordance with this code.
Noncompact section. Section that can develop the
yield stress in its compression elements before local
buckling occurs, but cannot develop a rotation
capacity of three.
Nondestructive testing. Inspection procedure
wherein no material is destroyed and the integrity
of the material or component is not affected.
Notch toughness. Energy absorbed at a specified
temperature as measured in the Charpy V-notch
impact test.
Notional load. Virtual load applied in a structural
analysis to account for destabilizing effects that are
not otherwise accounted for in the design provisions.
Ordinary cantilever column system (OCCS). A
seismic force resisting system in which the seismic
forces are resisted by one or more columns that are
cantilevered from the foundation or from the
diaphragm level below and that meets the
requirements of Section 12.3.3 .
Ordinary concentrically braced frame (OCBF).
Diagonally braced frame meeting the requirements of
Section 12.3.4 in which all members of the bracedframe system are subjected primarily to axial forces.
Ordinary moment frame (OMF). Moment frame
system that meets the requirements of Section 12.3.1
.
Out-of-plane buckling. Limit state of a beam, column
or beam-column involving lateral or lateral-torsional
buckling.
Overlapped connection. HSS truss connection in
which intersecting branch members overlap.
Panel zone. Web area of beam-to-column
connection delineated by the extension of beam
and column flanges through the connection,
transmitting moment through a shear panel.
Partial-joint-penetration (PJP) groove weld. Groove
weld in which the penetration is intentionally less
than the complete thickness of the connected
element.
Partially restrained moment connection. Connection
capable of transferring moment with rotation
between connected members that is not negligible.
Percent elongation. Measure of ductility, determined
in a tensile test as the maximum elongation of the
gage length divided by the original gage length
expressed as a percentage.
Pipe. See HSS.
Pitch. Longitudinal center-to-center spacing of
fasteners. Center-to-center spacing of bolt threads
along axis of bolt.
Plastic analysis. Structural analysis based on the
assumption of rigid-plastic behavior, that is, that
equilibrium is satisfied and the stress is at or below
the yield stress throughout the structure.
Plastic hinge. Fully yielded zone that forms in a
structural member when the plastic moment is
attained.
Plastic moment. Theoretical resisting moment
developed within a fully yielded cross section.
Plastic stress distribution method. In a composite
member, method for determining stresses assuming
that the steel section and the concrete in the cross
section are fully plastic.
Plastification. In an HSS connection, limit state based
on an out-of-plane flexural yield line mechanism in
the chord at a branch member connection.
Plastic hinge. Yielded zone that forms in a structural
member when the plastic moment is attained. The
member is assumed to rotate further as if hinged,
except that such rotation is restrained by the plastic
moment.
Plate girder. Built-up beam.
Plug weld. Weld made in a circular hole in one
element of a joint fusing that element to another
element.
Ponding. Retention of water due solely to the
deflection of flat roof framing.
Positive flexural strength. Flexural strength of a
composite beam in regions with compres- sion due
to flexure on the top surface.
Pretensioned bolt. Bolt tightened to the specified
minimum pretension.
Pretensioned joint. Joint with high-strength bolts
tightened to the specified minimum pretension.
Properly developed. Reinforcing bars detailed to
yield in a ductile manner before crushing of the
concrete occurs. Bars meeting the provisions of SBC
304, insofar as development length, spacing and
cover, are deemed to be properly developed.
SBC 306-CR-18
24
GLOSSARY
Protected zone. Area of members or connections of
members in which limitations apply to fabrication
and attachments.
Prying action. Amplification of the tension force in
a bolt caused by leverage between the point of
applied load, the bolt and the reaction of the
connected elements.
Punching load. In an HSS connection, component of
branch member force perpendicular to a chord.
P- effect. Effect of loads acting on the deflected
shape of a member between joints or nodes.
P-Δeffect. Effect of loads acting on the displaced
location of joints or nodes in a structure. In tiered
building structures, this is the effect of loads acting
on the laterally displaced location of floors and roofs.
Quality assurance. Monitoring and inspection tasks
to ensure that the material provided and work
performed by the fabricator and erector meet the
requirements of the approved construction documents
and referenced standards. Quality assurance
includes those tasks designated “special inspection”
by the applicable building code.
Quality assurance inspector (QAI). Individual
designated to provide quality assurance inspection
for the work being performed.
Quality assurance plan (QAP). Program in which
the agency or firm responsible for quality
assurance maintains detailed monitoring and
inspection procedures to ensure conformance with
the approved construction documents and referenced
standards.
Quality control. Controls and inspections
implemented by the fabricator or erector, as applicable, to ensure that the material provided and work
performed meet the requirements of the approved
construction documents and referenced standards.
Quality control inspector (QCI). Individual
designated to perform quality control inspection tasks
for the work being performed.
Quality control program (QCP). Program in which
the fabricator or erector, as applicable, maintains
detailed fabrication or erection and inspection
procedures to ensure conformance with the approved
design drawings, specifications and referenced
standards.
Reentrant. In a cope or weld access hole, a cut at an
abrupt change in direction in which the exposed
surface is concave.
Relative brace. Brace that controls the relative
movement of two adjacent brace points along the
length of a beam or column or the relative lateral
displacement of two stories in a frame (see nodal
brace).
Required
strength*.
Forces,
stresses
and
deformations acting on a structural component,
determined by either structural analysis, for the
LRFD load combinations.
Required strength*. Forces, stresses and
deformations acting on a structural component,
determined by structural analysis, for the LRFD load
combinations.
Resistance factor . Factor that accounts for
unavoidable deviations of the nominal strength from
the actual strength and for the manner and
consequences of failure.
Restrained construction. Floor and roof assemblies
and individual beams in buildings where the
surrounding or supporting structure is capable of
resisting substantial thermal expansion throughout
the range of anticipated elevated temperatures.
Response modification coefficient, R. Factor that
reduces seismic load effects to strength level as
specified by the applicable building code.
Reverse curvature. See double curvature.
Risk category. Classification assigned to a structure
based on its use as specified by the applicable
building code.
Root of joint. Portion of a joint to be welded where
the members are closest to each other.
Rotation capacity. Incremental angular rotation that a
given shape can accept prior to excessive load
shedding, defined as the ratio of the inelastic rotation
attained to the idealized elastic rotation at first yield..
Rupture strength. Strength limited by breaking or
tearing of members or connecting elements.
Second-order effect. Effect of loads acting on the
deformed configuration of a structure; includes Peffect and P-Δeffect.
Seismic response modification factor. Factor that
reduces seismic load effects to strength level.
Seismic design category. Classification assigned to a
building by the applicable building code based upon
its risk category and the design spectral response
acceleration coefficients.
Seismic force resisting system (SFRS). That part of
the structural system that has been considered in the
SBC 306-CR-18
25
GLOSSARY
design to provide the required resistance to the
seismic forces prescribed in SBC 301.
Slot weld. Weld made in an elongated hole fusing an
element to another element.
Service load. Load under which serviceability limit
states are evaluated.
Snug-tightened joint. Joint with the connected plies in
firm contact as specified in Chapter J.
Service load combination. Load combination under
which serviceability limit states are evaluated.
Specifications. Written documents containing the
requirements for materials, standards and
workmanship.
Serviceability limit state. Limiting condition
affecting the ability of a structure to preserve its
appearance, maintainability, durability or the
comfort of its occupants or function of machinery,
under normal usage.
Shear buckling. Buckling mode in which a plate
element, such as the web of a beam, deforms under
pure shear applied in the plane of the plate.
Shear lag. Nonuniform tensile stress distribution in a
member or connecting element in the vicinity of a
connection.
Shear wall. Wall that provides resistance to lateral
loads in the plane of the wall and provides stability
for the structural system.
Shear yielding (punching). In an HSS connection,
limit state based on out-of-plane shear strength of
the chord wall to which branch members are attached.
Sheet steel. In a composite floor system, steel used for
closure plates or miscellaneous trimming in a formed
steel deck.
Shim. Thin layer of material used to fill a space
between faying or bearing surfaces.
Sidesway buckling (frame). Stability limit state
involving lateral sidesway instability of a frame.
Simple connection. Connection that transmits
negligible bending moment between connected
members.
Single-concentrated force. Tensile or compressive
force applied normal to the flange of a member.
Single curvature. Deformed shape of a beam with no
inflection point within the span.
Slender-element section. Cross section possessing
plate components of sufficient slenderness such that
local buckling in the elastic range will occur.
Slip. In a bolted connection, limit state of relative
motion of connected parts prior to the attainment of
the design strength of the connection.
Slip-critical connection. Bolted connection designed
to resist movement by friction on the faying surface
of the connection under the clamping force of the
bolts.
Specified minimum tensile strength. Lower limit of
tensile strength specified for a material as defined by
ASTM.
Specified minimum yield stress. Lower limit of
yield stress specified for a material as defined by
ASTM.
Splice. Connection between two structural elements
joined at their ends to form a single, longer element.
Stability. Condition in the loading of a structural
component, frame or structure in which a slight
disturbance in the loads or geometry does not
produce large displacements.
Statically loaded. Not subject to significant fatigue
stresses. Gravity, wind and seismic loadings are
considered to be static loadings.
Steel anchor. Headed stud or hot rolled channel
welded to a steel member and embodied in concrete
of a composite member to transmit shear, tension or a
combination of shear and tension at the interface of
the two materials.
Stiffened element. Flat compression element with
adjoining out-of-plane elements along both edges
parallel to the direction of loading.
Stiffener. Structural element, usually an angle or
plate, attached to a member to distribute load,
transfer shear or prevent buckling.
Stiffness. Resistance to deformation of a member or
structure, measured by the ratio of the applied force
(or moment) to the corresponding displacement (or
rotation).
Strain compatibility method. In a composite
member, method for determining the stresses
considering the stress-strain relationships of each
material and its location with respect to the neutral
axis of the cross section.
Steel core. Axial-force-resisting element of a
buckling-restrained brace. The steel core contains a
yielding segment and connections to transfer its axial
force to adjoining elements; it may also contain
projections beyond the casing and transition segments
between the projections and yielding segment.
SBC 306-CR-18
26
GLOSSARY
Strength limit state. Limiting condition in which the
maximum strength of a structure or its components is
reached.
Stress. Force per unit area caused by axial force,
moment, shear or torsion.
Stress concentration. Localized stress considerably
higher than average due to abrupt changes in
geometry or localized loading.
Strong axis. Major principal centroidal axis of a cross
section.
Story drift angle. Inter story displacement divided by
story height.
Structural analysis. Determination of load effects on
members and connections based on principles of
structural mechanics.
Structural
component.
Member,
connecting element or assemblage.
connector,
Structural steel. Steel elements as defined in
Section 2.1 of the AISC (2010a) Code of Standard
Practice for Steel Buildings and Bridges.
Structural system. An assemblage of load-carrying
components that are joined together to provide
interaction or interdependence.
System overstrength factor, Ωo. Factor specified by
the applicable building code in order to determine the
amplified seismic load, where required by these
Provisions.
T-connection. HSS connection in which the branch
member or connecting element is perpendicular to
the main member and in which forces transverse to
the main member are primarily equilibriated by shear
in the main member.
Tensile strength (of material). Maximum tensile
stress that a material is capable of sustaining as
defined by ASTM.
Tensile strength (of member). Maximum tension
force that a member is capable of sustaining.
Tension and shear rupture. In a bolt or other type of
mechanical fastener, limit state of rupture due to
simultaneous tension and shear force.
Tension field action. Behavior of a panel under
shear in which diagonal tensile forces develop in
the web and compressive forces develop in the
transverse stiffeners in a manner similar to a Pratt
truss.
Thermally cut. Cut with gas, plasma or laser.
Tie plate. Plate element used to join two parallel
components of a built-up column, girder or strut
rigidly connected to the parallel components and
designed to transmit shear between them.
Toe of fillet. Junction of a fillet weld face and base
metal. Tangent point of a fillet in a rolled shape.
Torsional bracing. Bracing resisting twist of a beam
or column.
Torsional buckling. Buckling mode in which a
compression member twists about its shear center
axis.
Transverse reinforcement. In an encased composite
column, steel reinforcement in the form of closed ties
or welded wire fabric providing confinement for the
concrete surrounding the steel shape.
Transverse stiffener. Web stiffener oriented
perpendicular to the flanges, attached to the web.
Tubing. See HSS.
Turn-of-nut method. Procedure whereby the
specified pretension in high-strength bolts is
controlled by rotating the fastener component a
predetermined amount after the bolt has been snug
tightened.
Unbraced length. Distance between braced points of
a member, measured between the centers of gravity
of the bracing members.
Uneven load distribution. In an HSS connection,
condition in which the load is not distributed through
the cross section of connected elements in a manner
that can be readily determined.
Unframed end. The end of a member not restrained
against rotation by stiffeners or connection elements.
Unrestrained construction. Floor and roof assemblies
and individual beams in buildings that are assumed to
be free to rotate and expand throughout the range of
anticipated elevated temperatures.
Unstiffened element. Flat compression element
with an adjoining out-of-plane element along one
edge parallel to the direction of loading.
Vertical boundary element (VBE). A column with a
connection to one or more web plates in an SPSW.
V-braced frame. Concentrically braced frame
(OCBF, C-OBF) in which a pair of diagonal braces
located either above or below a beam is connected to
a single point within the clear beam span. Where the
diagonal braces are below the beam, the system is
also referred to as an inverted-V-braced frame.
SBC 306-CR-18
27
GLOSSARY
Weak axis. Minor principal centroidal axis of a cross
section.
Weathering steel. High-strength, low-alloy steel that,
with suitable precautions, can be used in normal
atmospheric exposures (not marine) without
protective paint coating.
Web crippling. Limit state of local failure of web
plate in the immediate vicinity of a concentrated load
or reaction.
Web sidesway buckling. Limit state of lateral
buckling of the tension flange opposite the location
of a concentrated compression force.
Weld metal. Portion of a fusion weld that has been
completely melted during welding. Weld metal has
elements of filler metal and base metal melted in the
weld thermal cycle.
Weld root. See root of joint.
X-braced frame. Concentrically braced frame
(OCBF, C-OBF) in which a pair of diagonal braces
crosses near the mid-length of the diagonal braces.
Y-connection. HSS connection in which the branch
member or connecting element is not perpendicular
to the main member and in which forces transverse to
the main member are primarily equilibriated by shear
in the main member.
Yield moment. In a member subjected to bending, the
moment at which the extreme outer fiber first attains
the yield stress.
Yield point. First stress in a material at which an
increase in strain occurs without an increase in
stress as defined by ASTM.
Yield strength. Stress at which a material exhibits a
specified limiting deviation from the proportionality
of stress to strain as defined by ASTM.
Yield stress. Generic term to denote either yield point
or yield strength, as appropriate for the material.
Yielding. Limit state of inelastic deformation that
occurs when the yield stress is reached.
Yielding (plastic moment). Yielding throughout the
cross section of a member as the bending moment
reaches the plastic moment.
Yielding (yield moment). Yielding at the extreme fiber
on the cross section of a member when the bending
moment reaches the yield moment.
SBC 306-CR-18
28
CHAPTER 1—GENERAL PROVISIONS
CHAPTER 1—GENERAL PROVISIONS
This chapter states the scope of the Code,
summarizes referenced specifications, codes
and standards, and provides requirements for
materials and structural design documents.
The chapter is organized as follows:
1.1
—Scope
1.2
—Referenced Specifications, Codes and
Standards
designs are permitted to be based on tests or
analysis, subject to the approval of the authority
having jurisdiction.
Alternative methods of analysis and design are
permitted, provided such alternative methods or
criteria are acceptable to the authority having
jurisdiction.
and
1.1—Scope
User Note: For the design of cold-formed
structural members, other than hollow structural
sections (HSS) that are cold-formed to shapes
with elements not more than 25 mm in thickness,
the provisions of the AISI North American
Specification for the Design of Cold-Formed
Steel Structural Members (AISI S100) are
recommended.
The Saudi Building Code for Steel Structures
(SBC 306), hereafter referred to as the Code,
provides minimum requirements for design and
construction of Steel Structures. This Code shall
apply to the design of the structural steel system
or systems with structural steel acting
compositely with reinforced concrete.
1.1.1 Seismic Applications.
The Seismic
Provisions for Structural Steel Buildings in Chapter
12 shall apply to the design of seismic force
resisting systems of structural steel or of structural
steel acting compositely with reinforced concrete,
unless specifically exempted by other Saudi
building codes.
1.3
—Material
1.4
—Structural Design
Specifications
Drawings
This Code includes the Symbols, the Glossary,
Chapter 1 through Chapter 16, and Appendix A
through Appendix G. The Commentary and the
Notes interspersed through-out are not part of
the Code.
User Note: Notes are intended to provide concise
and practical guidance in the application of the
provisions.
This Code sets forth criteria for the design,
fabrication and erection of structural steel
buildings and other structures, where other
structures are defined as structures designed,
fabricated and erected in a manner similar to
buildings, with building-like vertical and lateral
load resisting-elements.
Wherever this Code refers to the applicable
building code and there is none, the loads, load
combinations, system limitations, and general
design requirements shall be those in Saudi
Building Code: Minimum Design Loads for
Buildings and other Structures (SBC 301).
Where conditions are not covered by the Code,
User Note: SBC 301 (Table 12-1, Item H)
specifically exempts structural steel systems,
but not composite systems, in seismic design
categories B and C from the provisions of
Chapter 12 if the seismic loads are computed
using a seismic response modification factor,
R, of 3. For Seismic Design Category A, SBC
301 does specify lateral forces to be used as the
seismic loads and effects, but these
calculations do not involve the use of an R
factor. Thus for Seismic Design Category A, it
is not necessary to define a seismic force
resisting system that meets any special
requirements and the Seismic Provisions for
Structural Steel Buildings do not apply.
The provisions of Appendix A of this Code shall
not apply to the seismic design of buildings and
other structures.
1.1.2 Nuclear Applications. The design,
fabrication and erection of nuclear structures
shall comply with the requirements of the
Specification for Safety-Related Steel Structures
SBC 306-CR-18
29
CHAPTER 1—GENERAL PROVISIONS
for Nuclear Facilities (ANSI/AISC N690), in
addition to the provisions of this Code.
1.2—Referenced Specifications, Codes
and Standards
The following specifications, codes and standards
are referenced in this code:
Saudi Building Codes (SBC)
SBC 301-18 Saudi Building Code- General.
SBC 301-18 Saudi Building Code for Loading and
Forces.
SBC 304-18 Saudi Building Code for Concrete
Structures.
ACI International (ACI)
ACI 349-13 Code Requirements for Nuclear SafetyRelated Concrete Structures and Commentary
American Institute of Steel Construction (AISC)
AISC 303-10 Code of Standard Practice for Steel
Buildings and Bridges
A6/A6M-09 Standard Specification for General
Requirements for Rolled Structural Steel Bars,
Plates, Shapes, and Sheet Piling
A36/A36M-08 Standard Specification for Carbon
Structural Steel
A53/A53M-07 Standard Specification for Pipe,
Steel, Black and Hot-Dipped, Zinc- Coated, Welded
and Seamless
A193/A193M-08b Standard Specification for
Alloy-Steel and Stainless Steel Bolting Materials for
High Temperature or High Pressure Service and
Other Special Purpose Applications
A194/A194M-09 Standard Specification for
Carbon and Alloy Steel Nuts for Bolts for High
Pressure or High Temperature Service, or Both
A216/A216M-08 Standard Specification for Steel
Castings, Carbon, Suitable for Fusion Welding, for
High Temperature Service
A242/A242M-04 (2009) Standard Specification for
High-Strength Low-Alloy Structural Steel
for
A283/A283M-03 Standard Specification for Low
and Intermediate Tensile Strength Carbon Steel
Plates
ANSI/AISC N690-12 Specification for SafetyRelated Steel Structures for Nuclear Facilities
A307-07b Standard Specification for Carbon Steel
Bolts and Studs, 60,000 PSI (420 MPa) Tensile
Strength
ANSI/AISC 341-10 Seismic
Structural Steel Buildings
Provisions
American Society of Civil Engineers (ASCE)
ASCE/SEI/SFPE 29-05 Standard Calculation
Methods for Structural Fire Protection
American
(ASME)
Society
of
Mechanical
Engineers
ASME B18.2.6-10 Fasteners for Use in Structural
Applications
ASME B46.1-09 Surface Texture,
Roughness, Waviness, and Lay
Surface
American Society for Nondestructive Testing
(ASNT)
ANSI/ASNT
CP-189-2011
Standard
for
Qualification and Certification of Nondestructive
Testing Personnel
Recommended Practice No. SNT-TC-1A-2011
Personnel Qualification and Certification in
Nondestructive Testing
ASTM International (ASTM)
A325M-09 Standard Specification for Structural
Bolts, Steel, Heat Treated 830 MPa Minimum
Tensile Strength
A354-07a Standard Specification for Quenched
and Tempered Alloy Steel Bolts, Studs, and Other
Externally Threaded Fasteners
A370-09 Standard Test Methods and Definitions
for Mechanical Testing of Steel Products
A449-07b Standard Specification for Hex Cap
Screws, Bolts and Studs, Steel, Heat Treated,
120/105/90 ksi (830/730/630MPa) Minimum
Tensile Strength, General Use
A490-08b Standard Specification for HeatTreated Steel Structural Bolts, Alloy Steel, Heat
Treated, 150 ksi ( 1040MPa) Minimum Tensile
Strength
A490M-08 Standard Specification for HighStrength Steel Bolts, Classes 10.9 and 10.9.3, for
Structural Steel Joints
A500/A500M-07 Standard Specification for ColdFormed Welded and Seamless Carbon Steel
Structural Tubing in Rounds and Shapes
SBC 306-CR-18
30
CHAPTER 1—GENERAL PROVISIONS
A501-07 Standard Specification for Hot-Formed
Welded and Seamless Carbon Steel Structural
Tubing
A502-03 Standard Specification
Structural Rivets, Steel, Structural
for
Steel
A514/A514M-05 Standard Specification for HighYield Strength, Quenched and Tempered Alloy Steel
Plate, Suitable for Welding
A529/A529M-05 Standard Specification for HighStrength Carbon-Manganese Steel of Structural
Quality
A563M-07 Standard Specification for Carbon and
Alloy Steel Nuts
A568/A568M-09 Standard Specification for Steel,
Sheet, Carbon, Structural, and High-Strength, LowAlloy, Hot-Rolled and Cold-Rolled
A572/A572M-07 Standard Specification for HighStrength Low-Alloy Columbium - Vanadium
Structural Steel
A588/A588M-05 Standard Specification for HighStrength Low-Alloy Structural Steel, up to 345 MPa
Minimum Yield Point, with Atmospheric Corrosion
Resistance
A606/A606M-09 Standard Specification for Steel,
Sheet and Strip, High-Strength, Low-Alloy, HotRolled and Cold-Rolled, with Improved
Atmospheric Corrosion Resistance
A618/A618M-04 Standard Specification for HotFormed Welded and Seamless High-Strength LowAlloy Structural Tubing
A668/A668M-04 Standard Specification for Steel
Forgings, Carbon and Alloy, for General Industrial
Use
A673/A673M-04 Standard Specification for
Sampling Procedure for Impact Testing of
Structural Steel
A709/A709M-09 Standard
Structural Steel for Bridges
Specification
for
A751-08 Standard Test Methods, Practices, and
Terminology for Chemical Analysis of Steel
Products
A847/A847M-05 Standard Specification for ColdFormed Welded and Seamless High-Strength, LowAlloy Structural Tubing with Improved
Atmospheric Corrosion Resistance
A852/A852M-03 (2007) Standard Specification for
Quenched and Tempered Low- Alloy Structural
Steel Plate with 485 MPa Minimum Yield Strength
to 100 mm Thick
A913/A913M-07 Standard Specification for HighStrength Low-Alloy Steel Shapes of Structural
Quality, Produced by Quenching and SelfTempering Process (QST)
A992/A992M-06a Standard
Structural Steel Shapes
Specification
for
A1011/A1011M-09a Standard Specification for
Steel, Sheet and Strip, Hot-Rolled, Carbon,
Structural, High-Strength Low-Alloy, HighStrength Low-Alloy with Improved Formability,
and Ultra-High Strength
A1043/A1043M-05 Standard Specification for
Structural Steel with Low Yield to Tensile Ratio for
Use in Buildings
C567-05a Standard Test Method for Determining
Density of Structural Lightweight Concrete
E119-08a Standard Test Methods for Fire Tests of
Building Construction and Materials
E165-02 Standard Test Method for Liquid
Penetrant Examination E709-08 Standard Guide
for Magnetic Particle Examination
F436-09 Standard Specification for Hardened Steel
Washers
F436M-09 Standard Specification for Hardened
Steel Washers
F606-07 Standard Test Methods for Determining
the Mechanical Properties of Externally and
Internally Threaded Fasteners, Washers, Direct
Tension Indicators, and Rivets
F606M-07 Standard Test Methods for Determining
the Mechanical Properties of Externally and
Internally Threaded Fasteners, Washers, and
Rivets
F844-07a Standard Specification for Washers,
Steel, Plain (Flat), Unhardened for General Use
F959-09 Standard Specification for CompressibleWasher-Type Direct Tension Indicators for Use
with Structural Fasteners
F959M-07
Standard
Specification
for
Compressible-Washer-Type
Direct
Tension
Indicators for Use with Structural Fasteners
F1554-07a Standard Specification for Anchor
Bolts, Steel, 36, 55, and 105 ksi (240,380, and 730
MPa) Yield Strength
SBC 306-CR-18
31
CHAPTER 1—GENERAL PROVISIONS
User Note: ASTM F1554 is the most
commonly referenced specification for anchor
rods.
F1852-08 Standard Specification for “Twist-Off”
Type Tension Control Structural Bolt/Nut/Washer
Assemblies, Steel, Heat Treated, 120/105 ksi
(830/730MPa) Minimum Tensile Strength
F2280-08 Standard Specification for “Twist Off”
Type Tension Control Structural Bolt/ Nut/Washer
Assemblies, Steel, Heat Treated, 150 ksi (1040
MPa) Minimum Tensile Strength
American Welding Society (AWS)
AWS D1.3 -2008 Structural Welding Code—Sheet
Steel
AWS D1.4/D1.4M-2005
Code—Reinforcing Steel
Structural
Welding
AWS D1.4/D1.4M-2005 Structural
Code—Seismic Supplement
Welding
Research Council on Structural Connections
(RCSC)
Specification for Structural Joints Using HighStrength Bolts, 2009
1.3—Material
AWS A5.1/A5.1M-2004 Specification for Carbon
Steel Electrodes for Shielded Metal Arc Welding
AWS A5.18/A5.18M-2005 Specification for
Carbon Steel Electrodes and Rods for Gas Shielded
Arc Welding
1.3.1 Structural Steel Materials. Material test
reports or reports of tests made by the fabricator or
a testing laboratory shall constitute sufficient
evidence of conformity with one of the ASTM
standards listed in Section 1.3.1.1 For hot-rolled
structural shapes, plates, and bars, such tests shall
be made in accordance with ASTM A6/A6M; for
sheets, such tests shall be made in accordance with
ASTM A568/A568M; for tubing and pipe, such
tests shall be made in accordance with the
requirements of the applicable ASTM standards
listed above for those product forms.
AWS A5.20/A5.20M-2005 Specification for
Carbon Steel Electrodes for Flux Cored Arc
Welding
1.3.1.1 ASTM Designations. Structural steel
material conforming to one of the following ASTM
specifications is approved for use under this Code:
AWS A5.23/A5.23M-2007 Specification for LowAlloy Steel Electrodes and Fluxes for Submerged
Arc Welding
1.3.1.1.1
ASTM A36/A36M
ASTM A709/A709M
AWS A5.25/A5.25M-1997 (R2009) Specification
for Carbon and Low-Alloy Steel Electrodes and
Fluxes for Electroslag Welding
ASTM A529/A529M
ASTM A913/A913M
ASTM A572/A572M
ASTM A992/ A992M
ASTM A588/A588M
ASTM A1043/A1043M
AWS A5.5/A5.5M-2004 Specification for LowAlloy Steel Electrodes for Shielded Metal Arc
Welding
AWS A5.17/A5.17M-1997 (R2007) Specification
for Carbon Steel Electrodes and Fluxes for
Submerged Arc Welding
AWS A5.26/A5.26M-1997 (R2009) Specification
for Carbon and Low-Alloy Steel Electrodes for
Electrogas Welding
AWS A5.28/A5.28M-2005 Specification for LowAlloy Steel Electrodes and Rods for Gas Shielded
Arc Welding
AWS A5.29/A5.29M-2005 Specification for LowAlloy Steel Electrodes for Flux Cored Arc Welding
AWS A5.32/A5.32M-1997 (R2007) Specification
for Welding Shielding Gases
AWS B5.1-2003 Specification for the Qualification
of Welding Inspectors
AWS D1.1M-2010 Structural Welding Code—
Steel
Hot-rolled structural shapes
1.3.1.1.2
Structural tubing
ASTM A500
ASTM A618/A618M
ASTM A501
ASTM A847/A847M
1.3.1.1.3
Pipe
ASTM A53/A53M, Gr. B
1.3.1.1.4
Plates
ASTM A36/A36M
ASTM A588/A588M
ASTM A242/A242M
ASTM A709/A709M
ASTM A283/A283M
ASTM A852/A852M
ASTM A514/A514M
ASTM A1011/A1011M
ASTM A529/A529M
ASTM A1043/A1043M
SBC 306-CR-18
32
CHAPTER 1—GENERAL PROVISIONS
ASTM A572/A572M
1.3.1.1.5
Bars
ASTM A36/A36M
ASTM A572/A572M
ASTM A529/A529M
ASTM A709/A709M
1.3.1.1.6
Sheets
ASTM A606/A606M
ASTM A1011/A1011M
HSLAS-F
SS,
HSLAS,
AND
User Note: Materials with other international
designations (e.g. JIS, EN) considered equivalent
to ASTM are also approved for use under this
code.
1.3.1.2 Unidentified Steel. Unidentified steel,
free of injurious defects, is permitted to be used only
for members or details whose failure will not
reduce the strength of the structure, either locally or
overall. Such use shall be subject to the approval of
the engineer of record.
User Note: Unidentified steel may be used for
details where the precise mechanical properties
and weldability are not of concern. These are
commonly curb plates, shims and other similar
pieces.
1.3.1.3 Rolled Heavy Shapes. ASTM A6/A6M
hot-rolled shapes with a flange thickness exceeding
50 mm are considered to be rolled heavy shapes.
Rolled heavy shapes used as members subject to
primary (computed) tensile forces due to tension
or flexure and spliced or connected using
complete-joint-penetration groove welds that fuse
through the thickness of the flange or the flange
and the web, shall be specified as follows. The
structural design documents shall require that
such shapes be supplied with Charpy V-notch
(CVN) impact test results in accordance with
ASTM A6/A6M, Supplementary Requirement
S30, Charpy V-Notch Impact Test for Structural
Shapes – Alternate Core Location. The impact test
shall meet a minimum average value of 27 J
absorbed energy at a maximum temperature of +21
ºC.
The above requirements do not apply if the splices
and connections are made by bolting. Where a
rolled heavy shape is welded to the surface of
another shape using groove welds, the requirement
above applies only to the shape that has weld metal
fused through the cross section.
User Note: Additional requirements for joints
in heavy rolled members are given in Sections
10.1.5 , 10.1.6 , 10.2.6 and 14.2.2 .
1.3.1.4 Built-Up Heavy Shapes. Built-up cross
sections consisting of plates with a thickness
exceeding 50 mm are considered built-up heavy
shapes. Built-up heavy shapes used as members
subject to primary (computed) tensile forces due
to tension or flexure and spliced or connected to
other members using complete-joint-penetration
groove welds that fuse through the thickness of
the plates, shall be specified as follows. The
structural design documents shall require that
the steel be supplied with Charpy V-notch
impact test results in accordance with ASTM
A6/A6M, Supplementary Requirement S5,
Charpy V-Notch Impact Test. The impact test shall
be conducted
in accordance with ASTM
A673/A673M, Frequency P, and shall meet a
minimum average value of 27 J absorbed energy
at a maximum temperature of +21 ºC.
When a built-up heavy shape is welded to the face
of another member using groove welds, the
requirement above applies only to the shape that
has weld metal fused through the cross section.
User Note: Additional requirements for joints
in heavy built-up members are given in
Sections 10.1.5 , 10.1.6 , 10.2.6 and 14.2.2 .
1.3.2 Steel Castings and Forgings. Steel
castings shall conform to ASTM A216/A216M,
Grade WCB with Supplementary Requirement
S11. Steel forgings shall conform to ASTM
A668/A668M. Test reports produced in accordance
with the above reference standards shall constitute
sufficient evidence of conformity with such
standards.
1.3.3 Bolts, Washers and Nuts. Bolt, washer
and nut material conforming to one of the
following ASTM specifications is approved for use
under this Code:
1.3.3.1 Bolts
ASTM A307
ASTM A490
ASTM A325
ASTM A490M
ASTM A325M
ASTM F1852
ASTM A354
ASTM F2280
ASTM A449
1.3.3.2 Nuts
SBC 306-CR-18
33
CHAPTER 1—GENERAL PROVISIONS
ASTM A194/A194M
AWS A5.17/A5.17M
AWS A5.28/A5.28M
ASTM A563
AWS A5.18/A5.18M
AWS A5.29/A5.29M
1.3.3.3 Washers
AWS A5.20/A5.20M
AWS A5.32/A5.32M
ASTM F436
ASTM A563M
ASTM F844
AWS A5.23/A5.23M
Direct
Manufacturer’s certification shall constitute
sufficient evidence of conformity with the
standards. Filler metals and fluxes that are suitable
for the intended application shall be selected.
Manufacturer’s certification shall constitute
sufficient evidence of conformity with the
standards.
1.3.6 Headed Stud Anchors. Steel headed stud
anchors shall conform to the requirements of
the
Structural Welding Code—Steel (AWS
D1.1/D1.1M).
ASTM F436M
1.3.3.4 Compressible-Washer-Type
Tension Indicators
ASTM F959
ASTM F959M
User Note: Materials with other international
designations (e.g. JIS, EN) considered equivalent
to ASTM are also approved for use under this
Code.
1.3.4 Anchor Rods and Threaded Rods.
Anchor rod and threaded rod material conforming
to one of the following ASTM specifications is
approved for use under this Code:
ASTM A36/A36M
ASTM A572/A572M
ASTM A193/A193M
ASTM A588/A588M
ASTM A354
ASTM F1554
Manufacturer’s certification shall constitute
sufficient evidence of conformity with AWS
D1.1/D1.1M.
1.4—Structural Design Drawings and
Specifications
The structural design drawings and specifications
shall meet the requirements in the Code of Standard
Practice for Steel Buildings and Bridges, AISC
303-10.
User Note: Provisions in this Code contain
information that is to be shown on design
drawings. These include:
ASTM A449
User Note: ASTM F1554 is the preferred
material specification for anchor rods.
Section 1.3.1.3 Rolled heavy shapes where
alternate core Charpy V-notch toughness
(CVN) is required
A449 material is acceptable for high-strength
anchor rods and threaded rods of any diameter.
Section 1.3.1.4 Built-up heavy shapes where
CVN toughness is required
Threads on anchor rods and threaded rods shall
conform to the Unified Standard Series of ASME
B18.2.6 and shall have Class 2A tolerances.
i)
Manufacturer’s certification shall constitute
sufficient evidence of conformity with the
standards.
User Note: Materials with other international
designations (e.g. JIS, EN) considered equivalent
to ASTM are also approved for use under this
Code.
1.3.5 Consumables for Welding. Filler metals
and fluxes shall conform to one of the following
specifications of the American Welding Society:
AWS A5.1/A5.1M
AWS A5.25/A5.25M
AWS A5.5/A5.5M
AWS A5.26/A5.26M
Section 10.3.1 Locations of connections
using pretensioned bolts
Other information is needed by the fabricator
or erector and should be shown on design
drawings including:
Fatigue details requiring nondestructive
testing (Appendix C; e.g., TABLE C-1, Cases
5.1 to 5.4)
Risk category (Chapter 15)
Indication of complete-joint-penetration (CJP)
welds subject to tension (Chapter 15)
SBC 306-CR-18
34
CHAPTER 1—GENERAL PROVISIONS
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SBC 306-CR-18
35
CHAPTER 2—DESIGN REQUIREMENTS
CHAPTER 2—DESIGN REQUIREMENTS
This chapter addresses general requirements for the
analysis and design of steel structures applicable to
all chapters of the Code. The chapter is organized
as follows:
2.1
—General Provisions
2.2
—Loads and Load Combinations
2.3
—Design Basis
2.4
—Member Properties
2.5
—Member Lengths
2.6
—Fabrication and Erection
2.7
—Quality Control and Quality Assurance
2.8
—Evaluation of Existing Structures
2.1—General Provisions
The design of members and connections shall be
consistent with the intended behavior of the framing
system and the assumptions made in the structural
analysis. Unless restricted by the Saudi Building
Code (SBC 301), lateral load resistance and
stability may be provided by any combination of
members and connections.
2.2—Loads and Load Combinations
The loads and load combinations shall be as
stipulated in SBC 301. For design purposes, the
nominal loads shall be taken as the loads stipulated
by the SBC 301.
2.3—Design Basis
Designs shall be made according to the provisions
for load and resistance factor design (LRFD).
2.3.1 Required Strength. The required strength
of structural members and connections shall be
determined by structural analysis for the
appropriate load combinations as stipulated in
Section 2.2. Design by elastic, inelastic or plastic
analysis is permitted. Provisions for inelastic and
plastic analysis are as stipulated in Appendix A,
Design by Inelastic Analysis.
2.3.2 Limit States. Design shall be based on the
principle that no applicable strength or
serviceability limit state shall be exceeded when the
structure is subjected to all appropriate load
combinations.
Design for structural integrity requirements shall be
based on nominal strength rather than design
strength. Limit states for connections based on
limiting deformations or yielding of the connection
components need not be considered for meeting
structural integrity requirements.
For the purpose of satisfying structural integrity
provisions of SBC 301, bearing bolts in
connections with short-slotted holes parallel to the
direction of the tension load are permitted, and shall
be assumed to be located at the end of the slot.
2.3.3 Design for Strength. Design shall satisfy
the requirements of this Code when the design
strength of each structural component equals or
exceeds the required strength determined on the
basis of the LRFD load combinations of SBC 301.
Design shall be performed in accordance with Eq.
(2-1):
𝑅𝑢 ≤ 𝜑 𝑅𝑛
(2-1)
where
Ru = required strength
Rn = nominal strength, specified in Chapter 2
through Chapter 11
= resistance factor, specified in Chapter 2
through Chapter 11
Rn = design strength
2.3.4 Design for Stability. General stability
shall be provided for the structure as a whole and
for each of its elements. Stability of the structure
and its elements shall be determined in accordance
with Chapter 3.
2.3.5 Design of Connections.
Connection
elements shall be designed in accordance with the
provisions of Chapters 10 and 11. The forces and
deformations used in design shall be consistent with
the intended performance of the connection and the
assumptions used in the structural analysis. Selflimiting inelastic deformations of the connections
are permitted. At points of support, beams, girders
and trusses shall be restrained against rotation about
their longitudinal axis unless it can be shown by
analysis that the restraint is not required.
SBC 306-CR-18
36
CHAPTER 2—DESIGN REQUIREMENTS
(a) Simple Connections: A simple connection
transmits a negligible moment. In the analysis
of the structure, simple connections may be
assumed to allow unrestrained relative
rotation between the framing elements being
connected. A simple connection shall have
sufficient rotation capacity to accommodate
the required rotation determined by the
analysis of the structure.
(b) Moment Connections: Two types of moment
connections, fully restrained and partially
restrained, are permitted, as specified below.
1. Fully
Restrained
(FR)
Moment
Connections. A fully restrained (FR)
moment connection transfers moment with
a negligible rotation between the
connected members. In the analysis of the
structure, the connection may be assumed
to allow no relative rotation. An FR
connection shall have sufficient strength
and stiffness to maintain the angle between
the connected members unchanged at the
strength limit states.
2. Partially Restrained (PR) Moment
Connections. Partially restrained (PR)
moment connections transfer moments, but
the rotation between connected members is
not negligible. In the analysis of the
structure, the force-deformation response
characteristics of the connection shall be
included. The response characteristics of a
PR connection shall be documented in the
technical literature or established by
analytical or experimental means. The
component elements of a PR connection
shall have sufficient strength, stiffness and
deformation capacity at the strength limit
states.
2.3.6 Moment Redistribution in Beams. The
required flexural strength of beams composed of
compact sections, as defined in Section 2.4.1 , and
satisfying the unbraced length requirements of
Section 6.13.5 may be taken as nine-tenths of the
negative moments at the points of support,
produced by the gravity loading and determined by
an elastic analysis satisfying the requirements of
Chapter 3, provided that the maximum positive
moment is increased by one-tenth of the average
negative moment determined by an elastic analysis.
This reduction is not permitted for moments in
members with Fy exceeding 450 MPa, for moments
produced by loading on cantilevers, for design
using partially restrained (PR) moment
connections, or for design by inelastic analysis
using the provisions of Appendix A. The required
axial strength shall not exceed 0.15 c Fy Ag; where
c is determined from Section 5.1, and Ag = gross
area of member, mm2, and Fy = specified minimum
yield stress, MPa.
2.3.7 Diaphragms and Collectors. Diaphragms
and collectors shall be designed for forces that
result from loads as stipulated in Section 2.2. They
shall be designed in conformance with the
provisions of Chapters 3 through 11, as applicable.
2.3.8 Design for Serviceability. The overall
structure and the individual members and
connections shall be checked for serviceability.
Requirements for serviceability design are given in
Chapter 13.
2.3.9 Design for Ponding. The roof system shall
be investigated through structural analysis to assure
adequate strength and stability under ponding
conditions, unless the roof surface is provided with
a slope of 20 mm per meter or greater toward points
of free drainage or an adequate system of drainage
is provided to prevent the accumulation of water.
Methods of checking ponding are provided in
Appendix B, Design for Ponding.
2.3.10 Design for Fatigue. Fatigue shall be
considered in accordance with Appendix C, Design
for Fatigue, for members and their connections
subject to repeated loading. Fatigue need not be
considered for seismic effects or for the effects of
wind loading on normal building lateral force
resisting systems and building enclosure
components.
2.3.11 Design for Fire Conditions. Two methods
of design for fire conditions are provided in
Appendix D, Structural Design for Fire Conditions:
by Analysis and by Qualification Testing.
Compliance with the fire protection requirements
given in SBC 801 shall be deemed to satisfy the
requirements of this section and Appendix D.
Nothing in this section is intended to create or imply
a contractual requirement for the engineer of record
responsible for the structural design or any other
member of the design team.
User Note: Design by qualification testing is the
prescriptive method specified in SBC 801.
Traditionally, on most projects where the
architect is the prime professional, the architect
has been the responsible party to specify and
coordinate fire protection requirements. Design
by analysis is a new engineering approach to fire
SBC 306-CR-18
37
CHAPTER 2—DESIGN REQUIREMENTS
protection. Designation of the person(s)
responsible for designing for fire conditions is a
contractual matter to be addressed on each
project.
2.3.12 Design for Corrosion Effects. Where
corrosion may impair the strength or serviceability
of a structure, structural components shall be
designed to tolerate corrosion or shall be protected
against corrosion.
2.3.13 Anchorage to Concrete.
Anchorage
between steel and concrete acting compositely shall
be designed in accordance with Chapter 9. The
design of column bases and anchor rods shall be in
accordance with Chapter 10.
2.4—Member Properties
2.4.1 Classification of Sections for Local
Buckling. For compression, sections are classified
as nonslender element or slender-element sections.
For a nonslender element section, the width-tothickness ratios of its compression elements shall
not exceed r from Table 2-1. If the width-tothickness ratio of any compression element exceeds
r, the section is a slender-element section.
For flexure, sections are classified as compact,
noncompact or slender-element sections. For a
section to qualify as compact, its flanges must be
continuously connected to the web or webs and the
width-to-thickness ratios of its compression
elements shall not exceed the limiting width-tothickness ratios, p, from Table 2-2. If the width-tothickness ratio of one or more compression
elements exceeds p, but does not exceed r from
Table 2-2, the section is noncompact. If the widthto-thickness ratio of any compression element
exceeds r, the section is a slender-element section.
(a) Unstiffened Elements. For unstiffened elements
supported along only one edge parallel to the
direction of the compression force, the width
shall be taken as follows:
1. For flanges of I-shaped members and tees,
the width, b, is one-half the full-flange
width, bf.
2. For legs of angles and flanges of channels
and zees, the width, b, is the full nominal
dimension.
3. For plates, the width, b, is the distance
from the free edge to the first row of
fasteners or line of welds.
4. For stems of tees, d is taken as the full
nominal depth of the section.
Refer to Table 2-1 and Table 2-2 for the graphic
representation of unstiffened element dimensions.
(b) Stiffened Elements. For stiffened elements
supported along two edges parallel to the
direction of the compression force, the width
shall be taken as follows:
1. For webs of rolled or formed sections, h is
the clear distance between flanges less the
fillet or corner radius at each flange; hc is
twice the distance from the center of
gravity to the inside face of the
compression flange less the fillet or corner
radius.
2. For webs of built-up sections, h is the
distance between adjacent lines of
fasteners or the clear distance between
flanges when welds are used, and hc is
twice the distance from the center of
gravity to the nearest line of fasteners at the
compression flange or the inside face of the
compression flange when welds are used;
hp is twice the distance from the plastic
neutral axis to the nearest line of fasteners
at the compression flange or the inside face
of the compression flange when welds are
used.
3. For flange or diaphragm plates in built-up
sections, the width, b, is the distance
between adjacent lines of fasteners or lines
of welds.
4. For flanges of rectangular hollow
structural sections (HSS), the width, b, is
the clear distance between webs less the
inside corner radius on each side. For webs
of rectangular HSS, h is the clear distance
between the flanges less the inside corner
radius on each side. If the corner radius is
not known, b and h shall be taken as the
corresponding outside dimension minus
three times the thickness. The thickness, t,
shall be taken as the design wall thickness,
per Section 2.4.2 .
5. For perforated cover plates, b is the
transverse distance between the nearest
line of fasteners, and the net area of the
plate is taken at the widest hole.
Refer to Table 2-1 and Table 2-2 for the graphic
representation of stiffened element dimensions.
SBC 306-CR-18
38
CHAPTER 2—DESIGN REQUIREMENTS
For tapered flanges of rolled sections, the thickness
is the nominal value halfway between the free edge
and the corresponding face of the web.
2.4.2 Design Wall Thickness for HSS. The
design wall thickness, t, shall be used in calculations
involving the wall thickness of hollow structural
sections (HSS). The design wall thickness, t, shall
be taken equal to 0.93 times the nominal wall
thickness for electric-resistance-welded (ERW)
HSS and equal to the nominal thickness for
submerged-arc-welded (SAW) HSS.
User Note: A pipe can be designed using the
provisions of the Code for round HSS sections
as long as the pipe conforms to ASTM A53
Class B and the appropriate limitations of the
Code are used.
ASTM A500 HSS and ASTM A53 Grade B
pipe are produced by an ERW process. The
SAW process is used for cross sections that are
larger than those permitted by ASTM A500.
2.4.3
Gross and Net Area Determination
(a) Gross Area. The gross area Ag of a member at
any section is the sum of the products of the
thickness and the gross width of each element
measured normal to the axis of the member. For
angles, the gross width is the sum of the widths
of the legs less the thickness.
(b) Net Area. The net area, An, of a member is the
sum of the products of the thickness and the net
width of each element computed as follows:
1. In computing net area for tension and
shear, the width of a bolt hole shall be
taken as 2 mm greater than the nominal
dimension of the hole.
2. For a chain of holes extending across a part
in any diagonal or zigzag line, the net
width of the part shall be obtained by
deducting from the gross width the sum of
the diameters or slot dimensions as
provided in this section, of all holes in the
chain, and adding, for each gage space in
the chain, the quantity s2/4g,
1. For angles, the gage for holes in opposite
adjacent legs shall be the sum of the gages
from the back of the angles less the
thickness.
2. For slotted HSS welded to a gusset plate,
the net area, An, is the gross area minus the
product of the thickness and the total width
of material that is removed to form the slot.
3. In determining the net area across plug or
slot welds, the weld metal shall not be
considered as adding to the net area.
4. For members without holes, the net area,
An, is equal to the gross area, Ag.
User Note: Section 10.4.1 (b) limits An to a
maximum of 0.85Ag for splice plates with
holes.
2.5—Member Lengths
For members in which the design is based on
compression, the slenderness ratio Kl/r preferably
should not exceed 200. For members in which the
design is based on tension, the slenderness ratio l / r
preferably should not exceed 300. The above
limitation does not apply to rods in tension.
Members in which the design is dictated by tension
loading, but which may be subject to some
compression under other load conditions, need not
satisfy the compression slenderness limit. For
beams, girders and trusses designed on the basis of
simple spans shall have an effective length equal to
the distance between centers of gravity of the
members to which they deliver their end reactions.
2.6—Fabrication and Erection
Shop drawings, fabrication, shop painting and
erection shall satisfy the requirements stipulated in
Chapter 14, Fabrication and Erection.
2.7—Quality Control and Quality
Assurance
Quality control and quality assurance activities
shall satisfy the requirements stipulated in Chapter
15, Quality Control and Quality Assurance.
2.8—Evaluation of Existing Structures
where
s = longitudinal center-to-center spacing
(pitch) of any two consecutive holes, mm
g = transverse center-to-center spacing
(gage) between fastener gage lines, mm
The evaluation of existing structures shall satisfy
the requirements stipulated in Chapter 16
Evaluation of Existing Structures.
SBC 306-CR-18
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CHAPTER 2—DESIGN REQUIREMENTS
TABLES OF CHAPTER 2
Case
Table 2-1 : Width-to-Thickness Ratios: Compression Elements Members Subject to Axial Compression
Unstiffened Elements
1
2
3
4
5
Stiffened Elements
6
7
8
9
Width-toThickness
Ratio
Limiting
Width-toThickness
Ratio r
(nonslender/slender)
𝑏
𝑡
0.56√
𝑏
𝑡
𝑘𝑐 𝐸
0.64√
𝐹𝑦
𝑏
𝑡
0.45√
𝐸
𝐹𝑦
𝑑
𝑡
0.75√
𝐸
𝐹𝑦
Webs of doublysymmetric I-shaped
sections and channels
ℎ
𝑡𝑤
1.49√
𝐸
𝐹𝑦
Walls of rectangular HSS
and boxes of uniform
thickness
𝑏
𝑡
1.40√
𝐸
𝐹𝑦
Flange cover plates and
diaphragm plates between
lines of fasteners or welds
𝑏
𝑡
1.40√
𝐸
𝐹𝑦
𝑏
𝑡
1.49√
𝐸
𝐹𝑦
Description of Element
Flanges of rolled
I-shaped sections, plates
projecting from rolled Ishaped sections;
outstanding legs of pairs
of angles connected with
continuous contact,
flanges of channels, and
flanges of tees
Flanges of built-up Ishaped sections and plates
or angle legs projecting
from built-up I-shaped
sections
Legs of single angles, legs
of double angles with
separators, and all other
unstiffened elements
Stems of tees
All other stiffened
elements
Examples
𝐸
𝐹𝑦
[𝑎]
Round HSS
𝐷
𝑡
0.11
𝐸
𝐹𝑦
SBC 306-CR-18
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CHAPTER 2—DESIGN REQUIREMENTS
Case
Unstiffened Elements
Table 2-2: Width-to-Thickness Ratios: Compression Elements Members Subject to Flexure
Description of
Element
Width
-toThick
ness
Ratio
10
Flanges of rolled Ishaped sections,
channels and tees
𝑏
𝑡
0.38√
11
Flanges of doubly
and singly
symmetric I-shaped
built-up sections
𝑏
𝑡
𝐸
0.38√
𝐹𝑦
0.95√
12
Legs of single
angles
𝑏
𝑡
0.54√
𝐸
𝐹𝑦
0.91√
13
Flanges of all Ishaped sections and
channels in flexure
about the weak axis
𝑏
𝑡
0.38√
𝐸
𝐹𝑦
1.0√
14
Stems of tees
𝑑
𝑡
0.84√
𝐸
𝐹𝑦
1.03√
𝐸
𝐹𝑦
15
Webs of doublysymmetric I-shaped
sections and
channels
ℎ
𝑡𝑤
𝐸
3.76√
𝐹𝑦
5.70√
𝐸
𝐹𝑦
16
Webs of singlysymmetric I-shaped
sections
ℎ𝑐
𝑡𝑤
5.70√
𝐸
𝐹𝑦
17
Flanges of
rectangular HSS and
boxes of uniform
thickness
𝑏
𝑡
1.40√
𝐸
𝐹𝑦
18
Flange cover plates
and diaphragm
plates between lines
of fasteners or welds
1.40√
𝐸
𝐹𝑦
19
Webs of rectangular
HSS and boxes
𝐸
𝐹𝑦
5.70√
𝐸
𝐹𝑦
𝐸
𝐹𝑦
0.31
Limiting Width-to-Thickness Ratio
r
(noncompact/
slender)
p
(compact/
noncompact)
𝐸
𝐹𝑦
1.0√
Examples
𝐸
𝐹𝑦
[a] [b]
𝑘𝑐 𝐸
𝐹𝐿
𝐸
𝐹𝑦
𝐸
𝐹𝑦
Stiffened Elements
[c]
20
Round HSS
𝒉𝒄
𝑬
√
𝒉𝒑 𝑭𝒚
(𝟎.𝟓𝟒
𝑴𝒑
𝑴𝒚
𝟐
−𝟎.𝟎𝟗)
1.12√
𝐸
𝐹𝑦
𝑏
𝑡
1.12√
𝐸
𝐹𝑦
ℎ
𝑡
2.42√
𝐷
𝑡
≤ 𝝀𝒓
0.07
𝐸
𝐹𝑦
Notes:
[a] kc= 4/ (h / tw) ½ but shall not be taken less than 0.35 nor greater than 0.76 for calculation purposes.
[b] FL =0.7Fy for major axis bending of compact and noncompact web built-up I-shaped members with Sxt /Sxc ≥ 0.7;
FL = FySxt /Sxc ≥ 0.5Fy for major-axis bending of compact and noncompact web built-up I-shaped members with Sxt /Sxc < 0.7.
[c] My is the moment at yielding of the extreme fiber. Mp =plastic bending moment, N-mm
E =modulus of elasticity of steel, 200 000 MPa
Fy = specified minimum yield stress, MPa.
SBC 306-CR-18
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CHAPTER 2—DESIGN REQUIREMENTS
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SBC 306-CR-18
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CHAPTER 3—DESIGN FOR STABILITY
CHAPTER 3—DESIGN FOR STABILITY
This chapter addresses requirements for the
design of structures for stability. The direct
analysis method is presented herein; alternative
methods are presented in Appendix F.
The chapter is organized as follows:
3.1 —General Stability Requirements
3.2 —Calculation of Required Strengths
3.3 Calculation of Design Strengths
3.1—General Stability Requirements
Stability shall be provided for the structure as a
whole and for each of its elements. The effects of
all of the following on the stability of the structure
and its elements shall be considered:
1 . Flexural, shear and axial member
deformations, and all other deformations
that contribute to displacements of the
structure.
2 . Second-order effects (both P-and P effects).
3. Geometric imperfections.
4 . Stiffness reductions due t o inelasticity.
5. Uncertainty in stiffness and strength.
All load-dependent effects shall be calculated at
a level of loading corresponding to LRFD load
combinations.
Any rational method of design for stability that
considers all of the listed effects is permitted; this
includes the methods identified in Sections 3.1.1
and 3.1.2.
For structures designed by inelastic analysis, the
provisions of Appendix A shall be satisfied.
User Note: The term “design” as used in this
Code is the combination of structural analysis
to determine the required strengths of
components and the proportioning of
components to have adequate design strength.
See Commentary of Section 3.1 for
explanation of how requirements (1)
through (5) of Section 3.1 are satisfied in the
methods of design listed in Sections 3.1.1 and
3.1.2 .
3.1.1 Direct Analysis Method of Design. The
direct analysis method of design, which consists of
the calculation of required strengths by structural
analysis method in accordance with Section 3.2
and the calculation of design strengths in
accordance with Section 3.3, is permitted for all
structures.
3.1.2 Alternative Methods of Design. The
effective length method and the first-order analysis
method, defined in Appendix F, are permitted as
alternatives to the direct analysis method for
structures that satisfy the constraints specified in
that Appendix.
3.2—Calculation of Required
Strengths
For the direct analysis method of design, the
required strengths of components of the structure
shall be determined from a structural analysis
conforming to Section 3.2.1 . The structural
analysis shall include consideration of initial
imperfections in accordance with Section 3.2.2 and
adjustments to stiffness in accordance with Section
3.2.3 .
3.2.1 General Analysis Requirements. The
structural analysis of the structure shall conform to
the following requirements:
1. The analysis shall consider flexural, shear
and axial member deformations, and all
other
component
and
connection
deformations
that
contribute
to
displacements of the structure. The
analysis shall include consideration for
initial imperfections as specified in Section
3.2.2 . Moreover, the analysis shall
incorporate reductions in all stiffnesses that
are considered to contribute to the stability
of the structure, as specified in Section
3.2.3 .
2. The analysis shall be a second-order
analysis that considers both P-and Peffects, except that it is permissible to
neglect the effect of P-on the response
of the structure when the following
SBC 306-CR-18
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CHAPTER 3—DESIGN FOR STABILITY
conditions are satisfied: (a) The structure
supports gravity loads primarily through
nominally-vertical columns, walls or
frames; (b) the ratio of maximum secondorder drift to maximum first-order drift
(both determined for LRFD load
combinations, with stiffnesses adjusted as
specified in Section 3.2.3 ) in all stories is
equal to or less than 1.7; and (c) no more
than one-third of the total gravity load on
the structure is supported by columns that
are part of moment-resisting frames in the
direction of translation being considered.
It is necessary in all cases to consider Peffects in the evaluation of individual
members subject to compression and
flexure.
User Note: A P--only second-order
analysis (one that neglects the effects of Pon the response of the structure) is permitted
under the conditions listed. The requirement
for considering P- effects in the evaluation
of individual members can be satisfied by
applying the B1 multiplier defined in Appendix
G.
Use of the approximate method of second-order
analysis provided in Appendix G is permitted as an
alternative to a rigorous second-order analysis.
3. The analysis shall consider all gravity and
other applied loads that may influence the
stability of the structure.
User Note: It is important to include in the
analysis all gravity loads, including loads on
leaning columns and other elements that are
not part of the lateral force resisting system.
4. The second-order analysis shall be carried
out under LRFD load combinations.
3.2.2 Consideration of Initial Imperfections.
The effect of initial imperfections on the stability of
the structure shall be taken into account either by
direct modeling of imperfections in the analysis
as specified in Section 3.2.2.1 or by the application
of notional loads as specified in Section 3.2.2.2 .
User Note: The imperfections considered in
this section are imperfections in the locations
of points of intersection of members. In typical
building structures, the important imperfection
of this type is the out-of-plumbness of
columns.
Initial out-of-straightness of
individual members is not addressed in this
section; it is accounted for in the compression
member design provisions of Chapter 5 and
need not be considered explicitly in the
analysis as long as it is within the limits
specified in Chapter 14.
3.2.2.1 Direct Modeling of Imperfections. In all
cases, it is permissible to account for the effect
of initial imperfections by including the
imperfections directly in the analysis. The structure
shall be analyzed with points of intersection of
members displaced from their nominal locations.
The magnitude of the initial displacements shall be
the maximum amount considered in the design; the
pattern of initial displacements shall be such that it
provides the greatest destabilizing effect.
User Note: Initial displacements similar in
configuration to both displacements due to
loading and anticipated buckling modes should
be considered in the modeling
of
imperfections. The magnitude of the initial
displacements should be
based on
permissible construction tolerances, as
specified in Chapter 14 or on actual
imperfections if known
In the analysis of structures that support gravity
loads primarily through nominally- vertical
columns, walls or frames, where the ratio of
maximum second-order drift to maximum firstorder drift (both determined for LRFD load
combinations, with stiffnesses adjusted as specified
in Section 3.2.3 ) in all stories is equal to or less
than 1.7, it is permissible to include initial
imperfections only in the analysis for gravity-only
load combinations and not in the analysis for load
combinations that include applied lateral loads.
3.2.2.2 Use of Notional Loads to Represent
Imperfections. For structures that support gravity
loads primarily through nominally-vertical
columns, walls or frames, it is permissible to use
notional loads to represent the effects of initial
imperfections in accordance with the requirements
of this section. The notional load shall be applied
to a model of the structure based on its nominal
geometry.
User Note: The notional load concept is
applicable to all types of structures, but the
specific requirements in Sections 3.2.2.2 (1)
SBC 306-CR-18
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CHAPTER 3—DESIGN FOR STABILITY
adjust the notional
proportionally.
through 3.2.2.2 (4) are applicable only for the
particular class of structure identified above.
1. Notional loads shall be applied as lateral
loads at all levels. The notional loads shall
be additive to other lateral loads and shall
be applied in all load combinations, except
as indicated in 3.2.2.2 (4), below. The
magnitude of the notional loads shall be:
𝑁𝑖 = 0.002 𝑌𝑖
(3-1)
Ni notional load applied at level i, N
Yi
=gravity load applied at level i from the
LRFD load combination, N
User Note: The notional loads can lead to
additional (generally small) fictitious base
shears in the structure. The correct horizontal
reactions at the foundation may be obtained
by applying an additional horizontal force at
the base of the structure, equal and opposite
in direction to the sum of all notional loads,
distributed among vertical load-carrying
elements in the same proportion as the gravity
load supported by those elements. The
notional loads can also lead to additional
overturning effects, which are not fictitious.
2. The notional load at any level, Ni, shall be
distributed over that level in the same
manner as the gravity load at the level. The
notional loads shall be applied in the
direction that provides the greatest
destabilizing effect.
User Note: For most building structures, the
requirement regarding notional load direction
may be satisfied as follows: For load
combinations that do not include lateral
loading, consider two alternative orthogonal
directions of notional load application, in a
positive and a negative sense in each of the
two directions, in the same direction at all
levels; for load combinations that include
lateral loading, apply all notional loads in the
direction of the resultant of all lateral loads in
the combination.
3. The notional load coefficient of 0.002 in
Eq. (3-1) is based on a nominal initial story
out-of-plumbness ratio of 1/500; where the
use of a different maximum out-ofplumbness is justified, it is permissible to
load
coefficient
User Note: An out-of-plumbness of 1/500
represents the maximum tolerance on column
plumbness specified in Chapter 14. In some
cases, other specified tolerances such as those
on plan location of columns will govern and
will require a tighter plumbness tolerance.
4. For structures in which the ratio of
maximum second-order drift to maximum
first-order drift (both determined for
LRFD load combinations, with stiffnesses
adjusted as specified in Section 3.2.3 in all
stories is equal to or less than 1.7, it is
permissible to apply the notional load, Ni,
only in gravity-only load combinations and
not in combinations that include other
lateral loads.
3.2.3 Adjustments to Stiffness. The analysis of
the structure to determine the required strengths of
components shall use reduced stiffnesses, as
follows:
1. A factor of 0.80 shall be applied to all
stiffnesses that are considered to contribute
to the stability of the structure. It is
permissible to apply this reduction factor
to all stiffnesses in the structure.
User Note: Applying the stiffness reduction to
some members and not others can, in some cases,
result in artificial distortion of the structure under
load and possible unintended redistribution of
forces. This can be avoided by applying the
reduction to all members, including those that do
not contribute to the stability of the structure.
2. An additional factor, 𝜏𝑏 , shall be applied to
the flexural stiffnesses of all members
whose flexural stiffnesses are considered
to contribute to the stability of the
structure.
When 𝑃𝑟 ⁄𝑃𝑦 ≤ 0.5
𝜏𝑏 = 1.0
(3-2)
When 𝑃𝑟 ⁄𝑃𝑦 > 0.5
𝜏𝑏 = 4(𝑃𝑟 ⁄𝑃𝑦 ) [1 − (𝑃𝑟 ⁄𝑃𝑦 )]
(3-3)
where
SBC 306-CR-18
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CHAPTER 3—DESIGN FOR STABILITY
𝑃𝑟
= required axial compressive strength, N
𝑃𝑦
= 𝐹𝑦 𝐴𝑔 = axial yield strength, N
User Note: Taken together, sections (1) and (2)
require the use of 0.8b times the nominal elastic
flexural stiffness and 0.8 times other nominal
elastic stiffnesses for structural steel members in
the analysis.
3. In structures to which Section 3.2.2.2 is
applicable, in lieu of using b 1.0 where
𝑃𝑟 ⁄𝑃𝑦 > 0.5, it is permissible to use 𝜏𝑏 =
1.0 for all members if a notional load of
0.001 𝑌𝑖 [where Yi is as defined in Section
3.2.2.2 (1)] is applied at all levels, in the
direction specified in Section 3.2.2.2 (2),
in all load combinations. These notional
loads shall be added to those, if any, used
to account for imperfections and shall not
be subject to Section 3.2.2.2 (4).
4. Where components comprised of materials
other than structural steel are considered to
contribute to the stability of the structure
and
the
governing
codes
and
specifications for the other materials
require greater reductions in stiffness, such
greater stiffness reductions shall be applied
to those components.
3.3Calculation of Design Strengths
For the direct analysis method of design, the
design strengths of members and connections shall
be calculated in accordance with the provisions of
Chapter 4, Chapter 5, Chapter 6, Chapter 7, Chapter
8, Chapter 9, Chapter 10 and Chapter 11 as
applicable, with no further consideration of overall
structure stability. The effective length factor, K, of
all members shall be taken as unity unless a smaller
value can be justified by rational analysis.
Bracing intended to define the unbraced lengths
of members shall have sufficient stiffness and
strength to control member movement at the braced
points.
Methods of satisfying bracing requirements for
individual columns, beams and beam-columns are
provided in Appendix E. The requirements of
Appendix E are not applicable to bracing that is
included as part of the overall force-resisting
system.
SBC 306-CR-18
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CHAPTER 3—DESIGN FOR STABILITY
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SBC 306-CR-18
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CHAPTER 4—DESIGN OF MEMBERS FOR TENSION
CHAPTER 4—DESIGN OF MEMBERS FOR TENSION
This chapter applies to prismatic members subject
to axial tension caused by static forces acting
through the centroidal axis.
The chapter is organized as follows:
𝑃𝑛 = 𝐹𝑦 𝐴𝑔
(b) For tensile rupture in the net section:
𝜑𝑡 = 0.75
𝑃𝑛 = 𝐹𝑢 𝐴𝑒
(4-2)
4.1 —Slenderness Limitations
where
4.2 —Design Tensile Strength
Ae
4.3 —Effective Net Area
Ag gross area of member, mm2
4.4 —Built-up Members
4.5 —Pin-Connected Members
4.6 —Eyebars
(4-1)
effective net area, mm2
Fy
specified minimum yield stress, MPa
Fu
specified minimum tensile strength, MPa
Chapter 8 Design for Combined Forces and
Torsion
When members without holes are fully connected
by welds, the effective net area used in Eq. (4-2)
shall be as defined in Section 4.3. When holes are
present in a member with welded-end connections,
or at the welded connection in the case of plug or
slot welds, the effective net area through the holes
shall be used in Eq. (4-2).
10.3
Threaded rods
4.3—Effective Net Area
10.4.1
Connecting elements in tension
10.4.3
Block shear rupture strength at
end connections of tension
members
The gross area, Ag, and net area, An, of tension
members shall be determined in accordance with
the provisions of Section 2.4.3.
User Note: For cases not included in this
chapter the following sections apply:
Appendix C
Design for Fatigue
The effective net area of tension members shall be
determined as follows:
𝐴𝑒 = 𝐴𝑛 𝑈
4.1—Slenderness Limitations
There is no maximum slenderness limit for
members in tension.
User Note: For members designed on the basis
of tension, the slenderness ratio L /r preferably
should not exceed 300. This suggestion does not
apply to rods or hangers in tension.
4.2—Design Tensile Strength
The design strength of tension members, tPn, shall
be the lower value obtained according to the limit
states of yielding in the gross section and fracture
in the net section.
(a) For tesile yielding in the gross section:
𝜑𝑡 = 0.90
(4-3)
where U, the shear lag factor, is determined as
shown in Table 4-1.
For open cross sections such as W, M, S, C or HP
shapes, WTs, STs, and single and double angles, the
shear lag factor, U, need not be less than the ratio of
the gross area of the connected element(s) to the
member gross area. This provision does not apply
to closed sections, such as HSS sections, nor to
plates.
User Note: For bolted splice plates Ae An
0.85Ag, according to Section 10.4.1 .
4.4—Built-up Members
For limitations on the longitudinal spacing of
connectors between elements in continuous contact
SBC 306-CR-18
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CHAPTER 4—DESIGN OF MEMBERS FOR TENSION
consisting of a plate and a shape or two plates, see
Section 10.3.5 .
User Note: The longitudinal spacing of
connectors
between
components
should
preferably limit the slenderness ratio in any
component between the connectors to 300.
Either perforated cover plates or tie plates without
lacing are permitted to be used on the open sides of
built-up tension members. Tie plates shall have a
length not less than two-thirds the distance between
the lines of welds or fasteners connecting them to
the components of the member. The thickness of
such tie plates shall not be less than one-fiftieth of
the distance between these lines. The longitudinal
spacing of intermittent welds or fasteners at tie
plates shall not exceed 150 mm.
4.5—Pin-Connected Members
4.5.1 Design Strength. The design strength of
pin-connected members tPn, shall be the lowest of
the following limit states:
(a) Tensile rupture on the net effective area:
𝜑𝑡 = 0.75
𝑃𝑛 = 𝐹𝑢 (2𝑡𝑏𝑒 )
(4-4)
(b) Shear rupture on the effective area:
𝜑𝑡 = 0.75
𝑃𝑛 = 0.6𝐹𝑢 𝐴𝑠𝑓
(4-5)
(c) For bearing on the projected area of the pin,
use Section 10.7.
(d) For yielding on the gross section, use Section
4.2.
where
Asf area on the shear failure path 2t(a
d/2), mm2
a shortest distance from edge of the pin
hole to the edge of the member
measured parallel to the direction of the
force, mm
be 2t 16, but not more than the actual
distance from the edge of the hole to the
edge of the part measured in the direction
normal to the applied force, mm
d pin diameter, mm
t thickness of plate, mm
force. When the pin is expected to provide for
relative movement between connected parts while
under full load, the diameter of the pin hole shall
not be more than 1 mm greater than the diameter of
the pin.
The width of the plate at the pin hole shall not be
less than 2be d and the minimum extension, a,
beyond the bearing end of the pin hole, parallel to
the axis of the member, shall not be less than 1.33be.
The corners beyond the pin hole are permitted to
be cut at 45 to the axis of the member, provided
the net area beyond the pin hole, on a plane
perpendicular to the cut, is not less than that
required beyond the pin hole parallel to the axis
of the member.
4.6—Eyebars
4.6.1 Design Strength. The design strength of
eyebars shall be determined in accordance with
Section 4.2, with Ag taken as the cross-sectional
area of the body.
For calculation purposes, the width of the body of
the eyebars shall not exceed eight times its
thickness.
4.6.2 Dimensional Requirements.
Eyebars
shall be of uniform thickness, without
reinforcement at the pin holes, and have circular
heads with the periphery concentric with the pin
hole.
The radius of transition between the circular head
and the eyebar body shall not be less than the head
diameter.
The pin diameter shall not be less than seveneighths times the eyebar body width, and the pin
hole diameter shall not be more than 1 mm greater
than the pin diameter.
For steels having Fy greater than 485 MPa, the hole
diameter shall not exceed five times the plate
thickness, and the width of the eyebar body shall
be reduced accordingly.
A thickness of less than 12 mm is permissible only
if external nuts are provided to tighten pin plates
and filler plates into snug contact. The width from
the hole edge to the plate edge perpendicular to the
direction of applied load shall be greater than twothirds and, for the purpose of calculation, not more
than three-fourths times the eyebar body width.
4.5.2 Dimensional Requirements. The pin hole
shall be located midway between the edges of the
member in the direction normal to the applied
SBC 306-CR-18
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CHAPTER 4—DESIGN OF MEMBERS FOR TENSION
TABLES AND FIGURES OF CHAPTER 4
Table 4-1 : Shear Lag Factors for Connections to Tension Members
Case
1
2
Description of Element
All tension members where the tension load is
transmitted directly to each of the cross-sectional
elements by fasteners or welds (except as in Cases 4,
5 and 6).
All tension members, except plates and HSS, where
the tension load is trans- mitted to some but not all of
the cross- sectional elements by fasteners or
longitudinal welds or by longitudinal welds in
combination with transverse welds. (Alternatively,
for W, M, S and HP, Case 7 may be used. For angles
Case 8 may be used.)
Shear Lag Factor, U
Example
U = 1.0
---
𝑈 = 1 − 𝑥̅⁄1
3
U = 1.0
All tension members where the tension load is
and
transmitted only by transverse welds to some but not
An = area of the directly
all of the cross-sectional elements.
connected elements
4
Plates where the tension load is transmitted by / 2w…U 1.0
2w / 1.5w…U 0.87
longitudinal welds only.
1.5w / w…U 0.75
5
Round HSS with a single concentric gusset plate
---
/ 1.3D…U 1.0
with a single
concentric gusset plate
6
Rectangular HSS
with two side gusset
plates
̅⁄
D ≤ l < 1.3D... U = 1 – x
l
𝑥̅ = 𝐷⁄𝜋
l ≥ H... 𝑈 = 1 − 𝑥̅⁄1
𝑥̄ =
𝐵2 + 2𝐵𝐻
4(𝐵 + 𝐻)
l ≥ H... 𝑈 = 1 − 𝑥̅⁄1
𝐵2
𝑥̅ =
4(𝐵 + 𝐻)
with flange con- nected
Bf ≥ 2/3d…U = 0.90
with 3 or more
W, M, S or HP
--bf < 2/3d…U = 0.85
Shapes or Tees cut from fasteners per line in the
these shapes. (If U is direction of loading
7
calculated per Case 2, the with web connected
larger value is per- mitted to with 4 or more fasU = 0.70
be used.)
teners per line in the
direction of loading
with 4 or more fas--teners per line in the
U =0.80
direction of loading
Single and double angles (If
With 3 fasteners per
U is calculated per Case 2,
8
the larger value is permitted line in the direction of
loading (With fewer
to be used.)
--U =0.60
than 3 fasteners per
line in the direction of
loading, use Case 2.)
l = length of connection, mm; w= plate width, mm; x– = eccentricity of connection, mm; B = overall width of rectangular
HSS member, measured 90° to the plane of the connection, mm; H = overall height of rectangular HSS member, measured
in the plane of the connection, mm
SBC 306-CR-18
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CHAPTER 4—DESIGN OF MEMBERS FOR TENSION
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SBC 306-CR-18
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CHAPTER 5—DESIGN FOR COMPRESSION
CHAPTER 5—DESIGN FOR COMPRESSION
This chapter addresses members subject to axial
compression through the centroidal axis. The
chapter is organized as follows:
5.1 —General Provisions
5.2 —Effective Length
5.3 —Flexural Buckling of Members Without
Slender Elements
5.4 —Torsional
and
Flexural-Torsional
Buckling of Members Without Slender
Elements
5.5 —Single Angle Compression Members
5.6 —Built-up Members
5.7 —Members With Slender Elements
User Note: For cases not included in this
chapter, the following sections apply:
8.1 – 8.2 Members subject to combined axial
compression and flexure
8.3
Members subject to axial compression
and torsion
9.2
L = laterally unbraced length of the member,
mm
r = radius of gyration, mm
For members designed on the basis of compression,
the effective slenderness ratio KL /r preferably
should not exceed 200.
5.3—Flexural Buckling of Members
Without Slender Elements
This section applies to nonslender element
compression members as defined in Section 2.4.1
for elements in uniform compression.
User Note: When the torsional unbraced
length is larger than the lateral unbraced length,
Section 5.4 may control the design of wide
flange and similarly shaped columns.
The nominal compressive strength, Pn, shall be
determined based on the limit state of flexural
buckling.
𝑃𝑛 = 𝐹𝑐𝑟 𝐴𝑔
The critical stress, Fcr, is determined as follows:
Composite axially loaded members
10.4.4 Compressive strength of connecting
elements
(5-1)
(a) When
𝐾𝐿
𝑟
≤ 4.71√
𝐸
𝐹𝑦
( or
𝐹𝑦
𝐹𝑒
≤ 2.25)
𝐹𝑦
𝐹𝑐𝑟 = [0.658𝐹𝑒 ] ⋅ 𝐹𝑦
(5-2)
(b) When
5.1—General Provisions
𝐾𝐿
The design compressive strength, c Pn, is
determined as follows.
The nominal compressive strength, Pn, shall be the
lowest value obtained based on the applicable limit
states of flexural buckling, torsional buckling, and
flexural- torsional buckling.
𝜑𝑐 = 0.85
𝑟
𝐹𝑦
𝐹𝑐𝑟 = 0.877𝐹𝑒
( or
𝐹𝑦
𝐹𝑒
> 2.25)
(5-3)
Where, Fe = elastic buckling stress determined
according to Eq. (5-4), as specified in Appendix F,
Section F.2.3(b), or through an elastic buckling
analysis, as applicable, MPa
𝐹𝑒 =
5.2—Effective Length
𝜋2𝐸
(
The effective length factor, K, for calculation of
member slenderness, KL/r, shall be determined in
accordance with Chapter 3 or Appendix F,
𝐸
> 4.71√
𝐾𝐿 2
)
𝑟
(5-4)
User Note: The two inequalities for
calculating the limits and applicability of
where
SBC 306-CR-18
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CHAPTER 5—DESIGN FOR COMPRESSION
Sections 5.3(a) and 5.3(b), one based on KL/r
and one based on Fy /Fe, provide the same
result.
5.4—Torsional and Flexural-Torsional
Buckling of Members Without Slender
Elements
This section applies to singly symmetric and
unsymmetric members and certain doubly
symmetric members, such as cruciform or built-up
columns without slender elements, as defined in
Section 2.4.1 for elements in uniform compression.
In addition, this section applies to all doubly
symmetric members without slender elements when
the torsional unbraced length exceeds the lateral
unbraced length. These provisions are required for
single angles with b/t > 20.
The nominal compressive strength, Pn, shall be
determined based on the limit states of torsional and
flexural-torsional buckling, as follows:
𝑃𝑛 = 𝐹𝑐𝑟 𝐴𝑔
(5-5)
The critical stress, Fcr, is determined as follows:
(a) For double angle and tee-shaped compression
members:
𝐹𝑐𝑟 = (
𝐹𝑐𝑟𝑦 +𝐹𝑐𝑟𝑧
2𝐻
) [1 − √1 −
4𝐹𝑐𝑟𝑦 𝐹𝑐𝑟𝑧 𝐻
(𝐹𝑐𝑟𝑦 +𝐹𝑐𝑟𝑧 )
2
]
(5-6)
where Fcry is taken as Fcr from Eq. (5-2) or
(5-3) for flexural buckling about the y-axis
of symmetry, and KL/r = KyL/ry for teeshaped compression members, and KL/r =
(KL/r)m from Section 5.6 for double angle
compression members, and
𝐺𝐽
𝐹𝑐𝑟𝑧 =
𝐴𝑔 𝑟̄02
𝜋 2 𝐸𝐶𝑤
1
𝐹𝑒 = [
+ 𝐺𝐽]
2
(𝐾𝑧 𝐿)
𝐼𝑥 + 𝐼𝑦
(5-8)
For singly symmetric members where y
is the axis of symmetry
2𝐻
) [1 − √1 −
𝑥
4𝐹𝑒𝑦 𝐹𝑒𝑧 𝐻
(𝐹𝑒𝑦 +𝐹𝑒𝑧 )
2
2
𝑦
2
𝐹𝑒𝑦 ) ( 𝑜 ) − 𝐹𝑒2 (𝐹𝑒 − 𝐹𝑒𝑥 ) ( 𝑜 ) = 0
𝑟̄𝑜
(5-10)
𝑟̄𝑜
where
Ag = gross cross-sectional area of member, mm2
Cw = warping constant, mm6
𝐹𝑒𝑥 =
𝐹𝑒𝑦 =
𝜋2𝐸
𝐾 𝐿 2
( 𝑥 )
𝑟𝑥
𝜋2𝐸
(5-11)
𝐾𝑦 𝐿 2
)
𝑟𝑦
(5-12)
(
𝜋2 𝐸𝐶𝑤
𝐹𝑒𝑧 = ( (𝐾
𝑧
𝐿)2
+ 𝐺𝐽)
1
(5-13)
𝐴𝑔 𝑟̄02
G = shear modulus of elasticity of steel
= 77 200 MPa
𝐻
𝑥 2 +𝑦 2
=1− 0 2 0
(5-14)
𝑟̄0
Ix, Iy = moment of inertia about the principal
axes, mm4.
J
= torsional constant, mm4.
Kx
= effective length factor for flexural
buckling about x-axis.
Ky
= effective length factor for flexural
buckling about y-axis.
Kz
= effective length factor for torsional
buckling.
𝑟̄0
= polar radius of gyration about the shear
center, mm.
r02 x02 y02
Ix Iy
(5-15)
Ag
rx = radius of gyration about x-axis, mm.
ry = radius of gyration about y-axis, mm.
For doubly symmetric members:
𝐹𝑒𝑦 +𝐹𝑒𝑧
(𝐹𝑒 − 𝐹𝑒𝑥 )(𝐹𝑒 − 𝐹𝑒𝑦 )(𝐹𝑒 − 𝐹𝑒𝑧 ) − 𝐹𝑒2 (𝐹𝑒 −
(5-7)
(b) For all other cases, Fcr shall be determined
according to Eq. (5-2) or (5-3), using the
torsional or flexural-torsional elastic buckling
stress, Fe, determined as follows:
𝐹𝑒 = (
For unsymmetric members, Fe is the
lowest root of the cubic equation
] (5-9)
xo, yo = coordinates of the shear center with
respect to the centroid, mm.
User Note: For doubly symmetric I-shaped
ℎ2
sections, Cw may be taken as 𝐼𝑦 𝑜 where ho is
4
the distance between flange centroids, in lieu of
a more precise analysis. For tees and double
angles, omit the term with Cw when computing
Fez and take xo as 0.
SBC 306-CR-18
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CHAPTER 5—DESIGN FOR COMPRESSION
5.5—Single Angle Compression
Members
adjacent web members attached to the same
side of the gusset plate or chord:
When
The nominal compressive strength, Pn, of single
angle members shall be determined in accordance
with Section 5.3 or Section 5.7, as appropriate, for
axially loaded members. For single angles with b/t
> 20, Section 5.4 shall be used. Members meeting
the criteria imposed in Section 5.5(a) or 5.5(b) are
permitted to be designed as axially loaded members
using the specified effective slenderness ratio, KL/r.
The effects of eccentricity on single angle members
are permitted to be neglected when evaluated as
axially loaded compression members using one of
the effective slenderness ratios specified in Section
5.5(a) or 5.5(b), provided that:
1. members are loaded at the ends in
compression through the same one leg;
𝐿
𝑟𝑥
≤ 75
𝐾𝐿
𝐿
= 60 + 0.8
𝑟
𝑟𝑥
When
𝐿
𝑟𝑥
(5-18)
> 75
𝐾𝐿
𝐿
= 45 + ≤ 200
𝑟
𝑟𝑥
(5-19)
For unequal-leg angles with leg length ratios less
than 1.7 and connected through the shorter leg, KL/r
from Eqs. (5-18) and (5-19) shall be increased by
adding 6[(bl/bs)2 - 1], but KL/r of the member shall
not be taken as less than 0.82L/rz
where
L
= length of member between work points at
truss chord centerlines, mm.
bl
= length of longer leg of angle, mm.
3. There are no intermediate transverse loads.
bs
= length of shorter leg of angle, mm.
Single angle members with different end conditions
from those described in Section 5.5(a) or (b), with
the ratio of long leg width to short leg width greater
than 1.7 or with transverse loading, shall be
evaluated for combined axial load and flexure using
the provisions of Chapter 8.
rx
= radius of gyration about the geometric
axis parallel to the connected leg, mm,
rz
= radius of gyration about the minor
principal axis, mm.
2. members are attached by welding or by
connections with a minimum of two bolts;
and
(a) For equal-leg angles or unequal-leg angles
connected through the longer leg that are
individual members or are web members of
planar trusses with adjacent web members
attached to the same side of the gusset plate
or chord:
When
𝐿
𝑟𝑥
≤ 80
𝐾𝐿
𝐿
= 72 + 0.75
𝑟
𝑟𝑥
When
𝐿
𝑟𝑥
(5-16)
> 80
𝐾𝐿
𝐿
= 32 + 1.25 ≤ 200
𝑟
𝑟𝑥
(5-17)
For unequal-leg angles with leg length ratios less
than 1.7 and connected through the shorter leg, KL/r
from Eqs. (5-16) and (5-17) shall be increased by
adding 4[(bl/bs)2-1], but KL/r of the members shall
not be taken as less than 0.95L/rz.
(b) For equal-leg angles or unequal-leg angles
connected through the longer leg that are web
members of box or space trusses with
5.6—Built-up Members
5.6.1 Compressive Strength.
This section
applies to built-up members composed of two
shapes either (a) interconnected by bolts or welds,
or (b) with at least one open side interconnected by
perforated cover plates or lacing with tie plates.
The end connection shall be welded or connected
by means of pretensioned bolts with Class A or B
faying surfaces.
User Note: It is acceptable to design a bolted
end connection of a built-up compression
member for the full compressive load with
bolts in bearing and bolt design based on the
shear strength; however, the bolts must be
pretensioned. In built-up compression members,
such as double-angle struts in trusses, a small
relative slip between the elements especially at
the end connections can increase the effective
length of the combined cross section to that of the
individual components and significantly reduce
the compressive strength of the strut. Therefore,
the connection between the elements at the ends
SBC 306-CR-18
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CHAPTER 5—DESIGN FOR COMPRESSION
of built-up members should be designed to resist
slip.
The nominal compressive strength of built-up
members composed of two shapes that are
interconnected by bolts or welds shall be
determined in accordance with Sections 5.3, 5.4 or
5.7 subject to the following modification. In lieu of
more accurate analysis, if the buckling mode
involves relative deformations that produce shear
forces in the connectors between individual shapes,
KL/r is replaced by (KL/r)m determined as follows:
(a) For intermediate connectors that are bolted
snug-tight:
(
𝐾𝐿
𝐾𝐿 2
𝑎 2
) = √( ) + ( )
𝑟 𝑚
𝑟 0
𝑟𝑖
(5-20)
(b) For intermediate connectors that are welded or
are connected by means of pre- tensioned bolts:
When
(
𝑎
𝑟𝑖
≤ 40
𝐾𝐿
𝐾𝐿
) =( )
𝑟 𝑚
𝑟 𝑜
When
𝑎
𝑟𝑖
(5-21)
> 40
𝐾𝐿
𝐾𝐿 2
𝐾𝑖 𝑎 2
√
( ) = ( ) +(
)
𝑟 𝑚
𝑟 0
𝑟𝑖
(5-22)
where
𝐾𝐿
( )
𝑟
𝑚
= modified slenderness ratio of built up
member
𝐾𝐿
( )
𝑟
𝑜
= slenderness ratio of built-up member
acting as a unit in the buckling direction
being considered
Ki
built-up member. The least radius of gyration, ri,
shall be used in computing the slenderness ratio of
each component part.
At the ends of built-up compression members
bearing on base plates or finished surfaces, all
components in contact with one another shall be
connected by a weld having a length not less than
the maximum width of the member or by bolts
spaced longitudinally not more than four diameters
apart for a distance equal to 1.5 times the maximum
width of the member.
Along the length of built-up compression members
between the end connections required above,
longitudinal spacing for intermittent welds or bolts
shall be adequate to provide for the transfer of the
required strength. For limitations on the
longitudinal spacing of fasteners between elements
in continuous contact consisting of a plate and a
shape or two plates, see Section 10.3.5 . Where a
component of a built-up compression member
consists of an outside plate, the maximum spacing
shall not exceed the thickness of the thinner outside
plate times 0.75√𝐸 ⁄𝐹𝑦 nor 300 mm, when
intermittent welds are provided along the edges of
the components or when fasteners are provided on
all gage lines at each section. When fasteners are
staggered, the maximum spacing of fasteners on
each gage line shall not exceed the thickness of the
thinner outside plate times 1.12√𝐸 ⁄𝐹𝑦 nor 450
mm.
Open sides of compression members built up from
plates or shapes shall be provided with continuous
cover plates perforated with a succession of access
holes. The unsupported width of such plates at
access holes, as defined in Section 2.4.1 , is
assumed to contribute to the design strength
provided the following requirements are met:
1. The width-to-thickness ratio shall conform
to the limitations of Section 2.4.1 .
= 0.50 for angles back-to-back
= 0.75 for channels back-to-back
= 0.86 for all other cases
a
= distance between connectors, mm.
ri
= minimum radius of gyration of
individual component, mm.
5.6.2 Dimensional Requirements. Individual
components of compression members composed of
two or more shapes shall be connected to one
another at intervals, a, such that the effective
slenderness ratio, Ki a/ri, of each of the component
shapes between the fasteners does not exceed threefourths times the governing slenderness ratio of the
User Note: It is conservative to use the limiting
width-to-thickness ratio for Case 7 in Table
2-1 and Table 2-2 with the width, b, taken as
the transverse distance between the nearest
lines of fasteners. The net area of the plate is
taken at the widest hole. In lieu of this
approach, the limiting width-to-thickness
ratio may be determined through analysis.
2. The ratio of length (in direction of stress)
to width of hole shall not exceed 2.
SBC 306-CR-18
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CHAPTER 5—DESIGN FOR COMPRESSION
3. The clear distance between holes in the
direction of stress shall be not less than the
transverse distance between nearest lines
of connecting fasteners or welds.
For additional spacing requirements, see Section
10.3.5 .
4. The periphery of the holes at all points
shall have a minimum radius of 38 mm.
This section applies to slender-element
compression members, as defined in Section 2.4.1
for elements in uniform compression.
As an alternative to perforated cover plates, lacing
with tie plates is permitted at each end and at
intermediate points if the lacing is interrupted. Tie
plates shall be as near the ends as practicable. In
members providing design strength, the end tie
plates shall have a length of not less than the
distance between the lines of fasteners or welds
connecting them to the components of the member.
Intermediate tie plates shall have a length not less
than one-half of this distance. The thickness of tie
plates shall be not less than one-fiftieth of the
distance between lines of welds or fasteners
connecting them to the segments of the members.
In welded construction, the welding on each line
connecting a tie plate shall total not less than onethird the length of the plate. In bolted construction,
the spacing in the direction of stress in tie plates
shall be not more than six diameters and the tie
plates shall be connected to each segment by at least
three fasteners.
Lacing, including flat bars, angles, channels or
other shapes employed as lacing, shall be so spaced
that the L/r ratio of the flange element included
between their connections shall not exceed threefourths times the governing slenderness ratio for the
member as a whole. Lacing shall be proportioned to
provide a shearing strength normal to the axis of the
member equal to 2% of the design compressive
strength of the member. The L/r ratio for lacing bars
arranged in single systems shall not exceed 140. For
double lacing this ratio shall not exceed 200.
Double lacing bars shall be joined at the
intersections. For lacing bars in compression, L is
permitted to be taken as the unsupported length of
the lacing bar between welds or fasteners
connecting it to the components of the built-up
member for single lacing, and 70% of that distance
for double lacing.
User Note: The inclination of lacing bars to
the axis of the member shall preferably be not
less than 60 for single lacing and 45 for
double lacing. When the distance between the
lines of welds or fasteners in the flanges is
more than 375 mm, the lacing shall preferably
be double or be made of angles.
5.7—Members With Slender Elements
The nominal compressive strength, Pn, shall be the
lowest value based on the applicable limit states of
flexural buckling, torsional buckling, and flexuraltorsional buckling.
𝑃𝑛 = 𝐹𝑐𝑟 𝐴𝑔
(5-23)
The critical stress, Fcr, shall be determined as
follows:
(a) When
𝐾𝐿
𝑟
≤ 4.71√
𝐸
𝑄𝐹𝑦
(or
𝑄𝐹𝑦
𝐹𝑒
≤ 2.25)
𝑄𝐹𝑦
𝐹𝑐𝑟 = 𝑄 [0.658 𝐹𝑒 ] ⋅ 𝐹𝑦
(b) When
𝐾𝐿
𝑟
> 4.71√
𝐸
𝑄𝐹𝑦
( or
𝐹𝑐𝑟 = 0.877𝐹𝑒
(5-24)
𝑄𝐹𝑦
𝐹𝑒
> 2.25)
(5-25)
where
Fe
= elastic buckling stress, calculated using Eqs.
(5-4) and (5-8) for doubly symmetric
members, Eqs. (5-4) and (5-9) for singly
symmetric members, and Eq. (5-10) for
unsymmetric members, except for single
angles with b/t ≤ 20, where Fe is calculated
using Eq. (5-4), MPa
Q
= net reduction factor accounting for all
slender compression elements;
= 1.0 for members without slender elements, as
defined in Section 2.4.1 , for elements in
uniform compression
= Qs Qa for members with slender-element
sections, as defined in Section 2.4.1 , for
elements in uniform compression.
User Note: For cross sections composed of only
unstiffened slender elements,
Q Qs (Qa
1.0). For cross sections composed of only
stiffened slender elements, Q Qa (Qs 1.0).
For cross sections composed of both stiffened
and unstiffened slender elements, Q Qs Qa. For
cross sections composed of multiple unstiffened
slender elements, it is conservative to use the
smaller Qs from the more slender element in
SBC 306-CR-18
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CHAPTER 5—DESIGN FOR COMPRESSION
t
determining the member strength for pure
compression.
h = Clear distance between flanges less the
fillet or corner radius for rolled shapes;
distance between adjacent lines of fasteners
or the clear distance between flanges when
welds are used for built-up shapes, mm.
5.7.1 Slender Unstiffened Elements, Qs. The
reduction factor, Qs, for slender unstiffened
elements is defined as follows:
(a) For flanges, angles and plates projecting from
rolled columns or other compression members:
(c) For single angles
𝑏
𝐸
𝑡
𝐹𝑦
When ≤ 0.45√
𝑏
𝐸
𝑡
𝐹𝑦
When ≤ 0.56√
= thickness of element, mm
𝑄𝑠 = 1.0
𝑄𝑠 = 1.0
(5-26)
(5-32)
𝐸
When 0.45√
When 0.56√
𝐸
𝐹𝑦
<
𝑏
< 1.03√
𝑡
𝑏
𝐹𝑦
𝑡
𝐸
𝑏
𝐸
𝑡
𝐹𝑦
When ≥ 1.03√
𝐸
𝐹𝑦
𝑄𝑠 = 1.415 − 0.74 ( ) √
(5-27)
When
When
𝑏
𝑡
When 0.64√
𝐹𝑦
<
𝑡
When
≤ 1.17√
𝐹𝑦
𝑏
𝑄𝑠 = 1.415 − 0.65 ( ) √
𝑡
𝐸𝑘𝑐
𝑏
𝐸𝑘𝑐
𝑡
𝐹𝑦
When > 1.17√
𝑄𝑠 =
4
ℎ
√𝑡
𝑤
𝑡
(5-33)
𝐸
> 0.91√
𝐹𝑦
0.53𝐸
𝑏 2
𝐹𝑦 ( )
𝑡
(5-34)
𝑡
𝐸
≤ 0.75√
𝐹𝑦
𝑄𝑠 = 1.0
𝐹𝑦
𝐸
When 0.75√
𝐹𝑦
(5-30)
<
(5-35)
𝑑
𝑡
𝑑
𝐹𝑦
𝑡
𝐸
𝑑
𝑡
𝐸
≤ 1.03√
𝐹𝑦
𝑄𝑠 = 1.908 − 1.22 ( ) √
When
(5-36)
𝐸
> 1.03√
𝐹𝑦
0.90𝐸𝑘𝑐
𝑏 2
𝐹𝑦 ( )
𝑡
(5-31)
𝑄𝑠 =
b = width of unstiffened compression element,
as defined in Section 2.4.1 , mm
=
𝑑
𝐸𝑘𝑐
where
𝑘𝑐
𝐸
𝐹𝑦
b = full width of longest leg, mm.
(5-29)
𝑏
≤ 0.91√
where
𝐹𝑦
𝑄𝑠 = 1.0
𝐸𝑘𝑐
𝑡
(d) For stems of tees
𝐸𝑘𝑐
≤ 0.64√
𝑏
𝑄𝑠 =
2
(5-28)
𝑏
𝐹𝑦 ( )
𝑡
(b) For flanges, angles and plates projecting from
built-up
I-shaped
columns
or
other
compression members:
𝑏
𝑏 𝐹𝑦
𝑄𝑠 = 1.34 − 0.76 ( ) √
𝑡
𝐸
0.69𝐸
𝑄𝑠 =
<
𝐹𝑦
, and shall not be taken less than
0.35 nor greater than 0.76 for calculation
purposes
0.69𝐸
𝑑 2
𝐹𝑦 ( )
𝑡
(5-37)
where
d
= full nominal depth of tee, mm.
5.7.2 Slender Stiffened Elements, Qa. The
reduction factor, Qa, for slender stiffened elements
is defined as follows:
SBC 306-CR-18
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CHAPTER 5—DESIGN FOR COMPRESSION
𝑄𝑎 =
𝐴𝑒
𝐴𝑔
(5-38)
where
Ag = gross cross-sectional area of member, mm2.
Ae
= summation of the effective areas of the cross
section based on the reduced effective width,
be, mm2.
The reduced effective width, be, is determined as
follows:
(a) For uniformly compressed slender elements,
𝑏
𝐸
𝑡
𝑓
with ≥ 1.49√ except flanges of square and
rectangular sections of uniform thickness:
𝐸
0.34
𝑓
( )
𝑏𝑒 = 1.92 𝑡√ [1 −
𝑏
𝑡
𝐸
√𝑓 ] ≤ 𝑏
(5-39)
Where, f is taken as Fcr with Fcr calculated based on
Q = 1.0
(b) For flanges of square and rectangular slender𝑏
element sections of uniform thickness with ≥
𝑡
𝐸
1.40√ ;
𝑓
𝐸
0.38
𝑓
( )
𝑏𝑒 = 1.92 𝑡√ [1 −
𝑏
𝑡
𝐸
√𝑓 ] ≤ 𝑏
(5-40)
where, 𝑓 = 𝑃𝑛 ⁄𝐴𝑒
User Note: In lieu of calculating f Pn /Ae,
which requires iteration, f may be taken
equal to Fy. This will result in a slightly
conservative estimate of column design
strength.
(c) For axially loaded circular sections:
When 0.11
𝐸
𝐹𝑦
<
𝑄 = 𝑄𝑎 =
𝐷
𝑡
≤ 0.45
𝐸
𝐹𝑦
0.038𝐸 2
+
𝐷
𝐹𝑦 ( ) 3
𝑡
(5-41)
where
D
= outside diameter of round HSS, mm.
t
= thickness of wall, mm.
SBC 306-CR-18
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CHAPTER 5—DESIGN FOR COMPRESSION
TABLES AND FIGURES OF CHAPTER 5
TABLE 5-1 : SELECTION TABLE FOR THE APPLICATION OF CHAPTER 5 SECTIONS
Cross Section
Without Slender Elements
Sections in
Limit States
Chapter 5
5.3
5.4
FB
TB
5.7
LB
FB
TB
5.3
5.4
FB
FTB
5.7
LB
FB
FTB
5.3
FB
5.7
LB
FB
5.3
FB
5.7
LB
FB
5.3
5.4
FB
FTB
5.7
LB
FB
FTB
5.3
5.4
0
FB
FTB
5.6
5.7
LB
FB
FTB
5.5
LB
FB
5.5
Unsymmetrical shapes other
than single angles
With Slender Elements
Sections in
Limit States
Chapter 5
5.3
FB
N/A
5.4
FTB
5.7
FB = flexural buckling, TB = torsional buckling,
LB = local buckling
N/A
LB
FTB
FTB = flexural-torsional buckling,
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CHAPTER 5—DESIGN FOR COMPRESSION
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SBC 306-CR-18
60
CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
This chapter applies to members subject to simple
bending about one principal axis. For simple
bending, the member is loaded in a plane parallel
to a principal axis that passes through the shear
center or is restrained against twisting at load points
and supports.
Appendix C
Members subject to fatigue
For guidance in determining the appropriate
sections of this chapter to apply, Table 6-1 can
be used.
6.1—General Provisions
The chapter is organized as follows:
6.1 —General Provisions
6.2 —Doubly Symmetric Compact I-Shaped
Members and Channels Bent About Their
Major Axis
The design flexural strength, b Mn, shall be
determined as follows:
1. For all provisions in this chapter
𝜑𝑏 = 0.90
6.3 —Doubly Symmetric I-Shaped Members
with Compect Webs and Noncompect or
Slender Flanges Bent about Their Major Axis
and the nominal flexural strength, Mn, shall
be determined according to Sections 6.2
through 6.13.
6.4 —Other I-Shaped Members with Compact or
Noncompact Webs Bent About Their Major
Axis
2. The provisions in this chapter are based on
the assumption that points of support for
beams and girders are restrained against
rotation about their longitudinal axis.
6.5 —Doubly
Symmectric
and
Singly
Symmetric I-Shaped Members with Slender
Webs Bent About Their Majout Axis
6.6 —I-Shaped Members and Channels Bent
About Their Minor Axis
6.7 —Square and Rectangular HSS and BoxShaped Members
6.8 —Round HSS
3. For singly symmetric members in single
curvature and all doubly symmetric
members:
Cb, the lateral-torsional buckling modification
factor for non-uniform moment diagrams when
both ends of the segment are braced is determined
as follows:
12.5𝑀𝑚𝑎𝑥
2.5𝑀𝑚𝑎𝑥 + 3𝑀𝐴 + 4𝑀𝐵 + 3𝑀𝐶
6.9 —Tees and Double Angles Loaded in The
Plane of Symmetry
𝐶𝑏 =
6.10 —Single Angles
where
6.11 —Rectangular Bars and Rounds
Mmax absolute value of maximum moment in the
unbraced segment, N-mm
6.12 —Unsymmetrical Shapes
6.13 —Proportions of Beams and Girders
User Note: For cases not included in this chapter
the following sections apply:
MA
absolute value of moment at quarter point
of the unbraced segment, N-mm
MB
absolute value of moment at centerline of
the unbraced segment, N-mm
MC
absolute value of moment at three-quarter
point of the unbraced segment, N-mm
Chapter 7 Design for shear
8.1–8.3
8.3
Members subject to biaxial flexure or
to combined flexure and axial force
Members subject to flexure and torsion
(6-1)
For cantilevers or overhangs where the free end is
unbraced, 𝐶𝑏 = 1.0.
User Note: For doubly symmetric members
with no transverse loading between brace
SBC 306-CR-18
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CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
points, Eq. (6-1) reduces to 1.0 for the case of
equal end moments of opposite sign (uniform
moment), 2.27 for the case of equal end
moments of the same sign (reverse curvature
bending), and to 1.67 when one end moment
equals zero. For singly symmetric members, a
more detailed analysis for Cb is presented in
the Commentary.
4. In singly symmetric members subject to
reverse curvature bending, the lateraltorsional buckling strength shall be
checked for both flanges. The design
flexural strength shall be greater than or
equal to the maximum required moment
causing compression within the flange
under consideration.
6.2—Doubly Symmetric Compact IShaped Members and Channels Bent
About Their Major Axis
This section applies to doubly symmetric I-shaped
members and channels bent about their major
axis, having compact webs and compact flanges
as defined in Section 2.4.1 for flexure.
The nominal flexural strength, Mn, shall be the lower
value obtained according to the limit states of
yielding (plastic moment) and lateral-torsional
buckling.
6.2.1
where
Lb
= length between points that are either
braced against lateral displacement of the
compression flange or braced against twist of
the cross section, mm
𝐶𝑏 𝜋 2 𝐸
𝐹𝑐𝑟 =
𝐿
( 𝑏)
𝑟𝑡𝑠
√1 + 0.078
2
(6-5)
and where
E modulus of elasticity of steel 200 000
MPa
J torsional constant, mm4
Sx elastic section modulus taken about the xaxis, mm3
ho distance between the flange centroids, mm
User Note: The square root term in Eq. (6-5)
may be conservatively taken equal to 1.0.
User Note: Eqs. (6-4) and (6-5) provide
identical solutions to the following expression
for lateral-torsional buckling of doubly
symmetric sections that has been presented in
SBC 306:
Yielding
𝑀𝑐𝑟 = 𝐶𝑏
𝑀𝑛 = 𝑀𝑃 = 𝐹𝑦 𝑍𝑥
𝐽𝑐 𝐿𝑏 2
( )
𝑆𝑥 ℎ0 𝑟𝑡𝑠
(6-2)
𝜋
𝜋𝐸 2
√𝐸𝐼𝑦 𝐺𝐽 + (
) 𝐼𝑦 𝐶𝑤
𝐿𝑏
𝐿𝑏
Fy
specified minimum yield stress of the type of
steel being used, MPa
The advantage of Eqs. (6-4) and (6-5) is that
the form is very similar to the expression for
lateral-torsional buckling of singly symmetric
sections given in Eqs. (6-16) and (6-17).
Zx
plastic section modulus about the x-axis,
mm3
The limiting lengths Lp and Lr are determined as
follows:
where
6.2.2
Lateral-Torsional Buckling
(a) When Lb Lp, the limit state of lateraltorsional buckling does not apply.
(b) When Lp Lb Lr
𝐿𝑟 = 1.95𝑟𝑡𝑠
𝐿 −𝐿𝑝
𝑀𝑛 = 𝐶𝑏 [𝑀𝑃 − (𝑀𝑃 − 0.7𝐹𝑦 𝑆𝑥 ) ( 𝑏
𝐿𝑟 −𝐿𝑝
)] ≤ 𝑀𝑝 (6-3)
(6-6)
𝐸
√𝐴 + √(𝐴)2 + 6.76(𝐵)2
0.7𝐹𝑦
(6-7)
Where,
𝐴=
(c) When Lb > Lr
𝑀𝑛 = 𝐹𝑐𝑟 𝑆𝑥 ≤ 𝑀𝑝
𝐸
𝐹𝑦
𝐿𝑝 = 1.76𝑟𝑦 √
𝐽𝑐
𝑆𝑥 ℎ𝑜
(6-4)
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CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
𝐵=
2
𝑟𝑡𝑠
=
0.7𝐹𝑦
𝐸
6.3.1 Lateral-Torsional Buckling. For lateraltorsional buckling, the provisions of Section 6.2.2
shall apply.
6.3.2
√𝐼𝑦 𝐶𝑤
𝑆𝑥
(6-8)
and the coefficient c is determined as follows:
(a) For doubly symmetric I-shapes:
𝑐=1
(6-9)
(b) For channels
𝐼𝑦 ℎ20
(6-11)
(6-12)
𝑏𝑓
2𝑡𝑓
pf
= p is the limiting slenderness for a compact
flange, Table 2-2
rf
= r is the limiting slenderness for a noncompact flange, Table 2-2
𝑘𝑐 =
4
√ℎ⁄𝑡𝑤
and shall not be taken less than 0.35 nor
greater than 0.76 for calculation purpose
4
and thus Eq. (6-8) becomes
h
𝐼𝑦 ℎ0
2𝑆𝑥
rts may be approximated accurately and
conservatively as the radius of gyration of
the compression flange plus one-sixth of the
web:
𝑟𝑡𝑠 =
(b) For sections with slender flanges
0.9𝐸 𝑘𝑐 𝑆𝑥
𝑀𝑛 =
𝜆2
where
(6-10)
User Note: For doubly symmetric I-shapes
with rectangular flanges,
2
𝑟𝑡𝑠
=
(a) For sections with non-compact flanges
𝜆 − 𝜆𝑝𝑓
𝑀𝑛 = 𝑀𝑝 − (𝑀𝑝 − 0.7𝐹𝑦 𝑆𝑥 ) (
)
𝜆𝑟𝑓 − 𝜆𝑝𝑓
𝜆=
ℎ0 𝐼𝑦
𝑐= √
2 𝐶𝑤
𝐶𝑤 =
Compression Flange Local Buckling
𝑏𝑓
1ℎ𝑡
√12 (1 + 6 𝑏 𝑡𝑤 )
𝑓 𝑓
6.3—Doubly Symmetric I-Shaped
Members with Compect Webs and
Noncompect or Slender Flanges Bent
about Their Major Axis
This section applies to doubly symmetric I-shaped
members bent about their major axis having
compact webs and non-compact or slender flanges
as defined in Section 2.4.1 for flexure.
The nominal flexural strength, Mn, shall be the
lower value obtained according to the limit states of
lateral-torsional buckling and compression flange
local buckling.
= distance as defined in Section 2.4.1 b, mm
6.4—Other I-Shaped Members with
Compact or Noncompact Webs Bent
About Their Major Axis
This section applies to doubly symmetric I-shaped
members bent about their major axis with noncompact webs and singly symmetric I-shaped
members with webs attached to the mid-width of
the flanges, bent about their major axis, with
compact or non-compact webs, as defined in
Section 2.4.1 for flexure.
User Note: I-shaped members for which this
section is applicable may be designed
conservatively using Section 6.5.
The nominal flexural strength, Mn, shall be the
lowest value obtained according to the limit states
of compression flange yielding, lateral-torsional
buckling, compression flange local buckling, and
tension flange yielding.
6.4.1
Compression Flange Yielding
𝑀𝑛 = 𝑅𝑝𝑐 𝑀𝑦𝑐 = 𝑅𝑝𝑐 𝐹𝑦 𝑆𝑥𝑐
(6-13)
where
SBC 306-CR-18
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CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
yield moment in the compression
flange, N-mm
Myc
6.4.2
Lateral-Torsional Buckling
(a) When Lb Lp, the limit state of lateral-torsional
buckling does not apply.
(b) When Lp < Lb Lr
𝑀𝑛 = 𝐶𝑏 [𝑅𝑝𝑐 𝑀𝑦𝑐 − (𝑅𝑝𝑐 𝑀𝑦𝑐 −
𝐿𝑏 −𝐿𝑝
𝐹𝐿 𝑆𝑥𝑐 ) (
𝐿𝑟 −𝐿𝑝
)] ≤ 𝑅𝑝𝑐 𝑀𝑦
𝐴=
𝐹𝐿
𝐸
The web plastification factor, Rpc, shall be
determined as follows:
𝐵=
(i) When Iyc /Iy 0.23
(6-14)
(a) When
(c) When Lb Lr
(6-15)
(b) When
where
𝑀𝑦𝑐 = 𝐹𝑦 𝑆𝑥𝑐
𝐽
𝐿𝑏 2
√
(
)
𝐹𝑐𝑟 =
1
+
0.078
𝑆𝑥𝑐 ℎ0 𝑟𝑡
𝐿𝑏 2
( )
𝑟𝑡
𝐶𝑏 𝜋 2 𝐸
For
𝐼𝑦𝑐
𝐼𝑦
(6-16)
𝑀𝑝
𝑀𝑦𝑐
𝑀𝑝
𝑆
𝑆𝑥𝑐
𝐹𝐿 = 𝐹𝑦
𝐸
𝐹𝑦
𝑀𝑝
𝑀𝑦𝑐
(6-23)
(6-24)
= 𝐹𝑦 𝑍𝑥 ≤ 1.6𝐹𝑦 𝑆𝑥𝑐
(6-18)
rw
r, the limiting slenderness for a noncompact web, Table 2-2
hc
twice the distance from the centroid to the
following: the inside face of the compression
flange less the fillet or corner radius, for
rolled shapes; the nearest line of fasteners at
the compression flange or the inside faces of
the compression flange when welds are used,
for built-up sections, mm
(6-19)
(6-20)
The limiting unbraced length for the limit state of
inelastic lateral-torsional buckling, Lr, is
determined as:
𝐸
𝐿𝑟 = 1.95𝑟𝑡 √𝐴 + √(𝐴)2 + 6.76(𝐵)2 (6-21)
𝐹𝐿
ℎ𝑐
𝑡𝑤
p, the limiting slenderness for a compact
web, Table 2-2
The limiting laterally unbraced length for the limit
state of yielding, Lp, is determined as:
𝐿𝑃 = 1.1𝑟𝑡 √
)] ≤
pw
< 0.7
𝑆𝑥𝑡
≥ 0.5𝐹𝑦
𝑆𝑥𝑐
𝜆−𝜆𝑝𝑤
𝜆𝑟𝑤 −𝜆𝑝𝑤
𝜆=
When 𝑥𝑡 ≥ 0.7
𝑆𝑥𝑐
− 1) (
Sxc, Sxt elastic section modulus referred to
compression and tension flanges,
respectively, mm3
The stress, FL, is determined as follows:
When
𝑀𝑝
𝑀𝑦𝑐
> 𝜆𝑝𝑤
where
= moment of inertia of the compression
flange about the y-axis, mm4
𝑆𝑥𝑡
−(
ℎ𝑐
𝑡𝑤
(6-22)
𝑅𝑝𝑐 = 1.0
(6-17)
≤ 0.23, J shall be taken as zero
𝐹𝐿 = 0.7𝐹𝑦
≤ 𝜆𝑝𝑤
(ii) When Iyc /Iy 0.23
where
Iyc
𝑅𝑝𝑐 = [
ℎ𝑐
𝑡𝑤
𝑀𝑝
𝑀𝑦𝑐
𝑅𝑝𝑐 =
𝑀𝑛 = 𝐹𝑐𝑟 𝑆𝑥𝑐 ≤ 𝑅𝑝𝑐 𝑀𝑦𝑐
𝐽
𝑆𝑥𝑐 ℎ𝑜
The effective radius of gyration for lateral-torsional
buckling, rt, is determined as follows:
i.
𝑟𝑡 =
Where,
For I-shapes with
compression flange
a
rectangular
𝑏𝑓𝑐
ℎ
1
ℎ2
√12 ( 0 + 𝑎𝑤
)
𝑑 6
ℎ0 𝑑
(6-25)
where
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CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
𝑎𝑤 =
ℎ𝑐 𝑡𝑤
𝑏𝑓𝑐 𝑡𝑓𝑐
(6-26)
bfc width of compression flange, mm
𝑏𝑓
𝜆=
𝑐
2 𝑡𝑓
𝑐
pf = p, the limiting slenderness for a compact
flange, Table 2-2
tfc compression flange thickness, mm
rf = r, the limiting slenderness for a noncompact flange, Table 2-2
ii. For I-shapes with a channel cap or a cover
plate attached to the compression flange
6.4.4
Tension Flange Yielding
rt radius of gyration of the flange components
in flexural compression plus one-third of the
web area in compression due to application of
major axis bending moment alone, mm
(a) When Sxt Sxc, the limit state of tension flange
yielding does not apply.
the ratio of two times the web area in
compression due to application of major axis
bending moment alone to the area of the
compression flange components
(6-29)
aw
User Note: For I-shapes with a rectangular
compression flange, rt may be approximated
accurately and conservatively as the radius of
gyration of the compression flange plus onethird of the compression portion of the web; in
other words
𝑟𝑡 =
6.4.3
𝑀𝑦𝑡 = 𝐹𝑦 𝑆𝑥𝑡
The web plastification factor corresponding to the
tension flange yielding limit state, Rpt, is
determined as follows:
ℎ
When 𝑐 ≤ 𝜆𝑝𝑤
𝑡𝑤
𝑅𝑝𝑡 =
𝑀𝑝
𝑀𝑦𝑡
(6-30)
ℎ
𝑡𝑤
√12 (1 + 1 𝑎𝑤 )
6
𝑀𝑛 = 𝑅𝑝𝑐 𝑀𝑦𝑐 − (𝑅𝑝𝑐 𝑀𝑦𝑐 − 𝐹𝐿 𝑆𝑥𝑐 ) (
𝑅𝑝𝑡 = [
𝜆−𝜆𝑝𝑓
𝜆𝑟𝑓 −𝜆𝑝𝑓
) (6-27)
(c) For sections with slender flanges
0.9𝐸𝑘𝑐 𝑆𝑥𝑐
(6-28)
𝑀𝑛 =
𝜆2
where
FL
is defined in Eqs. (6-18) and (6-19)
Rpc
is the web plastification factor, determined
by Eq. (6-22)
√ℎ⁄𝑡𝑤
where
When 𝑐 > 𝜆𝑝𝑤
(a) For sections with compact flanges, the limit
state of local buckling does not apply.
(b) For sections with non-compact flanges
4
𝑀𝑛 = 𝑅𝑝𝑡 𝑀𝑦𝑡
𝑏𝑓𝑐
Compression Flange Local Buckling
𝑘𝑐 =
(b) When Sxt Sxc
and shall not be taken less than
0.35 nor greater than 0.76 for calculation
purposes
𝑀𝑝
𝑀𝑦𝑡
−(
𝑀𝑝
𝑀𝑦𝑡
− 1) (
𝜆−𝜆𝑝𝑤
𝜆𝑟𝑤 −𝜆𝑝𝑤
)] ≤
𝑀𝑝
𝑀𝑦𝑡
(6-31)
Where
𝜆=
ℎ𝑐
𝑡𝑤
pw p, the limiting slenderness for a compact
web, defined in Table 2-2
rw r, the limiting slenderness for a noncompact web, defined in Table 2-2
6.5—Doubly Symmectric and Singly
Symmetric I-Shaped Members with
Slender Webs Bent About Their Majout
Axis
This section applies to doubly symmetric and
singly symmetric I-shaped members with slender
webs attached to the mid-width of the flanges and
bent about their major axis as defined in Section
2.4.1 for flexure.
SBC 306-CR-18
65
CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
The nominal flexural strength, Mn, shall be the
lowest value obtained according to the limit states
of compression flange yielding, lateral-torsional
buckling, compression flange local buckling, and
tension flange yielding.
6.5.1
Compression Flange Yielding
𝑀𝑛 = 𝑅𝑝𝑔 𝐹𝑦 𝑆𝑥𝑐
6.5.2
𝐹𝑐𝑟 =
4
√ℎ⁄𝑡𝑤
(6-32)
𝑀𝑛 = 𝑅𝑝𝑔 𝐹𝑐𝑟 𝑆𝑥𝑐
(a) When Lb Lp, the limit state of lateral-torsional
buckling does not apply.
(b) When Lp Lb Lr
𝐿𝑏 − 𝐿𝑝
𝐹𝑐𝑟 = 𝐶𝑏 [𝐹𝑦 − (0.3𝐹𝑦 ) (
)] ≤ 𝐹𝑦 (6-34)
𝐿𝑟 − 𝐿𝑝
(c) When Lb > Lr
𝐶𝑏 𝜋 2 𝐸
𝐹𝑐𝑟 =
≤ 𝐹𝑦
𝐿𝑏 2
( )
𝑟𝑡
(6-35)
(6-40)
and shall not be taken less than 0.35 nor
greater than 0.76 for calculation purpose.
𝜆=
(6-33)
𝑏𝑓 2
(2𝑡 )
𝑓
where
𝑘𝑐 =
Lateral-Torsional Buckling
0.9 𝐸 𝑘𝑐
𝑏𝑓
𝑐
2 𝑡𝑓
𝑐
pf p, the limiting slenderness for a compact
flange, Table 2-2
rf
r, the limiting slenderness for a noncompact flange, Table 2-2
6.5.4
Tension Flange Yielding
(a) When Sxt Sxc, the limit state of tension flange
yielding does not apply.
(b) When Sxt Sxc
𝑀𝑛 = 𝐹𝑦 𝑆𝑥𝑡
(6-41)
where
6.6—I-Shaped Members and Channels
Bent About Their Minor Axis
Lp is defined by Eq. (6-20)
𝐸
0.7𝐹𝑦
(6-36)
This section applies to I-shaped members and
channels bent about their minor axis.
Rpg, the bending strength reduction factor is
determined as follows:
The nominal flexural strength, Mn, shall be the
lower value obtained according to the limit states of
yielding (plastic moment) and flange local buckling.
𝐿𝑟 = 𝜋 𝑟𝑡 √
𝑅𝑝𝑔 = 1 −
𝑎𝑤
1,200+300𝑎𝑤
ℎ
𝐸
𝑡𝑤
𝐹𝑦
( 𝑐 − 5.7√ ) ≤ 1.0 (6-37)
Yielding
𝑀𝑛 = 𝑀𝑝 = 𝐹𝑦 𝑍𝑦 ≤ 1.6𝐹𝑦 𝑆𝑦
where
aw
rt
6.5.3
6.6.1
is defined by Eq. (6-26) but shall not
exceed 10
is the effective radius of gyration for
lateral buckling as defined in Section 6.4
Compression Flange Local Buckling
𝑀𝑛 = 𝑅𝑝𝑔 𝐹𝑐𝑟 𝑆𝑥𝑐
(6-38)
(a) For sections with compact flanges, the limit
state of compression flange local buckling
does not apply
(b) For sections with non-compact flanges
𝐹𝑐𝑟 = [𝐹𝑦 − (0.3𝐹𝑦 ) (
𝜆−𝜆𝑝𝑓
𝜆𝑟𝑓 −𝜆𝑝𝑓
)]
6.6.2
(6-42)
Flange Local Buckling
(a) For sections with compact flanges the limit
state of flange local buckling does not apply.
(b) For sections with non-compact flanges
𝜆 − 𝜆𝑝𝑓
𝑀𝑛 = [𝑀𝑝 − (𝑀𝑝 − 0.7𝐹𝑦 𝑆𝑦 ) (
)] (6-43)
𝜆𝑟𝑓 − 𝜆𝑝𝑓
(c) For sections with slender flanges
(6-39)
(c) For sections with slender flanges
𝑀𝑛 = 𝐹𝑐𝑟 𝑆𝑦
where
𝐹𝑐𝑟 =
0.69𝐸
𝑏 2
( )
𝑡𝑓
𝜆=
SBC 306-CR-18
(6-44)
(6-45)
𝑏
𝑡𝑓
66
CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
pf = p, the limiting slenderness for a compact
flange, Table 2-2
rf = r, the limiting slenderness for a noncompact flange, Table 2-2
b
= for flanges of I-shaped members, half the
full-flange width, bf ; for flanges of
channels, the full nominal dimension of the
flange, mm
tf
= thickness of the flange, mm
Sy
= elastic section modulus taken about the
y-axis, mm3; for a channel, the minimum
section modulus
𝑀𝑛 = 𝑀𝑝 − (𝑀𝑝 −
𝐹𝑦 𝑆) [3.57
This section applies to square and rectangular
HSS, and doubly symmetric box- shaped
members bent about either axis, having compact
or non-compact webs and compact, non-compact
or slender flanges as defined in Section 2.4.1 for
flexure.
The nominal flexural strength, Mn, shall be the
lowest value obtained according to the limit states
of yielding (plastic moment), flange local buckling
and web local buckling under pure flexure.
User Note: Very long rectangular HSS bent
about the major axis are subject to lateraltorsional buckling; however, the Code provides
no strength equation for this limit state since
beam deflection will control for all reasonable
cases.
6.7.1
Yielding
𝑀𝑛 = 𝑀𝑝 = 𝐹𝑦 𝑍
(6-46)
Z plastic section modulus about the axis of
bending, mm3
𝑀𝑛 = 𝐹𝑦 𝑆𝑒
(6-48)
where
Se effective section modulus determined with
the effective width, be, of the compression
flange taken as:
𝑏𝑒 = 1.92𝑡𝑓 √
𝐸
0.38 𝐸
[1 −
√ ]≤𝑏
𝐹𝑦
𝑏⁄𝑡𝑓 𝐹𝑦
(6-49)
Web Local Buckling
(a) For compact sections, the limit state of web
local buckling does not apply
(b) For sections with non-compact webs
𝑀𝑛 = 𝑀𝑝 − (𝑀𝑝 −
𝐹𝑦 𝑆𝑥 ) [0.305
ℎ
𝑡𝑓𝑤
𝐹
√ 𝑦 − 0.738] ≤ 𝑀𝑝
(6-50)
𝐸
6.8—Round HSS
This section applies to round HSS having D/t ratios
of less than 0.45 E/ Fy.
The nominal flexural strength, Mn, shall be the
lower value obtained according to the limit states of
yielding (plastic moment) and local buckling.
6.8.1
Yielding
𝑀𝑛 = 𝑀𝑝 = 𝐹𝑦 𝑍
6.8.2
(6-51)
Local Buckling
(a) For compact sections, the limit state of flange
local buckling does not apply.
(b) For non-compact sections
0.021𝐸
+ 𝐹𝑦 ) 𝑆
𝐷
𝑡
(c) For sections with slender walls
Flange Local Buckling
(a) For compact sections, the limit state of flange
local buckling does not apply.
(b) For sections with non-compact flanges
(6-47)
𝐸
𝑀𝑛 = (
where
6.7.2
√ 𝑦 − 4.0] ≤ 𝑀𝑝
(c) For sections with slender flanges
6.7.3
6.7—Square and Rectangular HSS and
Box-Shaped Members
𝐹
𝑏
𝑡𝑓
(6-52)
𝑀𝑛 = 𝐹𝑐𝑟 𝑆
(6-53)
0.33𝐸
𝐷
( )
𝑡
(6-54)
where
𝐹𝑐𝑟 =
S = elastic section modulus, mm3
SBC 306-CR-18
67
CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
t = thickness of wall, mm
where
6.9—Tees and Double Angles Loaded
in The Plane of Symmetry
This section applies to tees and double angles
loaded in the plane of symmetry.
The nominal flexural strength, Mn, shall be the
lowest value obtained according to the limit states
of yielding (plastic moment), lateral-torsional
buckling, flange local buckling, and local buckling
of tee stems.
6.9.1
Yielding
𝑀𝑛 = 𝑀𝑝
(6-55)
where
(a) For stems in tension
𝑀𝑃 = 𝐹𝑦 𝑍𝑥 ≤ 1.6𝑀𝑦
6.9.2
=
𝜋√𝐸𝐼𝑦 𝐺𝐽
𝐿𝑏
𝑏𝑓
2𝑡𝑓
pf p, the limiting slenderness for a compact
flange, Table 2-2
rf r, the limiting slenderness for a noncompact flange, Table 2-2
User Note: For double angles with flange legs in
compression, Mn based on local buckling is to be
determined using the provisions of Section
6.10.3 with b /t of the flange legs and Eq. (6-66)
as an upper limit.
(6-57)
6.9.4 Local Buckling of Tee Stems in Flexural
Compression
𝑀𝑛 = 𝐹𝑐𝑟 𝑆𝑥
Lateral-Torsional Buckling
𝑀𝑛 = 𝑀𝑐𝑟 =
(6-62)
where
( 𝐵 + √1 + 𝐵2 )
(6-58)
Sx elastic section modulus, mm3
The critical stress, Fcr, is determined as follows:
where
d Iy
B 2.3
Lb J
(6-59)
The plus sign for B applies when the stem is in
tension and the minus sign applies when the stem
is in compression. If the tip of the stem is in
compression anywhere along the unbraced length,
the negative value of B shall be used.
6.9.3
𝜆
(6-56)
(b) For stems in compression
𝑀𝑝 = 𝐹𝑦 𝑍𝑥 ≤ 𝑀𝑦
Sxc elastic section modulus referred to the
compression flange, mm3
(a) When
(a) For sections with a compact flange in flexural
compression, the limit state of flange local
buckling does not apply.
(b) For sections with a non-compact flange in
flexural compression
𝜆𝑟𝑓 −𝜆𝑝𝑓
) ≤ 1.6𝑀𝑦
(b) When
𝑏𝑓 2
(2𝑡 )
𝑓
𝐸
𝑑
𝐸
𝑦
𝑤
𝑦
0.84√ < ≤ 1.03√
𝐹
𝑡
𝐹
(6-61)
𝑑 𝐹𝑦
√ ]𝐹
𝑡𝑤 𝐸 𝑦
(6-64)
𝑑
𝐸
> 1.03√
𝑡𝑤
𝐹𝑦
𝐹𝑐𝑟 =
0.69𝐸
(
0.7𝐸𝑆𝑥𝑐
(6-63)
(c) When
(6-60)
(c) For sections with a slender flange in flexural
compression
𝑀𝑛 =
𝐸
𝐹𝑦
𝐹𝑐𝑟 = 𝐹𝑦
𝑀𝑛 = 𝑀𝑝 − (𝑀𝑝 −
0.7𝐹𝑦 𝑆𝑥𝑐 ) (
≤ 0.84√
𝐹𝑐𝑟 = [2.55 − 1.84
Flange Local Buckling of Tees
𝜆−𝜆𝑝𝑓
𝑑
𝑡𝑤
𝑑 2
)
𝑡𝑤
(6-65)
User Note: For double angles with web legs in
compression, Mn based on local buckling is to
be determined using the provisions of Section
SBC 306-CR-18
68
CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
6.10.3 with b /t of the web legs and Eq. (6-66)
as an upper limit.
6.10—Single Angles
This section applies to single angles with and
without continuous lateral restraint along their
length.
(b) When 𝑀𝑒 > 𝑀𝑦
My
M 1.5M (6-68)
M n 1.92 1.17
y
y
M
e
where
Me, the elastic lateral-torsional buckling moment, is
determined as follows:
For bending about the major principal axis of
equal-leg angles:
Single angles with continuous lateral-torsional
restraint along the length are permitted to be
designed on the basis of geometric axis (x, y)
bending. Single angles without continuous lateraltorsional restraint along the length shall be designed
using the provisions for principal axis bending
except where the provision for bending about a
geometric axis is permitted.
If the moment resultant has components about both
principal axes, with or without axial load, or the
moment is about one principal axis and there is axial
load, the combined stress ratio shall be determined
using the provisions of Section 8.2.
User Note: For geometric axis design, use
section properties computed about the x- and yaxis of the angle, parallel and perpendicular to the
legs. For principal axis design, use section
properties computed about the major and minor
principal axes of the angle.
The nominal flexural strength, Mn, shall be the
lowest value obtained according to the limit states
of yielding (plastic moment), lateral-torsional
buckling, and leg local buckling.
User Note: For bending about the minor axis,
only the limit states of yielding and leg local
buckling apply.
6.10.1 Yielding
𝑀𝑛 = 1.5𝑀𝑦
(6-66)
where
My
Me
Me
0.17𝑀𝑒
) 𝑀𝑒
𝑀𝑦
2
Lb t
4.9 EI z C b
2
0
.
052
w (6-70)
w
2
Lb
rz
where
Cb
is computed using Eq. (6-1) with a
maximum value of 1.5
Lb
= laterally unbraced length of member, mm
Iz
= minor principal axis moment of inertia,
mm4
rz
= radius of gyration about the minor
principal axis, mm
t
= thickness of angle leg, mm
w = section property for unequal leg angles,
positive for short legs in compression and
negative for long legs in compression. If
the long leg is in compression anywhere
along the unbraced length of the member,
the negative value of w shall be used.
User Note: The equation for w and values for
common angle sizes are listed in the
Commentary.
For bending moment about one of the
geometric axes of an equal-leg angle with
no axial compression
(a) And with no lateral-torsional restraint:
With maximum compression at the
toe
(a) When 𝑀𝑒 ≤ 𝑀𝑦
𝑀𝑛 = (0.92 −
(6-69)
For bending about the major principal axis of
unequal-leg angles:
= yield moment about the axis of bending,
N-mm
6.10.2 Lateral-Torsional Buckling. For single
angles without continuous lateral-torsional restraint
along the length
0.46Eb2t 2C b
Lb
(6-67)
SBC 306-CR-18
69
CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
Me
2
0.66 Eb 4 t C b
Lb t
1
0
.
78
1
2
L2b
b
(6-71)
With maximum tension at the toe
Me
2
0.66 Eb 4 t C b
Lb t
1
0
.
78
1
(6-72)
2
2
Lb
b
My shall be taken as 0.80 times the yield moment
calculated using the geometric section modulus.
6.11—Rectangular Bars and Rounds
This section applies to rectangular bars bent about
either geometric axis and rounds. The nominal
flexural strength, Mn, shall be the lower value
obtained according to the limit states of yielding
(plastic moment) and lateral-torsional buckling.
6.11.1 Yielding.
0.08𝐸
𝐹𝑦
where
For rectangular with
𝐿𝑏 𝑑
𝑡2
≤
bent about their major axis, rectangular bars
bent about their minor axis and rounds:
b full width of leg in compression, mm
𝑀𝑛 = 𝑀𝑝 = 𝐹𝑦 𝑍 ≤ 1.6𝑀𝑦
User Note: Mn may be taken as My for single
angles with their vertical leg toe in compression,
and having a span-to-depth ratio less than or
equal to
𝐹
1.64𝐸
𝑡 2
√( ) − 1.4 𝑦
𝐹𝑦
𝑏
𝐸
6.11.2 Lateral-Torsional Buckling
(a) For rectangular bars with
0.08𝐸
𝐹𝑦
My shall be taken as the yield moment calculated
using the geometric section modulus.
6.10.3 Leg Local Buckling. The limit state of leg
local buckling applies when the toe of the leg is in
compression.
(a) For compact sections, the limit state of leg local
buckling does not apply.
(b) For sections with non-compact legs:
𝐹𝑦
𝑡
𝐸
(6-73)
1.9𝐸
𝑡
𝐹𝑦
bent about
(6-78)
1.9𝐸𝐶𝑏
𝐿𝑏 𝑑
𝑡2
Lb = length between points that are either
braced against lateral displacement of the
compression region, or between points
braced to prevent twist of the cross section,
mm
𝐹𝑐𝑟 =
d = depth of rectangular bar, mm
(6-74)
= width of rectangular bar parallel to axis of
bending, mm
(c) For rounds and rectangular bars bent
about their minor axis, the limit state of
lateral-torsional buckling need not be
considered.
(6-75)
Sc = elastic section modulus to the toe in
compression relative to the axis of bending,
mm3. For bending about one of the geometric
axes of an equal-leg angle with no lateraltorsional restraint, Sc shall be 0.80 of the
geometric axis section modulus
𝐿 𝑑
where
0.71𝐸
𝑏 2
( )
𝑡
bent about their major axis:
𝑀𝑛 = 𝐹𝑐𝑟 𝑆𝑥 ≤ 𝑀𝑝
where
𝐹𝑐𝑟 =
𝐹𝑦
their major axis:
t
(c) For sections with slender legs:
𝑀𝑛 = 𝐹𝑐𝑟 𝑆𝑐
1.9𝐸
𝑡
(b) For rectangular bars with 𝑏2 >
Me shall be taken as 1.25 times Me computed
using Eq. (6-71) or (6-72).
𝑏
𝐿 𝑑
< 𝑏2 ≤
𝐿𝑏 𝑑 𝐹𝑦
𝑀𝑛 = 𝐶𝑏 [1.52 − 0.274 ( 2 ) ] 𝑀𝑦 ≤ 𝑀𝑝
(6-77)
𝑡
𝐸
(b) and with lateral-torsional restraint at the point of
maximum moment only:
𝑀𝑛 = 𝐹𝑦 𝑆𝑐 (2.43 − 1.72 ( ) √ )
(6-76)
6.12—Unsymmetrical Shapes
This section applies to all unsymmetrical shapes,
except single angles.
SBC 306-CR-18
70
CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
The nominal flexural strength, Mn, shall be the
lowest value obtained according to the limit states
of yielding (yield moment), lateral-torsional
buckling, and local buckling where
𝑀𝑛 =
𝐹𝑢 𝐴𝑓𝑛
𝑆
𝐴𝑓𝑔 𝑥
(6-83)
where
(6-79)
Afg gross area of tension flange, calculated in
accordance with the provisions of Section
2.4.3a, mm2
Smin
= lowest elastic section modulus relative to
the axis of bending, mm3
Afn net area of tension flange, calculated in
accordance with the provisions of
Section 2.4.3b, mm2
𝑀𝑛 = 𝐹𝑛 𝑆𝑚𝑖𝑛
where
6.12.1 Yielding
𝐹𝑛 = 𝐹𝑦
(6-80)
6.12.2 Lateral-Torsional Buckling
𝐹𝑛 = 𝐹𝑐𝑟 ≤ 𝐹𝑦
(6-81)
Yt
1.0 for Fy /Fu 0.8
1.1 otherwise
6.13.2 Proportioning Limits for I-Shaped
Members. Singly symmetric I-shaped members
shall satisfy the following limit:
where
0.1 ≤
Fcr = lateral-torsional buckling stress for the
section as determined by analysis, MPa
User Note: In the case of Z-shaped members, it
is recommended that Fcr be taken as 0.5Fcr of a
channel with the same flange and web properties.
(a) When
𝑎
ℎ
≤ 1.5
(
(6-82)
(b) When
Where
(6-84)
I-shaped members with slender webs shall also
satisfy the following limits:
6.12.3 Local Buckling
𝐹𝑛 = 𝐹𝑐𝑟 ≤ 𝐹𝑦
𝐼𝑦𝑐
≤ 0.9
𝐼𝑦
Fcr = local buckling stress for the section as
determined by analysis, MPa
(
𝑎
ℎ
ℎ
𝐸
)√
𝑡𝑤 𝐹𝑦
(6-85)
𝑚𝑎𝑥
> 1.5
ℎ 0.40𝐸
)
𝑡𝑤
𝐹𝑦 𝑚𝑎𝑥
(6-86)
where
6.13—Proportions of Beams and
Girders
a
6.13.1 Strength Reductions for Members with
Holes in the Tension Flange. This section applies
to rolled or built-up shapes and cover-plated beams
with holes, proportioned on the basis of flexural
strength of the gross section.
In unstiffened girders h/ tw shall not exceed 260. The
ratio of the web area to the compression flange area
shall not exceed 10.
In addition to the limit states specified in other
sections of this Chapter, the nominal flexural
strength, Mn, shall be limited according to the limit
state of tensile rupture of the tension flange.
(a) When FuAfn Yt Fy Afg, the limit state of tensile
rupture does not apply.
(b) When Fu Afn Yt Fy Afg, the nominal flexural
strength, Mn, at the location of the holes in the
tension flange shall not be taken greater than
= clear distance between transverse stiffeners,
mm
6.13.3 Cover Plates. Flanges of welded beams or
girders may be varied in thickness or width by
splicing a series of plates or by the use of cover
plates.
The total cross-sectional area of cover plates of
bolted girders shall not exceed 70% of the total
flange area.
High-strength bolts or welds connecting flange to
web, or cover plate to flange, shall be proportioned
to resist the total horizontal shear resulting from the
bending forces on the girder. The longitudinal
SBC 306-CR-18
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CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
distribution of these bolts or intermittent welds
shall be in proportion to the intensity of the shear.
However, the longitudinal spacing shall not exceed
the maximum specified for compression or tension
members in Section 5.6 or 4.4, respectively. Bolts
or welds connecting flange to web shall also be
proportioned to transmit to the web any loads
applied directly to the flange, unless provision is
made to transmit such loads by direct bearing.
Partial-length cover plates shall be extended
beyond the theoretical cutoff point and the
extended portion shall be attached to the beam or
girder by high-strength bolts in a slip-critical
connection or fillet welds. The attachment shall be
adequate, at the applicable strength given in
Sections 10.2.2 , 10.3.8 or 2.3.10 to develop the
cover plate’s portion of the flexural strength in the
beam or girder at the theoretical cut-off point.
For welded cover plates, the welds connecting the
cover plate termination to the beam or girder shall
have continuous welds along both edges of the cover
plate in the length a, defined below, and shall be
adequate to develop the cover plate’s portion of the
design strength of the beam or girder at the distance
afrom the end of the cover plate.
(a) When there is a continuous weld equal to or
larger than three-fourths of the plate thickness
across the end of the plate
𝑎′ = 𝑤
(6-87)
where
w
unbraced length, Lb, of the compression flange
adjacent to the redistributed end moment locations
shall not exceed Lm determined as follows.
(a) For doubly symmetric and singly symmetric Ishaped beams with the compression flange
equal to or larger than the tension flange
loaded in the plane of the web:
𝑀1
𝐸
𝐿𝑚 = [0.12 + 0.076 ( )] ( ) 𝑟𝑦
(6-90)
𝑀2
𝐹𝑦
(b) For solid rectangular bars and symmetric box
beams bent about their major axis:
𝑀
𝐸
𝑀2
𝐹𝑦
𝐿𝑚 = [0.17 + 0.10 ( 1 )] ( ) 𝑟𝑦 ≥
𝐸
(6-91)
0.10 ( ) 𝑟𝑦
𝐹𝑦
where
Fy
= specified minimum yield stress of the
compression flange, MPa
M1 = smaller moment at end of unbraced length,
N-mm
M2 = larger moment at end of unbraced length,
N-mm
ry
= radius of gyration about y-axis, mm
(M1 /M2) is positive when moments cause reverse
curvature and negative for single curvature
There is no limit on Lb for members with round or
square cross sections or for any beam bent about
its minor axis.
width of cover plate, mm
(b) When there is a continuous weld smaller than
three-fourths of the plate thickness across the
end of the plate
𝑎′ = 1.5𝑤
(6-88)
(c) When there is no weld across the end of the
plate
𝑎′ = 2𝑤
(6-89)
6.13.4 Built-Up Beams. Where two or more
beams or channels are used side-by-side to form a
flexural member, they shall be connected together
in compliance with Section 5.6. When concentrated
loads are carried from one beam to another or
distributed between the beams, diaphragms having
sufficient stiffness to distribute the load shall be
welded or bolted between the beams.
6.13.5 Unbraced
Length
for
Moment
Redistribution.. For moment redistribution in
beams according to Section 2.3.6 , the laterally
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CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
TABLES AND FIGURES OF CHAPTER 6
Table 6-1 : Selection Table for the Application of Chapter 6 Sections
Section in
Chapter 6
Flange
Slenderness
Web Slenderness
Limit States
6.2
C
C
Y, LTB
6.3
NC, S
C
LTB, FLB
6.4
C, NC, S
C, NC
Y, LTB,
FLB, TFY
6.5
C, NC, S
S
Y, LTB,
FLB, TFY
6.6
C, NC, S
N/A
Y, FLB
6.7
C, NC, S
C, NC
Y, FLB, WLB
6.8
N/A
N/A
Y, LB
6.9
C, NC, S
N/A
Y, LTB, FLB
6.10
N/A
N/A
Y, LTB, LLB
6.11
N/A
N/A
Y, LTB
N/A
N/A
All limit states
6.12
Cross Section
Unsymmetrical shapes, other than
single angles
Y = yielding, LTB = lateral-torsional buckling, FLB = flange local buckling, WLB = web local buckling, TFY =
tension flange yielding, LLB = leg local buckling, LB = local buckling, C = compact, NC = non-compact, S = slender
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CHAPTER 6—DESIGN OF MEMBERS FOR FLEXURE
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SBC 306-CR-18
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CHAPTER 7—DESIGN OF MEMBERS FOR SHEAR
CHAPTER 7—DESIGN OF MEMBERS FOR SHEAR
This chapter addresses webs of singly or doubly
symmetric members subject to shear in the plane of
the web, single angles and HSS sections, and shear
in the weak direction of singly or doubly symmetric
shapes.
The chapter is organized as follows:
7.1 —General Provisions
7.2 —Members with Unstiffened or Stiffened
Webs
7.2—Members with Unstiffened or
Stiffened Webs
7.2.1 Shear Strength. This section applies to
webs of singly or doubly symmetric members and
channels subject to shear in the plane of the web.
The nominal shear strength, Vn, of unstiffened or
stiffened webs according to the limit states of shear
yielding and shear buckling, is
𝑉𝑛 = 0.6𝐹𝑦 𝐴𝑤 𝐶𝑣
7.3 —Tension Field Action
7.4 —Single Angles
7.5 —Rectangular
Members
HSS
and
Box-Shaped
7.6 —Round HSS
7.7 —Weak Axis Shear in Doubly Symmetric
and Singly Symmetric Shapes
7.8 —Beams and Girders with Web Openings
(7-1)
(a) For members of rolled I-shaped members with
ℎ⁄𝑡𝑤 ≤ 2.24√𝐸 ⁄𝐹𝑦 :
𝜑𝑣 = 1.00
𝐶𝑣 = 1.00
(7-2)
(b) For webs of all doubly symmetric shapes and
singly symmetric shapes and channels, except
round HSS, the web shear coefficient, Cv, is
determined as follows:
When
ℎ⁄𝑡𝑤 ≤ 1.10√𝑘𝑣 𝐸 ⁄𝐹𝑦
User Note: For cases not included in this
chapter, the following sections apply:
8.3.3
𝐶𝑣 = 1.00
Unsymmetric sections
When
1.10√𝑘𝑣 𝐸 ⁄𝐹𝑦 ≤ ℎ⁄𝑡𝑤 ≤ 1.37√𝑘𝑣 𝐸 ⁄𝐹𝑦
10.4.2 Shear strength of connecting elements
10.10.6 Web panel zone shear
𝐶𝑣 =
7.1—General Provisions
1.10√𝑘𝑣 𝐸 ⁄𝐹𝑦
ℎ⁄𝑡𝑤
(7-4)
When
Two methods of calculating shear strength are
presented below. The method presented in Section
7.2 does not utilize the post buckling strength of
the member (tension field action). The method
presented in Section 7.3 utilizes tension field
action.
The design shear strength, ϕvVn, shall be
determined as follows:
ℎ⁄𝑡𝑤 > 1.37√𝑘𝑣 𝐸 ⁄𝐹𝑦
𝐶𝑣 =
1.51 𝐸 𝑘𝑣
(ℎ⁄𝑡𝑤 )2 𝐹𝑦
(7-5)
where
Aw = area of web, the overall depth times the web
thickness, 𝑑𝑡𝑤 , mm2
For all provisions in this chapter
𝜑𝑣 = 0.90
(7-3)
h
= for rolled shapes, the clear distance between
flanges less the fillet or corner radii, mm
= for built-up welded sections, the clear
distance between flanges, mm
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CHAPTER 7—DESIGN OF MEMBERS FOR SHEAR
= for built-up bolted sections, the distance
between fastener lines, mm
= for tees, the overall depth, mm
tw
= thickness of web, mm
The web plate shear buckling coefficient, kv, is
determined as follows:
For webs without transverse stiffeners and
with ℎ⁄𝑡𝑤 < 260:
𝑘𝑣 = 5
Bolts connecting stiffeners to the girder web shall
be spaced not more than 300 mm on center. If
intermittent fillet welds are used, the clear
distance between welds shall not be more than 16
times the web thickness nor more than 250 mm.
7.3—Tension Field Action
except for the stem of tee shapes
7.3.1 Limits on the Use of Tension Field
Action. Consideration of tension field action is
permitted for flanged members when the web plate
is supported on all four sides by flanges or
stiffeners. Consideration of tension field action is
not permitted:
where
𝑘𝑣 = 1.2.
For webs with transverse stiffeners:
𝑘𝑣 = 5 +
thickness from the near toe to the web-to-flange
weld. When single stiffeners are used, they shall
be attached to the compression flange, if it
consists of a rectangular plate, to resist any uplift
tendency due to torsion in the flange.
5
(𝑎⁄ℎ)2
(7-6)
260
= 5 when 𝑎⁄ℎ > 3.0 or 𝑎⁄ℎ > [(ℎ⁄
𝑡𝑤
]
)
2
(a) for end panels in all members with transverse
stiffeners;
(b) when a/h exceeds 3.0 or [260⁄(ℎ⁄𝑡𝑤 )] 2 ;
where
(c) when 2𝐴𝑤 ⁄(𝐴𝑓𝑐 + 𝐴𝑓𝑡 ) > 2.5; or
a clear distance between transverse
stiffeners, mm
where
7.2.2 Transverse Stiffeners.
Transverse
stiffeners
are
not
required
where
ℎ⁄𝑡𝑤 ≤ 2.46√𝐸 ⁄𝐹𝑦 , or where the design shear
strength provided in accordance with Section 7.2.1
for 𝑘𝑣 = 5 is greater than the required shear
strength.
The moment of inertia, Ist, of transverse stiffeners
used to develop the design web shear strength, as
provided in Section 7.2.1 , about an axis in the web
center for stiffener pairs or about the face in contact
with the web plate for single stiffeners, shall meet
the following requirement
3
𝐼𝑠𝑡 ≥ 𝑏𝑡𝑤
𝑗
(7-7)
2.5
− 2 ≥ 0.5
𝑎 2
( )
ℎ
(7-8)
where
𝑗=
and b is the smaller of the dimensions a and h
Transverse stiffeners are permitted to be stopped
short of the tension flange, provided bearing is not
needed to transmit a concentrated load or reaction.
The weld by which transverse stiffeners are
attached to the web shall be terminated not less
than four times nor more than six times the web
(d) when ℎ⁄𝑏𝑓𝑐 or ℎ⁄𝑏𝑓𝑡 > 6.0
Afc = area of compression flange, mm2
Aft = area of tension flange, mm2
bfc = width of compression flange, mm
bft = width of tension flange, mm
In these cases, the nominal shear strength, Vn, shall
be determined according to the provisions of
Section 7.2.
7.3.2 Shear Strength with Tension Field
Action. When tension field action is permitted
according to Section 7.3.1 , the nominal shear
strength, Vn, with tension field action, according
to the limit state of tension field yielding, shall be
(a) When
ℎ⁄𝑡𝑤 ≤ 1.10√𝑘𝑣 𝐸 ⁄𝐹𝑦
𝑉𝑛 = 0.6𝐹𝑦 𝐴𝑤
(7-9)
(b) When ℎ⁄𝑡𝑤 > 1.10√𝑘𝑣 𝐸 ⁄𝐹𝑦
𝑉𝑛 = 0.6𝐹𝑦 𝐴𝑤 𝐶𝑣 +
(
1 − 𝐶𝑣
𝑎 2
1.15√1 + ( ) )
ℎ
(7-10)
where
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CHAPTER 7—DESIGN OF MEMBERS FOR SHEAR
kv and Cv are as defined in Section 7.2.1
7.3.3 Transverse Stiffeners.
Transverse
stiffeners subject to tension field action shall meet
the requirements of Section 7.2.2 and the
following limitations:
𝐸
(1) (𝑏⁄𝑡)𝑠𝑡 ≤ 0.56√𝐹
(7-11)
𝑦𝑠𝑡
7.4—Single Angles
The nominal shear strength, Vn, of a single angle
leg shall be determined using Eq. (7-1) and
Section 7.2.1 (b) with 𝐴𝑤 = 𝑏𝑡
where
b width of the leg resisting the shear force, mm
𝑉𝑟 −𝑉𝑐1
(2) 𝐼𝑠𝑡 ≥ 𝐼𝑠𝑡1 + (𝐼𝑠𝑡2 − 𝐼𝑠𝑡1 ) [𝑉 −𝑉 ]
𝑐2
(7-12)
𝑐1
t thickness of angle leg, mm
where
ℎ⁄𝑡𝑤
= 𝑏⁄𝑡
(b/t)st width-to-thickness ratio of the stiffener
𝑘𝑣
= 1.2
Fyst specified minimum yield stress of the
stiffener material, MPa
7.5—Rectangular HSS and Box-Shaped
Members
moment of inertia of the transverse
stiffeners about an axis in the web center for
stiffener pairs, or about the face in contact
with the web plate for single stiffeners, mm4
The nominal shear strength, Vn, of rectangular HSS
and box members shall be determined using the
provisions of Section 7.2.1 with 𝐴𝑤 = 2ℎ𝑡
Ist1 minimum moment of inertia of the
transverse
stiffeners
required
for
development of the web shear buckling
resistance in Section 7.2.2 , mm4
h width resisting the shear force, taken as the
clear distance between the flanges less the
inside corner radius on each side, mm
Ist
𝐼𝑠𝑡1 =
1.5
1.3 𝐹
ℎ4 𝜌𝑠𝑡
𝑦𝑤
40
(
𝐸
)
, mm4
2.5
ℎ
Vr
t
(7-13)
Ist2 minimum moment of inertia of the
transverse
stiffeners
required
for
development of the full web shear buckling
plus the web tension field resistance, Vr = Vc2
3
3
𝐼𝑠𝑡2 = [(𝑎⁄ )2 − 2] 𝑏𝑝 𝑡𝑤
≥ 0.5𝑏𝑝 𝑡𝑤
where
(7-14)
larger of the required shear strengths in the
adjacent web panels, N
Vc1 smaller of the design shear strengths in the
adjacent web panels with Vn as defined in
Section 7.2.1 , N
Vc2 smaller of the design shear strengths in the
adjacent web panels with Vn
as defined
in Section 7.3.2 , N
design wall thickness, equal to 0.93 times the
nominal wall thickness for electric resistancewelded (ERW) HSS and equal to the nominal
thickness for submerged-arc-welded (SAW)
HSS, mm
𝑡𝑤
= 𝑡, mm
𝑘𝑣
=5
If the corner radius is not known, h shall be
taken as the corresponding outside dimension
minus 3 times the thickness.
7.6—Round HSS
The nominal shear strength, Vn, of round HSS,
according to the limit states of shear yielding and
shear buckling, shall be determined as:
𝑉𝑛 = 𝐹𝑐𝑟 𝐴𝑔 ⁄2
where
Fcr
shall be the larger of
𝐹𝑐𝑟 =
st the larger of 𝐹𝑦𝑤 ⁄𝐹𝑦𝑠𝑡 and 1.0
Fyw specified minimum yield stress of the web
material, MPa
(7-15)
1.60𝐸
5
4
√𝐿𝑣 (𝐷)
𝐷 𝑡
(7-16)
and
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CHAPTER 7—DESIGN OF MEMBERS FOR SHEAR
𝐹𝑐𝑟 =
0.78𝐸
3
𝐷 2
( )
𝑡
(7-17)
but shall not exceed 0.6Fy
Ag
gross cross-sectional area of member, mm2
D
outside diameter, mm
Lv
distance from maximum to zero shear
force, mm
t
design wall thickness, equal to 0.93 times
the nominal wall thickness for ERW HSS
and equal to the nominal thickness for SAW
HSS, mm
User Note: The shear buckling equations, Eq.
(7-16) and (7-17), will control for D/t over 100,
high-strength steels, and long lengths. For
standard sections, shear yielding will usually
control.
7.7—Weak Axis Shear in Doubly
Symmetric and Singly Symmetric
Shapes
For doubly and singly symmetric shapes loaded in
the weak axis without torsion, the nominal shear
strength, Vn, for each shear resisting element
shall be determined using Eq. (7-1) and Section
7.2.1 (b) with ℎ⁄𝑡𝑤 = 𝑏𝑓 ⁄𝑡𝑓 , 𝑘𝑣 = 1.2, and b
for flanges of I-shaped members, half the fullflange width, bf ; for flanges of channels, the full
nominal dimension of the flange, mm
7.8—Beams and Girders with Web
Openings
The effect of all web openings on the shear
strength of steel and composite beams shall be
determined. Adequate reinforcement shall be
provided when the required strength exceeds the
design strength of the member at the opening.
SBC 306-CR-18
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CHAPTER 7—DESIGN OF MEMBERS FOR SHEAR
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SBC 306-CR-18
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CHAPTER 8—DESIGN OF MEMBERS FOR COMBINED FORCES AND TORSION
CHAPTER 8—DESIGN OF MEMBERS FOR COMBINED FORCES
AND TORSION
𝑃𝑟
< 0.2
𝑃𝑐
This chapter addresses members subject to axial
force and flexure about one or both axes, with or
without torsion, and members subject to torsion
only.
The chapter is organized as follows:
𝑃𝑟
𝑀𝑟𝑥 𝑀𝑟𝑦
+(
+
) ≤ 1.0
2𝑃𝑐
𝑀𝑐𝑥 𝑀𝑐𝑦
(8-2)
where
8.1
—Doubly and Singly Symmetric Members
Subject to Flexure and Axial Force
8.2
—Unsymmetric and Other Members Subject
to Flexure and Axial Force
Pc = 𝜑𝑐 𝑃𝑛 = design axial strength, determined in
accordance with Chapter 5, N
8.3
—Members Subject to Torsion and
Combined Torsion, Flexure, Shear and/or
Axial Force
Mr = required flexural strength, N-mm
8.4
Rupture of Flanges with Holes Subject to
Tension
User Note: For composite members, see
Chapter 9.
Pr
= required axial strength, N
Mc =𝜑𝑏 𝑀𝑛 = design flexural strength, determined
in accordance with Chapter 6, N-mm
x
= subscript relating symbol to strong axis
bending
y
= subscript relating symbol to weak axis
bending
𝜑𝑐 = resistance factor for compression = 0.85
𝜑𝑏 = resistance factor for flexure = 0.9
8.1—Doubly and Singly Symmetric
Members Subject to Flexure and Axial
Force
8.1.1 Doubly and Singly Symmetric Members
Subject to Flexure and Compression. The
interaction of flexure and compression in doubly
symmetric members and singly symmetric
members for which 0.1 ≤ (𝐼𝑦𝑐 ⁄𝐼𝑦 ) ≤ 0.9,
constrained to bend about a geometric axis (x and/or
y) shall be limited by Eqs. (8-1) and (8-2), where Iyc
is the moment of inertia of the compression flange
about the y-axis.
User Note: Section 8.2 is permitted to be used
in lieu of the provisions of this section.
(a) When
where
Pr
= required axial strength, N
Pc
= t P n = design axial strength, determined
in accordance with Section 4.2, N
Mr = required flexural strength, N-mm
Mc = b M n = design
flexural
strength,
determined in accordance with Chapter 6,
N-mm
𝜑𝑡 =resistance factor for tension (see Section
4.2)
𝑃𝑟
≥ 0.2
𝑃𝑐
𝑃𝑟 8 𝑀𝑟𝑥 𝑀𝑟𝑦
+ (
+
) ≤ 1.0
𝑃𝑐 9 𝑀𝑐𝑥 𝑀𝑐𝑦
8.1.2 Doubly and Singly Symmetric Members
Subject to Flexure and Tension. The interaction
of flexure and tension in doubly symmetric
members and singly symmetric members
constrained to bend about a geometric axis (x
and/or y) shall be limited by Eqs. (8-1) and (8-2),
𝜑𝑏 = resistance factor for flexure = 0.90
(8-1)
(b) When
SBC 306-CR-18
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CHAPTER 8—DESIGN OF MEMBERS FOR COMBINED FORCES AND TORSION
For doubly symmetric members, Cb in Chapter 6
may be multiplied by √1 +
𝑃𝑟
is permitted to use the provisions of this Section for
any shape in lieu of the provisions of Section 8.1.
𝑃𝑒𝑦
𝑓𝑟𝑎 𝑓𝑟𝑏𝑤 𝑓𝑟𝑏𝑧
|
| ≤ 1.0
+
+
𝐹𝑐𝑎 𝐹𝑐𝑏𝑤 𝐹𝑐𝑏𝑧
Where
𝑃𝑒𝑦 =
𝜋 2 𝐸𝐼𝑦
𝐿2𝑏
where
fra
A more detailed analysis of the interaction of
flexure and tension is permitted in lieu of Eqs. (8-1)
and (8-2).
8.1.3 Doubly Symmetric Rolled Compact
Members Subject to Single Axis Flexure and
Compression.
For doubly symmetric rolled
compact members with (𝐾𝐿)𝑧 ≤ (𝐾𝐿)𝑦 subjected
to flexure and compression with moments primarily
about their major axis, it is permissible to consider
the two independent limit states, in-plane
instability and out-of-plane buckling or lateraltorsional buckling, separately in lieu of the
combined approach provided in Section 8.1.1 .
For members with𝑀𝑟𝑦 ⁄𝑀𝑐𝑦 ≥ 0.05, the provisions
of Section 8.1.1 shall be followed.
(8-4)
For the limit state of in-plane instability,
Eq. (8-1) shall be used with Pc, Mrx and
Mcx determined in the plane of bending.
For the limit state of out-of-plane buckling
and lateral-torsional buckling:
= required axial stress at the point of
consideration, MPa
Fca = design axial stress at the point of
consideration, determined in accordance
with Chapter 5 for compression (𝜑𝑐 Fcr), or
Section 4.2 for tension (𝜑𝑡 Fcr), MPa
frbw , frbz = required flexural stress at the point of
consideration, MPa
𝜑 𝑀
𝐹𝑐𝑏𝑤 , 𝐹𝑐𝑏𝑧 = 𝑏 𝑛 = design flexural stress at the
𝑆
point of consideration, determined in
accordance with Chapter 6, MPa
w
= subscript relating symbol to major principal
axis bending
z
= subscript relating symbol to minor principal
axis bending
𝜑𝑏 = resistance factor for flexure = 0.9
𝜑𝑐 = resistance factor for compression = 0.85
𝜑𝑡 = resistance factor for tension (Section 4.2)
Pcy = design compressive strength out of the plane
of bending, N
Eq. (8-4) shall be evaluated using the principal
bending axes by considering the sense of the
flexural stresses at the critical points of the cross
section. The flexural terms are either added to or
subtracted from the axial term as appropriate. When
the axial force is compression, second order effects
shall be included according to the provisions of
Chapter 3.
Cb =lateral-torsional buckling modification factor
determined from Section 6.1
A more detailed analysis of the interaction of
flexure and tension is permitted in lieu of Eq. (8-4).
2
𝑃𝑟
𝑃𝑟
𝑀𝑟𝑥
) ≤ 1.0
(1.5 − 0.5 ) + (
𝑃𝑐𝑦
𝑃𝑐𝑦
𝐶𝑏 𝑀𝑐𝑥
(8-3)
where
Mcx = design lateral-torsional strength for strong
axis flexure determined in accordance with
Chapter 6 using𝐶𝑏 = 1.0, N-mm
User Note: In Eq.(8-3), 𝐶𝑏 𝑀𝑐𝑥 may be larger
than 𝜑𝑏 Mpx. The yielding resistance of the
beam-column is cap tured by Eq. (8-1).
8.2—Unsymmetric and Other Members
Subject to Flexure a n d Axial Force
8.3—Members Subject to Torsion and
Combined Torsion, Flexure, Shear
and/or Axial Force
8.3.1 Round and Rectangular HSS Subject to
Torsion. The design torsional strength, 𝜑 𝑇 𝑇𝑛 , for
round and rectangular HSS according to the limit
states of torsional yielding and torsional buckling
shall be determined as follows:
This section addresses the interaction of flexure and
axial stress for shapes not covered in Section 8.1. It
SBC 306-CR-18
𝜑 𝑇 = 0.90
𝑇𝑛 = 𝐹𝑐𝑟 𝐶
(8-5)
81
CHAPTER 8—DESIGN OF MEMBERS FOR COMBINED FORCES AND TORSION
where
C
User Note: the torsional constant, C may be
conservatively taken as :
is the HSS torsional constant
𝜋(𝐷−𝑡)2 𝑡
The critical stress, Fcr, shall be determined as
follows:
For round HSS : 𝐶 =
(a) For round HSS, Fcr shall be the larger of
For rectangular HSS: 𝐶 = 2(𝐵 − 𝑡) (𝐻 −
𝑡) 𝑡 − 4.5(4 − 𝜋) 𝑡 3
(i) 𝐹𝑐𝑟 =
1.23𝐸
𝐿 𝐷
𝐷 𝑡
5
(8-6)
√ ( )4
and
𝐹𝑐𝑟 =
(ii)
0.6𝐸
𝐷
3
(8-7)
( 𝑡 )2
but shall not exceed 0.6𝐹𝑦 ,
where
L = length of the member, mm
8.3.2 HSS Subject to Combined Torsion,
Shear, Flexure and Axial Force. When the
required torsional strength, Tr, is less than or equal
to 20% of the design torsional strength, Tc, the
interaction of torsion, shear, flexure and/or axial
force for HSS shall be determined by Section 8.1
and the torsional effects shall be neglected. When
Tr exceeds 20% of Tc, the interaction of torsion,
shear, flexure and/or axial force shall be limited, at
the point of consideration, by
𝑃𝑟 𝑀𝑟
𝑉𝑟 𝑇𝑟 2
( + ) + ( + ) ≤ 1.0
𝑃𝑐 𝑀𝑐
𝑉𝑐 𝑇𝑐
D = outside diameter, mm
(b) For rectangular HSS
(8-11)
where
When
ℎ
𝐸
≤ 2.45√
𝑡
𝐹𝑦
𝐹𝑐𝑟 = 0.6𝐹𝑦
Pr
= required axial strength , N
Pc
=𝜑 𝑃𝑛 = design tensile or compressive
strength in accordance with Chapter 4 or
Chapter 5, N
(8-8)
Mr = required flexural strength N-mm
When
Mc = 𝜑𝑏 𝑀𝑛 = design flexural strength
accordance with Chapter 6, N - mm
𝐸 ℎ
𝐸
2.45√ < ≤ 3.07√
𝐹𝑦 𝑡
𝐹𝑦
0.6𝐹𝑦 (2.45√𝐸⁄𝐹 )
𝐹𝑐𝑟 =
𝑦
ℎ
( )
𝑡
3.07√
𝐹𝑐𝑟 =
𝐸 ℎ
< ≤ 260
𝐹𝑦 𝑡
0.458 𝜋 2 𝐸
ℎ 2
( )
𝑡
(8-10)
where
h = flat width of longer side as defined in Section
2.4.1 b(4), mm
= design wall thickness defined in Section 2.4.2
, mm
in
Vr
= required shear strength, N
Vc
= 𝜑𝑣 𝑉𝑛 = design shear strength in accordance
with Chapter 7, N
Tr
= required torsional strength, N-mm
Tc
= 𝜑 𝑇 𝑇𝑛 = design torsional strength
accordance with Section 8.3.1 , N-mm
(8-9)
When
t
2
in
8.3.3 Non-HSS Members Subject to Torsion
and Combined Stress. The design torsional
strength for non-HSS members shall be the lowest
value obtained according to the limit states of
yielding under normal stress, shear yielding under
shear stress, or buckling, determined as follows:
𝜑 𝑇 = 0.90
(a) For the limit state of yielding under normal
stress
𝐹𝑛 = 𝐹𝑦
(8-12)
(b) For the limit state of shear yielding under shear
stress
SBC 306-CR-18
82
CHAPTER 8—DESIGN OF MEMBERS FOR COMBINED FORCES AND TORSION
𝐹𝑛 = 0.6𝐹𝑦
(8-13)
(c) For the limit state of buckling
𝐹𝑛 = 𝐹𝑐𝑟
(8-14)
where
Fcr = buckling stress for the section as determined
by analysis, MPa
Some constrained local yielding is permitted
adjacent to areas that remain elastic.
8.4Rupture of Flanges with Holes
Subject to Tension
At locations of bolt holes in flanges subject to
tension under combined axial force and major axis
flexure, flange tensile rupture strength shall be
limited by Eq. (8-15). Each flange subject to
tension due to axial force and flexure shall be
checked separately.
𝑃𝑟 𝑀𝑟𝑥
+
≤ 1.0
𝑃𝑐 𝑀𝑐𝑥
(8-15)
where
Pr
= required axial strength of the member at the
location of the bolt holes, positive in tension,
negative in compression, N
Pc
= 𝜑𝑡 𝑃𝑛 = design axial strength for the limit
state of tensile rupture of the net section at
the location of bolt holes, determined in
accordance with Section 4.2(b), N
Mrx
= required flexural strength at the location
of the bolt holes; positive for tension in
the flange under consideration, negative for
compression, N-mm
Mcx = 𝜑𝑏 𝑀𝑛 = design flexural strength about xaxis for the limit state of tensile rupture of
the flange, determined according to Section
6.13.1 . When the limit state of tensile
rupture in flexure does not apply, use the
plastic bending moment, Mp, determined
with bolt holes not taken into consideration,
N-mm
𝜑𝑏 = resistance factor for tensile rupture = 0.75
𝜑𝑡 = resistance factor for flexure = 0.9
SBC 306-CR-18
83
CHAPTER 8—DESIGN OF MEMBERS FOR COMBINED FORCES AND TORSION
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SBC 306-CR-18
84
CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
This chapter addresses composite members
composed of rolled or built-up structural steel
shapes or HSS and structural concrete acting
together, and steel beams supporting a reinforced
concrete slab so interconnected that the beams and
the slab act together to resist bending. Simple and
continuous composite beams with steel headed
stud anchors, concrete-encased, and concrete filled
beams, constructed with or without temporary
shores, are included.
The chapter is organized as follows:
9.1 —General Provisions
9.2 —Axial Force
9.3 —Flexure
9.4 —Shear
9.5 —Combined Flexure and Axial Force
9.6 —Load Transfer
9.7 —Composite Diaphragms and Collector
Beams
9.8 —Steel Anchors
(b) Concrete and steel reinforcement material
limitations shall be as specified in Section
9.1.3 .
(c) Transverse reinforcement limitations shall be as
specified in Section 9.2.1.1 (2), in addition to
those specified in SBC 304.
(d) The minimum longitudinal reinforcing ratio
for encased composite members shall be as
specified in Section 9.2.1.1 (3).
User Note: It is the intent of the Code that
the concrete and reinforcing steel portions of
composite concrete members be detailed
utilizing the non-composite provisions of ACI
318 as modified by the Code. All requirements
specific to composite members are covered in
the Code.
9.1.2 Nominal
Strength
of
Composite
Sections. The nominal strength of composite
sections shall be determined in accordance with the
plastic stress distribution method or the strain
compatibility method as defined in this section.
The tensile strength of the concrete shall be
neglected in the determination of the nominal
strength of composite members.
9.9 —Special Cases
9.1—General Provisions
In determining load effects in members and
connections of a structure that includes composite
members, consideration shall be given to the
effective sections at the time each increment of load
is applied.
9.1.1 Concrete and Steel Reinforcement. The
design, detailing and material properties related to
the concrete and reinforcing steel portions of
composite construction shall comply with the
reinforced concrete and reinforcing bar design
specifications stipulated by the applicable building
code. Additionally, the provisions in SBC 304
shall apply with the following exceptions and
limitations:
(a) SBC 304 Sections 7.8.2 and 10.13, and
Chapter 21 shall be excluded in their entirety.
Local buckling effects shall be considered for filled
composite members as defined in Section 9.1.4 .
Local buckling effects need not be considered for
encased composite members.
9.1.2.1 Plastic Stress Distribution Method. For
the plastic stress distribution method, the nominal
strength shall be computed assuming that steel
components have reached a stress of Fy in either
tension or compression and concrete components
in compression due to axial force and/or flexure
have reached a stress of 0.85𝑓𝑐′ . For round HSS
filled with concrete, a stress of 0.95 𝑓𝑐′ is permitted
to be used for concrete components in
compression due to axial force and/or flexure to
account for the effects of concrete confinement.
9.1.2.2 Strain Compatibility Method. For the
strain compatibility method, a linear distribution of
strains across the section shall be assumed, with
the maximum concrete compressive strain equal
to 0.003 mm/mm. The stress-strain relationships
SBC 306-CR-18
85
CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
for steel and concrete shall be obtained from tests
or from published results for similar materials.
User Note: The strain compatibility method
should be used to determine nominal strength
for irregular sections and for cases where
the steel does not exhibit elasto-plastic
behavior. General guidelines for the strain
compatibility method for encased members
subjected to axial load, flexure or both are
given in AISC (2003) Design Guide 6 and
SBC 304.
9.1.3 Material Limitations. For concrete,
structural steel, and steel reinforcing bars in
composite systems, the following limitations shall
be met, unless justified by testing or analysis:
1. For the determination of the design
strength, concrete
shall
have
a
′
compressive strength, 𝑓𝑐 , of not less than
21 MPa nor more than 70 MPa for normal
weight concrete and not less than 21 MPa
nor more than 42 MPa for lightweight
concrete.
User Note: Higher strength concrete material
properties may be used for stiffness calculations
but may not be relied upon for strength
calculations unless justified by testing or
analysis.
2. The specified minimum yield stress of
structural steel and reinforcing bars used
in calculating the strength of composite
members shall not exceed 525 MPa.
9.1.4 Classification of Filled Composite
Sections for Local Buckling. For compression,
filled composite sections are classified as compact,
noncompact or slender. For a section to qualify as
compact, the maximum width-to-thickness ratio of
its compression steel elements shall not exceed
the limiting width-to-thickness ratio, λp, from
Table 9-1. If the maximum width-to-thickness ratio
of one or more steel compression elements exceeds
λp, but does not exceed λr from Table 9-1, the filled
composite section is noncompact. If the maximum
width-to-thickness ratio of any compression steel
element exceeds λr, the section is slender. The
maximum permitted width-to-thickness ratio shall
be as specified in the table.
For flexure, filled composite sections are classified
as compact, noncompact or slender. For a section to
qualify as compact, the maximum width-to-
thickness ratio of its compression steel elements
shall not exceed the limiting width-to-thickness
ratio, λp, from
Table 9-2. If the maximum width-to-thickness ratio
of one or more steel compression elements exceeds
λp, but does not exceed λr from
Table 9-2, the section is noncompact. If the widthto-thickness ratio of any steel element exceeds λr,
the section is slender. The maximum permitted
width-to-thickness ratio shall be as specified in the
table.
Refer to Table 2-1 and Table 2-2 for definitions of
width (b and D) and thickness (t) for rectangular
and round HSS sections.
9.2—Axial Force
This section applies to two types of composite
members subject to axial force: encased composite
members and filled composite members.
9 . 2 . 1 Encased Composite Members
9.2.1.1 Limitations. For encased composite
members, the following limitations shall be met:
1. The cross-sectional area of the steel core
shall comprise at least 1% of the total
composite cross section.
2. Concrete encasement of the steel core shall
be reinforced with continuous longitudinal
bars and lateral ties or spirals.
Where lateral ties are used, a minimum of
either a 10 mm bar spaced at a maximum
of 300 mm on center, or a 14 mm bar or
larger spaced at a maximum of 400 mm on
center shall be used. Deformed wire or
welded wire reinforcement of equivalent
area are permitted.
Maximum spacing of lateral ties shall not
exceed 0.5 times the least column
dimension.
3. The minimum reinforcement ratio for
continuous longitudinal reinforcing, 𝜌𝑠𝑟 ,
shall be 0.004, where 𝜌𝑠𝑟 is given by:
𝜌𝑠𝑟 =
𝐴𝑠𝑟
𝐴𝑔
(9-1)
where
Ag
SBC 306-CR-18
= gross area of composite member, mm2
86
CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
Asr = area of continuous reinforcing bars, mm2
User Note: Refer to Sections 7.10 and 10.9.3
of SBC 304 for additional tie and spiral
reinforcing provisions.
9.2.1.2 Compressive Strength. The design
compressive strength, 𝜑𝑐 𝑃𝑛 , of doubly symmetric
axially loaded encased composite members shall
be determined for the limit state of flexural
buckling based on member slenderness as follows:
Fysr = specified minimum yield stress of
reinforcing bars, MPa
Ic
= moment of inertia of concrete section
about the elastic neutral axis of the
composite section, mm4
Is
= moment of inertia of steel shape about the
elastic neutral axis of the composite
section, mm4
Isr
= moment of inertia of reinforcing bars
about the elastic neutral axis of the
composite section, mm4
K
= effective length factor
L
= laterally unbraced length of the member,
mm
𝑓𝑐′
= specified compressive
concrete, MPa
wc
= weight of concrete per unit volume (1500
≤ 𝑤𝑐 ≤2500 kg/m3)
𝜑𝑐 = 0.75
(a) When
𝑃𝑛𝑜
≤ 2.25
𝑃𝑒
𝑃𝑛𝑜
𝑃𝑛 = 𝑃𝑛𝑜 [0.658 𝑃𝑒 ]
(9-2)
(b) When
𝑃𝑛𝑜
> 2.25
𝑃𝑒
𝑃𝑛 = 0.877 𝑃𝑒
(9-3)
where
𝑃𝑛𝑜 = 𝐹𝑦 𝐴𝑠 + 𝐹𝑦𝑠𝑟 𝐴𝑠𝑟 + 0.85𝑓𝑐′ 𝐴𝑐
Pe
(9-4)
= elastic critical buckling load determined
in accordance to with Chapter 3, or
Appendix F, N
= 𝜋 2 (𝐸𝐼𝑒𝑓𝑓 )/(𝐾𝐿)2
Ac
= area of concrete, mm2
As
= area of steel, mm2
Ec
= modulus of elasticity of concrete
(9-5)
EIeff = effective stiffness of composite section,
N-mm2
(9-6)
C1 = coefficient for calculation of effective
rigidity of an encased composite
compression member
= 0.1 + 2 (
𝐴𝑠
) ≤ 0.3
of
The design compressive strength need not be less
than that specified for bare steel member as required
by Chapter 5.
9.2.1.3 Tensile Strength. The design tensile
strength of axially loaded encased composite
members shall be determined for the limit state of
yielding as follows:
𝑃𝑛 = 𝐹𝑦 𝐴𝑠 + 𝐹𝑦𝑠𝑟 𝐴𝑠𝑟
𝜑𝑡 = 0.9
(9-8)
9.2.1.4 Load
Transfer.
Load
transfer
requirements for encased composite members shall
be determined in accordance with Section 9.6.
9.2.1.5 Detailing Requirements. Clear spacing
between the steel core and longitudinal reinforcing
shall be a minimum of 1.5 reinforcing bar diameters,
but not less than 40mm.
= 0.043𝑤𝑐1.5 √𝑓𝑐′ , MPa
= 𝐸𝑠 𝐼𝑠 + 0.5𝐸𝑠 𝐼𝑠𝑟 + 𝐶1 𝐸𝑐 𝐼𝑐
strength
(9-7)
If the composite cross section is built up from two
or more encased steel shapes, the shapes shall be
interconnected with lacing, tie plates, batten plates
or similar components to prevent buckling of
individual shapes due to loads applied prior to
hardening of the concrete.
9.2.2
Filled Composite Members
Es
= modulus of elasticity of steel = 200 000
MPa
9.2.2.1 Limitations. For filled composite members,
the cross-sectional area of the steel section shall
comprise at least 1% of the total composite cross
section.
Fy
= specified minimum yield stress of steel
section, MPa
Filled composite members shall be classified for
local buckling according to Section 9.1.4 .
𝐴𝑐 +𝐴𝑠
SBC 306-CR-18
87
CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
9.2.2.2 Compressive Strength. The design
compressive strength of axially loaded doubly
symmetric filled composite members shall be
determined for the limit state of flexural buckling in
accordance with Section 9.2.1.2 with the following
modifications:
(a) For compact sections
𝑃𝑛𝑜 = 𝑃𝑝
The design compressive strength need not be less
than specified for the bare steel member as required
by Chapter 5.
9.2.2.3 Tensile Strength. The design tensile
strength of axially loaded filled composite
members shall be determined for the limit state of
yielding as follows:
(9-9)
𝑃𝑛 = 𝐹𝑦 𝐴𝑠 + 𝐹𝑦𝑠𝑟 𝐴𝑠𝑟
𝜑𝑡 = 0.9
where
𝑃𝑝 = 𝐹𝑦 𝐴𝑠 + 𝐶2 𝑓𝑐′ (𝐴𝑐 + 𝐴𝑠𝑟
𝐸𝑠
)
𝐸𝑐
(9-10)
C2 = 0.85 for rectangular sections and 0.95 for
round section
(b) For noncompact sections
𝑃𝑃 − 𝑃𝑦
(𝜆 − 𝜆𝑃 )2
𝑃𝑛𝑜 = 𝑃𝑃 −
(𝜆𝑟 − 𝜆𝑃 )2
Where 𝜆, 𝜆𝑝 , 𝑎𝑛𝑑 𝜆𝑟 are
determined from Table 9-1
slenderness
(9-11)
ratios
𝑃𝑦 = 𝐹𝑦 𝐴𝑠 + 0.7𝑓𝑐′ (𝐴𝑐 + 𝐴𝑠𝑟
9.2.2.4 Load
Transfer.
Load
transfer
requirements for filled composite members shall
be determined in accordance with Section 9.6.
9.3—Flexure
This section applies to three types of composite
members subject to flexure: composite beams with
steel anchors consisting of steel headed stud
anchors or steel channel anchors, encased
composite members, and filled composite members.
9.3.1
Pp is determined from Eq. (9-10)
𝐸𝑠
)
𝐸𝑐
(9-12)
𝐸𝑠
)
𝐸𝑐
(9-13)
(c) For slender sections
𝑃𝑛𝑜 = 𝐹𝑐𝑟 𝐴𝑠 + 0.7𝑓𝑐′ (𝐴𝑐 + 𝐴𝑠𝑟
(9-18)
General
9.3.1.1 Effective Width. The effective width of the
concrete slab shall be the sum of the effective
widths for each side of the beam centerline, each of
which shall not exceed:
1. one-eighth of the beam span, center-tocenter of supports;
2. one-half the distance to the centerline of
the adjacent beam; or
where
For rectangular filled sections
𝐹𝑐𝑟 =
3. the distance to the edge of the slab.
9𝐸𝑠
𝑏 2
( )
𝑡
(9-14)
For round filled sections
𝐹𝑐𝑟 =
0.72𝐹𝑦
0.2
𝐷 𝐹𝑦
(( ) )
𝑡 𝐸𝑠
(9-15)
The effective stiffness of the composite section,
EIeff, for all sections shall be:
𝐸𝐼𝑒𝑓𝑓 = 𝐸𝑠 𝐼𝑠 + 𝐸𝑠 𝐼𝑠𝑟 + 𝐶3 𝐸𝑐 𝐼𝑐
(9-16)
where
C3
= coefficient for calculation of effective
rigidity of filled composite compression member
= 0.6 + 2 [
𝐴𝑠
] ≤ 0.9
𝐴𝑐 + 𝐴𝑠
(9-17)
9.3.1.2 Strength During Construction. When
temporary shores are not used during construction,
the steel section alone shall have adequate strength
to support all loads applied prior to the concrete
attaining 75% of its specified strength 𝑓𝑐′ . The
design flexural strength of the steel section shall be
determined in accordance with Chapter 6.
9.3.2 Composite Beams With Steel Headed
Stud or Steel Channel Anchors
9.3.2.1 Positive Flexural Strength. The design
positive flexural strength, 𝜑𝑏 M n, shall be
determined for the limit state of yielding as
follows:
𝜑𝑏 = 0.9
(a) when ℎ⁄𝑡𝑤 ≤ 3.76√𝐸 ⁄𝐹𝑦 , Mn shall be
determined from the plastic stress distribution
on the composite section for the limit state of
yielding (plastic moment).
SBC 306-CR-18
88
CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
(b) when ℎ⁄𝑡𝑤 > 3.76√𝐸 ⁄𝐹𝑦 , Mn shall be
determined from the superposition of elastic
stresses, considering the effects of shoring, for
the limit state of yielding (yield moment).
9.3.2.2 Negative Flexural Strength. The design
negative flexural strength shall be determined for
the steel section alone, in accordance with the
requirements of Chapter 6.
Alternatively, the design negative flexural strength
shall be determined from the plastic stress
distribution on the composite section, for the limit
state of yielding (plastic moment), with 𝜑𝑏 = 0.9
provided that the following limitations are met:
1. The steel beam is compact and is
adequately braced in accordance with
Chapter 6.
2. Steel headed stud or steel channel anchors
connect the slab to the steel beam in the
negative moment region.
3. The slab reinforcement parallel to the steel
beam, within the effective width of the slab,
Composite Beams With Formed Steel
Deck
9.3.2.2.1
General. The design flexural
strength of composite construction consisting of
concrete slabs on formed steel deck connected to
steel beams shall be determined by the applicable
portions of Sections 9.3.2.1 and 9.3.2.2 , with the
following requirements:
1. The nominal rib height shall not be greater
than 75 mm. The average width of concrete
rib or haunch, wr, shall be not less than 50
mm, but shall not be taken in calculations
as more than the minimum clear width near
the top of the steel deck.
2. The concrete slab shall be connected to the
steel beam with welded steel headed stud
anchors, 20 mm or less in diameter (AWS
D1.1/D1.1M). Steel headed stud anchors
shall be welded either through the deck or
directly to the steel cross section. Steel
headed stud anchors, after installation, shall
extend not less than 40 mm above the top
of the steel deck and there shall be at least
15 mm of specified concrete cover above
the top of the steel headed stud anchors.
3. The slab thickness above the steel deck
shall be not less than 50 mm.
4. Steel deck shall be anchored to all
supporting members at a spacing not to
exceed 450 mm. Such anchorage shall be
provided by steel headed stud anchors, a
combination of steel headed stud anchors
and arc spot (puddle) welds, or other
devices specified by the contract
documents.
9.3.2.2.2
Deck
Ribs
Oriented
Perpendicular to Steel Beam. Concrete below the
top of the steel deck shall be neglected in
determining composite section properties and in
calculating Ac for deck ribs oriented
perpendicular to the steel beams.
9.3.2.2.3
Deck Ribs Oriented Parallel to
Steel Beam. Concrete below the top of the steel
deck is permitted to be included in determining
composite section properties and shall be included
in calculating Ac.
Formed steel deck ribs over supporting beams are
permitted to be split longitudinally and separated to
form a concrete haunch.
When the nominal depth of steel deck is 38 mm or
greater, the average width, wr, of the supported
haunch or rib shall be not less than 50 mm for the
first steel headed stud anchor in the transverse row
plus four stud diameters for each additional steel
headed stud anchor.
9.3.2.3 Load Transfer Between Steel Beam and
Concrete Slab
9.3.2.3.1
Load Transfer for Positive
Flexural Strength. The entire horizontal shear at
the interface between the steel beam and the
concrete slab shall be assumed to be transferred by
steel headed stud or steel channel anchors, except
for concrete-encased beams as defined in Section
9.3.3 . For composite action with concrete subject
to flexural compression, the nominal shear force
between the steel beam and the concrete slab
transferred by steel anchors, 𝑉 ′ , between the point
of maximum positive moment and the point of
zero moment shall be determined as the lowest
value in accordance with the limit states of
concrete crushing, tensile yielding of the steel
section, or the shear strength of the steel anchors:
(a) Concrete crushing
𝑉 ′ = 0.85𝑓𝑐′ 𝐴𝑐
(b) Tensile yielding of the steel section
𝑉 ′ = 𝐹𝑦 𝐴𝑠
(9-19)
(9-20)
(c) Shear strength of steel headed stud or steel
channel anchors
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CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
𝑉 ′ = ∑ 𝑄𝑛
(9-21)
where
Ac
= area of concrete slab within effective
width, mm2
2
As = area of steel cross section, mm
∑ 𝑄𝑛 = sum of nominal shear strengths of steel
headed stud or steel channel anchors
between the point of maximum positive
moment and the point of zero moment, N
9.3.2.3.2
Load Transfer for Negative
Flexural Strength. In continuous composite beams
where longitudinal reinforcing steel in the negative
moment regions is considered to act compositely
with the steel beam, the total horizontal shear
between the point of maximum negative moment
and the point of zero moment shall be determined
as the lower value in accordance with the following
limit states:
(a) For the limit state of tensile yielding of the slab
reinforcement
𝑉 ′ = 𝐹𝑦𝑠𝑟 𝐴𝑠𝑟
(9-22)
where
the limit state of yielding (plastic moment) on
the composite section. For concrete-encased
members, steel anchors shall be provided.
9 . 3 . 4 Filled Composite Members
9.3.4.1 Limitations. Filled composite sections
shall be classified for local buckling according to
Section 9.1.4 .
9.3.4.2 Flexural Strength. The design flexural
strength, bMn, of filled composite members shall
be determined as follows:
𝜑𝑏 = 0.9
The nominal flexural strength, Mn, shall be
determined as follows:
(a) For compact sections
𝑀𝑛 = 𝑀𝑝
where
Mp moment corresponding to plastic stress
distribution over the composite cross
section, N-mm
(b) For noncompact sections
𝑀𝑛 = 𝑀𝑝 − (𝑀𝑝 − 𝑀𝑦 ) (
Asr = area of adequately developed
longitudinal reinforcing steel within the
effective width of the concrete slab, mm2
Fysr = specified minimum yield stress of the
reinforcing steel, MPa
(b) For the limit state of shear strength of steel
headed stud or steel channel anchors
𝑉 ′ = ∑ 𝑄𝑛
(9-23)
9.3.3 Encased Composite. The design flexural
strength, b Mn, of concrete-encased members shall
be determined as follows:
𝜑𝑏 = 0.9
The nominal flexural strength, Mn, shall be
determined using one of the following methods:
(a) The superposition of elastic stresses on the
composite section, considering the effects of
shoring for the limit state of yielding (yield
moment).
(b) The plastic stress distribution on the steel
section alone, for the limit state of yielding
(plastic moment) on the steel section.
(c) The plastic stress distribution on the composite
section or the strain-compatibility method, for
(9-24)
𝜆−𝜆𝑝
𝜆𝑟 −𝜆𝑝
)
(9-25)
where
𝜆, 𝜆𝑝 𝑎𝑛𝑑 𝜆𝑟 are the slenderness
determined from Table 9-2
rations
My = yield moment corresponding to yielding of
the tension flange and first yield of the
compression flange, N-mm. The capacity at
the first yield shall be calculated assuming a
linear elastic stress distribution with the
maximum concrete compressive stress
limited to 0.70𝑓𝑐′ and the maximum steel
stress limited to Fy.
( c ) For slender sections, Mn, shall be determined as
the first yield moment. The compression flange
stress shall be limited to the local buckling
stress, Fcr, determined using Eqs. (9-14) or
(9-15). The concrete stress distribution shall
be linear elastic with the maximum
compressive stress limited to 0.70f c.
9.4—Shear
9.4.1 Filled
and
Encased
Composite
Members. The design shear strength, vVn,, shall
be determined based on one of the following:
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CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
(a) The design shear strength of the steel section
alone as specified in Chapter 7.
(b) The design shear strength of the reinforced
concrete portion (concrete plus steel
reinforcement) alone as defined by SBC 304
with
v 0.75
(c) The nominal shear strength of the steel section
as defined in Chapter 7 plus the nominal
strength of the reinforcing steel as defined by
SBC 304 with a combined resistance factor of
v 0.75
accordance with the requirements for
allocation presented in this section.
The design strength, 𝜑Rn, of the applicable force
transfer mechanisms as determined in accordance
with Section 9.6.3 shall equal or exceed the
required longitudinal shear force to be
transferred,𝑉𝑟′ , as determined in accordance with
Section 9.6.2 .
9.6.2 Force Allocation. Force allocation shall
be determined based upon the distribution of
external force in accordance with the following
requirements:
9.4.2 Composite Beams with Formed Steel
Deck. The design shear strength of composite
beams with steel headed stud or steel channel
anchors shall be determined based upon the
properties of the steel section alone in accordance
with Chapter 7.
9.5—Combined Flexure and Axial
Force
The interaction between flexure and axial forces in
composite members shall account for stability as
required by Chapter 3. The design compressive
strength and the design flexural strength shall be
determined as defined in Sections 9.2 and 9.3,
respectively. To account for the influence of length
effects on the axial strength of the member, the
nominal axial strength of the member shall be
determined in accordance with Section 9.2.
For encased composite members and for filled
composite members with compact sections, the
interaction between axial force and flexure shall be
based on the interaction equations of Section 8.1.1
or one of the methods as defined in Section 8.1.2 .
For filled composite members with noncompact or
slender sections, the interaction between axial
forces and flexure shall be based on the
interaction equations of Section 8.1.1 .
User Note: Methods for determining the capacity
of composite beam-columns are discussed in the
Commentary.
force
User Note: Bearing strength provisions for
externally applied forces are provided in
Section 10.8. For filled composite members,
𝐴
the term √ 2 in Eq. (10-31) may be taken equal
𝐴1
to 2.0 due to confinement effects.
9.6.2.1 External Force Applied to Steel Section.
When the entire external force is applied directly
to the steel section, the force required to be
transferred to the concrete,𝑉𝑟′ , shall be determined
as follows:
𝑉𝑟′ = 𝑃𝑟 (1 −
𝐹𝑦 𝐴𝑠
)
𝑃𝑛𝑜
(9-26)
where
Pno = nominal axial compressive strength without
consideration of length effects, determined by
Eq. (9-4) for encased composite members, and
Eq. (9-9) for filled composite members, N
Pr
= required external force applied to the
composite member, N
9.6.2.2 External Force Applied to Concrete.
When the entire external force is applied directly to
the concrete encasement or concrete fill, the force
required to be transferred to the steel, 𝑉𝑟′ , shall be
determined as follows:
𝐹𝑦 𝐴𝑠
)
𝑉𝑟′ = 𝑃𝑟 (
𝑃𝑛𝑜
(9-27)
where
9.6—Load Transfer
9.6.1 General Requirements. When external
forces are applied to an axially loaded encased or
filled composite member, the introduction of force
to the member and the transfer of longitudinal
shears within the member shall be assessed in
Pno = nominal axial compressive strength without
consideration of length effects, determined by
Eq. (9-4) for encased composite members, and
Eq. (9-9) for filled composite members, N
Pr
= required external force applied to the
composite member, N
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CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
9.6.2.3 External Force Applied Concurrently to
Steel and Concrete. When the external force is
applied concurrently to the steel section and
concrete encasement or concrete fill, 𝑉𝑟′ shall be
determined as the force required to establish
equilibrium of the cross section.
User Note: The Commentary provides an
acceptable method of determining the
longitudinal shear force required for equilibrium
of the cross section.
9.6.3 Force Transfer Mechanisms.
The
nominal strength, Rn, of the force transfer
mechanisms of direct bond interaction, shear
connection, and direct bearing shall be determined
in accordance with this section. Use of the force
transfer mechanism providing the largest nominal
strength is permitted. Force transfer mechanisms
shall not be superimposed.
The force transfer mechanism of direct bond
interaction shall not be used for encased composite
members.
9.6.3.1 Direct Bearing. Where force is transferred
in an encased or filled composite member by direct
bearing from internal bearing mechanisms, the
design bearing strength of the concrete for the limit
state of concrete crushing shall be determined as
follows:
𝑅𝑛 = 1.7𝑓𝑐′ 𝐴1
𝜑𝐵 = 0.65
(9-28)
where
A1
2
= loaded area of concrete, mm
User Note: An example of force transfer via an
internal bearing mechanism is the use of internal
steel plates within a filled composite member.
9.6.3.2 Shear Connection. Where force is
transferred in an encased or filled composite
member by shear connection, the design shear
strength of steel headed stud or steel channel
anchors shall be determined as follows:
𝑅𝑐 = ∑ 𝑄𝑐𝑣
(9-29)
where
∑ 𝑄𝑐𝑣 = sum of design shear strengths, 𝜑 𝑄𝑛𝑣 ,
of steel headed stud or steel channel
anchors, determined in accordance with
Section 9.8.3.1 or Section 9.8.3.4 ,
respectively, placed within the load
introduction length as defined in Section
9.6.4 , N
9.6.3.3 Direct Bond Interaction. Where force is
transferred in a filled composite member by direct
bond interaction, the design bond strength
between the steel and concrete shall be determined
as follows:
𝜑 = 0.45
(a) For rectangular steel sections filled with
concrete:
𝑅𝑛 = 𝐵2 𝐶𝑖𝑛 𝐹𝑖𝑛
(9-30)
(b) For round steel sections filled with concrete:
𝑅𝑛 = 0.25𝜋𝐷 2 𝐶𝑖𝑛 𝐹𝑖𝑛
(9-31)
where
Cin = 2 if the filled composite member extends
to one side of the point of force transfer
= 4 if the filled composite member extends
on both sides of the point of force transfer
Rn
= nominal bond strength, N
Fin = nominal bond stress = 0.40 MPa
B
= overall width of rectangular steel section
along face transferring load, mm
D
= outside diameter of round HSS, mm
9.6.4
Detailing Requirements
9.6.4.1 Encased Composite Members. Steel
anchors utilized to transfer longitudinal shear shall
be distributed within the load introduction length,
which shall not exceed a distance of two times the
minimum transverse dimension of the encased
composite member above and below the load
transfer region. Anchors utilized to transfer
longitudinal shear shall be placed on at least two
faces of the steel shape in a generally symmetric
configuration about the steel shape axes.
Steel anchor spacing, both within and outside of
the load introduction length, shall conform to
Section 9.8.3.5 .
9.6.4.2 Filled Composite Members. Where
required, steel anchors transferring the required
longitudinal shear force shall be distributed within
the load introduction length, which shall not exceed
a distance of two times the minimum transverse
dimension of a rectangular steel member or two
times the diameter of a round steel member both
above and below the load transfer region. Steel
SBC 306-CR-18
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CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
anchor spacing within the load introduction length
shall conform to Section 9.8.3.5 .
(b) any number of steel headed stud anchors
welded in a row directly to the steel shape;
(c) any number of steel headed stud anchors
welded in a row through steel deck with the
deck oriented parallel to the steel shape and
the ratio of the average rib width to rib
depth ≥1.5
9.7—Composite Diaphragms and
Collector Beams
Composite slab diaphragms and collector beams
shall be designed and detailed to transfer loads
between the diaphragm, the diaphragm’s boundary
members and collector elements, and elements of
the lateral force resisting system.
= 0.85 for:
(a) two steel headed stud anchors welded in a
steel deck rib with the deck oriented
perpendicular to the steel shape;
(b) one steel headed stud anchor welded
through steel deck with the deck oriented
parallel to the steel shape and the ratio of
the average rib width to rib depth ≥1.5
User Note: Design guidelines for composite
diaphragms and collector beams can be found in
the Commentary.
9.8—Steel Anchors
9.8.1 General. The diameter of a steel headed
stud anchor shall not be greater than 2.5 times the
thickness of the base metal to which it is welded,
unless it is welded to a flange directly over a web.
Section 9.8.2 applies to a composite flexural
member where steel anchors are embedded in a
solid concrete slab or in a slab cast on formed steel
deck. Section 9.8.3 applies to all other cases.
= 0.7 for three or more steel headed stud
anchors welded in a steel deck rib with the
deck oriented perpendicular to the steel
shape
Rp
= 0.75 for:
(a) steel headed stud anchors welded
directly to the steel shape;
(b) steel headed stud anchors welded in a
composite slab with the deck oriented
perpendicular to the beam and emid-ht
≥ 50 mm;
(c) steel headed stud anchors welded
through steel deck, or steel sheet used as
girder filler material, and embedded in a
composite slab with the deck oriented
parallel to the beam
9.8.2 Steel Anchors in Composite Beams. The
length of steel headed stud anchors shall not be
less than four stud diameters from the base of the
steel headed stud anchor to the top of the stud head
after installation.
9.8.2.1 Strength of Steel Headed Stud Anchors
The nominal shear strength of one steel headed stud
anchor embedded in a solid concrete slab or in a
composite slab with decking shall be determined as
follows:
𝑄𝑛 = 0.5𝐴𝑠𝑎 √𝑓𝑐′ 𝐸𝑐 ≤ 𝑅𝑔 𝑅𝑝 𝐴𝑠𝑎 𝐹𝑢
= 0.6 for steel headed stud anchors welded
in a composite slab with deck oriented
perpendicular to the beam and emid-ht < 50
mm
(9-32)
emid-ht
where
Asa = cross-sectional area of steel headed stud
anchor, mm2
Ec
= modulus of elasticity
0.043 𝑤𝑐1.5 √𝑓𝑐′ , MPa
of
concrete
Fu
= specified minimum tensile strength of a steel
headed stud anchor, MPa
Rg
= 1.0 for:
(a) one steel headed stud anchor welded in a
steel deck rib with the deck oriented
perpendicular to the steel shape;
= distance from the edge of steel headed
stud anchor shank to the steel deck web,
measured at mid-height of the deck rib,
and in the load bearing direction of the
steel headed stud anchor (in other words, in
the direction of maximum moment for a
simply supported beam), mm
User Note: The table below presents values of
Rg and Rp for several cases.
Condition
Rg
Rp
No decking
1.0
0.75
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CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
maximum bending moment, positive or negative,
and the adjacent section of zero moment shall be
equal to the horizontal shear as determined in
Sections 9.3.2.3.1 and 9.3.2.3.2 divided by the
nominal shear strength of one steel anchor as
determined from Section 9.8.2.1 or Section 9.8.2.2
The number of steel anchors required between any
concentrated load and the nearest point of zero
moment shall be sufficient to develop the
maximum moment required at the concentrated
load point.
Decking
oriented
parallel to the steel
shape
𝑤𝑟
≥ 1.5
ℎ𝑟
1.0
0.75
𝑤𝑟
< 1.5
ℎ𝑟
0.85**
0.75
Decking
oriented
perpendicular to the
steel shape
9.8.2.4 Detailing Requirements. Steel anchors
required on each side of the point of maximum
bending moment, positive or negative, shall be
distributed uniformly between that point and the
adjacent points of zero moment, unless specified
otherwise on the contract documents.
Number of steel
headed stud anchors
occupying the same
decking rib
1
1.0
0.6+
2
0.85
0.6+
3 or more
0.7
0.6+
hr = nominal rib height, mm
wr = average width of concrete rib or haunch
(as defined in Section 9.3.2.3 ), mm
**
for a single steel headed stud anchor
+
this value may be increased to 0.75 when
emin-ht ≥ 50 mm
9.8.2.2 Strength of Steel Channel Anchors. The
nominal shear strength of one hot-rolled channel
anchor embedded in a solid concrete slab shall be
determined as follows:
𝑄𝑛 = 0.3 (𝑡𝑓 + 0.5𝑡𝑤 )𝑙𝑎 √𝑓𝑐′ 𝐸𝑐
(9-33)
Steel anchors shall have at least 25 mm of lateral
concrete cover in the direction perpendicular to the
shear force, except for anchors installed in the
ribs of formed steel decks. The minimum distance
from the center of an anchor to a free edge in the
direction of the shear force shall be 200 mm if
normal weight concrete is used and 250 mm if
lightweight concrete is used. The provisions of SBC
304, Chapter 17 are permitted to be used in lieu of
these values.
The minimum center-to-center spacing of steel
headed stud anchors shall be six diameters along
the longitudinal axis of the supporting composite
beam and four diameters transverse to the
longitudinal axis of the supporting composite
beam, except that within the ribs of formed steel
decks oriented perpendicular to the steel beam the
minimum center-to-center spacing shall be four
diameters in any direction. The maximum centerto-center spacing of steel anchors shall not exceed
eight times the total slab thickness or 900 mm.
9.8.3 Steel
Anchors
in
Composite
Components. This section shall apply to the
design of cast-in-place steel headed stud anchors
and steel channel anchors in composite components.
where
la
= length of channel anchor, mm
tf
mm
= thickness of flange of channel anchor,
tw
= thickness of channel anchor web, mm
The strength of the channel anchor shall be
developed by welding the channel to the beam
flange for a force equal to Qn, considering
eccentricity on the anchor.
9.8.2.3 Required Number of Steel Anchors. The
number of anchors required between the section of
The provisions of SBC 304, Chapter 17 may be used
in lieu of the provisions in this section.
User Note: The steel headed stud anchor
strength provisions in this section are
applicable to anchors located primarily in the
load transfer (connection) region of composite
columns and beam-columns, concrete-encased
and filled composite beams, composite
coupling beams, and composite walls, where
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CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
the steel and concrete are working compositely
within a member. They are not intended for
hybrid construction where the steel and
concrete are not working compositely, such as
with embed plates.
For normal weight concrete: Steel headed stud
anchors subjected to shear only shall not be less
than five stud diameters in length from the base of
the steel headed stud to the top of the stud head
after installation. Steel headed stud anchors
subjected to tension or interaction of shear and
tension shall not be less than eight stud diameters
in length from the base of the stud to the top of the
stud head after installation.
For lightweight concrete: Steel headed stud anchors
subjected to shear only shall not be less than seven
stud diameters in length from the base of the steel
headed stud to the top of the stud head after
installation. Steel headed stud anchors subjected to
tension shall not be less than ten stud diameters in
length from the base of the stud to the top of the
stud head after installation. The nominal strength of
steel headed stud anchors subjected to interaction
of shear and tension for lightweight concrete shall
be determined as stipulated by SBC 304, Chapter 17.
Steel headed stud anchors subjected to tension or
interaction of shear and tension shall have a
diameter of the head greater than or equal to 1.6
times the diameter of the shank.
User Note: The following table presents
values of minimum steel headed stud anchor
h/d ratios for each condition covered in the
Code.
Loading
Condition
Normal
Weight
Concrete
Lightweight
Concrete
h/d ≥5
h/d≥7
Tension
h/d ≥8
h/d≥10
Shear
and
h/d ≥8
Tension
Section 9.8.2 specifies the strength of steel
anchors embedded in a solid concrete slab or
in a concrete slab with formed steel deck in a
composite beam.
Limit states for the steel shank of the anchor
and for concrete breakout in shear are covered
directly in this Section. Additionally, the
spacing and dimensional limitations provided
in these provisions preclude the limit states of
concrete pry- out for anchors loaded in shear
and concrete breakout for anchors loaded in
tension as defined by SBC 304, Chapter 17.
Shear
N/A*
h/d = ratio of steel headed stud anchor shank
length to the top of the stud head, to shank
diameter
*
Refer to SBC 304, Chapter 17 for the
calculation of interaction effects of anchors
embedded in lightweight concrete.
9.8.3.1 Shear Strength of Steel Headed Stud
Anchors in Composite Components. Where
concrete breakout strength in shear is not an
applicable limit state, the design shear strength,
𝜑𝑣 𝑄𝑛𝑣 of one steel headed stud anchor shall be
determined as follows:
𝑄𝑛𝑣 = 𝐹𝑢 𝐴𝑠𝑎
𝜑𝑣 = 0.65
(9-34)
where
Qnv
= nominal shear strength of steel headed stud
anchor, N
Asa
= cross-sectional area of steel headed stud
anchor, mm2
Fu
= specified minimum tensile strength of a
steel headed stud anchor, MPa
Where concrete breakout strength in shear is an
applicable limit state, the design shear strength of
one steel headed stud anchor shall be determined by
one of the following:
(1) Where anchor reinforcement is developed in
accordance with Chapter 25 of SBC 304 on
both sides of the concrete breakout surface
for the steel headed stud anchor, the
minimum of the steel nominal shear strength
from Eq. (9-34) and the nominal strength of
the anchor reinforcement shall be used for
the nominal shear strength, Qnv, of the steel
headed stud anchor.
(2) As stipulated by the SBC 304, Chapter 17.
User Note: If concrete breakout strength in shear
is an applicable limit state (for example, where
the breakout prism is not restrained by an
adjacent steel plate, flange or web), appropriate
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CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
anchor reinforcement is required for the
provisions of this Section to be used.
9.8.3.2 Tensile Strength of Steel Headed Stud
Anchors in Composite Components. Where the
distance from the center of an anchor to a free
edge of concrete in the direction perpendicular to
the height of the steel headed stud anchor is greater
than or equal to 1.5 times the height of the steel
headed stud anchor measured to the top of the stud
head, and where the center-to-center spacing of steel
headed stud anchors is greater than or equal to three
times the height of the steel headed stud anchor
measured to the top of the stud head, the design
tensile strength of one steel headed stud anchor shall
be determined as follows:
𝑄𝑛𝑡 = 𝐹𝑢 𝐴𝑠𝑎
𝜑𝑡 = 0.75
(9-35)
9.8.3.3 Strength of Steel Headed Stud Anchors
for Interaction of Shear and Tension in
Composite Components. Where concrete
breakout strength in shear is not a governing limit
state, and where the distance from the center of an
anchor to a free edge of concrete in the direction
perpendicular to the height of the steel headed stud
anchor is greater than or equal to 1.5 times the
height of the steel headed stud anchor measured to
the top of the stud head, and where the center-tocenter spacing of steel headed stud anchors is
greater than or equal to three times the height of
the steel headed stud anchor measured to the top
of the stud head, the nominal strength for interaction
of shear and tension of one steel headed stud anchor
shall be determined as follows:
5
5
𝑄𝑟𝑡 3
𝑄𝑟𝑣 3
) ] ≤ 1.0
[( ) + (
𝑄𝑐𝑡
𝑄𝑐𝑣
(9-36)
where
Qnt
= nominal tensile strength of steel headed
stud anchor, N
Where the distance from the center of an anchor
to a free edge of concrete in the direction
perpendicular to the height of the steel headed stud
anchor is less than 1.5 times the height of the steel
headed stud anchor measured to the top of the stud
head, or where the center-to-center spacing of steel
headed stud anchors is less than three times the
height of the steel headed stud anchor measured to
the top of the stud head, the nominal tensile strength
of one steel headed stud anchor shall be determined
by one of the following:
1. Where anchor reinforcement is developed
in accordance with Chapter 25 of SBC 304
on both sides of the concrete breakout
surface for the steel headed stud anchor,
the minimum of the steel nominal tensile
strength from Eq. (9-35) and the nominal
strength of the anchor reinforcement shall
be used for the nominal tensile strength,
Qnt, of the steel headed stud anchor.
2. As stipulated by the SBC 304, Chapter 17.
User
Note:
Supplemental
confining
reinforcement is recommended around the
anchors for steel headed stud anchors subjected
to tension or interaction of shear and tension to
avoid edge effects or effects from closely
spaced anchors. See the Commentary and SBC
304, Section 17.4.2.9 for guidelines.
where
Qrt = required tensile strength, N
Qct = 𝜑𝑡 Qnt = design tensile strength, determined
in accordance with Section 9.8.3.2 , N
Qrv = required shear strength, N
Qcv=𝜑𝑣 Qnv = design shear strength, determined
in accordance with Section 9.8.3.1 , N
𝜑𝑡 = resistance factor for tension = 0.75
𝜑𝑣 = resistance factor for shear
= 0.65
Where concrete breakout strength in shear is a
governing limit state, or where the distance from
the center of an anchor to a free edge of
concrete in the direction perpendicular to the
height of the steel headed stud anchor is less than
1.5 times the height of the steel headed stud anchor
measured to the top of the stud head, or where the
center-to-center spacing of steel headed stud
anchors is less than three times the height of the
steel headed stud anchor measured to the top of the
stud head, the nominal strength for interaction of
shear and tension of one steel headed stud anchor
shall be determined by one of the following:
(a) Where anchor reinforcement is developed in
accordance with Chapter 25, SBC 304 on both
sides of the concrete breakout surface for the
steel headed stud anchor, the minimum of the
steel nominal shear strength from Eq. (9-34)
and the nominal strength of the anchor
reinforcement shall be used for the nominal
shear strength, Qnv, of the steel headed stud
SBC 306-CR-18
96
CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
anchor, and the minimum of the steel nominal
tensile strength from Eq. (9-35) and the
nominal strength of the anchor reinforcement
shall be used for the nominal tensile strength,
Qnt, of the steel headed stud anchor for use in
Eq. (9-36).
(b) As stipulated by the SBC 304, Chapter 17.
9.8.3.4 Shear Strength of Steel Channel
Anchors in Composite Components. The design
shear strength of steel channel anchors shall be
based on the provisions of Section 9.8.2.2 with the
resistance factor and safety factor as specified
below.
𝜑𝑣 = 0.75
9.8.3.5 Detailing Requirements in Composite
Components. Steel anchors shall have at least 25
mm of lateral clear concrete cover. The minimum
center-to-center spacing of steel headed stud
anchors shall be four diameters in any direction.
The maximum center-to-center spacing of steel
headed stud anchors shall not exceed 32 times the
shank diameter. The maximum center-to-center
spacing of steel channel anchors shall be 600 mm.
User Note: Detailing requirements provided in
this section are absolute limits. See Sections
9.8.3.1 , 9.8.3.2 and 9.8.3.3 for additional
limitations required to preclude edge and group
effect considerations.
9.9—Special Cases
When composite construction does not conform to
the requirements of Section 9.1 through Section
9.8, the strength of steel anchors and details of
construction shall be established by testing.
SBC 306-CR-18
97
CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
TABLES AND FIGURES OF CHAPTER 9
Table 9-1: Limiting Width-to-Thickness Ratios for Compression Steel Elements in Composite Members
Subject to Axial Compression For Use with Section 9.2.2 .
Description of element
Width-toThickness Ratio
Walls of Rectangular
HSS and Boxes of
Uniform Thickness
b/t
Round HSS
D/t
𝜆𝑝
Compact/
Noncompact
2.26 √
𝐸
𝐹𝑦
0.15E
Fy
𝝀𝒓
Noncompact/
Slender
3.00 √
𝐸
𝐹𝑦
0.19E
Fy
Maximum
Permitted
5.00 √
𝐸
𝐹𝑦
0.31E
Fy
Table 9-2: Limiting Width-to-Thickness Ratios for Compression Steel Elements in Composite Members
Subject to Flexure For Use with Section 9.3.4 .
Description of element
Flanges of Rectangular
HSS and Boxes of
Uniform Thickness
Webs of Rectangular
HSS and Boxes of
Uniform Thickness
Round HSS
Width-toThickness Ratio
𝜆𝑝
Compact/
Noncompact
𝝀𝒓
Noncompact/
Slender
Maximum
Permitted
b/t
2.26 √
𝐸
𝐹𝑦
3.00 √
𝐸
𝐹𝑦
5.00 √
𝐸
𝐹𝑦
h/t
3.00 √
𝐸
𝐹𝑦
5.70 √
𝐸
𝐹𝑦
5.70 √
𝐸
𝐹𝑦
0.09 E
Fy
0.31E
Fy
D/t
SBC 306-CR-18
0.31E
Fy
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CHAPTER 9—DESIGN OF COMPOSITE MEMBERS
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SBC 306-CR-18
99
CHAPTER 10—DESIGN OF CONNECTIONS
CHAPTER 10—DESIGN OF CONNECTIONS
This chapter addresses connecting elements,
connectors and the affected elements of connected
members not subject to fatigue loads.
The chapter is organized as follows:
10.1 —General Provisions
10.2 —Welds
10.3 —Bolts and Threaded Parts
10.4 —Affected Elements of Members and
Connecting Elements
10.5 —Fillers
10.6 —Splices
10.7 —Bearing Strength
10.8 —Column Bases and Bearing on Concrete
10.9 —Anchor Rods and Embedments
10.10—Flanges and Webs With Concentrated
Forces
User Note: For cases not included in this chapter,
the following sections apply:
Chapter 11
Design of HSS and Box Member
Connections
Appendix C
Design for Fatigue
10.1—General Provisions
10.1.1 Design Basis. The design strength, ϕRn of
connections shall be determined in accordance
with the provisions of this chapter and the
provisions of Chapter 2.
10.1.2 Simple Connections. Simple connections
of beams, girders and trusses shall be designed as
flexible and are permitted to be proportioned for
the reaction shears only, except as otherwise
indicated in the design documents. Flexible beam
connections shall accommodate end rotations of
simple beams. Some inelastic but self-limiting
deformation in the connection is permitted to
accommodate the end rotation of a simple beam.
10.1.3 Moment Connections. End connections of
restrained beams, girders and trusses shall be
designed for the combined effect of forces resulting
from moment and shear induced by the rigidity of
the connections. Response criteria for moment
connections are provided in Section 2.3.5 (b).
User Note: See Chapter 3 and Appendix F for
analysis requirements to establish the required
strength for the design of connections.
10.1.4 Compression Members with Bearing
Joints. Compression members relying on bearing
for load transfer shall meet the following
requirements:
1. When columns bear on bearing plates or are
finished to bear at splices, there shall be
sufficient connectors to hold all parts
securely in place.
2. When compression members other than
columns are finished to bear, the splice
material and its connectors shall be
arranged to hold all parts in line and their
required strength shall be the lesser of:
The required strength of the connections shall be
determined by structural analysis for the specified
design loads, consistent with the type of
construction specified, or shall be a proportion of
the required strength of the connected members
when so specified herein.
Where the gravity axes of intersecting axially
loaded members do not intersect at one point, the
effects of eccentricity shall be considered.
SBC 306-CR-18
An axial tensile force of 50% of the
required compressive strength of the
member; or
The moment and shear resulting from
a transverse load equal to 2% of the
required compressive strength of the
member. The transverse load shall be
applied at the location of the splice
exclusive of other loads that act on the
member. The member shall be taken as
pinned for the determination of the
shears and moments at the splice.
100
CHAPTER 10—DESIGN OF CONNECTIONS
User Note: All compression joints should also
be proportioned to resist any tension
developed by the load combinations stipulated
in Section 2.2.
10.1.5 Splices in Heavy Sections. When tensile
forces due to applied tension or flexure are to be
transmitted through splices in heavy sections, as
defined in Sections 1.3.1.3 and 1.3.1.4 , by
complete-joint-penetration groove (CJP) welds, the
following provisions apply: (1) material notchtoughness requirements as given in Sections 1.3.1.3
and 1.3.1.4 ; (2) weld access hole details as given in
Section 10.1.6 ; (3) filler metal requirements as
given in Section 10.2.6 ; and (4) thermal cut surface
preparation and inspection requirements as given in
Section 14.2.2 . The foregoing provision is not
applicable to splices of elements of built-up shapes
that are welded prior to assembling the shape.
User Note: CJP groove welded splices of heavy
sections can exhibit detrimental effects of weld
shrinkage. Members that are sized for
compression that are also subject to tensile
forces may be less susceptible to damage from
shrinkage if they are spliced using partial-jointpenetration PJP groove welds on the flanges and
fillet-welded web plates, or using bolts for some
or all of the splice.
10.1.6 Weld Access Holes. All weld access holes
required to facilitate welding operations shall be
detailed to provide room for weld backing as
needed. The access hole shall have a length from
the toe of the weld preparation not less than 1.5
times the thickness of the material in which the
hole is made, nor less than 40 mm. The access hole
shall have a height not less than the thickness of the
material with the access hole, nor less than 20 mm,
nor does it need to exceed 50 mm.
For sections that are rolled or welded prior to
cutting, the edge of the web shall be sloped or
curved from the surface of the flange to the
reentrant surface of the access hole. In hot-rolled
shapes, and built-up shapes with CJP groove welds
that join the web-to-flange, weld access holes shall
be free of notches and sharp reentrant corners. No
arc of the weld access hole shall have a radius less
than 10 mm.
In built-up shapes with fillet or partial-jointpenetration groove welds that join the web-toflange, weld access holes shall be free of notches
and sharp reentrant corners. The access hole shall
be permitted to terminate perpendicular to the
flange, providing the weld is terminated at least a
distance equal to the weld size away from the
access hole.
For heavy sections as defined in Sections 1.3.1.3
and 1.3.1.4 , the thermally cut surfaces of weld
access holes shall be ground to bright metal and
inspected by either magnetic particle or dye
penetrant methods prior to deposition of splice
welds. If the curved transition portion of weld
access holes is formed by predrilled or sawed
holes, that portion of the access hole need not be
ground. Weld access holes in other shapes need not
be ground nor inspected by dye penetrant or
magnetic particle methods.
10.1.7 Placement of Welds and Bolts. Groups of
welds or bolts at the ends of any member which
transmit axial force into that member shall be sized
so that the center of gravity of the group coincides
with the center of gravity of the member, unless
provision is made for the eccentricity. The foregoing
provision is not applicable to end connections of
single angle, double angle and similar members.
10.1.8 Bolts in Combination with Welds. Bolts
shall not be considered as sharing the load in
combination with welds, except that shear
connections with any grade of bolts permitted by
Section 1.3.3 , installed in standard holes or short
slots transverse to the direction of the load, are
permitted to be considered to share the load with
longitudinally loaded fillet welds. In such
connections the design strength of the bolts shall not
be taken as greater than 50% of the design strength
of bearing-type bolts in the connection.
In making welded alterations to structures,
existing rivets and high-strength bolts tightened to
the requirements for slip-critical connections are
permitted to be utilized for carrying loads present at
the time of alteration and the welding need only
provide the additional required strength.
10.1.9 High-Strength Bolts in Combination
with Rivets. In both new work and alterations, in
connections designed as slip-critical connections
in accordance with the provisions of Section 10.3,
high-strength bolts are permitted to be considered
as sharing the load with existing rivets.
10.1.10 Limitations on Bolted and Welded
Connections. Joints with pretensioned bolts or
welds shall be used for the following connections:
1. Column splices in all multi-story structures
over 38 m in height
SBC 306-CR-18
101
CHAPTER 10—DESIGN OF CONNECTIONS
2. Connections of all beams and girders to
columns and any other beams and girders
on which the bracing of columns is
dependent in structures over 38 m in
height
3. In all structures carrying cranes of over 50
kN capacity: roof truss splices and
connections of trusses to columns;
column splices; column bracing; knee
braces; and crane supports
4. Connections for the support of
machinery and other live loads that
produce impact or reversal of load
Snug-tightened joints or joints with ASTM A307
bolts shall be permitted except where otherwise
specified.
10.2—Welds
All provisions of AWS D1.1/D1.1M apply under
this Code, with the exception that the provisions
of the listed sections apply under this Code in lieu
of the cited AWS provisions as follows:
1. Section 10.1.6
in lieu
D1.1/D1.1M, Section 5.17.1
of
AWS
2. Section 10.2.2 a in lieu of AWS
D1.1/D1.1M, Section 2.3.2
3. TABLE 10-2 in lieu of AWS D1.1/D1.1M,
Table 2.1
4. TABLE 10-5 in lieu of AWS D1.1/D1.1M,
Table 2.3
5. APPENDIX C, TABLE C-1 in lieu of
AWS D1.1/D1.1M, Table 2.5
6. Section 2.3.10 and APPENDIX C in lieu
of AWS D1.1/D1.1M, Section 2, Part C
7. Section 14.2.2
in lieu of AWS
D1.1/D1.1M, Sections 5.15.4.3 and
5.15.4.4
10.2.1 Groove Welds
10.2.1.1
Effective Area. The effective area
of groove welds shall be considered as the length of
the weld times the effective throat.
The effective throat of a complete-joint-penetration
(CJP) groove weld shall be the thickness of the
thinner part joined.
The effective throat of a partial-joint-penetration
(PJP) groove weld shall be as shown in TABLE
10-1.
User Note: The effective throat of a partialjoint-penetration groove weld is dependent on
the process used and the weld position. The
design drawings should either indicate the
effective throat required or the weld strength
required, and the fabricator should detail the
joint based on the weld process and position to
be used to weld the joint.
The effective weld throat for flare groove welds
when filled flush to the surface of a round bar or a
90bend in a formed section or rectangular HSS,
shall be as shown in TABLE 10-2, unless other
effective throats are demonstrated by tests. The
effective throat of flare groove welds filled less than
flush shall be as shown in TABLE 10-2, less the
greatest perpendicular dimension measured from a
line flush to the base metal surface to the weld
surface.
Larger effective throats than those in TABLE 10-2
are permitted for a given welding procedure
specification (WPS), provided the fabricator can
establish by qualification the consistent production
of such larger effective throat. Qualification shall
consist of sectioning the weld normal to its axis, at
mid-length and terminal ends. Such sectioning shall
be made on a number of combinations of material
sizes representative of the range to be used in the
fabrication.
10.2.1.2
Limitations.
The
minimum
effective throat of a partial-joint-penetration groove
weld shall not be less than the size required to
transmit calculated forces nor the size shown in
TABLE 10-3. Minimum weld size is determined by
the thinner of the two parts joined.
1 0 .2 .2
Fillet Welds
10.2.2.1
Effective Area. The effective area
of a fillet weld shall be the effective length
multiplied by the effective throat. The effective
throat of a fillet weld shall be the shortest distance
from the root to the face of the diagrammatic weld.
An increase in effective throat is permitted if
consistent penetration beyond the root of the
diagrammatic weld is demonstrated by tests using
the production process and procedure variables.
For fillet welds in holes and slots, the effective
length shall be the length of the centerline of the
weld along the center of the plane through the
throat. In the case of overlapping fillets, the
effective area shall not exceed the nominal cross-
SBC 306-CR-18
102
CHAPTER 10—DESIGN OF CONNECTIONS
sectional area of the hole or slot, in the plane of the
faying surface.
10.2.2.2
Limitations. The minimum size of
fillet welds shall be not less than the size required
to transmit calculated forces, nor the size as shown
in TABLE 10-4. These provisions do not apply to
fillet weld reinforcements of partial- or completejoint-penetration groove welds.
The maximum size of fillet welds of connected parts
shall be:
(a) Along edges of material less than 6 mm thick;
not greater than the thickness of the material.
(b) Along edges of material 6 mm or more in
thickness; not greater than the thickness of the
material minus 2 mm, unless the weld is
especially designated on the drawings to be
built out to obtain full-throat thickness. In the
as-welded condition, the distance between the
edge of the base metal and the toe of the weld
is permitted to be less than 2 mm provided the
weld size is clearly verifiable.
The minimum length of fillet welds designed on the
basis of strength shall be not less than four times the
nominal weld size, or else the effective size of the
weld shall be considered not to exceed one quarter
of its length. If longitudinal fillet welds are used
alone in end connections of flat-bar tension
members, the length of each fillet weld shall be not
less than the perpendicular distance between them.
For the effect of longitudinal fillet weld length in
end connections upon the effective area of the
connected member, see Section 4.3.
For end-loaded fillet welds with a length up to 100
times the weld size, it is permitted to take the
effective length equal to the actual length. When
the length of the end-loaded fillet weld exceeds
100 times the weld size, the effective length shall
be determined by multiplying the actual length by
the reduction factor, , determined as follows:
𝛽 = 1.2 − 0.002 (𝑙 ⁄𝑤 ) < 1.0
(10-1)
where
l actual length of end-loaded weld, mm
w size of weld leg, mm
When the length of the weld exceeds 300 times the
leg size, w, the effective length shall be taken as
180w.
Intermittent fillet welds are permitted to be used to
transfer calculated stress across a joint or faying
surfaces and to join components of built-up
members. The length of any segment of intermittent
fillet welding shall be not less than four times the
weld size, with a minimum of 40 mm.
In lap joints, the minimum amount of lap shall be
five times the thickness of the thinner part joined,
but not less than 25 mm. Lap joints joining plates
or bars subjected to axial stress that utilize
transverse fillet welds only shall be fillet welded
along the end of both lapped parts, except where the
deflection of the lapped parts is sufficiently
restrained to prevent opening of the joint under
maximum loading.
Fillet weld terminations are permitted to be
stopped short or extend to the ends or sides of parts
or be boxed except as limited by the following:
1. For overlapping elements of members in
which one connected part extends
beyond an edge of another connected part
that is subject to calculated tensile stress,
fillet welds shall terminate not less than
the size of the weld from that edge.
2. For connections where flexibility of the
outstanding elements is required, when
end returns are used the length of the return
shall not exceed four times the nominal
size of the weld nor half the width of the
part.
3. Fillet welds joining transverse stiffeners
to plate girder webs 20 mm thick or less
shall end not less than four times nor more
than six times the thickness of the web
from the web toe of the web-to-flange
welds, except where the ends of stiffeners
are welded to the flange.
Fillet welds that occur on opposite sides of a
common plane shall be interrupted at the corner
common to both welds.
User Note: Fillet weld terminations should be
located approximately one weld size from the
edge of the connection to minimize notches in the
base metal. Fillet welds terminated at the end of
the joint, other than those connecting stiffeners
to girder webs, are not a cause for correction.
Fillet welds in holes or slots are permitted to be
used to transmit shear and resist loads
perpendicular to the faying surface in lap joints or
to prevent the buckling or separation of lapped
parts and to join components of built-up members.
Such fillet welds may overlap, subject to the
SBC 306-CR-18
103
CHAPTER 10—DESIGN OF CONNECTIONS
provisions of Section 10.2. Fillet welds in holes or
slots are not to be considered plug or slot welds.
10.2.3 Plug and Slot Welds
10.2.3.1
Effective Area. The effective
shearing area of plug and slot welds shall be
considered as the nominal cross-sectional area of
the hole or slot in the plane of the faying surface.
10.2.3.2
Limitations. Plug or slot welds are
permitted to be used to transmit shear in lap joints
or to prevent buckling or separation of lapped parts
and to join component parts of built-up members.
The diameter of the holes for a plug weld shall not
be less than the thickness of the part containing it
plus 8 mm, rounded to the next larger even mm,
nor greater than the minimum diameter plus 3 mm
or 2.25 times the thickness of the weld.
The minimum center-to-center spacing of plug
welds shall be four times the diameter of the hole.
The length of slot for a slot weld shall not exceed 10
times the thickness of the weld. The width of the
slot shall be not less than the thickness of the part
containing it plus 8 mm rounded to the next larger
even mm, nor shall it be larger than 2.25 times the
thickness of the weld. The ends of the slot shall be
semicircular or shall have the corners rounded to a
radius of not less than the thickness of the part
containing it, except those ends which extend to the
edge of the part.
The minimum spacing of lines of slot welds in a
direction transverse to their length shall be four
times the width of the slot. The minimum center-tocenter spacing in a longitudinal direction on any
line shall be two times the length of the slot.
The thickness of plug or slot welds in material 16
mm or less in thickness shall be equal to the
thickness of the material. In material over 16 mm
thick, the thickness of the weld shall be at least
one-half the thickness of the material but not less
than 16 mm.
𝑅𝑛 = 𝐹𝑛𝑤 𝐴𝑤𝑒
where
FnBM = nominal stress of the base metal,
MPa
Fnw = nominal stress of the weld metal,
MPa
ABM = cross-sectional area of the base
metal, mm2
Awe = effective area of the weld, mm2
The values of , FnBM and Fnw and limitations
thereon are given in TABLE 10-5.
Alternatively, for fillet welds the design strength is
permitted to be determined as follows:
𝜑 = 0.75
(a) For a linear weld group with a uniform leg
size, loaded through the center of gravity
𝑅𝑛 = 𝐹𝑛𝑤 𝐴𝑤𝑒
(10-4)
where
𝐹𝑛𝑤 = 0.60𝐹𝐸𝑋𝑋 (1.0 + 0.5 𝑠𝑖𝑛1.5 𝜃)
(10-5)
and
FEXX filler metal classification strength, MPa
angle of loading measured from the weld
longitudinal axis, degrees
User Note: A linear weld group is one in which
all elements are in a line or are parallel.
(b) For weld elements within a weld group that are
analyzed using an instantaneous center of
rotation method, the components of the
nominal strength, Rnx and Rny, and the nominal
moment capacity, Mn, are permitted to be
determined as follows:
𝑅𝑛𝑥 = ∑ 𝐹𝑛𝑤𝑖𝑥 𝐴𝑤𝑒𝑖
(10-6)
𝑅𝑛𝑦 = ∑ 𝐹𝑛𝑤𝑖𝑦 𝐴𝑤𝑒𝑖
(10-7)
10.2.4 Strength. The design strength, Rn of
welded joints shall be the lower value of the base
material strength determined according to the limit
states of tensile rupture and shear rupture and the
weld metal strength determined according to the
limit state of rupture as follows:
where
For the base metal
𝐹𝑛𝑤𝑖 = 0.60𝐹𝐸𝑋𝑋 (1.0 + 0.5 𝑠𝑖𝑛1.5 𝜃𝑖 )𝑓(𝑝𝑖 )
𝑅𝑛 = 𝐹𝑛𝐵𝑀 𝐴𝐵𝑀
(10-3)
𝑀𝑛 = ∑[𝐹𝑛𝑤𝑖𝑦 𝐴𝑤𝑒𝑖 (𝑥𝑖 ) − 𝐹𝑛𝑤𝑖𝑥 𝐴𝑤𝑒𝑖 (𝑦𝑖 )] (10-8)
Awei effective area of weld throat of the ith
weld element, mm2
(10-2)
𝑓(𝑝𝑖 ) = [𝑝𝑖 (1.9 − 0.9𝑝𝑖 )]0.3
(10-9)
10-10)
For the weld metal
SBC 306-CR-18
104
CHAPTER 10—DESIGN OF CONNECTIONS
Fnwi nominal stress in the ith weld element,
MPa
Fnwix x-component of nominal stress, Fnwi,
MPa
Rnwl
total nominal strength of longitudinally
loaded fillet welds, as determined in
accordance with TABLE 10-5, N
Rnwt
total nominal strength of transversely
loaded fillet welds, as determined in
accordance with TABLE 10-5 without the
alternate in Section 10.2.4 a, N
Fnwiy y-component of nominal stress, Fnwi,
MPa
i /mi , ratio of element i
deformation to its deformation at
maximum stress
pi
ri distance from instantaneous center of
rotation to ith weld element, mm
xi x component of ri
yi y component of ri
= 𝑟𝑖 𝛥𝑢𝑐𝑟 ⁄𝑟𝑐𝑟 deformation of the ith
𝛥𝑖
weld element at an intermediate
stress level, linearly proportioned to
the critical deformation based on
distance from the instantaneous
center of rotation, ri, mm
𝛥𝑚𝑖
= 0.209(𝜃𝑖 + 2)−0.32 𝑤, deformation of
the ith weld element at maximum
stress, mm
ucr
𝛥𝑢𝑖
i
deformation of the weld element
with minimum ui /ri ratio at ultimate
stress (rupture), usually in the
element furthest from instantaneous
center of rotation, mm
= 1.087(𝜃𝑖 + 6)−0.65 𝑤 ≤ 0.17𝑤
,
deformation of the ith weld element
at ultimate stress (rupture), mm
angle between the longitudinal axis of
ith weld element and the direction of the
resultant force acting on the element,
degrees
(c) For fillet weld groups concentrically loaded
and consisting of elements with a uniform leg
size that are oriented both longitudinally and
transversely to the direction of applied load,
the combined strength, Rn, of the fillet weld
group shall be determined as the greater of
(i) 𝑅𝑛 = 𝑅𝑛𝑤𝑙 + 𝑅𝑛𝑤𝑡
(10-11)
(ii) 𝑅𝑛 = 0.85𝑅𝑛𝑤𝑙 + 1.5𝑅𝑛𝑤𝑡
(10-12)
or
where
10.2.5 Combination of Welds. If two or more of
the general types of welds (groove, fillet, plug, slot)
are combined in a single joint, the strength of each
shall be separately computed with reference to the
axis of the group in order to determine the strength
of the combination.
10.2.6 Filler Metal Requirements. The choice
of filler metal for use with complete-jointpenetration groove welds subject to tension normal
to the effective area shall comply with the
requirements for matching filler metals given in
AWS D1.1/D1.1M.
Filler metal with a specified minimum Charpy Vnotch toughness of 27 J at 4 °C or lower shall be
used in the following joints:
1. Complete-joint-penetration groove welded
T- and corner joints with steel backing left
in place, subject to tension normal to the
effective area, unless the joints are
designed using the nominal strength and
resistance factor or safety factor as
applicable for a partial-joint-penetration
groove weld
2. Complete-joint-penetration groove welded
splices subject to tension normal to the
effective area in heavy sections as defined
in Sections 1.3.1.3 and 1.3.1.4
The manufacturer’s Certificate of Conformance
shall be sufficient evidence of compliance.
10.2.7 Mixed Weld Metal. When Charpy Vnotch toughness is specified, the process
consumables for all weld metal, tack welds, root
pass and subsequent passes deposited in a joint shall
be compatible to ensure notch-tough composite
weld metal.
10.3—Bolts and Threaded Parts
10.3.1 High-Strength Bolts. Use of highstrength bolts shall conform to the provisions of
the Specification for Structural Joints Using HighStrength Bolts, hereafter referred to as the RCSC
Specification, as approved by the Research Council
on Structural Connections, except as otherwise
provided in this Code. High-strength bolts in this
SBC 306-CR-18
105
CHAPTER 10—DESIGN OF CONNECTIONS
Code are grouped according to material strength as
follows:
Group A—ASTM A325, A325M, F1852, A354
Grade BC, and A449
Group B—ASTM A490, A490M, F2280, and A354
Grade BD
When assembled, all joint surfaces, including those
adjacent to the washers, shall be free of scale,
except tight mill scale.
requirements of the RCSC Specification with
modifications as required for the increased
diameter and/or length to provide the design
pretension.
10.3.2 Size and Use of Holes. The maximum
sizes of holes for bolts are given in TABLE 10-8,
except that larger holes, required for tolerance on
location of anchor rods in concrete foundations, are
permitted in column base details.
(a) bearing-type connections except as noted in
Section 5.6 or Section 10.1.10
(d) tension or combined shear and tension
applications, for Group A bolts only, where
loosening or fatigue due to vibration or load
fluctuations are not design considerations
Standard holes or short-slotted holes transverse to
the direction of the load shall be provided in
accordance with the provisions of this Code,
unless oversized holes, short-slotted holes parallel
to the load, or long-slotted holes are approved by
the engineer of record. Finger shims up to 6 mm
are permitted in slip- critical connections designed
on the basis of standard holes without reducing
the nominal shear strength of the fastener to that
specified for slotted holes.
The snug-tight condition is defined as the tightness
required to bring the connected plies into firm
contact. Bolts to be tightened to a condition other
than snug tight shall be clearly identified on the
design drawings.
Oversized holes are permitted in any or all plies of
slip-critical connections, but they shall not be used
in bearing-type connections. Hardened washers
shall be installed over oversized holes in an outer
ply.
All high-strength bolts specified on the design
drawings to be used in pretensioned or slip-critical
joints shall be tightened to a bolt tension not less
than that given in TABLE 10-6. Installation shall
be by any of the following methods: turn-of-nut
method, a direct-tension-indicator, twist-off-type
tension-control bolt, calibrated wrench, or
alternative design bolt.
Short-slotted holes are permitted in any or all plies
of slip-critical or bearing-type connections. The
slots are permitted without regard to direction of
loading in slip- critical connections, but the length
shall be normal to the direction of the load in
bearing-type connections. Washers shall be
installed over short-slotted holes in an outer ply;
when high-strength bolts are used, such washers
shall be hardened washers conforming to ASTM
F436.
Bolts are permitted to be installed to the snug-tight
condition when used in:
User Note: There are no specific minimum or
maximum tension requirements for snug-tight
bolts. Fully pretensioned bolts such as ASTM
F1852 or F2280 are permitted unless specifically
prohibited on design drawings.
When bolt requirements cannot be provided within
the RCSC Specification limitations because of
requirements for lengths exceeding 12 diameters
or diameters exceeding 38 mm, bolts or threaded
rods conforming to Group A or Group B materials
are permitted to be used in accordance with the
provisions for threaded parts in TABLE 10-7.
When ASTM A354 Grade BC, A354 Grade BD, or
A449 bolts and threaded rods are used in slipcritical connections, the bolt geometry including
the thread pitch, thread length, head and nut(s) shall
be equal to or (if larger in diameter) proportional to
that required by the RCSC Specification.
Installation shall comply with all applicable
When Group B bolts over 25 mm in diameter are
used in slotted or oversized holes in external plies,
a single hardened washer conforming to ASTM
F436, except with 8 mm minimum thickness, shall
be used in lieu of the standard washer.
User Note: Washer requirements are provided
in the RCSC Specification, Section 6.
Long-slotted holes are permitted in only one of the
connected parts of either a slip-critical or bearingtype connection at an individual faying surface.
Long-slotted holes are permitted without regard
to direction of loading in slip-critical connections,
but shall be normal to the direction of load in
bearing-type connections. Where long-slotted
holes are used in an outer ply, plate washers, or a
continuous bar with standard holes, having a size
SBC 306-CR-18
106
CHAPTER 10—DESIGN OF CONNECTIONS
sufficient to completely cover the slot after
installation, shall be provided. In high-strength
bolted connections, such plate washers or
continuous bars shall be not less than 8 mm thick
and shall be of structural grade material, but need
not be hardened. If hardened washers are required
for use of high-strength bolts, the hardened
washers shall be placed over the outer surface of
the plate washer or bar.
10.3.3 Minimum Spacing. The distance between
centers of standard, oversized or slotted holes shall
not be less than 2.67 times the nominal diameter, d,
of the fastener; a distance of 3d is preferred.
User Note: ASTM F1554 anchor rods may be
furnished in accordance to product
specifications with a body diameter less than
the nominal diameter. Load effects such as
bending and elongation should be calculated
based on minimum diameters permitted by
the product specification. See ASTM F1554
and the “Applicable ASTM Specifications
for Various Types of Structural Fasteners,”
in CHAPTER 1.
10.3.4 Minimum Edge Distance. The distance
from the center of a standard hole to an edge of a
connected part in any direction shall not be less
than either the applicable value from TABLE 10-9,
or as required in Section 10.3.10 . The distance from
the center of an oversized or slotted hole to an edge
of a connected part shall be not less than that
required for a standard hole to an edge of a
connected part plus the applicable increment, C2,
from TABLE 10-10.
User Note: The edge distances in TABLE
10-8 are minimum edge distances based on
standard
fabrication
practices
and
workmanship tolerances. The appropriate
provisions of Sections 10.3.10 and 10.4 must
be satisfied.
10.3.5 Maximum Spacing and Edge Distance.
The maximum distance from the center of any bolt
to the nearest edge of parts in contact shall be 12
times the thickness of the connected part under
consideration, but shall not exceed 150 mm. The
longitudinal spacing of fasteners between
elements consisting of a plate and a shape or two
plates in continuous contact shall be as follows:
(a) For painted members or unpainted members not
subject to corrosion, the spacing shall not
exceed 24 times the thickness of the thinner part
or 300 mm.
(b) For unpainted members of weathering steel
subject to atmospheric corrosion, the spacing
shall not exceed 14 times the thickness of the
thinner part or 180 mm.
User Note: Dimensions in (a) and (b) do not
apply to elements consisting of two shapes in
continuous contact.
10.3.6 Tensile and Shear Strength of Bolts and
Threaded Parts. The design tensile or shear
strength, Rn of a snug-tightened or pretensioned
high-strength bolt or threaded part shall be
determined according to the limit states of tension
rupture and shear rupture as follows:
𝑅𝑛 = 𝐹𝑛 𝐴𝑏
(10-13)
𝜑 = 0.75
where
Ab = nominal unthreaded body area of bolt or
threaded part, mm2
Fn = nominal tensile stress, Fnt, or shear stress,
Fnv, from TABLE 10-7, MPa
The required tensile strength shall include any
tension resulting from prying action produced by
deformation of the connected parts.
User Note: The force that can be resisted by
a snug-tightened or pretensioned highstrength bolt or threaded part may be limited
by the bearing strength at the bolt hole per
Section 10.3.10 . The effective strength of an
individual fastener may be taken as the lesser
of the fastener shear strength per Section
10.3.6 or the bearing strength at the bolt hole
per Section 10.3.10 . The strength of the bolt
group is taken as the sum of the effective
strengths of the individual fasteners.
10.3.7 Combined Tension and Shear in
Bearing-Type Connections. The design tensile
strength of a bolt subjected to combined tension
and shear shall be determined according to the
limit states of tension and shear rupture as
follows:
′
𝑅𝑛 = 𝐹𝑛𝑡
𝐴𝑏
𝜑 = 0.75
(10-14)
where
SBC 306-CR-18
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CHAPTER 10—DESIGN OF CONNECTIONS
F nt
𝜇 = 0.30
= nominal tensile stress modified to include
the effects of shear stress, MPa
𝐹𝑛𝑡
′
𝐹𝑛𝑡
= 1.3𝐹𝑛𝑡 − (
) 𝑓 ≤ 𝐹𝑛𝑡
𝜑 𝐹𝑛𝑣 𝑟𝑣
For Class B surfaces (unpainted blastcleaned steel surfaces or surfaces with Class
B coatings on blast-cleaned steel)
(10-15)
Fnt
= nominal tensile stress from TABLE 10-7,
MPa
Fnv
= nominal shear stress from TABLE 10-7,
MPa
frv
= required shear stress using LRFD load
combinations, MPa
The design shear stress of the fastener shall equal
or exceed the required shear stress, frv.
𝜇 = 0.50
Du 1.13, a multiplier that reflects the ratio
of the mean installed bolt pretension to
the specified minimum bolt pretension.
The use of other values may be approved
by the engineer of record.
Tb minimum fastener tension given in
TABLE 10-6, kN
hf factor for fillers, determined as follows:
User Note: Note that when the required stress,
f, in either shear or tension, is less than or equal
to 30% of the corresponding design stress, the
effects of combined stress need not be
investigated. Also note that Eq. (10-15) can be
rewritten so as to find a nominal shear stress,
F nv, as a function of the required tensile stress,
ft.
Where there are no fillers or where bolts have
been added to distribute loads in the filler
10.3.8 High-Strength Bolts in Slip-Critical
Connections. Slip-critical connections shall be
designed to prevent slip and for the limit states of
bearing-type connections. When slip-critical bolts
pass through fillers, all surfaces subject to slip shall
be prepared to achieve design slip resistance.
(b) For two or more fillers between
connected parts
The design slip resistance for the limit state of slip
shall be determined as follows:
𝑅𝑛 = 𝜇 𝐷𝑢 ℎ𝑓 𝑇𝑏 𝑛𝑠
(10-16)
(a) For standard size and short-slotted holes
perpendicular to the direction of the load
(e) 𝜑 = 1.00
(b) For oversized and short-slotted holes parallel to
the direction of the load
(f) 𝜑 = 0.85
(c) For long-slotted holes
(g) 𝜑 = 0.70
where
μ mean slip coefficient for Class A or B surfaces,
as applicable, and determined as follows, or as
established by tests:
For Class A surfaces (unpainted clean mill
scale steel surfaces or surfaces with Class A
coatings on blast-cleaned steel or hotdipped
galvanized and roughened surfaces)
ℎ𝑓 = 1.0
Where bolts have not been added to distribute
the load in the filler:
(a) For one filler between connected parts
ℎ𝑓 = 1.0
ℎ𝑓 = 0.85
ns number of slip planes required to permit
the connection to slip
10.3.9 Combined Tension and Shear in SlipCritical Connections.
When a slip-critical
connection is subjected to an applied tension that
reduces the net clamping force, the design slip
resistance per bolt, from Section 10.3.8 , shall be
multiplied by the factor, ksc, as follows:
𝑘𝑠𝑐 = 1 − (𝑇𝑢 ⁄𝐷𝑢 𝑇𝑏 𝑛𝑏 )
(10-17)
where
Tu required tension force, kN
nb number of bolts carrying the applied
tension
10.3.10 Bearing Strength at Bolt Holes. The
design bearing strength, Rn at bolt holes shall be
determined for the limit state of bearing as
follows:
𝜑 = 0.75
The nominal bearing strength of the connected
material, Rn, is determined as follows:
SBC 306-CR-18
108
CHAPTER 10—DESIGN OF CONNECTIONS
(a) For a bolt in a connection with standard,
oversized and short-slotted holes, independent
of the direction of loading, or a long-slotted
hole with the slot parallel to the direction of the
bearing force
When deformation at the bolt hole at service
load is a design consideration
𝑅𝑛 = 1.2 𝑙𝑐 𝑡 𝐹𝑢 ≤ 2.4 𝑑 𝑡 𝐹𝑢
(10-18)
When deformation at the bolt hole at service
load is not a design consideration
𝑅𝑛 = 1.5 𝑙𝑐 𝑡 𝐹𝑢 ≤ 3.0 𝑑 𝑡 𝐹𝑢
(10-19)
(b) For a bolt in a connection with long-slotted
holes with the slot perpendicular to the
direction of force
𝑅𝑛 = 1.0 𝑙𝑐 𝑡 𝐹𝑢 ≤ 2.0 𝑑 𝑡 𝐹𝑢
(10-20)
(c) For connections made using bolts that pass
completely through an unstiffened box
member or HSS, see Section 10.7 and Eq.
(10-27);
where
Fu = specified minimum tensile strength of the
connected material, MPa
d = nominal bolt diameter, mm
lc
t
= clear distance, in the direction of the
force, between the edge of the hole and
the edge of the adjacent hole or edge of
the material, mm
= thickness of connected material, mm
For connections, the bearing resistance shall be
taken as the sum of the bearing resistances of the
individual bolts.
Bearing strength shall be checked for both bearingtype and slip-critical connections. The use of
oversized holes and short- and long-slotted holes
parallel to the line of force is restricted to slipcritical connections per Section 10.3.2 .
User Note: The effective strength of an
individual fastener is the lesser of the fastener
shear strength per Section 10.3.6 or the
bearing strength at the bolt hole per Section
10.3.10 . The strength of the bolt group is the
sum of the effective strengths of the individual
fasteners.
10.3.11 Special Fasteners. The nominal strength
of special fasteners other than the bolts presented in
TABLE 10-7 shall be verified by tests.
10.3.12 Tension Fasteners. When bolts or other
fasteners in tension are attached to an unstiffened
box or HSS wall, the strength of the wall shall be
determined by rational analysis.
10.4—Affected Elements of Members
and Connecting Elements
This section applies to elements of members at
connections and connecting elements, such as
plates, gussets, angles and brackets.
10.4.1 Strength of Elements in Tension. The
design strength, Rn , of affected and connecting
elements loaded in tension shall be the lower value
obtained according to the limit states of tensile
yielding and tensile rupture.
(a) For tensile yielding of connecting elements
𝑅𝑛 = 𝐹𝑦 𝐴𝑔
(10-21)
𝜑 = 0.90
(b) For tensile rupture of connecting elements
𝑅𝑛 = 𝐹𝑢 𝐴𝑒
(10-22)
𝜑 = 0.75
where
Ae effective net area as defined in Section
4.3, mm2; for bolted splice plates, 𝐴𝑒 =
𝐴𝑛 ≤ 0.85𝐴𝑔 .
User Note: The effective net area of the
connection plate may be limited due to stress
distribution as calculated by methods such as the
Whitmore section.
10.4.2 Strength of Elements in Shear. The
design shear strength of affected and connecting
elements in shear shall be the lower value obtained
according to the limit states of shear yielding and
shear rupture:
(a) For shear yielding of the element:
𝑅𝑛 = 0.60𝐹𝑦 𝐴𝑔𝑣
(10-23)
𝜑 = 1.00
where
Agv gross area subject to shear, mm2
(b) For shear rupture of the element:
𝑅𝑛 = 0.60𝐹𝑢 𝐴𝑛𝑣
𝜑 = 0.75
(10-24)
where
Anv net area subject to shear, mm2
SBC 306-CR-18
109
CHAPTER 10—DESIGN OF CONNECTIONS
10.4.3 Block Shear Strength. The design
strength for the limit state of block shear rupture
along a shear failure path or paths and a
perpendicular tension failure path shall be taken as
𝑅𝑛 = 0.60𝐹𝑢 𝐴𝑛𝑣 + 𝑈𝑏𝑠 𝐹𝑢 𝐴𝑛𝑡 ≤
0.60𝐹𝑦 𝐴𝑔𝑣 + 𝑈𝑏𝑠 𝐹𝑢 𝐴𝑛𝑡
(10-25)
𝜑 = 0.75
where
Ant net area subject to tension, mm2
Where the tension stress is uniform, Ubs 1; where
the tension stress is nonuniform, Ubs 0.5.
User Note: Typical cases where Ubs should be
taken equal to 0.5 are illustrated in the
Commentary.
10.4.4 Strength of Elements in Compression.
The design strength of connecting elements in
compression for the limit states of yielding and
buckling shall be determined as follows:
(a) When 𝐾𝐿⁄𝑟 ≤ 25
𝑃𝑛 = 𝐹𝑦 𝐴𝑔
(10-26)
𝜑 = 0.90
(b) When 𝐾𝐿⁄𝑟 > 25, the provisions of Chapter 5
apply.
10.4.5 Strength of Elements in Flexure. The
design flexural strength of affected elements shall be
the lower value obtained according to the limit
states of flexural yielding, local buckling, flexural
lateral- torsional buckling and flexural rupture.
10.5—Fillers
10.5.1 Fillers
in
Welded
Connections.
Whenever it is necessary to use fillers in joints
required to transfer applied force, the fillers and the
connecting welds shall conform to the requirements
of Section 10.5.1.1 or Section 10.5.1.2 as
applicable.
10.5.1.1
Thin Fillers. Fillers less than 6
mm thick shall not be used to transfer stress. When
the thickness of the fillers is less than 6 mm, or
when the thickness of the filler is 6 mm or greater
but not adequate to transfer the applied force
between the connected parts, the filler shall be kept
flush with the edge of the outside connected part,
and the size of the weld shall be increased over the
required size by an amount equal to the thickness
of the filler.
10.5.1.2
Thick Fillers. When the thickness
of the fillers is adequate to transfer the applied
force between the connected parts, the filler shall
extend beyond the edges of the outside connected
base metal. The welds joining the outside connected
base metal to the filler shall be sufficient to
transmit the force to the filler and the area
subjected to the applied force in the filler shall
be adequate to avoid overstressing the filler. The
welds joining the filler to the inside connected
base metal shall be adequate to transmit the
applied force.
10.5.2 Fillers in Bolted Connections. When a
bolt that carries load passes through fillers that are
equal to or less than 6 mm thick, the shear strength
shall be used without reduction. When a bolt that
carries load passes through fillers that are greater
than 6 mm thick, one of the following requirements
shall apply:
(a) The shear strength of the bolts shall be
multiplied by the factor 1 − 0.0154 (𝑡 − 6)
but not less than 0.85, where t is the total
thickness of the fillers; mm
(b) The fillers shall be extended beyond the joint
and the filler extension shall be secured with
enough bolts to uniformly distribute the total
force in the connected element over the
combined cross section of the connected
element and the fillers;
(c) The size of the joint shall be increased to
accommodate a number of bolts that is
equivalent to the total number required in (b)
above; or
(d) The joint shall be designed to prevent slip in
accordance with Section 10.3.8 using either
Class B surfaces or Class A surfaces with turnof-nut tightening.
10.6—Splices
Groove-welded splices in plate girders and beams
shall develop the nominal strength of the smaller
spliced section. Other types of splices in cross
sections of plate girders and beams shall develop
the strength required by the forces at the point of
the splice.
10.7—Bearing Strength
The design bearing strength, Rn, surfaces in
contact shall be determined for the limit state of
bearing (local compressive yielding) as follows:
SBC 306-CR-18
𝜑 = 0.75
110
CHAPTER 10—DESIGN OF CONNECTIONS
The nominal bearing strength, Rn, shall be
determined as follows:
(a) For finished surfaces, pins in reamed, drilled,
or bored holes, and ends of fitted bearing
stiffeners
𝑅𝑛 = 1.8𝐹𝑦 𝐴𝑝𝑏
(10-27)
where
Apb projected area in bearing, mm2
specified minimum yield stress, MPa
Fy
(b) For expansion rollers and rockers
When d 635 mm
𝑅𝑛 = 1.2(𝐹𝑦 − 90) 𝑙𝑏 𝑑 ⁄20
(10-28)
When d > 635 mm
𝑅𝑛 = 30.2(𝐹𝑦 − 90) 𝑙𝑏 √𝑑 ⁄20
(10-29)
where
d = diameter, mm
lb length of bearing, mm
10.8—Column Bases and Bearing on
Concrete
Proper provision shall be made to transfer the
column loads and moments to the footings and
foundations.
In the absence of code regulations, the design
bearing strength, cPp, for the limit state of
concrete crushing are permitted to be taken as
follows:
𝜑𝑐 = 0.65
The nominal bearing strength, Pp, is determined as
follows:
(a) On the full area of a concrete support:
𝑃𝑝 = 0.85𝑓𝑐′ 𝐴1
(10-30)
(b) On less than the full area of a concrete support:
𝑃𝑝 = 0.85𝑓𝑐′ 𝐴1 √𝐴2 /𝐴1 ≤ 1.7𝑓𝑐′ 𝐴1
(10-31)
where
A1 = area of steel concentrically bearing on a
concrete support, mm2
A2 = maximum area of the portion of the
supporting surface that is geometrically
similar to and concentric with the
loaded area, mm2
f c =
specified compressive
concrete, MPa
strength
of
10.9—Anchor Rods and Embedments
Anchor rods shall be designed to provide the
required resistance to loads on the completed
structure at the base of columns including the net
tensile components of any bending moment that
may result from load combinations stipulated in
Section 2.2. The anchor rods shall be designed in
accordance with the requirements for threaded parts
in TABLE 10-7.
Design of column bases and anchor rods for the
transfer of forces to the concrete foundation
including bearing against the concrete elements
shall satisfy the requirements of SBC 304 or ACI
349.
User Note: When columns are required to resist
a horizontal force at the base plate, bearing
against the concrete elements should be
considered.
When anchor rods are used to resist horizontal
forces, hole size, anchor rod setting tolerance, and
the horizontal movement of the column shall be
considered in the design.
Larger oversized holes and slotted holes are
permitted in base plates when adequate bearing is
provided for the nut by using ASTM F844 washers
or plate washers to bridge the hole.
User Note: The permitted hole sizes,
corresponding washer dimensions and nuts are
given in the AISC Steel Construction Manual,
AISC (2005b) and ASTM F1554.
10.10—Flanges and Webs With
Concentrated Forces
This section applies to single- and doubleconcentrated forces applied normal to the flange(s)
of wide flange sections and similar built-up shapes.
A single-concentrated force can be either tensile or
compressive. Double-concentrated forces are one
tensile and one compressive and form a couple on
the same side of the loaded member.
When the required strength exceeds the design
strength as determined for the limit states listed in
this section, stiffeners and/or doublers shall be
provided and shall be sized for the difference
between the required strength and the design
SBC 306-CR-18
111
CHAPTER 10—DESIGN OF CONNECTIONS
strength for the applicable limit state. Stiffeners
shall also meet the design requirements in
Section 10.10.8 . Doublers shall also meet the
design requirement in Section 10.10.9 .
(b)When the concentrated force to be resisted is
applied at a distance from the member end that is
less than or equal to the depth of the member, d.
𝑅𝑛 = 𝐹𝑦𝑤 𝑡𝑤 (2.5𝑘 + 𝑙𝑏 )
User Note: See Appendix E.3 for
requirements for the ends of cantilever
members.
where
Stiffeners are required at unframed ends of beams
in accordance with the requirements of Section
10.10.7 .
k
10.10.1 Flange Local Bending. This section
applies to tensile single-concentrated forces and the
tensile component of double-concentrated forces.
The design strength, Rn, for the limit state of
flange local bending shall be determined as
follows:
𝑅𝑛 = 6.25𝐹𝑦𝑓 𝑡𝑓2
(10-32)
𝜑 = 0.90
where
Fyf specified minimum yield stress of the
flange, MPa
tf
thickness of the loaded flange, mm
If the length of loading across the member flange is
less than 0.15bf, where bf is the member flange
width, Eq. (10-32) need not be checked.
When the concentrated force to be resisted is
applied at a distance from the member end that is
less than 10tf, Rn shall be reduced by 50%.
When required, a pair of transverse stiffeners shall
be provided
10.10.2 Web Local Yielding. This section applies
to single-concentrated forces and both components
of double-concentrated forces.
The design strength for the limit state of web local
yielding shall be determined as follows:
(10-34)
Fyw specified minimum yield stress of the
web material, MPa
distance from outer face of the flange to
the web toe of the fillet, mm
lb length of bearing (not less than k for end
beam reactions), mm
tw thickness of web, mm
When required, a pair of transverse stiffeners or a
doubler plate shall be provided.
10.10.3 Web Local Crippling. This section
applies to compressive single-concentrated forces
or the compressive component of doubleconcentrated forces.
The design strength for the limit state of web local
crippling shall be determined as follows:
𝜑 = 0.75
The nominal strength, Rn, shall be determined as
follows:
(a) When the concentrated compressive force to be
resisted is applied at a distance from the
member end that is greater than or equal to d/ 2:
𝑙
𝑡
𝑑
𝑡𝑓
1.5
2 [1
𝑅𝑛 = 0.80𝑡𝑤
+ 3 ( 𝑏) ( 𝑤)
𝐸𝐹𝑦𝑤 𝑡𝑓
]√
𝑡𝑤
(10-35)
(b) When the concentrated compressive force to be
resisted is applied at a distance from the
member end that is less than d/ 2:
For 𝑙𝑏 ⁄𝑑 ≤ 0.2
𝑙
𝑡
𝑑
𝑡𝑓
1.5
2 [1
𝑅𝑛 = 0.40𝑡𝑤
+ 3 ( 𝑏) ( 𝑤)
𝐸𝐹𝑦𝑤 𝑡𝑓
]√
𝑡𝑤
(10-36)
For 𝑙𝑏 ⁄𝑑 > 0.2
𝜑 = 1.00
The nominal strength, Rn, shall be determined as
follows:
(a) When the concentrated force to be resisted is
applied at a distance from the member end that
is greater than the depth of the member, d,
𝑅𝑛 = 𝐹𝑦𝑤 𝑡𝑤 (5𝑘 + 𝑙𝑏 )
(10-33)
4𝑙
𝑡
𝑑
𝑡𝑓
1.5
𝐸𝐹𝑦𝑤 𝑡𝑓
2
𝑅𝑛 = 0.40𝑡𝑤
[1 + ( 𝑏 − 0.2) ( 𝑤) ] √
𝑡𝑤
(10-37)
where
d full nominal depth of the section, mm
When required, a transverse stiffener, a pair of
transverse stiffeners, or a doubler plate extending
at least one-half the depth of the web shall be
provided.
SBC 306-CR-18
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CHAPTER 10—DESIGN OF CONNECTIONS
10.10.4 Web Sidesway Buckling. This section
applies only to compressive single-concentrated
forces applied to members where relative lateral
movement between the loaded compression flange
and the tension flange is not restrained at the point
of application of the concentrated force.
Mu required flexural strength using LRFD
load combinations, N-mm
bf
width of flange, mm
h
clear distance between flanges less the
fillet or corner radius for rolled shapes;
distance between adjacent lines of
fasteners or the clear distance between
flanges when welds are used for built-up
shapes, mm
The design strength of the web for the limit state
of sidesway buckling shall be determined as
follows:
0.85
The nominal strength, Rn, shall be determined as
follows:
User Note: For determination of adequate
restraint, refer to Appendix E.
(a) If the compression flange is restrained against
rotation
10.10.5 Web Compression Buckling.
This
section applies to a pair of compressive singleconcentrated forces or the compressive components
in a pair of double-concentrated forces, applied at
both flanges of a member at the same location.
When (ℎ⁄𝑡𝑤 )⁄(𝐿𝑏 ⁄𝑏𝑓 ) ≤ 2.3
𝑅𝑛 =
3
𝐶𝑟 𝑡𝑤
𝑡𝑓
h2
h/𝑡𝑤
3
[1 + 0.4 (
) ]
𝐿𝑏 /𝑏𝑓
(10-38)
When(ℎ⁄𝑡𝑤 )⁄(𝐿𝑏 ⁄𝑏𝑓 ) > 2.3, the limit state
of web sidesway buckling does not apply.
When the required strength of the web exceeds the
design strength, local lateral bracing shall be
provided at the tension flange or either a pair of
transverse stiffeners or a doubler plate shall be
provided.
(b) If the compression flange is not restrained
against rotation
When (ℎ⁄𝑡𝑤 )⁄(𝐿𝑏 ⁄𝑏𝑓 ) ≤ 1.7
𝑅𝑛 =
3
𝐶𝑟 𝑡𝑤
𝑡𝑓
h2
h/𝑡𝑤
3
[0.4 (
) ]
𝐿𝑏 /𝑏𝑓
(10-39)
When (ℎ⁄𝑡𝑤 )⁄(𝐿𝑏 ⁄𝑏𝑓 ) > 1.7, the limit state
of web sidesway buckling does not apply.
When the required strength of the web exceeds the
design strength, local lateral bracing shall be
provided at both flanges at the point of application
of the concentrated forces.
In Eq. (10-38) and (10-39), the following
definitions apply:
𝐶𝑟
= 6.62 × 106 MPa when Mu My at the
location of the force
The design strength for the limit state of web local
buckling shall be determined as follows:
𝑅𝑛 =
ℎ
𝜑 = 0.90
(10-40)
When the pair of concentrated compressive forces
to be resisted is applied at a distance from the
member end that is less than d/2, Rn shall be
reduced by 50%.
When required, a single transverse stiffener, a pair
of transverse stiffeners, or a doubler plate extending
the full depth of the web shall be provided.
10.10.6 Web Panel Zone Shear. This section
applies to double-concentrated forces applied to
one or both flanges of a member at the same
location.
The design strength of the web panel zone for the
limit state of shear yielding shall be determined as
follows:
𝜑 = 0.90
The nominal strength, Rn, shall be determined as
follows:
(a) When the effect of panel-zone deformation on
frame stability is not considered in the analysis:
For 𝑃𝑟 ≤ 0.4𝑃𝑐
3.31 × 106 MPa when Mu My at the
location of the force
Lb largest laterally unbraced length along
either flange at the point of load, mm
3
24𝑡𝑤
√𝐸 𝐹𝑦𝑤
𝑅𝑛 = 0.60𝐹𝑦 𝑑𝑐 𝑡𝑤
(10-41)
(b) For 𝑃𝑟 > 0.4𝑃𝑐
SBC 306-CR-18
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CHAPTER 10—DESIGN OF CONNECTIONS
𝑃𝑟
)
(10-42)
𝑃𝑐
(c) When frame stability, including plastic panelzone deformation, is considered in the analysis:
𝑅𝑛 = 0.60𝐹𝑦 𝑑𝑐 𝑡𝑤 (1.4 −
For 𝑃𝑟 ≤ 0.75𝑃𝑐
𝑅𝑛 = 0.60𝐹𝑦 𝑑𝑐 𝑡𝑤 (1 +
2
3𝑏𝑐𝑓 𝑡𝑐𝑓
𝑑𝑏 𝑑𝑐 𝑡 𝑤
)
(10-43)
For 𝑃𝑟 > 0.75𝑃𝑐
𝑅𝑛 = 0.60𝐹𝑦 𝑑𝑐 𝑡𝑤 (1 +
2
3𝑏𝑐𝑓 𝑡𝑐𝑓
𝑑𝑏 𝑑𝑐 𝑡𝑤
) (1.9 −
1.2𝑃𝑟
𝑃𝑐
) (10-44)
In Eq. (10-41) through (10-44), the following
definitions apply:
Ag
gross cross-sectional area of member,
mm2
bcf width of column flange, mm
db depth of beam, mm
dc depth of column, mm
Fy
specified minimum yield stress of the
column web, MPa
Pc Py, N
Pr required axial
combinations, N
strength
using
load
Py Fy Ag, axial yield strength of the column,
N
tcf thickness of column flange, mm
tw thickness of column web, mm
When required, doubler plate(s) or a pair of
diagonal stiffeners shall be provided within the
boundaries of the rigid connection whose webs lie
in a common plane.
See Section 10.10.9
requirements.
for doubler plate design
10.10.7 Unframed Ends of Beams and Girders.
At unframed ends of beams and girders not
otherwise restrained against rotation about their
longitudinal axes, a pair of transverse stiffeners,
extending the full depth of the web, shall be
provided.
10.10.8 Additional Stiffener Requirements for
Concentrated Forces. Stiffeners required to resist
tensile concentrated forces shall be designed in
accordance with the requirements of Section 10.4.1
and welded to the loaded flange and the web. The
welds to the flange shall be sized for the difference
between the required strength and design strength.
The stiffener to web welds shall be sized to transfer
to the web the algebraic difference in tensile force
at the ends of the stiffener.
Stiffeners required to resist compressive
concentrated forces shall be designed in
accordance with the requirements in Section
10.4.4 and shall either bear on or be welded to
the loaded flange and welded to the web. The welds
to the flange shall be sized for the difference
between the required strength and the applicable
limit state strength. The weld to the web shall be
sized to transfer to the web the algebraic difference
in compression force at the ends of the stiffener. For
fitted bearing stiffeners, see Section 10.7.
Transverse full depth bearing stiffeners for
compressive forces applied to a beam or plate
girder flange(s) shall be designed as axially
compressed members (columns) in accordance
with the requirements of Section 5.6.2 and
Section 10.4.4 . The member properties shall be
determined using an effective length of 0.75h and a
cross section composed of two stiffeners, and a strip
of the web having a width of 25tw at interior
stiffeners and 12tw at the ends of members. The
weld connecting full depth bearing stiffeners to the
web shall be sized to transmit the difference in
compressive force at each of the stiffeners to the
web.
Transverse and diagonal stiffeners shall comply
with the following additional requirements:
1. The width of each stiffener plus one-half
the thickness of the column web shall not
be less than one-third of the flange or
moment connection plate width delivering
the concentrated force.
2. The thickness of a stiffener shall not be
less than one-half the thickness of the
flange or moment connection plate
delivering the concentrated load, nor less
than the width divided by 16.
3. Transverse stiffeners shall extend a
minimum of one-half the depth of the
member except as required in Section
10.10.5 and Section 10.10.7 .
10.10.9 Additional Doubler Plate Requirements
for Concentrated Forces. Doubler plates required
for compression strength shall be designed in
accordance with the requirements of Chapter 5.
SBC 306-CR-18
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CHAPTER 10—DESIGN OF CONNECTIONS
Doubler plates required for tensile strength shall be
designed in accordance with the requirements of
Chapter 4.
Doubler plates required for shear strength (see
Section 10.10.6 ) shall be designed in accordance
with the provisions of Chapter 7.
Doubler plates shall comply with the following
additional requirements:
1. The thickness and extent of the doubler
plate shall provide the additional material
necessary to equal or exceed the strength
requirements.
2. The doubler plate shall be welded to
develop the proportion of the total force
transmitted to the doubler plate.
SBC 306-CR-18
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CHAPTER 10—DESIGN OF CONNECTIONS
TABLES AND FIGURES OF CHAPTER 10
TABLE 10-1 : EFFECTIVE THROAT OF PARTIAL-JOINT-PENETRATION GROOVE WELDS
Welding Process
Shielded metal arc
(SMAW)
Gas metal arc (GMAW)
Flux cored arc (FCAW)
Submerged arc (SAW)
Gas metal arc (GMAW)
Flux cored arc (FCAW)
Shielded metal arc
(SMAW)
Gas metal arc (GMAW)
Flux cored arc (FCAW)
Welding
Position
F (flat),
H (horizontal),
V (vertical),
OH (overhead)
Groove Type (AWS D1.1/D1.1M,
Figure 3.3)
All
J or U groove
60° V
F
J or U groove 60° bevel or V
F, H
45° bevel
depth of groove
45° bevel
depth of groove minus 3
mm
Effective Throat
depth of groove
All
V, OH
TABLE 10-2 : EFFECTIVE WELD THROATS OF FLARE GROOVE WELDS
Welding Process
GMAW and FCAW-G
SMAW and FCAW-S
SAW
Flare Bevel Groove [a]
5/8 R
5/16 R
5/16 R
Flare V-Groove
3/4 R
5/8 R
1/2 R
[a] For flare bevel groove with R < 10 mm, use only reinforcing fillet weld on filled flush joint.
General note: R = radius of joint surface (can be assumed to be 2t for HSS), mm
TABLE 10-3 : MINIMUM EFFECTIVE THROAT OF PARTIAL-JOINT-PENETRATION GROOVE
WELDS
Material Thickness of
Thinner Part Joined, mm
To 6 inclusive
Over 6 to 13
Over 13 to 19
Over 19 to 38
Over 38 to 57
Over 57 to 150
Over 150
[a]
See TABLE 10-1.
Minimum Effective
Throat, [a] mm
3
5
6
8
10
13
16
TABLE 10-4 : MINIMUM SIZE OF FILLET WELDS
Material Thickness of
Thinner Part Joined, mm
To 6 inclusive
Over 6 to 13
Over 13 to 19
Over 19
[a]
Leg dimension of fillet welds. Single pass welds must be used.
Note: See Section 10.2.2.2 for maximum size of fillet welds.
SBC 306-CR-18
Minimum Size of
Fillet Weld, [a] mm
3
5
6
8
116
CHAPTER 10—DESIGN OF CONNECTIONS
TABLE 10-5: DESIGN STRENGTH OF WELDED JOINTS, MPA
Nominal
Effective
Required Filler
Stress
Pertinent
Area (ABM
Metal Strength
(FnBM or
ϕ
Metal
or Awe)
Level [a][b]
Fnw)
mm2
MPa
COMPLETE-JOINT-PENETRATION GROOVE WELDS
Matching filler metal shall be
used. For T- and corner joints
Tension
Strength of the joint is controlled
with backing left in place, notch
Normal to weld axis
by the base metal
tough filler metal is required.
See Section 10.2.6 .
Filler metal with a strength
Compression
level equal to or one strength
Strength of the joint is controlled
Normal to weld axis
by the base metal
level less than matching filler
metal is permitted.
Filler metal with a strength
Tension or
Tension or compression in parts joined parallel to
level equal to or less than
compression Parallel
a weld need not be considered in design
matching filler metal is
of welds joining the parts.
to weld axis
permitted.
Strength of the joint is controlled by the base
Matching filler metal shall
Shear
metal
be used.[c]
PARTIAL-JOINT-PENETRATION GROOVE WELDS INCLUDING FLARE V-GROOVE AND
FLARE BEVEL GROOVE WELDS
Fu
Base
ϕ = 0.75
See 10.4
Tension
Normal to weld axis
0.60FEXX
Weld
ϕ = 0.80
See 10.2.1.1
Compression Column to
Compressive stress need not be considered in design
base plate and column
of welds joining the parts.
splices designed per
Section 10.1.4 (1)
Compression
Fy
ϕ = 0.90
Base
See 10.4
Connections of
Filler metal with a
members designed to
strength
level equal
bear other than
0.60 FEXX
ϕ = 0.80
Weld
See 10.2.1.1
to
or
less
than
columns as described in
matching
filler
metal
Section 10.1.4 (2)
is
permitted.
Compression
Fy
ϕ = 0.90
Base
See 10.4
Connections not
0.90 FEXX
ϕ = 0.80
Weld
See 10.2.1.1
finished-to-bear
Tension or
Tension or compression in parts joined parallel to a
compression Parallel
weld need not be considered in design
to weld axis
of welds joining the parts.
Base
Governed by 10.4
Shear
0.60 FEXX
ϕ = 0.75
Weld
See 10.2.1.1
Load Type and
Direction Relative to
Weld Axis
SBC 306-CR-18
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CHAPTER 10—DESIGN OF CONNECTIONS
TABLE 10-5: (CONTINUED) DESIGN STRENGTH OF WELDED JOINTS, MPa
Load Type and
Direction Relative to
Weld Axis
Pertinent
Metal
ϕ
Nominal
Stress
(FnBM or
Fnw)
MPa
Effective
Area
(ABM or
Awe)
mm2
Required Filler
Metal Strength
Level [a][b]
FILLET WELDS INCLUDING FILLETS IN HOLES AND SLOTS AND SKEWED T–JOINTS
Base
Governed by 10.4
Shear
Weld
Tension or compression
Parallel to weld axis
Shear Parallel to faying
surface on the surface
on the effective area
ϕ = 0.75
0.60 FEXX [d]
See 10.2.2.1
Tension or compression in parts joined parallel to a
weld need not be considered in design
of welds joining the parts.
Base
PLUG AND SLOT WELDS
Governed by 10.4
Weld
ϕ = 0.75
0.60 FEXX
See 10.2.3.1
Filler metal with a strength
level equal to or less than
matching filler metal is
permitted.
Filler metal with a strength
level equal to or less than
matching filler metal is
permitted.
[a] For matching weld metal see AWS D1.1/D1.1M, Section 3.3.
[b] Filler metal with a strength level one strength level greater than matching is permitted.
[c] Filler metals with a strength level less than matching may be used for groove welds between the webs and flanges of built-up
sections transferring shear loads, or in applications where high restraint is a concern. In these applications, the weld joint shall
be detailed and the weld shall be designed using the thickness of the material as the effective throat, where ϕ =0.80 and 0.60
FEXX is the nominal strength.
[d] Alternatively, the provisions of Section 10.2.4 a are permitted provided the deformation compatibility of the various weld
elements is considered. Sections 10.2.4 b and 10.2.4 c are special applications of Section 10.2.4 a, that provide for deformation
compatibility.
TABLE 10-6 : MINIMUM BOLT PRETENSION, KN*
Group A
Group B
( e.g., A325M Bolts)
( e.g., A490M Bolts)
M16
91
114
M20
142
179
M22
176
221
M24
205
257
M27
267
334
M30
326
408
M36
475
595
* Equal to 0.70 times the minimum tensile strength of bolts, rounded off to nearest kN, as specified in ASTM
specifications for A325M and A490M bolts with UNC threads.
Bolt Size, mm
SBC 306-CR-18
118
CHAPTER 10—DESIGN OF CONNECTIONS
TABLE 10-7 : NOMINAL STRENGTH OF FASTENERS AND THREADED PARTS, MPa
Description of Fasteners
A307 bolts
Group A (e.g., A325) bolts, when threads are not
excluded from shear planes
Group A (e.g., A325) bolts, when threads are
excluded from shear planes
Group B (e.g., A490) bolts, when threads are not
excluded from shear planes
Group B (e.g., A490) bolts, when threads are
excluded from shear planes
Threaded parts meeting the requirements of Section
1.3.4 , when threads are not excluded from shear
planes
Threaded parts meeting the requirements of Section
1.3.4 , when threads are excluded from shear planes
Nominal Tensile
Strength,
Fnt , MPa [a]
310
Nominal Shear Strength in BearingType Connections, Fnv , MPa [b]
620
372
620
457
780
457
780
579
0.75Fu
0.450Fu
0.75Fu
0.563Fu
188 [c] [d]
[a] For high-strength bolts subject to tensile fatigue loading, see Appendix C.
[b] For end loaded connections with a fastener pattern length greater than 965 mm, F
nv shall be reduced to 83.3% of the tabulated
values. Fastener pattern length is the maximum distance parallel to the line of force between the centerline of the bolts
connecting two parts with one faying surface.
[c] For A307 bolts the tabulated values shall be reduced by 1% for each 2 mm over 5 diameters of length in the grip.
[d] Threads permitted in shear planes.
TABLE 10-8 : NOMINAL HOLE DIMENSIONS, mm
Bolt Diameter, mm
Standard
(Dia.)
M16
M20
M22
M24
M27
M30
≥ M36
18
22
24
27 [a]
30
33
d+3
Bolt Diameter, mm
Oversize
Short-Slot (Width x
(Dia.)
Length)
20
24
28
30
35
38
d+8
18 x 22
22 x 26
24 x 30
27 x 32
30 x 37
33 x 40
(d + 3) x (d + 10)
Long-Slot
(Width x Length)
18 x 40
22 x 50
24 x 55
27 x 60
30 x 67
33 x 75
(d + 3) x 2.5d
[a] Clearance provided allows the use of a 25 mm bolt if desirable.
TABLE 10-9 : MINIMUM EDGE DISTANCE [a] FROM CENTER OF STANDARD HOLE [b] TO
EDGE OF CONNECTED PART, mm
Bolt Diameter, mm
16
20
22
24
27
30
36
Over 36
Minimum Edge Distance
22
26
28
30
34
38
46
1.25d
[a] If necessary, lesser edge distances are permitted provided the appropriate provisions from Sections 10.3.10 and 10.4 are
satisfied, but edge distances less than one bolt diameter are not permitted without approval from the engineer of record.
[b] For oversized or slotted holes, see TABLE 10-10
SBC 306-CR-18
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CHAPTER 10—DESIGN OF CONNECTIONS
TABLE 10-10 : VALUES OF EDGE DISTANCE INCREMENT C2, mm
Slotted Holes
Long Axis Perpendicular to
Oversized Holes
Long Axis Parallel to
Edge
Edge
Short Slots
Long Slots[a]
≤22
2
3
24
3
3
0.75d
0
≥ 27
3
5
[a]
When length of slot is less than maximum allowable (see TABLE 10-8), C2 is permitted to be reduced by one-half
the difference between the maximum and actual slot lengths.
Nominal Diameter of Fastener,
mm
SBC 306-CR-18
120
CHAPTER 10—DESIGN OF CONNECTIONS
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SBC 306-CR-18
121
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER
CONNECTIONS
This chapter addresses connections to HSS
members and box sections of uniform wall
thickness.
User Note: Connection strength is often
governed by the size of HSS members,
especially the wall thickness of truss chords, and
this must be considered in the initial design.
Bp
width of plate, measured 90to the
plane of the connection, mm
D outside diameter of round HSS, mm
Fy specified minimum yield stress of HSS
member material, MPa
Fyp specified minimum yield stress of plate
material, MPa
Fu specified minimum tensile strength of
HSS member material, MPa
The chapter is organized as follows:
11.1 —Concentrated Forces on HSS
11.2 —HSS-to-HSS Truss Connections
H
overall height of rectangular HSS
member, measured in the plane of the
connection, mm
S
elastic section modulus of member, mm3
lb
bearing length of the load, measured
parallel to the axis of the HSS member
(or measured across the width of the HSS
in the case of loaded cap plates), mm
t
design wall thickness of HSS member,
mm
tp
thickness of plate, mm
11.3 —HSS-to-HSS Moment Connections
11.4 —Welds of Plates and Branches to
Rectangular HSS
User Note:
See also Chapter 10 for additional
requirements for bolting to HSS. See
Section 10.3.10 (c) for through-bolts.
Connection parameters must be within the
limits of applicability. Limit states need only
be checked when connection geometry or
loading is within the parameters given in
the description of the limit state.
11.1.2 Round HSS.
The design strength of connections with
concentrated loads and within the limits in TABLE
11-2 shall be taken as shown in TABLE 11-1.
11.1.3 Rectangular HSS.
11.1—Concentrated Forces on HSS
The design strength, Rn of connections shall be
determined in accordance with the provisions of
this chapter and the provisions of Section 2.3.5 .
11.1.1 Definitions of Parameters
Ag gross cross-sectional area of member,
mm2
B
overall width of rectangular HSS
member, measured 90° to the plane of
the connection, mm
The design strength of connections with
concentrated loads and within the limits in TABLE
11-4 shall be taken as the lowest value of the
applicable limit states shown in TABLE 11-3. The
limits of applicability in TABLE 11-2 stem
primarily from limitations on tests conducted to
date.
11.2—HSS-to-HSS Truss Connections
The design strength, Pn, of connections shall be
determined in accordance with the provisions of
this chapter and the provisions of Section 2.3.5 .
HSS-to-HSS truss connections are defined as
connections that consist of one or more branch
SBC 306-CR-18
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
members that are directly welded to a continuous
chord that passes through the connection and shall
be classified as follows:
B
(a) When the punching load, Pr sin, in a branch
member is equilibrated by beam shear in the
chord member, the connection shall be
classified as a T-connection when the branch is
perpendicular to the chord, and a Y-connection
otherwise.
Bb = overall width of rectangular HSS branch
member, measured 90° to the plane of the
connection, mm
(b) When the punching load, Pr sin, in a branch
member is essentially equilibrated (within
20%) by loads in other branch member(s) on
the same side of the connection, the connection
shall be classified as a K-connection. The
relevant gap is between the primary branch
members whose loads equilibrate. An Nconnection can be considered as a type of Kconnection.
User Note: A K-connection with one branch
perpendicular to the chord is often called an
N-connection.
(c) When the punching load, Pr sin, is transmitted
through the chord member and is equilibrated
by branch member(s) on the opposite side, the
connection shall be classified as a crossconnection.
(d) When a connection has more than two primary
branch members, or branch members in more
than one plane, the connection shall be
classified as a general or multiplanar
connection.
When branch members transmit part of their load as
K-connections and part of their load as T-, Y- or
cross-connections, the adequacy of the connections
shall be determined by interpolation on the
proportion of the design strength of each in total.
For the purposes of this Code, the centerlines of
branch members and chord members shall lie in a
common plane. Rectangular HSS connections are
further limited to have all members oriented with
walls parallel to the plane. For trusses that are made
with HSS that are connected by welding branch
members to chord members, eccentricities within
the limits of applicability are permitted without
consideration of the resulting moments for the
design of the connection.
11.2.1
Definitions of Parameters
Ag = gross cross-sectional area of member, mm2
= overall width of rectangular HSS main
member, measured 90° to the plane of the
connection, mm
D
= outside diameter of round HSS main
member, mm
Db = outside diameter of round HSS branch
member, mm
Fy = specified minimum yield stress of HSS
main member material, MPa
Fyb = specified minimum yield stress of HSS
branch member material, MPa
Fu = specified minimum tensile strength of
HSS material, MPa
H
= overall height of rectangular HSS main
member, measured in the plane of the
connection, mm
Hb = overall height of rectangular HSS
branch member, measured in the plane of
the connection, mm
Ov
𝑙
= 𝑜𝑣 ∗ 100 %
𝑙𝑝
S = elastic section modulus of member, mm3
e = eccentricity in a truss connection,
positive being away from the branches,
mm
g = gap between toes of branch members in a
gapped K-connection, neglecting the
welds, mm
lb = Hb /sin , mm
lov = overlap length measured along the
connecting face of the chord beneath the
two branches, mm
lp
= projected length of the overlapping
branch on the chord, mm
t
= design wall thickness of HSS main
member, mm
tb
= design wall thickness of HSS branch
member, mm
β = width ratio; the ratio of branch diameter
to chord diameter = Db /D for round HSS;
the ratio of overall branch width to chord
width = Bb /B for rectangular HSS
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
β eff = effective width ratio; the sum of the
perimeters of the two branch members in
a K-connection divided by eight times the
chord width
For the purposes of this Code, the centerlines of the
branch member(s) and the chord member shall lie
in a common plane.
γ = chord slenderness ratio; the ratio of onehalf the diameter to the wall thickness
11.3.1 Definitions of Parameters
Ag
gross cross-sectional area of member,
mm2
= B/2t for rectangular HSS
B
η = load length parameter, applicable only to
rectangular HSS; the ratio of the length of
contact of the branch with the chord in the
plane of the connection to the chord width
= lb /B
overall width of rectangular HSS main
member, measured 90 ° to the plane of
the connection, mm
Bb
overall width of rectangular HSS branch
member, measured 90 ° to the plane of
the connection, mm
D
outside diameter of round HSS main
member, mm
= D/2t for round HSS; the ratio of one-half
the width to wall thickness
= acute angle between the branch and
chord (degrees)
ζ = gap ratio; the ratio of the gap between the
branches of a gapped K-connection to the
width of the chord = g/B for rectangular
HSS.
Db outside diameter of round HSS branch
member, mm
specified minimum yield stress of HSS
main member material, MPa
Fy
11.2.2 Round HSS. The design strength of HSSto-HSS truss connections within the limits in Table
11-6 shall be taken as the lowest value of the
applicable limit states shown in TABLE 11-5.
Fyb specified minimum yield stress of HSS
branch member material, MPa
Fu
11.2.3 Rectangular HSS. The design strength of
HSS-to-HSS truss connections within the limits in
TABLE 11-8 shall be taken as the lowest value of
the applicable limit states shown in TABLE 11-7.
specified minimum tensile strength of
HSS member material, MPa
H
overall height of rectangular HSS main
member, measured in the plane of the
connection, mm
Hb overall height of rectangular HSS branch
member, measured in the plane of the
connection, mm
11.3—HSS-to-HSS Moment
Connections
The design strength, Mn, of connections shall be
determined in accordance with the provisions of
this chapter and the provisions of Section 2.3.5 .
HSS-to-HSS moment connections are defined as
connections that consist of one or two branch
members that are directly welded to a continuous
chord that passes through the connection, with the
branch or branches loaded by bending moments.
A connection shall be classified as:
S
elastic section modulus of member, mm3
Zb
Plastic section modulus of branch about
the axis of bending, mm3
t
design wall thickness of HSS main
member, mm
tb
design wall thickness of HSS branch
member, mm
β
width ratio
(a) A T-connection when there is one branch and it
is perpendicular to the chord and as a Yconnection when there is one branch but not
perpendicular to the chord.
(b) A cross-connection when there is a branch on
each (opposite) side of the chord
SBC 306-CR-18
Db/D for round HSS; ratio of branch
diameter to chord diameter
Bb/B for rectangular HSS; ratio of overall
branch width to chord width
chord slenderness ratio
124
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
D/2t for round HSS; ratio of one-half
the diameter to the wall thickness
B/2t for rectangular HSS; ratio of onehalf the width to the wall thickness
η load length parameter, applicable only
to rectangular HSS
lb/B; the ratio of the length of contact of
the branch with the chord in the plane of
the connection to the chord width,
where lb=Hb /sin θ
acute angle between the branch and
chord (degrees)
11.3.2 Round HSS. The design strength of
moment connections within the limits of TABLE
11-10 shall be taken as the lowest value of the
applicable limit states shown in TABLE 11-9.
11.3.3 Rectangular HSS. The design strength of
moment connections within the limits of TABLE
11-12 shall be taken as the lowest value of the
applicable limit states shown in TABLE 11-11.
11.4—Welds of Plates and Branches to
Rectangular HSS
The design strength, Rn, Mn and Pn, of
connections shall be determined in accordance
with the provisions of this chapter and the
provisions of Section 2.3.5 .
The design strength of branch connections shall be
determined for the limit state of nonuniformity of
load transfer along the line of weld, due to
differences in relative stiffness of HSS walls in
HSS-to-HSS connections and between elements in
transverse plate-to-HSS connections, as follows:
Rn or 𝑃𝑛 = 𝐹𝑛𝑤 𝑡𝑤 𝑙𝑒
𝑀𝑛−𝑖𝑝 = 𝐹𝑛𝑤 𝑆𝑖𝑝
𝑀𝑛−𝑜𝑝 = 𝐹𝑛𝑤 𝑆𝑜𝑝
Sip
= effective elastic section modulus of welds
for in-plane bending (TABLE 11-13),
mm3
Sop = effective elastic section modulus of welds
for out-of-plane bending (TABLE 11-13),
mm3
le
= total effective weld length of groove and
fillet welds to rectangular HSS for weld
strength calculations, mm
tw
= smallest effective weld throat around the
perimeter of branch or plate, mm
When an overlapped K-connection has been
designed in accordance with TABLE 11-7 of this
chapter, and the branch member component forces
normal to the chord are 80% “balanced” (i.e., the
branch member forces normal to the chord face
differ by no more than 20%), the “hidden” weld
under an overlapping branch may be omitted if the
remaining welds to the overlapped branch
everywhere develop the full capacity of the
overlapped branch member walls.
The weld checks in TABLE 11-13 are not required
if the welds are capable of developing the full
strength of the branch member wall along its entire
perimeter (or a plate along its entire length).
User Note: The approach used here to allow
down-sizing of welds assumes a constant weld
size around the full perimeter of the HSS
branch. Special attention is required for equal
width (or near-equal width) connections which
combine partial-joint-penetration groove welds
along the matched edges of the connection, with
fillet welds generally across the main member
face.
(11-1)
(11-2)
(11-3)
For interaction, see Eq. (11-71).
(a) For fillet welds
𝜑 = 0.75
(b) For partial-joint-penetration groove welds
𝜑 = 0.80
where
Fnw = nominal stress of weld metal (Chapter
10) with no increase in strength due to
directionality of load, MPa
SBC 306-CR-18
125
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLES AND FIGURES OF CHAPTER 11
TABLE 11-1 : DESIGN STRENGTHS OF PLATE-TO-ROUND HSS CONNECTIONS
Connection Type
Connection Design Strength
Transverse Plate T- and CrossConnections
Limit State: HSS Local Yielding Plate
Axial Load
𝑅𝑛 𝑠𝑖𝑛 𝜃 = 𝐹𝑦 𝑡 2 (
5.5
𝐵𝑝
𝐷
1−0.81
) 𝑄𝑓
Plate Bending
In-Plane
Out- of-Plane
-
𝑀𝑛 = 0.5𝐵𝑝 𝑅𝑛
𝑀𝑛 = 0.8𝑙𝑏 𝑅𝑛
-
-
-
-
-
(11-4)
𝜑 = 0.90
Longitudinal Plate T-, Y- and CrossConnections
Limit State: HSS Plastification Plate
Axial Load
𝑙𝑝
𝑅𝑛 𝑠𝑖𝑛 𝜃 = 5.5𝐹𝑦 𝑡 2 (1 + 0.25 ) 𝑄𝑓
𝐷
(11-5)
𝜑 = 0.90
Longitudinal Plate T-Connections
Limit States: Plate Limit States and
HSS Punching Shear Plate Shear
Load
For Rn , see Chapter 10. Additionally,
the following relationship shall be met:
𝑡𝑝 ≤
Cap Plate Connections
𝐹𝑢
𝑡
𝐹𝑦𝑝
(11-6)
Limit State: Local Yielding of HSS
Axial Load
𝑅𝑛 = 2𝐹𝑦 𝑡(5𝑡𝑝 + 𝑙𝑏 ) ≤ 𝐹𝑦 𝐴
(11-7)
𝜑 = 1.0
FUNCTIONS
Qf = 1 for HSS (connecting surface) in tension
= 1.0 − 0.3𝑈(1 + 𝑈) for HSS (connecting surface) in compression
𝑈=|
𝑃𝑢
𝐹𝑦 𝐴𝑔
+
𝑀𝑢
𝐹𝑦 𝑆
|
(11-8)
(11-9)
where Pu and Mu are determined on the side of the joint that has the lower compression stress.
Pu and Mu refer to required strengths in the HSS
SBC 306-CR-18
126
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-2: LIMITS OF APPLICABILITY OF TABLE 11-1
Plate load angle:
HSS wall
slenderness:
Width ratio:
Material strength:
Ductility:
≥ 30°
𝐷⁄𝑡 ≤ 50 for T-connections under branch plate axial load or bending
𝐷⁄𝑡 ≤ 40 for cross-connections under branch plate axial load or bending
𝐷⁄𝑡 ≤ 0.11 𝐸 ⁄𝐹𝑦 under branch plate shear loading
𝐷⁄𝑡 ≤ 0.11 𝐸 ⁄𝐹𝑦 for cap plate connections in compression
0.2 < 𝐵𝑝 ⁄𝐷 ≤ 1.0 for transverse branch plate connections
Fy ≤ 360 MPa
𝐹𝑦 ⁄𝐹𝑢 ≤ 0.8 Note: ASTM A500 Grade C is acceptable.
TABLE 11-3 : DESIGN STRENGTHS OF PLATE-TO-RECTANGULAR HSS CONNECTIONS
Connection Type
Connection Design Strength
Limit State: Local Yielding of Plate, For All
10
(11-10)
𝑅𝑛 =
𝐹 𝑡𝐵 ≤ 𝐹𝑦𝑝 𝑡𝑝 𝐵𝑝
𝐵⁄𝑡 𝑦 𝑝
𝜑 = 0.95
Transverse Plate T- and Cross-Connections, Under
Plate Axial Load
Limit State: HSS Shear Yielding (Punching),
When 0.85𝐵 ≤ 𝐵𝑝 ≤ 𝐵 − 2𝑡
𝑅𝑛 = 0.6𝐹𝑦 𝑡(2𝑡𝑝 + 2𝐵𝑒𝑝 )
(11-11)
𝜑 = 0.95
Limit State: Local Yielding of HSS Sidewalls, When 𝛽 =
1.0
𝑅𝑛 = 2𝐹𝑦 𝑡(5𝑘 + 𝑙𝑏 )
(11-12)
k= outside corner radius of HSS ≥1.5 t
𝜑 = 1.0
Limit State: Local Crippling of HSS Sidewalls, When
=1.0 and Plate is in Compression, for T-Connections
3𝑙𝑏
(11-13)
𝑅𝑛 = 1.6𝑡 2 (1 +
) √𝐸𝐹𝑦 𝑄𝑓
𝐻 − 3𝑡
𝜑 = 0.75
Limit State: Local Crippling of HSS Sidewalls, When
=1.0 and Plate is in Compression, for CrossConnections
48𝑡 3
(11-14)
𝑅𝑛 = (
) √𝐸𝐹𝑦 𝑄𝑓
𝐻 − 3𝑡
𝜑 = 0.95
SBC 306-CR-18
127
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-3 (CONTINUED) DESIGN STRENGTHS OF PLATE-TO-RECTANGULAR HSS
CONNECTIONS
Connection Type
Longitudinal Plate T-, Y- and Cross- Connections, Under Plate
Axial Load
Connection Design Strength
Limit State: HSS Plastification
𝑅𝑛 𝑠𝑖𝑛 𝜃 =
𝐹𝑦 𝑡 2 2𝑙𝑏
𝑡𝑝 ( 𝐵
1−
𝐵
(11-15)
𝑡𝑝
+ 4√1 − 𝑄𝑓 )
𝐵
𝜑 = 1.00
Longitudinal Through Plate T- and
Y-Connections, Under Plate Axial Load
Limit State: HSS Wall Plastification
𝑅𝑛 𝑠𝑖𝑛 𝜃 =
2𝐹𝑦 𝑡 2 2𝑙𝑏
𝑡𝑝 ( 𝐵
1−
𝐵
(11-16)
𝑡𝑝
+ 4√1 − 𝑄𝑓 )
𝐵
𝜑 = 1.00
Longitudinal Plate T-Connections, Under Plate Shear Load
Limit States: Plate Limit States and HSS
Punching Shear
For Rn , see Chapter 10
Additionally, the following relationship
shall be met:
𝑡𝑝 ≤
SBC 306-CR-18
𝐹𝑢
𝑡
𝐹𝑦𝑝
(11-17)
128
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-3 (CONTINUED) DESIGN STRENGTHS OF PLATE-TO-RECTANGULAR HSS
CONNECTIONS
Connection Type
Cap Plate Connections, under Axial
Load
Connection Design Strength
Limit State: Local Yielding of Sidewalls
𝑅𝑛 = 2𝐹𝑦 𝑡(5𝑡𝑝 + 𝑙𝑏 ), when (5𝑡𝑝 +
𝑙𝑏 ) < 𝐵
𝑅𝑛 = 𝐹𝑦 𝐴, when (5𝑡𝑝 + 𝑙𝑏 ) ≥ 𝐵
𝜑 = 1.00
(11-18)
(11-19)
Limit State: Local Crippling of Sidewalls, When Plate is in
Compression
𝑅𝑛 = 1.6𝑡 2 [1 +
6𝑙𝑏
𝐵
𝑡
1.5
( ) ] √𝐸𝐹𝑦
𝑡𝑝
𝑡𝑝
𝑡
(11-20)
, when (5𝑡𝑝 + 𝑙𝑏 ) < 𝐵
𝜑 = 0.75
FUNCTIONS
Qf = 1 for HSS (connecting surface) in tension
= 1.3 − 0.4 𝑈⁄𝛽 ≤ 1.0 for HSS (connecting surface)
in compression, for transverse plate connections
= √1 − 𝑈 2 for HSS (connecting surface) in
compression, for longitudinal plate and
longitudinal through plate connections
𝑈=|
𝑃𝑢
𝐹𝑦 𝐴𝑔
+
𝑀𝑢
𝐹𝑦 𝑆
|
(11-21)
(11-22)
(11-23)
where Pu and Mu are determined on the side of the joint that has the lower compression stress.
Pu and Mu refer to required strengths in the HSS
𝐵𝑒𝑝 =
10𝐵𝑝
𝐵⁄𝑡
≤ 𝐵𝑝
(11-24)
k = outside corner radious of HSS ≥ 1.5t
TABLE 11-4: LIMITS OF APPLICABILITY OF TABLE 11-3
Plate load angle:
HSS wall
slenderness:
≥ 30°
B /t or H /t
35 for loaded wall, for transverse branch plate connections
40 for loaded wall, for longitudinal branch plate and through plate
connections
(𝐵 − 3𝑡)⁄𝑡 or (𝐻 − 3𝑡)⁄𝑡 ≤ 1.40√𝐸 ⁄𝐹𝑦 for loaded wall, for branch plate shear
loading
⁄
0.25 ≤ 𝐵𝑝 𝐵 ≤ 1.0 for transverse branch plate connections
Width ratio:
Material strength: 𝐹𝑦 ≤ 360 MPa
𝐹𝑦 ≤ 360 Note: ASTM A500 Grade C is acceptable.
Ductility:
B /t or H /t
SBC 306-CR-18
129
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-5 : DESIGN STRENGTHS OF ROUND HSS-TO-HSS TRUSS CONNECTIONS
Connection Type
General Check For T-, Y-, Cross- and KConnections With Gap, When
𝐷𝑏 (𝑡𝑒𝑛𝑠⁄𝑐𝑜𝑚𝑝) < (𝐷 − 2𝑡)
T- and Y-Connections
Connection Design Axial Strength
Limit State: Shear Yielding (Punching)
1 + 𝑠𝑖𝑛 𝜃
𝑃𝑛 = 0.6𝐹𝑦 𝑡𝜋𝐷𝑏 (
)
2 𝑠𝑖𝑛2 𝜃
𝜑 = 0.95
Limit State: Chord Plastification
𝑃𝑛 𝑠𝑖𝑛 𝜃 = 𝐹𝑦 𝑡 2 (3.1 + 15.6𝛽 2 ) 𝛾 0.2 𝑄𝑓
(11-25)
(11-26)
𝜑 = 0.90
Cross-Connections
Limit State: Chord Plastification
𝑃𝑛 𝑠𝑖𝑛 𝜃 = 𝐹𝑦 𝑡 2 (
5.7
)𝑄
1 − 0.81𝛽 𝑓
(11-27)
𝜑 = 0.90
K-Connections With Gap or Overlap
Limit State: Chord Plastification
(𝑃𝑛 𝑠𝑖𝑛 𝜃)𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑜𝑛 𝑏𝑟𝑎𝑛𝑐ℎ
𝐷𝑏 𝑐𝑜𝑚𝑝
= 𝐹𝑦 𝑡 2 (2.0 + 11.33
) 𝑄𝑔 𝑄𝑓
𝐷
(11-28)
(𝑃𝑛 𝑠𝑖𝑛 𝜃)𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑏𝑟𝑎𝑛𝑐ℎ = (𝑃𝑛 𝑠𝑖𝑛 𝜃)𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑜𝑛 𝑏𝑟𝑎𝑛𝑐ℎ
(11-29)
𝜑 = 0.90
SBC 306-CR-18
130
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-5 (continued): Design Strengths of Round HSS-to-HSS Truss Connections
FUNCTIONS
Qf = 1 for chord (connecting surface) in tension
(11-30)
= 1.0 − 0.3𝑈(1 + 𝑈) for HSS (connecting surface) in
(11-31)
compression
𝑃𝑢
𝑀𝑢
|
𝑈=|
+
(11-32)
𝐹𝑦 𝐴𝑔 𝐹𝑦 𝑆
where Pu and Mu are determined on the side of the joint that has the lower compression stress. Pu and Mu
refer to required strengths in the HSS
[𝑎]
1.2
0.024𝛾
]
0.5𝑔
𝑒𝑥𝑝 (
− 1.33) + 1
𝑡
[a] Note that exp(x) is equal to ex, where e = 2.71828 is the base of the natural logarithm.
𝑄𝑔 = 𝛾 0.2 [1 +
(11-33)
Table 11-6: Limits of Applicability of TABLE 11-5
Joint eccentricity:
Branch angle:
Chord wall slenderness:
Branch wall slenderness:
Width ratio:
Gap:
Overlap:
Branch thickness:
Material strength:
Ductility:
−0.55 ≤ 𝑒⁄𝐷 ≤ 0.25 for K-connections
≥ 30°
𝐷⁄𝑡 ≤ 50 for T-, Y- and K-connections
𝐷⁄𝑡 ≤ 40 for cross-connections Branch wall
𝐷𝑏 ⁄𝑡 𝑏 ≤ 50 for compression branch
𝐷𝑏 ⁄𝑡 𝑏 ≤ 0.05 𝐸 ⁄𝐹𝑦𝑏 for compression branch
0.2 < 𝐷𝑏 ⁄𝐷 ≤ 1.0 for T-, Y-, cross- and overlapped K-connections
0.4 ≤ 𝐷𝑏 ⁄𝐷 ≤ 1.0 for gapped K-connections
𝑔 ≥ 𝑡𝑏 𝑐𝑜𝑚𝑝 + 𝑡𝑏 𝑡𝑒𝑛𝑠 for gapped K-connections
25% ≤ 𝑂𝑣 ≤ 100% for overlapped K-connections
𝑡𝑏 𝑜𝑣𝑒𝑟𝑙𝑎𝑝𝑝𝑖𝑛𝑔 ≤ 𝑡𝑏 𝑜𝑣𝑒𝑟𝑙𝑎𝑝𝑝𝑒𝑑 for branches in overlapped K-connections
𝐹𝑦 and 𝐹𝑦𝑏 ≤ 360
𝐹𝑦 ⁄𝐹𝑢 and 𝐹𝑦𝑏 ⁄𝐹𝑢𝑏 ≤ 0.8
SBC 306-CR-18
131
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-7 : DESIGN STRENGTHS OF RECTANGULAR HSS-TO-HSS TRUSS CONNECTIONS
Connection Type
Connection Design Axial Strength
T-, Y- and Cross-Connections
Limit State: Chord Wall Plastification, When 𝛽 ≤ 0.85
2𝜂
𝑃𝑛 𝑠𝑖𝑛 𝜃 = 𝐹𝑦 𝑡 2 [(1−𝛽) +
4
√1−𝛽
] 𝑄𝑓
(11-34)
𝜑 = 1.00
Limit State: Shear Yielding (Punching), When 0.85 <
𝛽 ≤ 1 − 1⁄𝛾 or 𝐵⁄𝑡 < 10
𝑃𝑛 𝑠𝑖𝑛 𝜃 = 0.6𝐹𝑦 𝑡𝐵(2𝜂 + 2𝛽𝑒𝑜𝑝 )
(11-35)
Case for checking limit state of shear of
chord side walls
𝜑 = 0.95
Limit State: Local Yielding of Chord Sidewalls,
When 𝛽 = 1.0
𝑃𝑛 𝑠𝑖𝑛 𝜃 = 2𝐹𝑦 𝑡(5𝑘 + 𝑙𝑏 )
(11-36)
𝜑 = 1.00
Limit State: Local Crippling of Chord Sidewalls, When
𝛽 = 1.0 and Branch is in Compression, for T- or YConnections
𝑃𝑛 𝑠𝑖𝑛 𝜃 = 1.6𝑡 2 (1 +
3𝑙𝑏
𝐻−3𝑡
) √𝐸𝐹𝑦 𝑄𝑓
(11-37)
𝜑 = 0.75
Limit State: Local Crippling of Chord Sidewalls, When
= 1.0 and Branches are in Compression, for CrossConnections
48𝑡 3
𝑃𝑛 𝑠𝑖𝑛 𝜃 = (
) √𝐸𝐹𝑦 𝑄𝑓
(11-38)
𝐻 − 3𝑡
𝜑 = 0.90
Limit State: Local Yielding of Branch/Branches Due
to Uneven Load Distribution, When 𝑏 > 0.85
𝑃𝑛 = 𝐹𝑦𝑏 𝑡𝑏 (2𝐻𝑏 + 2𝑏𝑒𝑜𝑖 − 4𝑡𝑏 )
(11-39)
𝜑 = 0.95
where
𝐹𝑦 𝑡
10
𝑏𝑒𝑜𝑖 =
(
) 𝐵 ≤ 𝐵𝑏
(11-40)
𝐵⁄𝑡 𝐹𝑦𝑏 𝑡𝑏 𝑏
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-7 (CONTINUED): DESIGN STRENGTHS OF RECTANGULAR HSS-TO-HSS TRUSS
CONNECTIONS
Connection Type
Connection Design Axial Strength
T-, Y- and Cross-Connections
Limit State: Shear of Chord Sidewalls For Cross-Connections
With < 90° and Where a Projected Gap is Created (See
Figure).
Determine Pn sin in accordance with Section 7.5.
Gapped K-Connections
Limit State: Chord Wall Plastification, for All
𝑃𝑛 𝑠𝑖𝑛 𝜃 = 𝐹𝑦 𝑡 2 (9.8𝛽𝑒𝑓𝑓 𝛾 0.5 ) 𝑄𝑓
(11-41)
𝜑 = 0.90
Limit State: Shear Yielding (Punching), when 𝐵𝑏 < 𝐵 − 2𝑡
Do not check for square branches.
𝑃𝑛 𝑠𝑖𝑛 𝜃 = 0.6𝐹𝑦 𝑡𝐵(2𝜂 + 𝛽 + 𝛽𝑒𝑜𝑝 )
𝜑 = 0.95
(11-42)
Limit State: Shear of Chord Sidewalls, in the Gap Region
Determine Pn sin in accordance with Section 7.5.
Do not check for square chords.
Limit State: Local Yielding of Branch /Branches Due to
Uneven Load Distribution.
Do not check for square branches or if
𝐵⁄𝑡 ≥ 15.
𝑃𝑛 = 𝐹𝑦𝑏 𝑡𝑏 (2𝐻𝑏 + 𝐵𝑏 + 𝑏𝑒𝑜𝑖 − 4𝑡𝑏 )
(11-43)
𝜑 = 0.95
where
𝐹𝑦 𝑡
10
𝑏𝑒𝑜𝑖 =
(
) 𝐵 ≤ 𝐵𝑏
(11-44)
𝐵⁄𝑡 𝐹𝑦𝑏 𝑡𝑏 𝑏
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-7 (CONTINUED): DESIGN STRENGTHS OF RECTANGULAR HSS-TO-HSS TRUSS
CONNECTIONS
Connection Type
Overlapped K-Connections
Connection Design Axial Strength
Limit State: Local Yielding of Branch /Branches
Due to Uneven Load Distribution
𝜑 = 0.95
When 25% < 𝑂𝑣 < 50%:
𝑂𝑣
𝑃𝑛,𝑖 = 𝐹𝑦𝑏𝑖 𝑡𝑏𝑖 [ (2𝐻𝑏𝑖 − 4𝑡𝑏𝑖 ) + 𝑏𝑒𝑜𝑖
50
(11-45)
+ 𝑏𝑒𝑜𝑣 ]
Note that the force arrows shown for overlapped
K-connections may be reversed;
i and j control member identification.
When 50% ≤ 𝑂𝑣 < 80%:
𝑃𝑛,𝑖 = 𝐹𝑦𝑏𝑖 𝑡𝑏𝑖 (2𝐻𝑏𝑖 − 4𝑡𝑏𝑖 + 𝑏𝑒𝑜𝑖 + 𝑏𝑒𝑜𝑣 )
(11-46)
When 80% ≤ 𝑂𝑣 < 100%:
𝑃𝑛,𝑖 = 𝐹𝑦𝑏𝑖 𝑡𝑏𝑖 (2𝐻𝑏𝑖 − 4𝑡𝑏𝑖 + 𝐵𝑏𝑖 + 𝑏𝑒𝑜𝑣 )
(11-47)
𝐹𝑦 𝑡
10
(
) 𝐵 ≤ 𝐵𝑏𝑖
𝐵⁄𝑡 𝐹𝑦𝑏𝑖 𝑡𝑏𝑖 𝑏𝑖
(11-48)
𝐹𝑦𝑏𝑗 𝑡𝑏𝑗
10
(
) 𝐵𝑏𝑖 ≤ 𝐵𝑏𝑖
𝐵𝑏𝑗 ⁄𝑡𝑏𝑗 𝐹𝑦𝑏𝑖 𝑡𝑏𝑖
(11-49)
𝑏𝑒𝑜𝑖 =
𝑏𝑒𝑜𝑣 =
Subscript i refers to the overlapping branch
Subscript j refers to the overlapped branch
𝐹𝑦𝑏𝑗 𝐴𝑏𝑗
𝑃𝑛,𝑗 = 𝑃𝑛,𝑖 (
)
(11-50)
𝐹𝑦𝑏𝑖 𝐴𝑏𝑖
FUNCTIONS
Qf = 1 for chord (connecting surface) in tension
for chord (connecting surface) in
𝑈
= 1.3 − 0.4 ≤ 1
compression, for T-, Y- and K-cross𝛽
connections
𝑈
for chord (connecting surface) in
= 1.3 − 0.4
≤ 1.0
compression, for gapped K-connections
𝛽𝑒𝑓𝑓
𝑈=|
𝑃𝑢
𝑀𝑢
|
+
𝐹𝑦 𝐴𝑔 𝐹𝑦 𝑆
(11-51)
(11-52)
(11-53)
(11-54)
where Pu and Mu are determined on the side of the joint that has the higher compression stress. Pu and
Mu refer to required strengths in the HSS.
𝛽𝑒𝑓𝑓 = [(𝐵𝑏 + 𝐻𝑏 )𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑜𝑛 𝑏𝑟𝑎𝑛𝑐ℎ + (𝐵𝑏 + 𝐻𝑏 )𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑏𝑟𝑎𝑛𝑐ℎ ]/4𝐵
(11-55)
5𝛽
(11-56)
𝛽𝑒𝑜𝑝 =
≤𝛽
𝛾
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-8: LIMITS OF APPLICABILITY OF TABLE 11-7
Joint eccentricity:
Branch angle:
Chord wall
slenderness:
Branch wall
slenderness:
−0.55 ≤ 𝑒⁄𝐻 ≤ 0.25 for K connections
≥ 30°
𝐵⁄𝑡 and 𝐻 ⁄𝑡 ≤ 35 for gapped K-connections and T-, Y- and cross-connections
𝐵⁄𝑡 ≤ 30 for overlapped K-connections
𝐻 ⁄𝑡 ≤ 35 for overlapped K-connections
𝐵𝑏 ⁄𝑡 𝑏 and 𝐻𝑏 ⁄𝑡 𝑏 ≤ 35 for tension branch
≤ 1.25√
𝐸
𝐹𝑦𝑏
For compression branch of gapped K-, T-, Y- and crossconnections
≤ 35 for compression branch of gapped K-, T-, Y- and cross-connections
≤ 1.1√
Width ratio:
Aspect ratio:
Overlap:
Branch width
ratio:
Branch thickness
ratio:
Material strength:
Ductility:
𝐸
𝐹𝑦𝑏
For compression branch of overlapped K-connections
𝐵𝑏 ⁄𝐵 and 𝐻𝑏 ⁄𝐵 ≥ 0.25 for T-, Y- cross- and overlapped K-connections
0.5 ≤ 𝐻𝑏 ⁄𝐵𝑏 ≤ 2.0 and 0.5 ≤ H /B ≤ 2.0
25% ≤ 𝑂𝑣 ≤ 100% for overlapped K-connections
𝐵𝑏𝑖 ⁄𝐵𝑏𝑗 ≤ 0.75 for overlapped K-connections, where subscript i refers to the
overlapping branch and subscript j refers to the overlapped branch
𝑡𝑏𝑖 ⁄𝑡𝑏𝑗 ≤ 1.0 for overlapped K-connections, where subscript i refers to the
overlapping branch and subscript j refers to the overlapped branch
Fy and 𝐹𝑦𝑏 ≤ 360MPa
𝐹𝑦 ⁄𝐹𝑢 and 𝐹𝑦𝑏 ⁄𝐹𝑢𝑏 ≤ 0.8 Note: ASTM A500 Grade C is acceptable
ADDITIONAL LIMITS FOR GAPPED K-CONNECTIONS
Width ratio:
𝐵𝑏
𝐵
and
𝐻𝑏
𝐵
≥ 0.1 +
𝛾
50
eff ≥ 0.35
𝜁 = 𝑔⁄𝐵 ≥ 0.5(1 − 𝛽𝑒𝑓𝑓 )
Gap ratio:
𝑔 ≥ 𝑡𝑏(𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑜𝑛 𝑏𝑟𝑎𝑛𝑐ℎ) + 𝑡𝑏(𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑏𝑟𝑎𝑛𝑐ℎ)
Gap:
smaller 𝐵𝑏 ≥ 0.63 ( larger Bb ), if both branches are square
Branch size:
Note: Maximum gap size will be controlled by the e /H limit. If gap is large, treat as two Y-connections.
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-9 : DESIGN STRENGTHS OF ROUND HSS-TO-HSS MOMENT CONNECTIONS
Connection Type
Branch(es) under In-Plane Bending T-, Yand Cross-Connections
Connection Design Flexural Strength
Limit State: Chord Plastification
𝑀𝑛 𝑠𝑖𝑛 𝜃 = 5.39𝐹𝑦 𝑡 2 𝛾 0.5 𝛽𝐷𝑏 𝑄𝑓
(11-57)
𝜑 = 0.90
Limit State: Shear Yielding (Punching), When 𝐷𝑏 <
(𝐷 − 2𝑡)
1
+ 3 𝑠𝑖𝑛 𝜃
(11-58)
)
𝑀𝑛 = 0.6𝐹𝑦 𝑡𝐷𝑏2 (
4 𝑠𝑖𝑛2 𝜃
𝜑 = 0.95
Branch(es) under Out-of-Plane Bending T, Y- and Cross-Connections
Limit State: Chord Plastification
3.0
)𝑄
𝑀𝑛 𝑠𝑖𝑛 𝜃 = 𝐹𝑦 𝑡 2 𝐷𝑏 (
(11-59)
1 − 0.81𝛽 𝑓
𝜑 = 0.90
Limit State: Shear Yielding (Punching), When 𝐷𝑏 <
(𝐷 − 2𝑡)
3 + 𝑠𝑖𝑛 𝜃
(11-60)
)
𝑀𝑛 = 0.6𝐹𝑦 𝑡𝐷𝑏2 (
4 𝑠𝑖𝑛2 𝜃
𝜑 = 0.95
For T-, Y- and cross-connections, with branch(es) under combined axial load, in-plane bending and
out-of-plane bending, or any combination of these load effects:
2
𝑀𝑟−𝑖𝑝
𝑀𝑟−𝑜𝑝
𝑃𝑟
(11-61)
+(
) +(
) ≤ 1.0
𝑃𝑐
𝑀𝑐−𝑖𝑝
𝑀𝑐−𝑜𝑝
𝑀𝑐−𝑖𝑝 = 𝜑𝑀𝑛 = design flexural strength for in-plane bending from TABLE 11-9, N-mm
𝑀𝑐−𝑜𝑝 = 𝜑𝑀𝑛 = design flexural strength for out-of-plane bending from TABLE 11-9, N-mm
M r-ip = required flexural strength for in-plane bending, N-mm
M r-op = required flexural strength for out-of-plane bending, N-mm
𝑃𝑐
= 𝜑𝑃𝑛 = design axial strength from TABLE 11-5, N
Pr
= required axial strength, N
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-9 (CONTINUED): DESIGN STRENGTHS OF ROUND HSS-TO-HSS MOMENT
CONNECTIONS
FUNCTIONS
Qf = 1 for chord (connecting surface) in tension
= 1.0 − 0.3𝑈(1 + 𝑈) for HSS (connecting surface) in compression
𝑈=|
𝑃𝑢
𝐹𝑦 𝐴𝑔
+
𝑀𝑢
𝐹𝑦 𝑆
|
(11-62)
(11-63)
where Pu and Mu are determined on the side of the joint that has the lower compression stress. Pu and Mu
refer to required strengths in the HSS.
TABLE 11-10: LIMITS OF APPLICABILITY OF TABLE 11-9
Branch angle:
Chord wall slenderness:
Branch wall slenderness:
Width ratio:
Material strength:
Ductility:
≥ 30°
𝐷⁄𝑡 ≤ 50 for T- and Y-connections
𝐷⁄𝑡 ≤ 40 for cross connections
𝐷𝑏 ⁄𝑡 𝑏 ≤ 50
𝐷𝑏 ⁄𝑡𝑏 ≤ 0.05 𝐸 ⁄𝐹𝑦𝑏
0.2 < 𝐷𝑏 ⁄𝐷 ≤ 1.0
Fy and 𝐹𝑦𝑏 ≤ 360 MPa
𝐹𝑦 ⁄𝐹𝑢 and 𝐹𝑦𝑏 ⁄𝐹𝑢𝑏 ≤ 0.8 Note: ASTM A500 Grade C is acceptable
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-11 : DESIGN STRENGTHS OF RECTANGULAR HSS-TO-HSS MOMENT
CONNECTIONS
Connection Type
Branch(es) under In-Plane Bending Tand Cross-Connections
Connection Design Flexural Strength
Limit State: Chord Wall Plastification, When 𝛽 ≤ 0.85
𝑀𝑛 = 𝐹𝑦 𝑡 2 𝐻𝑏 [
1
2𝜂
+
2
√1−𝛽
𝜂
+ (1−𝛽)] 𝑄𝑓
𝜑 = 1.00
Limit State: Sidewall Local Yielding,
When 𝛽 > 0.85
∗
𝑀𝑛 = 0.5𝐹𝑦 𝑡(𝐻𝑏 + 5𝑡)2
𝜑 = 1.00
(11-64)
(11-65)
Limit State: Local Yielding of Branch/Branches Due to
Uneven Load Distribution, When 𝛽 > 0.85
𝑏𝑒𝑜𝑖
) 𝐵𝑏 𝐻𝑏 𝑡𝑏 ]
(11-66)
𝑀𝑛 = 𝐹𝑦𝑏 [𝑍𝑏 − (1 −
𝐵𝑏
𝜑 = 0.95
Branch(es) under Out-of-Plane Bending
T- and Cross-Connections
Limit State: Chord Wall Plastification,
When 𝛽 ≤ 0.85
𝑀𝑛 = 𝐹𝑦 𝑡 2 [
0.5𝐻𝑏 (1 + 𝛽)
2𝐵𝐵𝑏 (1 + 𝛽)
+√
] 𝑄𝑓
(1 − 𝛽)
(1 − 𝛽)
(11-67)
𝜑 = 1.00
Limit State: Sidewall Local Yielding,When 𝛽 > 0.85
𝑀𝑛 = 𝐹𝑦∗ 𝑡(𝐵 − 𝑡) (𝐻𝑏 + 5𝑡)
(11-68)
𝜑 = 1.00
Limit State: Local Yielding of Branch/Branches Due to
Uneven Load Distribution, When 𝛽 > 0.85
𝑏
2
𝑀𝑛 = 𝐹𝑦𝑏 [𝑍𝑏 − 0.5 (1 − 𝑒𝑜𝑖 ) 𝐵𝑏2 𝑡𝑏 ]
𝐵𝑏
(11-69)
𝜑 = 0.95
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-11 (CONTINUED): DESIGN STRENGTHS OF RECTANGULAR HSS-TO-HSS
MOMENT CONNECTIONS
Connection Type
Branch(es) under Out-of-Plane Bending
T- and Cross-Connections (continued)
Connection Design Flexural Strength
Limit State: Chord Distortional Failure, for
T-Connections and Unbalanced Cross-Connections
(11-70)
𝑀𝑛 = 2𝐹𝑦 𝑡 [𝐻𝑏 𝑡 + √𝐵𝐻𝑡(𝐵 + 𝐻)]
𝜑 = 1.00
For T- and cross-connections, with branch(es) under combined axial load, in-plane bending and outof-plane bending, or any combination of these load effects:
𝑀𝑟−𝑖𝑝
𝑀𝑟−𝑜𝑝
𝑃𝑟
+(
)+(
) ≤ 1.0
(11-71)
𝑃𝑐
𝑀𝑐−𝑖𝑝
𝑀𝑐−𝑜𝑝
𝑀𝑐−𝑖𝑝 = 𝜑𝑀𝑛 = design flexural strength for in-plane bending from TABLE 11-11,
N-mm
𝑀𝑐−𝑜𝑝 = 𝜑𝑀𝑛 = design flexural strength for out-of-plane bending from TABLE 11-11, N-mm
Mr-ip = required flexural strength for in-plane bending, N-mm
Mr-op = required flexural strength for out-of-plane bending, N-mm
𝑃𝑐
= 𝜑𝑃𝑛 = design axial strength from TABLE 11-7, N
Pr = required axial strength, N
FUNCTIONS
Qf = 1 for chord (connecting surface) in tension
(11-72)
𝑈
= 1.3 − 0.4 ≤ 1.0 for chord (connecting surface) in compression
(11-73)
𝛽
𝑃𝑢
𝑀𝑢
|
+
(11-9)(11-74)
𝐹𝑦 𝐴𝑔 𝐹𝑦 𝑆
where Pu and Mu are determined on the side of the joint that , has the lower compression stress. Pu and
Mu refer to required strengths in the HSS.
𝐹𝑦∗ = 𝐹𝑦 for T-connections and = 0.8𝐹𝑦 for cross-connections
𝐹𝑦 𝑡
10
𝑏𝑒𝑜𝑖 =
(
) 𝐵 ≤ 𝐵𝑏
(11-75)
𝐵⁄𝑡 𝐹𝑦𝑏 𝑡𝑏 𝑏
𝑈 =|
TABLE 11-12: LIMITS OF APPLICABILITY OF TABLE 11-11
Branch angle:
Chord wall slenderness:
Branch wall slenderness:
𝜃 ≅ 90𝑜
𝐵⁄𝑡 and 𝐻 ⁄𝑡 ≤ 35
B b /tb and 𝐻𝑏 ⁄𝑡𝑏 ≤ 35
≤ 1.25√
Width ratio:
Aspect ratio:
Material strength:
Ductility:
𝐸
𝐹𝑦𝑏
𝐵𝑏 ⁄𝐵 ≥ 0.25
0.5 ≤ 𝐻𝑏 ⁄𝐵𝑏 ≤ 2.0 and 0.5 ≤ 𝐻 ⁄𝐵 ≤ 2.0
Fy and 𝐹𝑦𝑏 ≤ 360MPa
𝐹𝑦 ⁄𝐹𝑢 and 𝐹𝑦𝑏 ⁄𝐹𝑢𝑏 ≤ 0.8 Note: ASTM A500 Grade C is acceptable
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-13 : EFFECTIVE WELD PROPERTIES FOR CONNECTIONS TO RECTANGULAR
HSS
Connection Type
Connection Weld Strength
Transverse Plate T- and Cross- Connections
Under Plate Axial Load
Effective Weld Properties
𝐹𝑦 𝑡
10
)(
𝑙𝑒 = 2 (
) 𝐵 ≤ 2𝐵𝑝
𝐵⁄𝑡 𝐹𝑦𝑝 𝑡𝑝 𝑝
(11-76)
where le = total effective weld length for welds on both
sides of the transverse plate
T-, Y- and Cross-Connections Under Branch
Axial Load or Bending
Effective Weld Properties
2𝐻𝑏
(11-77)
𝑙𝑒 =
+ 2𝑏𝑒𝑜𝑖
𝑠𝑖𝑛 𝜃
𝑡𝑤 𝐻𝑏 2
𝐻𝑏
(11-78)
) + 𝑡𝑤 𝑏𝑒𝑜𝑖 (
)
𝑆𝑖𝑝 = (
3 𝑠𝑖𝑛 𝜃
𝑠𝑖𝑛 𝜃
(𝑡𝑤 ⁄3)(𝐵𝑏 − 𝑏𝑒𝑜𝑖 )3
𝐻𝑏
𝑡𝑤
) 𝐵𝑏 + (𝐵𝑏2 ) −
𝑆𝑜𝑝 = 𝑡𝑤 (
𝑠𝑖𝑛 𝜃
3
𝐵𝑏
(11-79)
𝐹𝑦 𝑡
10
𝑏𝑒𝑜𝑖 =
(
) 𝐵 ≤ 𝐵𝑏
(11-80)
𝐵⁄𝑡 𝐹𝑦𝑏 𝑡𝑏 𝑏
When 𝛽 > 0.85 or 𝜃 > 50𝑜 , beoi/2 shall not exceed 2t.
Gapped K-Connections Under Branch
Axial Load
Effective Weld Properties
When 𝜃 ≤ 50𝑜 :
2(𝐻𝑏 − 1.2𝑡𝑏 )
𝑙𝑒 =
+ 2(𝐵𝑏 − 1.2𝑡𝑏 )
𝑠𝑖𝑛 𝜃
When 𝜃 ≥ 60𝑜 ,
2(𝐻𝑏 − 1.2𝑡𝑏 )
𝑙𝑒 =
+ (𝐵𝑏 − 1.2𝑡𝑏 )
𝑠𝑖𝑛 𝜃
(11-81)
(11-82)
When 50° < < 60 linear interpolation shall be used to
determine le .
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CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
TABLE 11-13 (CONTINUED): EFFECTIVE WELD PROPERTIES FOR CONNECTIONS TO
RECTANGULAR HSS
Connection Type
Overlapped K-Connections under Branch
Axial Load
Note that the force arrows shown for
overlapped K-connections may be reversed;
i and j control member identification
Effective Weld: Eq. (11-88)
When 𝐵𝑏𝑗 ⁄𝐵 ≤ 0.85 and 𝜃𝑗 ≤ 50𝑜
When 𝐵𝑏𝑗 ⁄𝐵 > 0.85 and 𝜃𝑗 > 50𝑜
Connection Weld Strength
Overlapping Member Effective Weld Properties (all
dimensions are for the overlapping branch, i )
When 25% ≤ Ov < 50%:
2𝑂𝑣
𝑂𝑣
𝐻𝑏𝑖
𝑂𝑣
𝐻𝑏𝑖
[(1 −
)(
)+
𝑙𝑒,𝑖 =
(
)]
50
100 𝑠𝑖𝑛 𝜃𝑖
100 𝑠𝑖𝑛(𝜃𝑖 + 𝜃𝑗 )
+ 𝑏𝑒𝑜𝑖 + 𝑏𝑒𝑜𝑣
(11-83)
When 50% ≤ Ov < 80%:
𝑂𝑣
𝐻𝑏𝑖
)(
)
𝑙𝑒,𝑖 = 2 [(1 −
100 𝑠𝑖𝑛 𝜃𝑖
𝑂𝑣
𝐻𝑏𝑖
(11-84)
+
(
)] + 𝑏𝑒𝑜𝑖
100 𝑠𝑖𝑛(𝜃𝑖 + 𝜃𝑗 )
+ 𝑏𝑒𝑜𝑣
When 80% ≤ Ov ≤ 100%:
𝑂𝑣
𝐻𝑏𝑖
)(
)
𝑙𝑒,𝑖 = 2 [(1 −
100 𝑠𝑖𝑛 𝜃𝑖
𝑂𝑣
𝐻𝑏𝑖
(11-85)
+
(
)] + 𝐵𝑏𝑖
100 𝑠𝑖𝑛(𝜃𝑖 + 𝜃𝑗 )
+ 𝑏𝑒𝑜𝑣
𝐹𝑦 𝑡
10
𝑏𝑒𝑜𝑖 =
(
) 𝐵 ≤ 𝐵𝑏𝑖
(11-86)
𝐵⁄𝑡 𝐹𝑦𝑏𝑖 𝑡𝑏𝑖 𝑏𝑖
𝐹𝑦𝑏𝑗 𝑡𝑏𝑗
10
𝑏𝑒𝑜𝑣 =
(
) 𝐵𝑏𝑖 ≤ 𝐵𝑏𝑖
(11-87)
𝐵𝑏𝑗 ⁄𝑡𝑏𝑗 𝐹𝑦𝑏𝑖 𝑡𝑏𝑖
when Bbi /Bb > 0.85 or i > 50°, beoi /2 shall not
exceed 2t and when Bbi /Bbj > 0.85 or
(180 − 𝜃𝑖 − 𝜃𝑗 ) > 50𝑜 , beov /2 shall not exceed 2tbj
Subscript i refers to the overlapping branch
Subscript j refers to the overlapped branch
2𝐻𝑏𝑗
𝑙𝑒,𝑗 =
+ 2𝑏𝑒𝑜𝑗
𝑠𝑖𝑛 𝜃𝑗
𝐹𝑦 𝑡
10
𝑏𝑒𝑜𝑗 =
(
) 𝐵 ≤ 𝐵𝑏𝑗
𝐵⁄𝑡 𝐹𝑦𝑏𝑗 𝑡𝑏𝑗 𝑏𝑗
When Bbj /B > 0.85 or j > 50°,
𝑙𝑒,𝑗 = 2 (𝐻𝑏𝑗 − 1.2𝑡𝑏𝑗 )⁄𝑠𝑖𝑛 𝜃𝑗
SBC 306-CR-18
(11-88)
(11-89)
141
CHAPTER 11—DESIGN OF HSS AND BOX MEMBER CONNECTIONS
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SBC 306-CR-18
142
CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL
STEEL BUILDINGS
This chapter governs the design of earthquakeresistant steel structures. The chapter is organized
as follows:
12.1 —General Requirements
and
3. eccentrically braced frames
4. composite ordinary moment frames
5. composite intermediate moment frames
12.2 —General Seismic Design Requirements
12.3 —Moment-Frame
Systems
2. ordinary concentrically braced frames
Braced-Frame
12.4 —Composite Moment-Frame and BracedFrame Systems
12.5 —Fabrication and Erection
12.6 —Quality Control and Quality Assurance
12.7 Prequalification and cyclic qualification
testing provisions
12.1—General Requirements
The provisions of this chapter shall be applied in
conjunction with applicable requirements of this
code.
12.1.1 Scope. The seismic provisions in this
chapter shall apply to the design, fabrication and
erection of steel structures in Seismic Design
Categories (SDC) B through D. Structures assigned
to Seismic Design Category E or F shall be designed
and detailed in accordance with ANSI/AISC 341.
Where, applicable, the provisions in this chapter
shall apply to the design of structural steel members
and connections in the seismic force resisting
systems (SFRS), and splices and bases of columns
in gravity framing systems of buildings and other
structures with moment frames, braced frames and
composite systems. Other structures are defined as
those structures designed, fabricated and erected in
a manner similar to buildings, with building-like
vertical and lateral force-resisting-elements. The
seismic force resisting systems shall be of structural
steel or of structural steel acting compositely with
reinforced concrete, unless specifically exempted
by other Saudi building codes. The provisions in
this chapter covers only the following types of
SFRSs: ordinary and intermediate moment frames
1. ordinary column cantilever systems
6. composite ordinary braced frames
For other SFRSs refer to ANSI/AISC 341.
Saudi Building Code requirements for Concrete
Structures (SBC 304), as modified in this chapter,
shall be used for the design and construction of
reinforced concrete components in composite
construction.
User Note: SBC 301 (Table 12-1) specifically
exempts structural steel systems assigned to
SDCs B and C, but not composite systems,
from the provision of this chapter if the seismic
loads are computed using a response
modification coefficient, R of 3. For Seismic
Design Category A, SBC 301 specifies lateral
forces to be used as the seismic loads and
effects that do not involve the use of a response
modification coefficient. Thus for Seismic
Design Category A it is not necessary to define
a seismic force resisting system that meets any
special requirements and the provisions of this
chapter do not apply.
SBC 301 (Table 15-1) permits certain nonbuilding structures to be designed in
accordance with the applicable requirements of
this Code with an appropriately reduced R
factor and are not required to satisfy the
provisions of this chapter.
User Note: Composite seismic force resisting
systems include those systems with members
of structural steel acting compositely with
reinforced concrete, as well as systems in
which structural steel members and reinforced
concrete members act together to form a
seismic force resisting system.
12.1.2 Materials
SBC 306-CR-18
143
CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
12.1.2.1
Material
Specifications.
Structural steel used in SFRS shall satisfy the
requirements of Section 1.3.1 , except as modified
in this chapter. The specified minimum yield stress
of steel to be used for members in which inelastic
behavior is expected shall not exceed 345 MPa for
systems defined in Sections 12.3.2 , 12.3.3 and
12.4.2 . For systems defined in Sections 12.3.1 ,
12.3.4 , 12.4.1 and 12.4.3 such limits shall not
exceed 380 MPa. Either of these specified
minimum yield stress limits are permitted to be
exceeded when the suitability of the material is
determined by testing or other rational criteria.
Exception: Specified minimum yield stress of
structural steel shall not exceed 450 MPa for
columns in systems defined in Sections 12.3.4 and
12.4.3 .
The structural steel used in the SFRS described in
Sections 12.3 and 12.4 shall meet one of the
following ASTM Specifications:
1. A36/A36M
2. A53/A53M
3. A500/A500M (Gr. B or C)
4. A501
5. A529/A529M
6. A572/A572M [Gr. 42 (290), 50 (345) or 55
(380)]
7. A588/A588M
12.1.2.2
Expected Material Strength.
When required in this chapter, the required strength
of an element (a member or a connection of a
member) shall be determined from the expected
yield stress, RyFy, of the member or an adjoining
member, as applicable, where Fy is the specified
minimum yield stress of the steel to be used in the
member and Ry is the ratio of the expected yield
stress to the specified minimum yield stress, Fy , of
that material.
When required to determine the nominal strength,
Rn, for limit states within the same member from
which the required strength is determined, the
expected yield stress, RyFy, and the expected tensile
strength, RtFu, are permitted to be used in lieu of Fy
and Fu, respectively, where Fu is the specified
minimum tensile strength and Rt is the ratio of the
expected tensile strength to the specified minimum
tensile strength, Fu, of that material.
The values of Ry and Rt for various steel and steel
reinforcement materials are given in TABLE 12-1.
Other values of Ry and Rt are permitted if the values
are determined by testing of specimens, similar in
size and source to the materials to be used,
conducted in accordance with the testing
requirements per the ASTM Specifications for the
specified grade of steel.
User Note: The expected compressive strength
of concrete may be estimated using values from
Seismic Rehabilitation of Existing Buildings,
ASCE/SEI 41-06.
8. A913/A913M [Gr. 50 (345), 60 (415) or 65
(450)]
9. A992/A992M
10. A1011/A1011M HSLAS Gr. 55 (380)
11. (A1043/A1043M
The structural steel used for column base plates
shall meet one of the preceding ASTM
Specifications or ASTM A283/A283M Grade D.
User Note: This section only covers material
properties for structural steel used in the SFRS
and included in the definition of structural steel
given in Section 2.1 of the AISC Code of
Standard Practice, AISC (2010a). Other steel,
such as cables for permanent bracing, is not
covered. Steel reinforcement used in
components in composite SFRS is covered in
Section 12.1.2.5 .
12.1.2.3
Heavy Sections. For structural
steel in the SFRS, in addition to the requirements of
Section 1.3.1.3 , hot rolled shapes with flanges 38
mm thick and thicker shall have a minimum Charpy
V-notch toughness of 27 J at 21 °C, tested in the
alternate core location as described in ASTM A6
Supplementary Requirement S30. Plates 50 mm
thick and thicker shall have a minimum Charpy Vnotch toughness of 27 J at 21 °C, measured at any
location permitted by ASTM A673, Frequency P,
where the plate is used for the following:
(a) Members built up from plate
(b) Connection plates where inelastic strain under
seismic loading is expected
(c) The steel core of buckling-restrained braces.
12.1.2.4
Consumables for Welding
12.1.2.4.1
Seismic Force Resisting System
Welds. All welds used in members and connections
SBC 306-CR-18
144
CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
in the SFRS shall be made with filler metals
meeting the requirements specified in clause 6.3 of
Structural Welding Code—Seismic Supplement
(AWS D1.8/D1.8M), hereafter referred to as AWS
D1.8/D1.8M.
User Note: AWS D1.8/D1.8M sub-clauses
6.3.5, 6.3.6, 6.3.7 and 6.3.8 apply only to
demand critical welds.
12.1.2.4.2
Demand Critical Welds. Welds
designated as demand critical shall be made with
filler metals meeting the requirements specified in
AWS D1.8/D1.8M clause 6.3.
User Note: AWS D1.8/D1.8M requires that all
seismic force resisting system welds are to be
made with filler metals classified using AWS
A5 standards that achieve the following
mechanical properties:
Filler Metal Classification Properties for
Seismic Force Resisting System Welds
Classification
Property
480 MPa
550 MPa
Strength, 400 min.
470 min.
Tensile Strength, 480 min.
MPa
550 min.
Elongation, %
19 min.
Yield
MPa
22 min.
Mechanical Properties for Demand Critical
Welds
Classification
Property
480 MPa
550 MPa
Yield
400 min.
Strength, MPa
470 min.
Tensile
480 min.
Strength, MPa
550 min.
Elongation, %
22 min.
19 min.
CVN
Toughness,
(J)
54 min. @ 20 °Cb, c
b
For LAST of +10 °C. For LAST less than
+10 °C, see AWS D1.8/D1.8M sub-clause
6.3.6.
c
Tests conducted in accordance with AWS
D1.8/D1.8M Annex A meeting 54 J min. at
a temperature lower than +20 °C also meet
this requirement.
12.1.2.5
Concrete
and
Steel
Reinforcement. Concrete and steel reinforcement
used in composite components in composite
intermediate SFRS of Section 12.4.2 shall satisfy
the requirements of SBC 304, Chapter 18. Concrete
and steel reinforcement used in composite
components in composite ordinary SFRS of
Sections 12.4.1 and 12.4.3 shall satisfy the
requirements of SBC 304, Section 18.2.1.4.
CVN Toughness, 27 min. @ -18 °Ca
(J)
12.1.3 Structural
Specifications
a
Filler metals classified as meeting 27 J min.
at a temperature lower than
−18 °C also meet this requirement.
User Note: In addition to the above
requirements, AWS D1.8/D1.8M requires,
unless otherwise exempted from testing, that
all demand critical welds are to be made with
filler metals receiving Heat Input Envelope
Testing that achieve the following mechanical
properties in the weld metal:
Design
Drawings
and
12.1.3.1
General.
Structural
design
drawings and specifications shall indicate the work
to be performed, and include items required by this
Code, the AISC Code of Standard Practice for Steel
Buildings and Bridges, AISC (2010a), and SBC
201, in addition to the followings, as applicable:
1. Designation of the SFRS
2. Identification of the members and
connections that are part of the SFRS
3. Locations and dimensions of protected
zones
SBC 306-CR-18
145
CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
4. Connection details between concrete floor
diaphragms and the structural steel
elements of the SFRS
5. Shop drawing and erection drawing
requirements not addressed in Section
12.5.1
12.1.3.2
Steel Construction. In addition to
the requirements of Section 12.1.3.1 , structural
design drawings and specifications for steel
construction shall indicate the following items, as
applicable:
1. Configuration of the connections
2. Connection material specifications and
sizes
3. Locations of demand critical welds
for the steel components of reinforced concrete or
composite elements, structural design drawings and
specifications for composite construction shall
indicate the following items, as applicable:
1. Bar placement, cutoffs, lap and mechanical
splices, hooks and mechanical anchorage,
placement of ties and other transverse
reinforcement
2. Requirements for dimensional changes
resulting from temperature changes, creep
and shrinkage
3. Location, magnitude and sequencing of
any prestressing or post-tensioning present
4. Location of steel headed stud anchors and
welded reinforcing bar anchors
4. Locations where gusset plates are to be
detailed to accommodate inelastic rotation
12.2—General Seismic Design
Requirements
5. Locations of connection plates requiring
Charpy V-notch (CVN) toughness in
accordance with Section 12.1.2.3
The required strength and other seismic design
requirements for seismic design categories (SDCs),
risk categories, and the limitations on height and
irregularity shall be as specified in SBC 301.
6. Lowest anticipated service temperature
(LAST) of the steel structure, if the
structure is not enclosed and maintained at
a temperature of 10 °C or higher
7. Locations where weld backing is required
to be removed
8. Locations where fillet welds are required
when weld backing is permitted to remain
9. Locations where fillet welds are required
to reinforce groove welds or to improve
connection geometry
10. Locations where weld tabs are required to
be removed
11. Splice locations where tapered transitions
are required
12. The shape of weld access holes, if a shape
other than those provided in the Code are
required
13. Joints or groups of joints in which a
specific
assembly
order,
welding
sequence, welding technique or other
special precautions where such items are
designated to be submitted to the engineer
of record
12.1.3.3
Composite Construction.
In
addition to the requirements of Section 12.1.3.1 and
the requirements of Section 12.1.3.2 as applicable
The design story drift and the limitations on story
drift shall be determined as required in SBC 301.
12.2.1 Loads and Load Combinations. The
loads and load combinations shall be as stipulated
by SBC 301. Unless otherwise defined in these
provisions, where amplified seismic loads are
required by this chapter, the seismic load effect
including the system overstrength factor Ωo shall be
applied as prescribed by SBC 301. Where the
effects of horizontal forces including overstrength,
Emh, are defined in this chapter they shall be
combined with the vertical seismic load effect as
required by SBC 301.
User Note: The seismic load effect including
the system overstrength factor is defined in
SBC 301 Section 12.4.3. Where Emh is defined
in this chapter, it is intended to replace Emh in
SBC 301 Section 12.4.3.
In composite construction, incorporating reinforced
concrete components designed in accordance with
the requirements of SBC 304, the requirements of
Section 2.3.3 shall be used for the seismic force
resisting system (SFRS).
User Note: Ωo should be determined in
accordance with SBC 301.
12.2.2 Design Basis
SBC 306-CR-18
146
CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
12.2.2.1
Required Strength. The required
strength of structural members and connections
shall be the greater of:
1. The required strength as determined by
structural analysis for the appropriate load
combinations, as stipulated in SBC 301
and in Section 12.2.4
2. The required strength given in Sections
12.3 and 12.4
12.2.2.2
Design Strength. The design
strength of systems, members and connections,
stipulated as the design strength 𝜑 𝑅𝑛 , shall be
determined in accordance with applicable
requirements of this Code, except as modified
throughout the provisions of this chapter.
12.2.3 System Type. The seismic force resisting
system (SFRS) shall contain one or more moment
frame, braced frame or composite system
conforming to the requirements of one of the
seismic systems designated in Sections 12.3 and
12.4.
12.2.4 Analysis. An analysis conforming to the
requirements of the SBC 301 and this Code shall be
performed for design of the system. When the
design is based upon elastic analysis, the stiffness
properties of component members of steel systems
shall be based on elastic sections and those of
composite systems shall include the effects of
cracked sections. Additional analysis shall be
performed as specified in Sections 12.3 and 12.4.
When nonlinear analysis is required it shall be
performed in accordance with Chapter 12 of SBC
301.
12.2.5 Member Requirements. Members of
moment frames and braced frames in the seismic
force resisting system (SFRS) shall comply with
applicable requirements of this Code and this
section. Certain members of the SFRS that are
expected to undergo inelastic deformation under the
design earthquake are designated in this chapter as
moderately ductile members or highly ductile
members.
12.2.5.1
Classification of Sections for
Ductility. When required for the systems defined
in Sections 12.3, 12.4 and 12.2.5.5 , members
designated as moderately ductile members or highly
ductile members shall comply with this section.
members shall have flanges continuously connected
to the web or webs.
Encased composite columns shall comply with the
requirements of Section 12.2.5.4.2.1 for moderately
ductile members and Section 12.2.5.4.2.2 for highly
ductile members.
Filled composite columns shall comply with the
requirements of Section 12.2.5.4.3 for both
moderately and highly ductile members.
Concrete sections shall comply with the
requirements of SBC 304 Section 18.4 for
moderately ductile members and SBC 304 Section
18.7 for highly ductile members.
12.2.5.1.2
Width-to-Thickness Limitations
of Steel and Composite Sections. For members
designated as moderately ductile members, the
width-to-thickness ratios of compression elements
shall not exceed the limiting width-to-thickness
ratios, λmd, from TABLE 12-2.
For members designated as highly ductile members,
the width-to-thickness ratios of compression
elements shall not exceed the limiting width-tothickness ratios, λhd, from TABLE 12-2.
12.2.5.2
Stability Bracing of Beams.
When required in Sections 12.3 and 12.4, stability
bracing shall be provided as required in this section
to restrain lateral-torsional buckling of structural
steel or concrete-encased beams subject to flexure
and designated as moderately ductile members or
highly ductile members.
12.2.5.2.1
i.
Moderately Ductile Members
The bracing of moderately ductile steel
beams shall satisfy the following
requirements:
1. Both flanges of beams shall be laterally
braced or the beam cross section shall be
torsionally braced
2. Beam bracing shall meet the requirements
of Appendix E of the Code for lateral or
torsional bracing of beams, where the
required flexural strength of the member,
Mr, shall be:
𝑀𝑟 = 𝑅𝑦 𝐹𝑦 𝑍
(12-1)
where
12.2.5.1.1
Section
Requirements
for
Ductile Members. Structural steel sections for both
moderately ductile members and highly ductile
SBC 306-CR-18
Ry = ratio of the expected yield stress to the
specified minimum yield Stress
Z = plastic section modulus, mm3
147
CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
3.
Beam bracing shall have a maximum
spacing of
𝐿𝑏 = 0.17𝑟𝑦 𝐸/𝐹𝑦
ii.
(12-2)
2. The required strength of lateral bracing of
each flange provided adjacent to plastic
hinges shall be:
𝑃𝑢 = 0.06𝑅𝑦 𝐹𝑦 𝑍/ℎ𝑜
(12-4)
The bracing of moderately ductile concreteencased composite beams shall satisfy the
following requirements:
where
1. Both flanges of members shall be laterally
braced or the beam cross section shall be
torsionally braced
The required strength of torsional bracing provided
adjacent to plastic hinges shall be:
2.
Lateral bracing shall meet the
requirements of Appendix E for lateral or
torsional bracing of beams, where Mr =
Mp,exp and
Mp,exp = expected flexural strength of
beams, N-mm. For concrete-encased or
composite beams, Mp,exp shall be calculated
using the plastic stress distribution or the
strain compatibility method. Appropriate
Ry factors shall be used for different
elements of the cross-section while
establishing section force equilibrium and
calculating the flexural strength.
3. Member bracing shall have a maximum
spacing of
𝐿𝑏 = 0.17𝑟𝑦 𝐸/𝐹𝑦
(12-3)
ho = distance between flange centroids, mm
𝑀𝑢 = 0.06𝑅𝑦 𝐹𝑦 𝑍
3. The required bracing stiffness shall satisfy
the requirements of Appendix E for lateral
or torsional bracing of beams with Cd = 1.0
and where the expected flexural strength of
the beam shall be:
𝑀𝑟 = 𝑀𝑢 = 𝑅𝑦 𝐹𝑦 𝑍
12.2.5.2.3
Special Bracing at Plastic Hinge
Locations. Special bracing shall be located
adjacent to expected plastic hinge locations where
required by Sections 12.3 and 12.4.
For structural steel beams, such bracing shall
satisfy the following requirements:
1. Both flanges of beams shall be laterally
braced or the member cross section shall be
torsionally braced
(12-6)
For concrete-encased composite beams, such
bracing shall satisfy the following
requirements:
1. Both flanges of beams shall be laterally
braced or the beam cross section shall be
torsionally braced
2. The required strength of lateral bracing
provided adjacent to plastic hinges shall be
𝑃𝑢 = 0.06𝑀𝑜𝑝,𝑒𝑥𝑝
4. using the material properties of the steel
section and ry in the plane of buckling
calculated based on the elastic transformed
section.
12.2.5.2.2
Highly Ductile Members. In
addition to the requirements of Sections 12.2.5.2.1
(i) (1) and (2), and 12.2.5.2.1 (ii) (1) and (2), the
bracing of highly ductile beam members shall have
a maximum spacing of Lb = 0.086ryE/Fy. For
concrete-encased composite beams, the material
properties of the steel section shall be used and the
calculation for ry in the plane of buckling shall be
based on the elastic transformed section.
(12-5)
(12-7)
of the beam, where Mp,exp is determined
in accordance with Section 12.2.5.2.1
(ii)(2).
The required strength for torsional bracing
provided adjacent to plastic hinges shall be
Mu = 0.06Mp, exp of the beam.
3. The required bracing stiffness shall satisfy
the requirements of Appendix E for lateral
or torsional bracing of beams where Mr =
Mu = Mp, exp of the beam is determined in
accordance with Section 12.2.5.2.1 (ii)(2)
and Cd = 1.0
12.2.5.3
Protected Zones. Discontinuities
specified in Section 12.5.2.1 resulting from
fabrication and erection procedures and from other
attachments are prohibited in the area of a member
or a connection element designated as a protected
zone by the provision of this chapter or ANSI/AISC
358.
Exception: Welded steel headed stud anchors and
other connections are permitted in protected zones
when designated in ANSI/AISC 358, or as
SBC 306-CR-18
148
CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
otherwise determined with a connection
prequalification or as determined in a program of
qualification testing in accordance with Section
12.7.
12.2.5.4
Columns. Columns in moment
frames, braced frames and shear walls shall satisfy
the requirements of this section.
12.2.5.4.1
Required Strength. The required
strength of columns in the SFRS shall be
determined from the following:
1. The load effect resulting from the analysis
requirements for the applicable system per
Sections 12.3 and 12.4. Exception: Section
12.2.5.4.1 need not apply to Sections
12.4.1 or 12.4.3
2. The compressive axial strength and tensile
strength as determined using the load
combinations stipulated in SBC 301
including the amplified seismic load. It is
permitted to neglect applied moments in
this determination unless the moment
results from a load applied to the column
between points of lateral support. The
required axial compressive strength and
tensile strength need not exceed either of
the following:
(a) The maximum load transferred to the
column by the system, including the
effects of material overstrength and
strain hardening in those members
where yielding is expected
(b) The forces corresponding to the
resistance of the foundation to over
turning uplift
12.2.5.4.2
Encased
Composite
Columns. Encased composite columns shall
satisfy the requirements of Chapter 9, in addition to
the requirements of this section. Additional
requirements, as specified for moderately ductile
members and highly ductile members in Sections
12.2.5.4.2.1 and 12.2.5.4.2.2 , shall apply as
required in the descriptions of the composite
seismic systems in Section 12.4.
12.2.5.4.2.1
Moderately Ductile Members.
Encased composite columns used as moderately
ductile members shall satisfy the following
requirements:
1. The maximum spacing of transverse
reinforcement at the top and bottom shall
be the least of the following:
i.
One-half the least dimension of the
section
ii.
8 longitudinal bar diameters
iii.
24 tie bar diameters
iv.
300 mm
2. This spacing shall be maintained over a
vertical distance equal to the greatest of the
following lengths, measured from each
joint face and on both sides of any section
where flexural yielding is expected to
occur:
i. One-sixth the vertical clear height of
the column
ii.
iii.
The maximum
dimension
450 mm
cross-sectional
3. Tie spacing over the remaining column
length shall not exceed twice the spacing
defined in Section 12.2.5.4.2.1 (1)
4. Splices and end bearing details for encased
composite columns in composite ordinary
SFRS of sections 12.4.1 and 12.4.3 shall
satisfy the requirements of this Code and
SBC 304 Section 10.7.5.3.2. The design
shall comply with SBC 304 Sections 18.2.7
and 18.2.8. The design shall consider any
adverse behavioral effects due to abrupt
changes in either the member stiffness or
the nominal tensile strength. Transitions to
reinforced concrete sections without
embedded structural steel members,
transitions to bare structural steel sections,
and column bases shall be considered
abrupt changes
5. Welded wire fabric shall be prohibited as
transverse reinforcement in moderately
ductile members
12.2.5.4.2.2
Highly
Ductile
Members.
Encased composite columns used as highly ductile
members shall satisfy Section 12.2.5.4.2.1 in
addition to the following requirements:
1. Longitudinal
load-carrying
reinforcement
shall
satisfy
the
requirements of SBC 304 Section 18.7.4
2. Transverse reinforcement shall be hoop
reinforcement as defined in SBC 304 Chapter
18 and shall satisfy the following
requirements:
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
The minimum area of tie reinforcement,
Ash, shall be:
𝐴𝑠ℎ = 0.09 ℎ𝑐𝑐 𝑠 (1 −
𝐹𝑦 𝐴𝑠
𝑓𝑐′
) (
)
𝑃𝑛
𝐹𝑦𝑠𝑟
(12-8)
where
As
= cross-sectional area of the structural
steel core, mm2
Fy
= specified minimum yield stress of the
structural steel core, MPa
Fysr = specified minimum yield stress of the
ties, MPa
Pn
= nominal compressive strength of the
composite column calculated in
accordance with this Code, N
hcc = cross-sectional dimension of the
confined core measured center-to-center
of the tie reinforcement, mm
f ′c = specified compressive strength of
concrete, MPa
s
= spacing of transverse reinforcement
measured along the longitudinal axis of
the structural member, mm
Equation (12-8) need not be satisfied if the
nominal strength of the concrete-encased
structural steel section alone is greater than the
load effect from a load combination of 1.0D +
0.5L
3. Encased composite columns in braced frames
with required compressive strengths, without
consideration of the amplified seismic loads,
greater than 0.2Pn shall have transverse
reinforcement as specified in Section
12.2.5.4.2.2 (2)(iii) over the total element
length. This requirement need not be satisfied
if the nominal strength of the concreteencased steel section alone is greater than the
load effect from a load combination of 1.0D
+ 0.5L
4. Composite columns supporting reactions
from discontinued stiff members, such as
walls or braced frames, shall have transverse
reinforcement as specified in Section
12.2.5.4.2.2 (2)(iii) over the full length
beneath the level at which the discontinuity
occurs if the required compressive strengths,
without consideration of the amplified
seismic loads, exceeds 0.1Pn. Transverse
reinforcement shall extend into the
discontinued member for at least the length
required to develop full yielding in the
concrete-encased
steel
section
and
longitudinal reinforcement. This requirement
need not be satisfied if the nominal strength
of the concrete-encased steel section alone is
greater than the load effect from a load
combination of 1.0D + 0.5L
5.
where
D
= dead load due to the weight of the
structural elements and permanent
features on the building, N
L
= live load due to occupancy and
moveable equipment, N
The maximum spacing of transverse
reinforcement along the length of the
column shall be the lesser of six
longitudinal load-carrying bar diameters
or 150 mm.
When specified in Sections 12.2.5.4.2.2
(3) and (4), the maximum spacing of
transverse reinforcement along the
member length shall be the lesser of onefourth the least member dimension or 100
mm. Confining reinforcement shall be
spaced not more than 350 mm on center
in the transverse direction.
When the column terminates on a footing or
mat foundation, the transverse reinforcement
as specified in this section shall extend into
the footing or mat at least 300 mm. When the
column terminates on a wall, the transverse
reinforcement shall extend into the wall for
at least the length required to develop full
yielding in the concrete-encased shape and
longitudinal reinforcement
12.2.5.4.3
Filled Composite Columns. This
section applies to columns that meet the limitations
of Section 9.2.2 . Such columns shall be designed to
satisfy the requirements of Chapter 9, except that
the nominal shear strength of the composite column
shall be the nominal shear strength of the structural
steel section alone, based on its effective shear area.
12.2.5.5
H-PILES. Design of H-piles shall
comply with the requirements of this Code
regarding design of members subjected to
combined loads. H-piles shall satisfy the
requirements for highly ductile members of Section
12.2.5.1 . If battered (sloped) and vertical piles are
used in a pile group, the vertical piles shall be
designed to support the combined effects of the
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
dead and live loads without the participation of the
battered piles.
Tension in each pile shall be transferred to the pile
cap by mechanical means such as shear keys,
reinforcing bars, or studs welded to the embedded
portion of the pile.
At each pile, the length equal to the depth of the pile
cross section located directly below the bottom of
the pile cap shall be designated as a protected zone
meeting the requirements of Sections 12.2.5.3 and
12.5.2.1 .
12.2.5.6
Composite Slab Diaphragms.
The design of composite floor and roof slab
diaphragms for seismic effects shall meet the
following requirements.
12.2.5.6.1
Load Transfer. Details shall be
provided to transfer loads between the diaphragm
and boundary members, collector elements, and
elements of the horizontal framing system.
12.2.5.6.2
Nominal Shear Strength. The
nominal in-plane shear strength of composite
diaphragms and concrete slab on steel deck
diaphragms shall be taken as the nominal shear
strength of the reinforced concrete above the top of
the steel deck ribs in accordance with SBC 304
excluding Chapter 14. Alternatively, the composite
diaphragm nominal shear strength shall be
determined by in-plane shear tests of concrete-filled
diaphragms.
12.2.6 Connection Requirements. Connections,
joints and fasteners that are part of the SFRS shall
comply with Chapter 10, and with the additional
requirements of this section.
Splices and bases of columns that are not designated
as part of the SFRS shall satisfy the requirements of
Sections 12.2.6.4.1 , 12.2.6.4.3 and 12.2.6.5 .
Where protected zones are designated in connection
elements by this chapter or ANSI/AISC 358, they
shall satisfy the requirements of Sections 12.2.5.3
and 12.5.2.1 .
12.2.6.1
Bolted Joints. Bolted joints shall
satisfy the following requirements:
1. The design shear strength of bolted joints
using standard holes shall be calculated as
that for bearing-type joints in accordance
with Sections 10.3.6 and 10.3.10 . The
nominal bearing strength at bolt holes shall
not be taken greater than 2.4dtFu
2. Bolts and welds shall not be designed to
share force in a joint or the same force
component in a connection
User Note: A member force, such as a diagonal
brace axial force, must be resisted at the
connection entirely by one type of joint (in other
words, either entirely by bolts or entirely by
welds). A connection in which bolts resist a force
that is normal to the force resisted by welds, such
as a moment connection in which welded flanges
transmit flexure and a bolted web transmits
shear, is not considered to be sharing the force.
3. Bolt holes shall be standard holes or shortslotted holes perpendicular to the applied
load
Exception: For diagonal braces specified in Section
12.4, oversized holes are permitted in one
connection ply only when the connection is
designed as a slip-critical joint for the required
brace connection strength in this Section.
User Note: Diagonal brace connections with
oversized holes must also satisfy other limit
states including bolt bearing and bolt shear for
the required strength of the connection as
defined in Section 12.4. Alternative hole types
are permitted if designated in ANSI/AISC 358,
or if otherwise determined in a connection
prequalification in accordance with Section
12.7.1 or if determined in a program of
qualification testing in accordance with
Section 12.7.2 .
4. All bolts shall be installed as pretensioned
high-strength bolts. Faying surfaces shall
satisfy the requirements for slip-critical
connections in accordance with Section
10.3.8 with a faying surface with a Class
A slip coefficient or higher
Exceptions: Connection surfaces are permitted to
have coatings with a slip coefficient less than that
of a Class A faying surface for the following:
(a) End plate moment connections conforming to
the requirements of Section 12.3.1 , or
ANSI/AISC 358
(b) Bolted joints where the load effects due to
seismic are transferred either by tension in bolts
or by compression bearing but not by shear in
bolts
12.2.6.2
Welded Joints. Welded joints
shall be designed in accordance with Chapter 10.
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
12.2.6.3
Continuity Plates and Stiffeners.
The design of continuity plates and stiffeners
located in the webs of rolled shapes shall allow for
the reduced contact lengths to the member flanges
and web based on the corner clip sizes in Section
12.5.2.4 .
12.2.6.4
Column Splices
12.2.6.4.1
Location of Splices. For all
building columns, including those not designated as
part of the SFRS, column splices shall be located
1.2 m or more away from the beam-to-column
flange connections.
Exceptions:
1. When the column clear height between
beam-to-column flange connections is less
than 2.4 m, splices shall be at half the clear
height
2. Column splices with webs and flanges
joined by complete-joint-penetration
groove welds are permitted to be located
closer to the beam-to-column flange
connections, but not less than the depth of
the column
3. Splices in composite columns
User Note: Where possible, splices should be
located at least 1.2 m above the finished floor
elevation to permit installation of perimeter
safety cables prior to erection of the next tier and
to improve accessibility.
12.2.6.4.2
Required Strength. The required
strength of column splices in the SFRS shall be the
greater of:
(a) The required strength of the columns, including
that determined from Sections 12.3 and 12.4
and sub-section 12.2.5.4.1 ; or,
(b) The required strength determined using the load
combinations stipulated in the SBC 301
including the amplified seismic load. The
required strength need not exceed the
maximum loads that can be transferred to the
splice by the system
In addition, welded column splices in which any
portion of the column is subject to a calculated net
tensile load effect determined using the load
combinations stipulated in SBC 301, including the
amplified seismic load, shall satisfy all of the
following requirements:
1. The design strength of partial-jointpenetration (PJP) groove welded joints, if
used, shall be at least equal to 200% of the
required strength
2. The design strength for each flange splice
shall be at least equal to 0.5RyFybf tf , as
applicable, where RyFy is the expected
yield stress of the column material and bf
tf is the area of one flange of the smaller
column connected
3. Where butt joints in column splices are
made with complete-joint-penetration
(CJP) groove welds, when tension stress at
any location in the smaller flange exceeds
0.30Fy, tapered transitions are required
between flanges of unequal thickness or
width. Such transitions shall be in
accordance with AWS D1.8/D1.8M clause
4.2
12.2.6.4.3
Required Shear Strength. For all
building columns including those not designated as
part of the SFRS, the required shear strength of
column splices with respect to both orthogonal axes
of the column shall be Mpc/H, as applicable, where
Mpc is the lesser nominal plastic flexural strength of
the column sections for the direction in question,
and H is the height of the story.
The required shear strength of splices of columns in
the SFRS shall be the greater of the above
requirement or the required shear strength
determined per Section 12.2.6.4.2 (a) and (b).
12.2.6.4.4
Structural
Steel
Splice
Configurations. Structural steel column splices are
permitted to be either bolted or welded, or welded
to one column and bolted to the other. Splice
configurations shall meet all specific requirements
in Sections 12.3 and 12.4.
Splice plates or channels used for making web
splices in SFRS columns shall be placed on both
sides of the column web.
For welded butt joint splices made with groove
welds, weld tabs shall be removed in accordance
with AWS D1.8/D1.8M clause 6.11. Steel backing
of groove welds need not be removed.
12.2.6.4.5
Splices in Encased Composite
Columns. For encased composite columns, column
splices shall conform to Section 12.2.5.4.2 and SBC
304 Section 18.7.4.3.
12.2.6.5
Column Bases.
The required
strength of column bases, including those that are
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
not designated as part of the SFRS, shall be
calculated in accordance with this section.
The design strength of steel elements at the column
base, including base plates, anchor rods, stiffening
plates, and shear lug elements shall be in
accordance with this Code.
Where columns are welded to base plates with
groove welds, weld tabs and weld backing shall be
removed, except that weld backing located on the
inside of flanges and weld backing on the web of Ishaped sections need not be removed if backing is
attached to the column base plate with a continuous
8 mm fillet weld. Fillet welds of backing to the
inside of column flanges are prohibited.
12.2.6.5.2
Required Shear Strength. The
required shear strength of column bases, including
those not designated as part of the SFRS, and their
attachments to the foundations, shall be the
summation of the horizontal component of the
required connection strengths of the steel elements
that are connected to the column base as follows:
1. For diagonal braces, the horizontal
component shall be determined from the
required strength of diagonal brace
connections for the SFRS.
2. For columns, the horizontal component
shall be equal to the required shear strength
for column splices prescribed in Section
12.2.6.4.3 .
The design strength of concrete elements at the
column base, including anchor rod embedment and
reinforcing steel, shall be in accordance with SBC
304 Chapter 17.
Exception: Single story columns with simple
connections at both ends need not comply with
Section 12.2.6.5.2 (2).
User Note: When using concrete reinforcing
steel as part of the anchorage embedment
design, it is important to consider the anchor
failure modes and provide reinforcement that is
developed on both sides of the expected failure
surface. See SBC 304 Chapter 17, including
Commentary.
User Note: The horizontal components can
include the shear load from columns and the
horizontal component of the axial load from
diagonal members framing into the column
base. Section 12.2.6.4 includes references to
Section 12.2.5.4.1 (a) and Sections 12.3 and
12.4.
12.2.6.5.1
Required Axial Strength. The
required axial strength of column bases that are
designated as part of the SFRS, including their
attachment to the foundation, shall be the
summation of the vertical components of the
required connection strengths of the steel elements
that are connected to the column base, but not less
than the greater of:
1. The column axial load calculated using the
load combinations of SBC 301, including
the amplified seismic load
2. The required axial strength for column
splices, as prescribed in Section 12.2.6.4
User Note: The vertical components can
include both the axial load from columns and
the vertical component of the axial load from
diagonal members framing into the column
base. Section 12.2.6.4 includes references to
Section 12.2.5.4.1 and Sections 12.3 and 12.4.
Where diagonal braces frame to both sides of a
column, the effects of compression brace
buckling should be considered in the
summation of vertical components.
12.2.6.5.3
Required Flexural Strength.
Where column bases are designed as moment
connections to the foundation, the required flexural
strength of column bases that are designated as part
of the SFRS, including their attachment to the
foundation, shall be the summation of the required
connection strengths of the steel elements that are
connected to the column base as follows:
1. For diagonal braces, the required flexural
strength shall be at least equal to the
required flexural strength of diagonal
brace connections.
2. For columns, the required flexural strength
shall be at least equal to the lesser of the
following:
1.1RyFyZ, as applicable, of the column,
or
The moment calculated using the load
combinations of the SBC 301, including
the amplified seismic load.
User Note: Moments at column to column base
connections designed as simple connections may
be ignored.
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
12.2.6.6
Composite Connections. This
section applies to connections in buildings that
utilize composite steel and concrete systems
wherein seismic load is transferred between
structural steel and reinforced concrete
components. Methods for calculating the
connection strength shall satisfy the requirements in
this section. Unless the connection strength is
determined by analysis or testing, the models used
for design of connections shall satisfy the following
requirements:
beyond the point at which it is no longer
required to resist the forces. Development
lengths shall be determined in accordance
with SBC 304 Chapter 25
6. Composite connections shall satisfy the
following additional requirements:
When the slab transfers horizontal
diaphragm
forces,
the
slab
reinforcement shall be designed and
anchored to carry the in-plane tensile
forces at all critical sections in the slab,
including connections to collector
beams, columns, diagonal braces and
walls
1. Force shall be transferred between
structural steel and reinforced concrete
through:
(a) direct bearing from internal bearing
mechanisms;
(b) shear connection;
(c) shear friction with the necessary
clamping
force
provided
by
reinforcement normal to the plane of
shear transfer; or
(d) a combination of these means.
For connections between structural steel
or composite beams and reinforced
concrete or encased composite columns,
transverse hoop reinforcement shall be
provided in the connection region of the
column to satisfy the requirements of
SBC 304 Section 18.8, except for the
following modifications:
(a) Structural steel sections framing into
the connections are considered to
provide confinement over a width
equal to that of face bearing plates
welded to the beams between the
flanges.
(b) Lap splices are permitted for
perimeter ties when confinement of
the splice is provided by face bearing
plates or other means that prevents
spalling of the concrete cover in the
systems in Sections 12.4.1 , 12.4.2
and 12.4.3 .
(c) The longitudinal bar sizes and layout
in reinforced concrete and composite
columns shall be detailed to
minimize slippage of the bars
through
the
beam-to-column
connection due to high force transfer
associated with the change in column
moments over the height of the
connection.
The contribution of different mechanisms is
permitted to be combined only if the stiffness
and deformation capacity of the mechanisms
are compatible. Any potential bond strength
between structural steel and reinforced
concrete shall be ignored for the purpose of the
connection force transfer mechanism.
2.
The nominal bearing and shear-friction
strengths shall meet the requirements of
SBC 304 Chapter 22
3. Face bearing plates consisting of stiffeners
between the flanges of steel beams shall be
provided when beams are embedded in
reinforced concrete columns or walls.
4. The nominal shear strength of concreteencased steel panel zones in beam-to
column connections shall be calculated as
the sum of the nominal strengths of the
structural steel and confined reinforced
concrete shear elements as determined in
Section 10.10.6 and SBC 304 Section
18.8, respectively.
5. Reinforcement shall be provided to resist
all tensile forces in reinforced concrete
components
of
the
connections.
Additionally, the concrete shall be
confined with transverse reinforcement.
All reinforcement shall be fully developed
in tension or compression, as applicable,
12.2.6.7
Steel Anchors. Where steel
headed stud anchors or welded reinforcing bar
anchors are part of the intermediate moment frame
of Section 12.4.2 , their shear and tensile strength
shall be reduced by 25% from the specified
strengths given in Chapter 9.
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
User Note: The 25% reduction is not necessary
for gravity and collector components in
structures with intermediate or special seismic
force resisting systems designed for the amplified
seismic load.
12.2.7 Deformation Compatibility of NonSFRS Members and Connections.
Where
deformation compatibility of members and
connections that are not part of the seismic force
resisting system (SFRS) is required by SBC 301,
these elements shall be designed to resist the
combination of gravity load effects and the effects
of deformations occurring at the design story drift
calculated in accordance with SBC 301.
User Note: SBC 301 stipulates the above
requirement for both structural steel and
composite members and connections. Flexible
shear connections that allow member end
rotations per Section 10.1.2 of this Code
should be considered to meet these
requirements. Inelastic deformations are
permitted in connections or members provided
they are self-limiting and do not create
instability in the member. See the Commentary
for further discussion.
12.3—Moment-Frame and BracedFrame Systems
This section provides the basis of design, the
requirements for analysis, and the requirements for
the system, members and connections for steel
moment-frame and braced-frame systems.
The section is organized as follows:
12.3.1 Ordinary Moment Frames (OMF)
12.3.2 Intermediate Moment Frames (IMF)
12.3.3 Ordinary Cantilever Column Systems
(OCCS)
12.3.4 Ordinary Concentrically Braced Frames
(OCBF)
12.3.5 Eccentrically Braced Frames (EBF)
User Note: The requirements of this section are
in addition to those required by this Code and
SBC 301.
12.3.1 Ordinary Moment Frames (OMF)
12.3.1.1
Scope. Ordinary moment frames
(OMF) of structural steel shall be designed in
conformance with this section.
12.3.1.2
Basis of Design. OMF designed in
accordance with these provisions are expected to
provide minimal inelastic deformation capacity in
their members and connections.
12.3.1.3
Analysis. There are no additional
analysis requirements.
12.3.1.4
System Requirements. There are
no additional system requirements.
12.3.1.5
Members
12.3.1.5.1
Basic Requirements. There are
no limitations on width-to-thickness ratios of
members for OMF, beyond those in the Code .
There are no requirements for stability bracing of
beams or joints in OMF, beyond those in the Code.
Structural steel beams in OMF are permitted to be
composite with a reinforced concrete slab to resist
gravity loads.
12.3.1.5.2
Protected Zones. There are no
designated protected zones for OMF members.
12.3.1.6
Connections.
Beam-to-column
connections are permitted to be fully restrained
(FR) or partially restrained (PR) moment
connections in accordance with this section.
12.3.1.6.1
Demand
Critical
Welds.
Complete-joint-penetration (CJP) groove welds of
beam flanges to columns are demand critical welds,
and shall satisfy the requirements of Section
12.1.2.4.2 and 12.5.2.3 .
12.3.1.6.2
FR Moment Connections. FR
moment connections that are part of the seismic
force resisting system (SFRS) shall satisfy at least
one of the following requirements:
(a) FR moment connections shall be designed for a
required flexural strength that is equal to the
expected beam flexural strength multiplied by
1.1. The expected beam flexural strength shall
be determined as Ry Mp
The required shear strength, Vu, of the connection
shall be based on the load combinations in SBC 301
that include the amplified seismic load. In
determining the amplified seismic load the effect of
horizontal forces including overstrength, Emh, shall
be taken as:
𝐸𝑚ℎ = 2[1.1𝑅𝑦 𝑀𝑝 ]/𝐿𝑐𝑓
(12-9)
where
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
Lcf = clear length of beam, mm
reinforcement, or two-sided fillet welds.
The required strength of these joints shall
not be less than the design strength of the
contact area of the plate with the column
flange.
Mp = FyZ, N-mm
Ry
= ratio of expected yield stress to the
specified minimum yield stress, Fy
(b) FR moment connections shall be designed for a
required flexural strength and a required shear
strength equal to the maximum moment and
corresponding shear that can be transferred to
the connection by the system, including the
effects of material over-strength and strain
hardening
User Note: Factors that may limit the maximum
moment and corresponding shear that can be
transferred to the connection include:
(1) the strength of the columns, and
(2) the resistance of the foundations to uplift.
For options (a) and (b) in Section 12.3.1.6.2 ,
continuity plates should be provided as required by
Sections 10.10.1 , 10.10.2 and 10.10.3 . The
bending moment used to check for continuity plates
should be the same bending moment used to design
the beam-to-column connection; in other words,
either 1.1RyMp or the maximum moment that can be
transferred to the connection by the system.
(c) FR moment connections between wide flange
beams and the flange of wide flange columns
shall either satisfy the requirements of Section
12.3.2.6
or shall satisfy the following
requirements:
5. The beam web shall be connected to the
column flange using either a CJP groove
weld extending between weld access holes,
or using a bolted single plate shear
connection designed for required shear
strength per Eq. (12-9).
User Note: For FR moment connections,
panel zone shear strength should be checked
in accordance with Section 10.10.6 . The
required shear strength of the panel zone
should be based on the beam end moments
computed from the load combinations
stipulated by SBC 301, not including the
amplified seismic load.
12.3.1.6.3
PR Moment Connections. PR
moment connections shall satisfy the following
requirements:
1. Connections shall be designed for the
maximum moment and shear from the
applicable load combinations as described
in Sections 12.2.1 and 12.2.2
2. The stiffness, strength and deformation
capacity of PR moment connections shall
be considered in the design, including the
effect on overall frame stability
1. All welds at the beam-to-column
connection shall satisfy the requirements
of Chapter 3 of ANSI/AISC 358
3. The nominal flexural strength of the
connection, Mn,PR, shall be no less than
50% of Mp of the connected beam
2. Beam flanges shall be connected to column
flanges using complete-joint penetration
(CJP) groove welds
Exception: For one-story structures, Mn,PR
shall be no less than 50% of Mp of the
connected column.
3. The shape of weld access holes shall be in
accordance with sub-clause 6.10.1.2 of
AWS D1.8/D1.8M. Weld access hole
quality requirements shall be in
accordance with sub-clause 6.10.2 of AWS
D1.8/D1.8M
4. Vu, shall be determined per Section
12.3.1.6.2 (a) with Mp in Eq. (12-9) taken
as Mn,PR
4. Continuity plates shall satisfy
requirements of Section 12.3.2.6.6 .
the
Exception: The welded joints of the
continuity plates to the column flanges are
permitted to be complete-joint-penetration
groove welds, two-sided partial-jointpenetration
groove
welds
with
12.3.2 Intermediate Moment Frames (IMF)
12.3.2.1
Scope.
Intermediate moment
frames (IMF) of structural steel shall be designed in
conformance with this section.
12.3.2.2
Basis of Design. IMF designed in
accordance with these provisions are expected to
provide limited inelastic deformation capacity
through flexural yielding of the IMF beams and
columns, and shear yielding of the column panel
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
zones. Design of connections of beams to columns,
including panel zones and continuity plates, shall be
based on connection tests that provide the
performance required by Section 12.3.2.6.2 , and
demonstrate this conformance as required by
Section 12.3.2.6.3 .
12.3.2.3
Analysis. There are no additional
analysis requirements.
12.3.2.4
System Requirements
12.3.2.4.1
Stability Bracing of Beams.
Beams shall be braced to satisfy the requirements
for moderately ductile members in Section 12.2.5.2
a.
In addition, unless otherwise indicated by testing,
beam braces shall be placed near concentrated
forces, changes in cross section, and other locations
where analysis indicates that a plastic hinge will
form during inelastic deformations of the IMF. The
placement of stability bracing shall be consistent
with that documented for a prequalified connection
designated in ANSI/AISC 358, or as otherwise
determined in a connection prequalification in
accordance with Section 12.7.1 , or in a program of
qualification testing in accordance with Section
12.7.2 .
The required strength of lateral bracing provided
adjacent to plastic hinges shall be as required by
Section 12.2.5.2.3 .
12.3.2.5
Members
12.3.2.5.1
Basic Requirements. Beam and
column members shall satisfy the requirements of
Section 12.2.5 for moderately ductile members,
unless otherwise qualified by tests.
Structural steel beams in IMF are permitted to be
composite with a reinforced concrete slab to resist
gravity loads.
12.3.2.5.2
Beam Flanges. Abrupt changes in
beam flange area shall not be permitted in plastic
hinge regions. The drilling of flange holes or
trimming of beam flange width shall not be
permitted unless testing or qualification
demonstrates that the resulting configuration can
develop stable plastic hinges to accommodate the
required story drift angle. The configuration shall
be consistent with a prequalified connection
designated in ANSI/AISC 358, or as otherwise
determined in a connection prequalification in
accordance with Section 12.7.1 , or in a program of
qualification testing in accordance with Section
12.7.2 .
12.3.2.5.3
Protected Zones
The region at each end of the beam subject to
inelastic straining shall be designated as a protected
zone, and shall satisfy the requirements of Section
12.2.5.3 . The extent of the protected zone shall be
as designated in ANSI/AISC 358, or as otherwise
determined in a connection prequalification in
accordance with Section 12.7.1 , or as determined
in a program of qualification testing in accordance
with Section 12.7.2 .
12.3.2.6
Connections
12.3.2.6.1
Demand Critical Welds. The
following welds are demand critical welds, and
shall satisfy the requirements of Section 12.1.2.4.2
and 12.5.2.3 :
1. Groove welds at column splices
2. Welds at column-to-base plate connections
Exception: Where it can be shown that
column hinging at, or near, the base plate
is precluded by conditions of restraint, and
in the absence of net tension under load
combinations including the amplified
seismic load, demand critical welds are not
required
3. Complete-joint-penetration groove welds
of beam flanges and beam webs to
columns, unless otherwise designated by
ANSI/AISC 358, or otherwise determined
in a connection prequalification in
accordance with Section 12.7.1 , or as
determined in a program of qualification
testing in accordance with Section 12.7.2 .
User Note: For the designation of demand
critical welds, standards such as ANSI/AISC 358
and tests addressing specific connections and
joints should be used in lieu of the more general
terms of these Provisions. Where these
Provisions indicate that a particular weld is
designated demand critical, but the more specific
standard or test does not make such a
designation, the more specific standard or test
should govern. Likewise, these standards and
tests may designate welds as demand critical that
are not identified as such by these Provisions.
12.3.2.6.2
Beam-to-Column
Connection
Requirements. Beam-to-column connections used
in the SFRS shall satisfy the following
requirements:
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
1. The connection shall be capable of
accommodating a story drift angle of at
least 0.02 rad
2. The measured flexural resistance of the
connection, determined at the column face,
shall equal at least 0.80Mp of the connected
beam at a story drift angle of 0.02 rad
12.3.2.6.3
Conformance
Demonstration.
Beam-to-column connections used in the SFRS
shall satisfy the requirements of Section 12.3.2.6 b
by one of the following:
1. Use of IMF connections designed in
accordance with ANSI/AISC 358
2. Use of a connection prequalified for IMF
in accordance with Section 12.7.1 .
3. Provision of qualifying cyclic test results
in accordance with Section 12.7.2 . Results
of at least two cyclic connection tests shall
be provided and are permitted to be based
on one of the following:
Tests reported in the research literature
or documented tests performed for
other projects that represent the project
conditions, within the limits specified
in Section 12.7.2.
Tests that are conducted specifically
for the project and are representative
of project member sizes, material
strengths, connection configurations,
and matching connection processes,
within the limits specified in Section
12.7.2.
12.3.2.6.4
Required Shear Strength. The
required shear strength of the connection shall be
based on the load combinations in the SBC 301 that
include the amplified seismic load. In determining
the amplified seismic load the effect of horizontal
forces including overstrength, Emh, shall be taken
as:
Emh 2[1.1RyMp]/Lh
(12-10)
where
Exception: In lieu of Eq. (12-10), the required shear
strength of the connection shall be as specified in
ANSI/AISC 358, or as otherwise determined in a
connection prequalification in accordance with
Section 12.7.1 , or in a program of qualification
testing in accordance with Section 12.7.2.
12.3.2.6.5
Panel Zone. There
additional panel zone requirements.
are
no
User Note: Panel zone shear strength should be
checked in accordance with Section 10.10.6. The
required shear strength of the panel zone should
be based on the beam end moments computed
from the load combinations stipulated by the
applicable building code, not including the
amplified seismic load.
12.3.2.6.6
Continuity Plates.
Continuity
plates shall be provided in accordance with the
following:
12.3.2.6.6.1
Continuity Plate Requirements.
Continuity plates shall be provided with the
exception of the following conditions:
(a) When otherwise determined in a connection
prequalification in accordance with Section
12.7.1 , or as determined in a program of
qualification testing in accordance with Section
12.7.2 .
(b) When the beam flange is welded to the flange
of a wide-flange or built-up I-shaped column
having a thickness that satisfies Eqs. (12-11)
and (12-12), continuity plates need not be
provided:
𝑡𝑐𝑓 ≥ 0.4√1.8𝑏𝑏𝑓 𝑡𝑏𝑓
𝑡𝑐𝑓 ≥
𝑅𝑦𝑏 𝐹𝑦𝑏
𝑅𝑦𝑐 𝐹𝑦𝑐
𝑏𝑏𝑓
6
(12-11)
(12-12)
where
Fyb = specified minimum yield stress of the
beam flange, MPa
Fyc = specified minimum yield stress of the
column flange, MPa
Lh distance between beam plastic hinge
locations as defined within the test report or
ANSI/AISC 358, mm
Ryb = ratio of the expected yield stress of the
beam material to the specified minimum
yield stress
Mp FyZ nominal plastic flexural strength, Nmm
Ryc = ratio of the expected yield stress of the
column material to the
specified
minimum yield stress
Ry ratio of the expected yield stress to the
specified minimum yield stress, Fy
bbf = beam flange width, mm
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
tbf
= beam flange thickness, mm
tcf
= minimum required thickness of column
flange when no continuity plates are
provided, mm
(c) When the beam flange is welded to the flange
of the I-shape in a boxed wide flange column
having a thickness that satisfies Eqs. (12-13)
and (12-14), continuity plates need not be
provided:
𝑡𝑐𝑓 ≥ 0.4√[1 −
𝑏𝑏𝑓
2
𝑏𝑐𝑓
(𝑏𝑐𝑓 −
𝑏𝑏𝑓
4
)] 1.8𝑏𝑏𝑓 𝑡𝑏𝑓
𝐹𝑦𝑏 𝑅𝑦𝑏
𝐹𝑦𝑐 𝑅𝑦𝑐
(12-13)
𝑏𝑏𝑓
(12-14)
12
(d) For bolted connections, the continuity plate
provisions of ANSI/AISC 358 for the specific
connection type shall apply
𝑡𝑐𝑓 ≥
they shall be complete-joint-penetration groove
welds. When bolted column splices are used, they
shall have a required flexural strength that is at least
equal to RyFyZx of the smaller column, where Zx is
the plastic section modulus about the x-axis. The
required shear strength of column web splices shall
be at least equal to ΣMpc /H, where ΣMpc is the sum
of the nominal plastic flexural strengths of the
columns above and below the splice.
Exception: The required strength of the column
splice considering appropriate stress concentration
factors or fracture mechanics stress intensity factors
need not exceed that determined by a nonlinear
analysis as specified in section 12.2.4 .
12.3.3 Ordinary Cantilever Column Systems
(OCCS)
12.3.2.6.6.2
Continuity Plate Thickness.
Where continuity plates are required, the thickness
of the plates shall be determined as follows:
12.3.3.1
Scope.
Ordinary cantilever
column systems (OCCS) of structural steel shall be
designed in conformance with this section.
(a) For one-sided connections, continuity plate
thickness shall be at least one half of the
thickness of the beam flange
(d) For two-sided connections, the continuity
plate thickness shall be at least equal to the
thicker of the two beam flanges on either side
of the column. Continuity plates shall also
conform to the requirements of Section 10.10
12.3.3.2
Basis of Design. OCCS designed
in accordance with these provisions are expected to
provide minimal inelastic drift capacity through
flexural yielding of the columns.
12.3.2.6.6.3
Continuity
Plate
Welding.
Continuity plates shall be welded to column flanges
using CJP groove welds.
12.3.3.4.1
Columns.
Columns shall be
designed using the load combinations including the
amplified seismic load. The required axial strength,
Prc , shall not exceed 15% of the design axial
strength, Pc, for these load combinations only.
Continuity plates shall be welded to column webs
using groove welds or fillet welds. The required
strength of the sum of the welded joints of the
continuity plates to the column web shall be the
smallest of the following:
a) The sum of the design strengths in tension
of the contact areas of the continuity plates
to the column flanges that have attached
beam flanges
b) The design strength in shear of the contact
area of the plate with the column web
c) The design strength in shear of the column
panel zone
d) The sum of the expected yield strengths of
the beam flanges transmitting force to the
continuity plates
12.3.2.6.7
Column Splices. Column splices
shall comply with the requirements of Section
12.2.6 . Where welds are used to make the splice,
12.3.3.3
Analysis. There are no additional
analysis requirements.
12.3.3.4
System Requirements
12.3.3.4.2
Stability Bracing of Columns.
There are no additional stability bracing
requirements for columns.
12.3.3.5
Members
12.3.3.5.1
Basic Requirements. There are
no additional requirements.
12.3.3.5.2
Column Flanges. There are no
additional column flange requirements.
12.3.3.5.3
Protected Zones.
designated protected zones.
12.3.3.6
There are no
Connections
12.3.3.6.1
Demand Critical Welds. No
demand critical welds are required for this system.
12.3.3.6.2
Column Bases. There are no
additional column base requirements.
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
12.3.4 Ordinary Concentrically Braced Frames
(OCBF)
12.3.4.1
Scope. Ordinary concentrically
braced frames (OCBF) of structural steel shall be
designed in conformance with this section.
12.3.4.2
Basis of Design. This section is
applicable to braced frames that consist of
concentrically connected members. Eccentricities
less than the beam depth are permitted if they are
accounted for in the member design by
determination of eccentric moments using the
amplified seismic load.
OCBF designed in accordance with these
provisions are expected to provide limited inelastic
deformation capacity in their members and
connections
12.3.4.3
Analysis. There are no additional
analysis requirements.
12.3.4.4
System Requirements
12.3.4.4.1
V-Braced and Inverted VBraced Frames. Beams in V-type and inverted Vtype OCBF shall be continuous at brace
connections away from the beam-column
connection and shall satisfy the following
requirements:
1. The required strength shall be determined
based on the load combinations of the SBC
301 assuming that the braces provide no
support of dead and live loads. For load
combinations that include earthquake effects,
the seismic load effect, E, on the member shall
be determined as follows:
The forces in braces in tension shall be
assumed to be the least of the following:
a) The expected yield strength of the
brace in tension, RyFyAg
b) The load effect based upon the
amplified seismic load
c) The maximum force that can be
developed by the system
The forces in braces in compression shall
be assumed to be equal to 0.3Pn
2. As a minimum, one set of lateral braces is
required at the point of intersection of the
braces, unless the member has sufficient outof-plane strength and stiffness to ensure
stability between adjacent brace points
12.3.4.4.2
K-Braced Frames. K-type braced
frames are not permitted for OCBF.
12.3.4.5
Members
12.3.4.5.1
Basic Requirements. Braces shall
satisfy the requirements of Section 12.2.5.1 for
moderately ductile members.
12.3.4.5.2
inverted-V
4√𝐸/𝐹𝑦 .
12.3.4.6
Slenderness.
Braces in V or
configurations shall have𝐾𝐿/𝑟 ≤
Connections
12.3.4.6.1
Diagonal Brace Connections.
The required strength of diagonal brace
connections is the load effect based upon the
amplified seismic load.
Exception: The required strength of the brace
connection need not exceed the following:
1. In tension, the expected yield strength of
the brace. The expected yield strength shall
be determined as RyFyAg
2. In compression, the expected brace
strength in compression The expected
brace strength in compression is permitted
to be taken as the lesser of RyFyAg and
1.14FcreAg where Fcre is determined from
Chapter 5 using the equations for Fcr
except that the expected yield stress RyFy is
used in lieu of Fy. The brace length used
for the determination of Fcre shall not
exceed the distance from brace end to
brace end
3. When oversized holes are used, the
required strength for the limit state of bolt
slip need not exceed a load effect based
upon using the load combinations
stipulated by the applicable building code,
not including the amplified seismic load.
12.3.5 Eccentrically Braced Frames (EBF)
12.3.5.1
Scope.
Eccentrically braced
frames (EBF) of structural steel shall be designed in
conformance with this section.
12.3.5.2
Basis of Design. This section is
applicable to braced frames for which one end of
each brace intersects a beam at an eccentricity from
the intersection of the centerlines of the beam and
an adjacent brace or column, forming a link that is
subject to shear and flexure. Eccentricities less than
the beam depth are permitted in the brace
connection away from the link if the resulting
member and connection forces are addressed in the
design and do not change the expected source of
inelastic deformation capacity.
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
EBF designed in accordance with these provisions
are expected to provide significant inelastic
deformation capacity primarily through shear or
flexural yielding in the links.
Where links connect directly to columns, design of
their connections to columns shall provide the
performance required by Section 12.3.5.6.5.1 and
demonstrate this conformance as required by
Section 12.3.5.6.5.2 .
12.3.5.3
Analysis. The required strength of
diagonal braces and their connections, beams
outside links, and columns shall be based on the
load combinations in SBC 301 that include the
amplified seismic load. In determining the
amplified seismic load, the effect of horizontal
forces including overstrength, Emh, shall be taken as
the forces developed in the member assuming the
forces at the ends of the links correspond to the
adjusted link shear strength. The adjusted link shear
strength shall be taken as Ry times the link nominal
shear strength, Vn, given in Section 12.3.5.5.2.2
multiplied by 1.25 for I-shaped links and 1.4 for box
links.
Exceptions:
1. The effect of horizontal forces including
overstrength, Emh, is permitted to be taken
as 0.88 times the forces determined above
for the design of the following members:
(a) The portions of beams outside links
(b) Columns in frames of three or more
stories of bracing
2. It is permitted to neglect flexural forces
resulting from seismic drift in this
determination. Moment resulting from a
load applied to the column between points
of lateral support must be considered.
3. The required strength of columns need not
exceed the lesser of the following:
(a) Forces corresponding to the resistance
of the foundation to over turning uplift
(b) Forces as determined from nonlinear
analysis as defined in Section 12.2.4.
The inelastic link rotation angle shall be determined
from the inelastic portion of the design story drift.
Alternatively, the inelastic link rotation angle is
permitted to be determined from nonlinear analysis
as defined in Section 12.2.4.
User Note: The seismic load effect, E, used in
the design of EBF members, such as the required
axial strength used in the equations in Section
12.3.5.5, should be calculated from the analysis
above.
12.3.5.4
System Requirements
12.3.5.4.1
Link Rotation Angle. The link
rotation angle is the inelastic angle between the link
and the beam outside of the link when the total story
drift is equal to the design story drift, Δ. The link
rotation angle shall not exceed the following values:
a) For links of length 1.6Mp/Vp or less: 0.08
rad
b) For links of length 2.6Mp/Vp or greater: 0.02
rad
where
Mp= nominal plastic flexural strength, N-mm
Vp = nominal shear strength of an active link,
N
Linear interpolation between the above values shall
be used for links of length between 1.6Mp/Vp and
2.6Mp/Vp.
12.3.5.4.2
Bracing of Link. Bracing shall be
provided at both the top and bottom link flanges at
the ends of the link for I-shaped sections. Bracing
shall have an available strength and stiffness as
required for expected plastic hinge locations by
Section 12.2.5.2.3.
12.3.5.5
Members
12.3.5.5.1
Basic Requirements
Brace members shall satisfy width-to-thickness
limitations in Section 12.2.5.1 for moderately
ductile members.
Column members shall satisfy width-to-thickness
limitations in Section 12.2.5.1.2 for highly ductile
members.
Where the beam outside of the link is a different
section from the link, the beam shall satisfy the
width-to-thickness limitations in Section 12.2.5.1
for moderately ductile members.
User Note: The diagonal brace and beam
segment outside of the link are intended to
remain essentially elastic under the forces
generated by the fully yielded and strain
hardened link. Both the diagonal brace and beam
segment outside of the link are typically subject
to a combination of large axial force and bending
moment, and therefore should be treated as
beam-columns in design, where the available
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
strength is defined by Chapter 8. Where the beam
outside the link is the same member as the link,
its strength may be determined using expected
material properties as permitted by Section
12.1.2.2.
12.3.5.5.2
𝑉𝑝 = 0.6𝐹𝑦 𝐴𝑙𝑤 √1 − (𝑃𝑢 /𝑃𝑦 )2 for 𝑃𝑢 /𝑃𝑦 > 0.15
(12-17)
For I shaped Link Sections
𝐴𝑙𝑤 = (𝑑 − 2𝑡𝑓 )𝑡𝑤
(12-18)
Links
Links subject to shear and flexure due to
eccentricity between the intersections of brace
centerlines and the beam centerline (or between the
intersection of the brace and beam centerlines and
the column centerline for links attached to columns)
shall be provided. The link shall be considered to
extend from brace connection to brace connection
for center links and from brace connection to
column face for link-to-column connections except
as permitted by Section 12.3.5.6.5.
12.3.5.5.2.1
Limitations. Links shall be Ishaped cross sections (rolled wide-flange sections
or built-up sections), or built-up box sections. HSS
sections shall not be used as links. Links shall
satisfy the requirements of Section 12.2.5.1 for
highly ductile members.
Exception: Flanges of links with I-shaped sections
with link lengths, 𝑒 ≤ 1.6𝑀𝑝 /𝑉𝑝 , are permitted to
satisfy the requirements for moderately ductile
members.
The web or webs of a link shall be single thickness.
Doubler-plate reinforcement and web penetrations
are not permitted. For links made of built-up cross
sections, complete-joint-penetration groove welds
shall be used to connect the web (or webs) to the
flanges.
Links of built-up box sections shall have a moment
of inertia, Iy, about an axis in the plane of the EBF
limited to Iy > 0.67Ix, where Ix is the moment of
inertia about an axis perpendicular to the plane of
the EBF.
12.3.5.5.2.2
Shear Strength. The link design
shear strength, vVn, shall be the lower value
obtained in accordance with the limit states of shear
yielding in the web and flexural yielding in the
gross section. For both limit states:
v = 0.90
For Box link sections
= 2(𝑑 − 2𝑡𝑓 )𝑡𝑤
𝑃𝑢 = required axial strength, N
𝑃𝑦 = nominal axial yield strength
= 𝐹𝑦 𝐴𝑔
𝑉𝑛 = 𝑉𝑝
(12-15)
where
𝑉𝑝 = 0.6𝐹𝑦 𝐴𝑙𝑤 for 𝑃𝑢 /𝑃𝑦 ≤ 0.15
(12-16)
(12-20)
(b) For flexural yielding:
𝑉𝑛 = 2𝑀𝑝 /𝑒
(12-21)
where
𝑀𝑝 = 𝐹𝑦 𝑍 for 𝑃𝑢 /𝑃𝑦 ≤ 0.15
𝑃
𝑃𝑦
(12-22)
1− 𝑢
𝑀𝑝 = 𝐹𝑦 𝑍 (
e
0.85
) for 𝑃𝑢 /𝑃𝑦 > 0.15 (12-23)
= link length, defined as the clear dist ance
between the ends of two diagonal braces or
between the diagonal brace and the column
face, mm
12.3.5.5.2.3
Link Length. If Pu/Py > 0.15, the
length of the link shall be limited as follows:
When ρ′ ≤ 0.5
𝑒≤
1.6𝑀𝑝
𝑉𝑝
(12-24)
When ρ′ > 0.5
𝑒≤
1.6𝑀𝑝
𝑉𝑝
(1.15 − 0.3𝜌′ )
(12-25)
where
𝜌′ =
𝑃𝑢 /𝑃𝑦
(12-26)
𝑉𝑢 /𝑉𝑦
𝑉𝑢 = required shear strength, N
𝑉𝑦 = nominal shear yield strength, N
= 0.6𝐹𝑦 𝐴𝑙𝑤
(a) For shear yielding:
(12-19)
(12-27)
User Note: For links with low axial force
there is no upper limit on link length. The
limitations on link rotation angle in Section
12.3.5.4.1 result in a practical lower limit on
link length.
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
12.3.5.5.2.4
Link Stiffeners for I-Shaped
Cross Sections. Full-depth web stiffeners shall be
provided on both sides of the link web at the
diagonal brace ends of the link. These stiffeners
shall have a combined width not less than (bf − 2tw)
and a thickness not less than the larger of 0.75tw or
10 mm, where bf and tw are the link flange width and
link web thickness, respectively.
Links shall be provided with intermediate web
stiffeners as follows:
(a) Links of lengths 1.6Mp/Vp or less shall be
provided with intermediate web stiffeners
spaced at intervals not exceeding (30tw − d/5)
for a link rotation angle of 0.08 rad or (52tw −
d/5) for link rotation angles of 0.02 rad or less.
Linear interpolation shall be used for values
between 0.08 and 0.02 rad.
(b) Links of length greater than or equal to
2.6Mp/Vp and less than 5Mp/Vp shall be provided
with intermediate web stiffeners placed at a
distance of 1.5 times bf from each end of the
link.
(c) Links of length between 1.6Mp/Vp and 2.6Mp/Vp
shall be provided with intermediate web
stiffeners meeting the requirements of (a) and
(b) above.
Intermediate web stiffeners are not required in links
of length greater than 5Mp/Vp.
Intermediate web stiffeners shall be full depth. For
links that are less than 635 mm in depth, stiffeners
are required on only one side of the link web. The
thickness of one-sided stiffeners shall not be less
than tw or 10 mm, whichever is larger, and the width
shall be not less than (bf/2) − tw. For links that are
635 mm in depth or greater, similar intermediate
stiffeners are required on both sides of the web.
The required strength of fillet welds connecting a
link stiffener to the link web is FyAst, where Ast is
the horizontal cross-sectional area of the link
stiffener and Fy is the yield stress of the stiffener.
The required strength of fillet welds connecting the
stiffener to the link flanges is FyAst/4.
12.3.5.5.2.5
Link Stiffeners for Box Sections.
Full-depth web stiffeners shall be provided on one
side of each link web at the diagonal brace
connection. These stiffeners are permitted to be
welded to the outside or inside face of the link webs.
These stiffeners shall each have a width not less
than b/2, where b is the inside width of the box.
These stiffeners shall each have a thickness not less
than the larger of 0.75tw or 13 mm.
Box links shall be provided with intermediate
web stiffeners as follows:
(a) For links of length 1.6Mp/Vp or less and with
web depth-to-thickness ratio, h/tw, greater than
or equal to 0.64√𝐸/𝐹𝑦 , full-depth web
stiffeners shall be provided on one side of each
link web, spaced at intervals not exceeding 20tw
− (d − 2tf)/8.
(b) For links of length 1.6Mp/Vp or less and with
web depth-to-thickness ratio, h/tw, less than
0.64√𝐸/𝐹𝑦 , no intermediate web stiffeners are
required.
(c) For links of length greater than 1.6Mp/Vp, no
intermediate web stiffeners are required.
Intermediate web stiffeners shall be full depth, and
are permitted to be welded to the outside or inside
face of the link webs.
The required strength of fillet welds connecting a
link stiffener to the link web is FyAst, where Ast is
the horizontal cross-sectional area of the link
stiffener.
User Note: Stiffeners of box links need not be
welded to link flanges.
12.3.5.5.3
Protected Zones. Links in EBFs
are a protected zone, and shall satisfy the
requirements of Section 12.2.5.3.
12.3.5.6
Connections
12.3.5.6.1
Demand Critical Welds. The
following welds are demand critical welds and shall
satisfy the requirements of Sections 12.1.2.4.2 and
12.5.2.3:
1. Groove welds at column splices
2. Welds at column-to-base plate connections
Exception: Where it can be shown that
column hinging at, or near, the base plate
is precluded by conditions of restraint, and
in the absence of net tension under load
combinations including the amplified
seismic load, demand critical welds are not
required.
3. Welds at beam-to-column connections
conforming to Section 12.3.5.6.2(2).
4.
Welds attaching the link flanges and the
link web to the column where links connect
to columns
5. Welds connecting the webs to the flanges
in built-up beams within the link.
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
12.3.5.6.2
Beam-to-Column Connections.
Where a brace or gusset plate connects to both
members at a beam-to-column connection, the
connection shall conform to one of the following:
1. The connection shall be a simple
connection meeting the requirements of
Section 2.3.5a where the required rotation
is taken to be 0.025 radians; or
2. The connection shall be designed to resist
a moment equal to the lesser of the
following:
A moment corresponding to the
expected beam flexural strength
multiplied by 1.1. The expected beam
flexural strength shall be determined as
RyMp.
A moment corresponding to the sum of
expected column flexural strengths
multiplied by 1.1. The sum of expected
column flexural strengths shall be
Σ(RyFyZ).
This moment shall be considered in combination
with the required strength of the brace connection
and beam connection, including the amplified
diaphragm collector forces.
12.3.5.6.3
Diagonal Brace Connections.
When oversized holes are used, the required
strength for the limit state of bolt slip need not
exceed a load effect based upon using the load
combinations stipulated by the applicable building
code, including the amplified seismic load.
Connections of braces designed to resist a portion
of the link end moment shall be designed as fully
restrained.
12.3.5.6.5
12.3.5.6.5.1
Requirements. Link-to-column
connections shall be fully restrained (FR) moment
connections and shall satisfy the following
requirements:
1. The connection shall be capable of
sustaining the link rotation angle specified
in Section 12.3.5.4.1.
2. The shear resistance of the connection,
measured at the required link rotation
angle, shall be at least equal to the expected
shear strength of the link, RyVn, as defined
in Section 12.3.5.5.2.2.
3. The flexural resistance of the connection,
measured at the required link rotation
angle, shall be at least equal to the moment
corresponding to the nominal shear
strength of the link, Vn, as defined in
Section 12.3.5.5.2.2.
12.3.5.6.5.2
Conformance
Demonstration.
Link-to-column connections shall satisfy the above
requirements by one of the following:
(a) Use a connection prequalified for EBF in
accordance with Section 12.7.1.
User Note: There are no prequalified link-tocolumn connections..
(b) Provide qualifying cyclic test results in
accordance with Section 12.7.2. Results of at
least two cyclic connection tests shall be
provided and are permitted to be based on one
of the following:
12.3.5.6.4
Column Splices. Column splices
shall comply with the requirements of Section
12.2.6.4. Where groove welds are used to make the
splice, they shall be complete-joint-penetration
groove welds. Column splices shall be designed to
develop at least 50% of the lesser available flexural
strength of the connected members.
The required shear strength shall be ΣMpc/Hc,
where
Hc
=
Link-to-Column Connections
clear height of the column between beam
connections, including a structural slab,
if present, mm
ΣMpc = sum of the nominal plastic flexural
strengths, FycZc,of the columns above and
below the splice, N-mm.
SBC 306-CR-18
Tests reported in research literature or
documented tests performed for other projects
that are representative of project conditions,
within the limits specified in Section 12.7.2.
Tests that are conducted specifically for the
project and are representative of project
member sizes, material strengths, connection
configurations, and matching connection
material properties, within the limits specified
in Section 12.7.2.
Exception: Cyclic testing of the
connection is not required if the
following conditions are met:
1. Reinforcement at the beam-tocolumn connection at the link end
precludes yielding of the beam
over the reinforced length.
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
2. The available strength of the
reinforced section and the
connection equals or exceeds the
required strength calculated based
upon adjusted link shear strength as
described in Section 12.3.5.3.
3. The link length (taken as the beam
segment from the end of the
reinforcement to the brace
connection) does not exceed
1.6Mp/Vp.
4. Full depth stiffeners as required in
Section 12.3.5.5.2.4 are placed at
the link-toreinforcement interface.
12.4—Composite Moment-Frame and
Braced-Frame Systems
This section provides the basis of design, the
requirements for analysis, and the requirements for
the system, members and connections for
composite moment frame and braced-frame
systems.
User Note: Composite ordinary moment
frames, comparable to reinforced concrete
ordinary moment frames, are only permitted in
seismic design categories B or below in SBC
301. This is in contrast to steel ordinary
moment frames, which are permitted in higher
seismic design categories. The design
requirements
are
commensurate
with
providing minimal ductility in the members
and connections.
12.4.1.3
Analysis. There are no additional
analysis requirements.
12.4.1.4
System Requirements. There are
no additional system requirements.
12.4.1.5
Members. There are no additional
requirements for steel or composite members
beyond those in the Code. Reinforced concrete
columns shall satisfy the requirements of SBC 304,
excluding Chapter 18.
12.4.1.5.1
Protected Zones. There are no
designated protected zones.
12.4.2 Composite Intermediate Moment Frames
(C-IMF)
12.4.1.6
Connections. Connections shall
be fully restrained (FR). Connections shall be
designed for the applicable load combinations as
described in Sections 12.2.1 and 12.2.2 Beam-tocolumn connection design strengths shall be
determined in accordance with this Code and
Section 12.2.6.6 .
12.4.3 Composite Ordinary Braced Frames (COBF)
12.4.1.6.1
Demand Critical Welds. There
are no requirements for demand critical welds.
The section is organized as follows:
12.4.1 Composite Ordinary Moment Frames (COMF)
User Note: The requirements of this section
are in addition to those required by this Code
and SBC 301.
12.4.1 Composite Ordinary Moment Frames
(C-OMF)
12.4.1.1
Scope.
Composite ordinary
moment frames (C-OMF) shall be designed in
conformance with this section. This section is
applicable to moment frames with fully restrained
(FR) connections that consist of either composite or
reinforced concrete columns and structural steel,
concrete-encased composite, or composite beams.
12.4.1.2
Basis of Design. C-OMF designed
in accordance with these provisions are expected to
provide minimal inelastic deformation capacity in
their members and connections.
12.4.2 Composite
Frames (C-IMF)
Intermediate
Moment
12.4.2.1
Scope. Composite intermediate
moment frames (C-IMF) shall be designed in
conformance with this section. This section is
applicable to moment frames with fully restrained
(FR) connections that consist of composite or
reinforced concrete columns and structural steel,
concrete-encased composite or composite beams.
12.4.2.2
Basis of Design. C-IMF designed
in accordance with these provisions are expected to
provide limited inelastic deformation capacity
through flexural yielding of the C-IMF beams and
columns, and shear yielding of the column panel
zones. Design of connections of beams to columns,
including panel zones, continuity plates and
diaphragms shall provide the performance required
by Section 12.4.2.6.2 , and demonstrate this
conformance as required by Section 12.4.2.6.3 .
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
User Note: Composite intermediate moment
frames, comparable to reinforced concrete
intermediate moment frames, are only
permitted in seismic design categories C or
below in SBC 301. This is in contrast to steel
intermediate moment frames, which are
permitted in higher seismic design categories.
The design requirements are commensurate
with providing limited ductility in the members
and connections.
12.4.2.3
Analysis. There are no additional
analysis requirements.
12.4.2.4
System Requirements
12.4.2.4.1
Stability Bracing of Beams.
Beams shall be braced to satisfy the requirements
for moderately ductile members in Section
12.2.5.2.1 .
In addition, unless otherwise indicated by testing,
beam braces shall be placed near concentrated
forces, changes in cross section, and other locations
where analysis indicates that a plastic hinge will
form during inelastic deformations of the C-IMF.
The required strength of stability bracing provided
adjacent to plastic hinges shall be as required by
Section 12.2.5.2.3 .
12.4.2.5
Members
12.4.2.5.1
Basic Requirements. Steel and
composite members shall satisfy the requirements
of Sections 12.2.5 for moderately ductile members.
12.4.2.5.2
Beam Flanges. Abrupt changes in
the beam flange area are prohibited in plastic hinge
regions. The drilling of flange holes or trimming of
beam flange width is prohibited unless testing or
qualification demonstrates that the resulting
configuration can develop stable plastic hinges.
12.4.2.5.3
Protected Zones. The region at
each end of the beam subject to inelastic straining
shall be designated as a protected zone, and shall
satisfy the requirements of Section 12.2.5.3 .
User Note: The plastic hinge zones at the ends of
C-IMF beams should be treated as protected
zones. In general, the protected zone will extend
from the face of the composite column to onehalf of the beam depth beyond the plastic hinge
point.
12.4.2.6
Connections. Connections shall
be fully restrained (FR) and shall satisfy the
requirements of Sections 12.2.6 and this section.
12.4.2.6.1
Demand Critical Welds. There
are no requirements for demand critical welds.
12.4.2.6.2
Beam-to-Column
Connection
Requirements.
Beam-to-composite
column
connections used in the SFRS shall satisfy the
following requirements:
1. The connection shall be capable of
accommodating a story drift angle of at
least 0.02 rad
2. The measured flexural resistance of the
connection, determined at the column face,
shall equal at least 0.80Mp of the connected
beam at a story drift angle of 0.02 rad.
where Mp is defined as the nominal flexural
strength of the steel, concrete-encased or
composite beams and shall satisfy the
requirements, Chapter 9
12.4.2.6.3
Conformance
Demonstration.
Beam-to-column connections used in the SFRS
shall satisfy the requirements of Section 12.4.2.6.2
by connection testing or calculations that are
substantiated by mechanistic models and
component limit state design criteria consistent with
these provisions.
12.4.2.6.4
Required Shear Strength. The
required shear strength of the connection shall be
based on the load combinations in the SBC 301 that
include the amplified seismic load. In determining
the amplified seismic load the effect of horizontal
forces including overstrength, Emh, shall be taken
as:
Emh 2[1.1RyMp, exp]/Lh
(12-28)
where Mp,exp is the expected flexural strength of the
steel, concrete-encased or composite beams, N-mm.
For concrete-encased or composite beams, Mp, exp
shall be calculated using the plastic stress
distribution or the strain compatibility method.
Appropriate Ry factors shall be used for different
elements of the cross-section while establishing
section force equilibrium and calculating the
flexural strength. Lh shall be equal to the distance
between beam plastic hinge locations, mm.
User Note: For steel beams, Mp, exp in Eq
(12-28) may be taken as RyMp of the beam.
12.4.2.6.5
Connection Diaphragm Plates.
Connection diaphragm plates are permitted for
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
filled composite columns both external to the
column and internal to the column.
Where diaphragm plates are used, the thickness of
the plates shall be at least the thickness of the beam
flange.
The diaphragm plates shall be welded around the
full perimeter of the column using either completejoint-penetration welds or two sided fillet welds.
The required strength of these joints shall not be
less than the design strength of the contact area of
the plate with the column sides.
Internal diaphragms shall have circular openings
sufficient for placing the concrete.
12.4.2.6.6
Column Splices. In addition to the
requirements of Section 12.2.6.4 , column splices
shall comply with the requirements of this section.
Where groove welds are used to make the splice,
they shall be complete-joint-penetration groove
welds. When column splices are not made with
groove welds, they shall have a required flexural
strength that is at least equal to the nominal flexural
strength, Mpcc, of the smaller composite column.
The required shear strength of column web splices
shall be at least equal to ΣMpcc /H, where ΣMpcc is
the sum of the nominal flexural strengths of the
composite columns above and below the splice. For
composite columns, the nominal flexural strength
shall satisfy the requirements of Chapter 9 with
consideration of the required axial strength, Prc.
12.4.3 Composite Ordinary Braced Frames (COBF)
12.4.3.1
Scope.
Composite ordinary
braced frames (C-OBF) shall be designed in
conformance with this section. Columns shall be
structural steel, encased composite, filled
composite or reinforced concrete members. Beams
shall be either structural steel or composite beams.
Braces shall be structural steel or filled composite
members. This section is applicable to braced
frames that consist of concentrically connected
members where at least one of the elements
(columns, beams or braces) is a composite or
reinforced concrete member.
deformations in their members and connections. COBF shall satisfy the requirements of Section 12.3.4
, except as modified in this section.
User Note: Composite ordinary braced frames,
comparable to other steel braced frames
designed per this Code using R = 3, are only
permitted in seismic design categories C or
below in SBC 301. This is in contrast to steel
ordinary braced frames, which are permitted in
higher seismic design categories. The design
requirements
are
commensurate
with
providing minimal ductility in the members
and connections.
12.4.3.3
Analysis. There are no additional
analysis requirements.
12.4.3.4
System Requirements. There are
no additional system requirements.
12.4.3.5
Members
12.4.3.5.1
Basic Requirements. There are no
additional requirements.
12.4.3.5.2
Columns. There are no additional
requirements for structural steel and composite
columns. Reinforced concrete columns shall satisfy
the requirements of SBC 304, excluding Chapter
18.
12.4.3.5.3
Braces. There are no additional
requirements for structural steel and filled
composite braces.
12.4.3.5.4
Protected Zones. There are no
designated protected zones.
12.4.3.6
Connections. Connections shall
satisfy the requirements of Section 12.2.6.6 .
12.4.3.6.1
Demand Critical Welds. There
are no requirements for demand critical welds.
12.5—Fabrication and Erection
This section addresses requirements for fabrication
and erection.
User Note: All requirements of Chapter 14
also apply, unless specifically modified by
these Provisions.
12.4.3.2
Basis of Design. This section is
applicable to braced frames that consist of
concentrically connected members. Eccentricities
less than the beam depth are permitted if they are
accounted for in the member design by
determination of eccentric moments.
The section is organized as follows:
C-OBF designed in accordance with these
provisions are expected to provide limited inelastic
12.5.1 Shop and Erection Drawings
12.5.1 Shop and Erection Drawings
12.5.2 Fabrication and Erection
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
12.5.1.1
Shop Drawings for Steel
Construction. Shop drawings shall indicate the
work to be performed, and include items required
by the Code, the AISC Code of Standard Practice
for Steel Buildings and Bridges, SBC 301, the
requirements of Sections 12.1.3.1 and 12.1.3.2 ,
and the following, as applicable:
1.
Locations of pretensioned bolts
2. Locations of Class A, or higher, faying
surfaces
3.
Gusset plates drawn to scale when they are
designed to accommodate inelastic
rotation
4. Weld access hole dimensions, surface
profile and finish requirements
5. Nondestructive testing (NDT)
performed by the fabricator
where
12.5.1.2
Erection Drawings for Steel
Construction. Erection drawings shall indicate the
work to be performed, and include items required
by the Code, the AISC Code of Standard Practice
for Steel Buildings and Bridges, SBC 301, the
requirements of Sections 12.1.3.1 and 12.1.3.2 ,
and the following, as applicable:
1. Within the protected zone, holes, tack
welds, erection aids, air-arc gouging, and
unspecified
thermal
cutting
from
fabrication or erection operations shall be
repaired as required by the engineer of
record.
2. Steel headed stud anchors and decking
attachments that penetrate the beam flange
shall not be placed on beam flanges within
the protected zone. Arc spot welds as
required to secure decking shall be
permitted.
3. Welded, bolted, screwed or shot-in
attachments for perimeter edge angles,
exterior facades, partitions, duct work,
piping or other construction shall not be
placed within the protected zone.
Exception: Other attachments are
permitted where designated or approved
by the engineer of record. See Section
12.2.3 .
User Note: AWS D1.8/D1.8M clause 6.15
contains requirements for weld removal and
the repair of gouges and notches in the
protected zone.
1. Locations of pretensioned bolts
2. Those joints or groups of joints in which a
specific
assembly
order,
welding
sequence, welding technique or other
special precautions are required
12.5.1.3
Shop and Erection Drawings for
Composite Construction. Shop drawings and
erection drawings for the steel components of
composite steel concrete construction shall satisfy
the requirements of Sections 12.5.1.1 and 12.5.1.2
. The shop drawings and erection drawings shall
also satisfy the requirements of Section 12.1.3.3 .
User Note: For reinforced concrete and
composite steel-concrete construction, the
provisions of ACI 315 Details and Detailing of
Concrete Reinforcement and ACI 315-R Manual
of Engineering and Placing Drawings for
Reinforced Concrete Structures apply.
12.5.2 Fabrication and Erection
12.5.2.1
Protected Zone. A protected zone
designated by these Provisions or ANSI/AISC 358
shall comply with the following requirements:
12.5.2.2
Bolted Joints. Bolted joints shall
satisfy the requirements of Section 12.2.6.1 .
12.5.2.3
Welded Joints. Welding and
welded connections shall be in accordance with
Structural
Welding
Code-Steel
(AWS
D1.1/D1.1M), hereafter referred to as AWS
D1.1/D1.1M, and AWS D1.8/D1.8M.
Welding Procedure Specifications (WPSs) shall be
approved by the engineer of record.
Weld tabs shall be in accordance with AWS
D1.8/D1.8M clause 6.10, except at the outboard
ends of continuity-plate-to-column welds, weld
tabs and weld metal need not be removed closer
than 6 mm from the continuity plate edge.
AWS D1.8/D1.8M clauses relating to fabrication
shall apply equally to shop fabrication welding and
to field erection welding.
User Note: AWS D1.8/D1.8M was
specifically written to provide additional
requirements for the welding of seismic force
resisting systems, and has been coordinated
wherever possible with these Provisions. AWS
D1.8/D1.8M
requirements
related
to
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
fabrication and erection are organized as
follows, including normative (mandatory)
annexes:
12.7—Prequalification and Cyclic
Qualification Testing Provisions
1. General Requirements
This section addresses requirements
qualification and prequalification testing.
2. Reference Documents
This section is organized as follows:
3. Definitions
12.7.1. Prequalification of Beam-to-Column and
Link-to-Column Connections
4. Welded Connection Details
12.7.2. Cyclic Tests for Qualification of Beam-toColumn and Link-to-Column Connections
5. Welder Qualification
6. Fabrication
Annex A. WPS Heat Input Envelope Testing of
Filler Metals for Demand Critical Welds
Annex B. Intermix CVN Testing of Filler
Metal Combinations (where one of the filler
metals is FCAW-S)
Annex C. Supplemental Welder Qualification
for Restricted Access Welding
Annex D. Supplemental Testing for Extended
Exposure Limits for FCAW Filler Metals
AWS D1.8/D1.8M requires the complete
removal of all weld tab material, leaving only
base metal and weld metal at the edge of the
joint. This is to remove any weld
discontinuities at the weld ends, as well as
facilitate magnetic particle testing (MT) of this
area. At continuity plates, these Provisions
permit a limited amount of weld tab material to
remain because of the reduced strains at
continuity plates, and any remaining weld
discontinuities in this weld end region would
likely be of little significance. Also, weld tab
removal sites at continuity plates are not
subjected to MT.
AWS D1.8/D1.8M clause 6 is entitled
“Fabrication,” but the intent of AWS is that all
provisions of AWS D1.8/D1.8M apply
equally to fabrication and erection activities as
described in the Specification and in these
Provisions.
12.5.2.4
Continuity Plates and Stiffeners.
Corners of continuity plates and stiffeners placed in
the webs of rolled shapes shall be detailed in
accordance with AWS D1.8/D1.8M clause 4.1.
12.6—Quality Control and Quality
Assurance
All requirements of Chapter 15 shall apply.
for
12.7.1 Prequalification of Beam-to-Column
and Link-to-Column Connections
12.7.1.1
Scope.
This section contains
minimum requirements for prequalification of
beam-to-column moment connections intermediate
moment frames (IMF), and link-to-column
connections in eccentrically braced frames (EBF).
Prequalified connections are permitted to be used,
within the applicable limits of prequalification,
without the need for further qualifying cyclic tests.
When the limits of prequalification or design
requirements for prequalified connections conflict
with the requirements of these Provisions, the limits
of prequalification and design requirements for
prequalified connections shall govern.
12.7.1.2
General Requirements
12.7.1.2.1
Basis
for
Prequalification.
Connections shall be prequalified based on test data
satisfying Section 12.7.1.3, supported by analytical
studies and design models. The combined body of
evidence for prequalification must be sufficient to
assure that the connection can supply the required
story drift angle for IMF systems, or the required
link rotation angle for EBF, on a consistent and
reliable basis within the specified limits of
prequalification. All applicable limit states for the
connection that affect the stiffness, strength and
deformation capacity of the connection and the
seismic force resisting system (SFRS) must be
identified. These include rupture related limit states,
stability related limit states, and all other limit states
pertinent for the connection under con-sideration.
The effect of design variables listed in Section
12.7.1.4 shall be addressed for connection
prequalification.
12.7.1.2.2
Authority for Prequalification.
Prequalification of a connection and the associated
limits of prequalification shall be established by a
connection prequalification review panel (CPRP)
approved by the authority having jurisdiction.
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
12.7.1.3
Testing Requirements. Data used
to support connection prequalification shall be
based on tests conducted in accordance with
Section 12.7.2. The CPRP shall determine the
number of tests and the variables considered by the
tests for connection prequalification. The CPRP
shall also provide the same information when limits
are to be changed for a previously prequalified
connection. A sufficient number of tests shall be
performed on a sufficient number of nonidentical
specimens to demonstrate that the connection has
the ability and reliability to undergo the required
story drift angle for IMF and the required link
rotation angle for EBF, where the link is adjacent to
columns. The limits on member sizes for
prequalification shall not exceed the limits specified
in Section 12.7.2.3.2.
12.7.1.4
Prequalification Variables. In
order to be prequalified, the effect of the following
variables on connection performance shall be
considered. Limits on the permissible values for
each variable shall be established by the CPRP for
the prequalified connection.
12.7.1.4.1
to column web, beams or links are
connected to both the column flange and
web, or other
4. Depth
5. Weight per foot
6. Flange thickness
7. Material specification
8. Width-to-thickness ratio of cross-section
elements
9. Lateral bracing
10. Other parameters pertinent to the specific
connection under consideration
12.7.1.4.3
Beam-to-Column or Link-toColumn Relations
1. Panel zone strength
2. Doubler plate attachment details
3. Column-to-beam
moment ratio
12.7.1.4.4
Beam or Link Parameters
(or
column-to-link)
Continuity Plates
1. Cross-section shape: wide flange, box or
other
1. Identification of conditions under which
continuity plates are required
2. Cross-section fabrication method: rolled
shape, welded shape or other
2. Thickness, width and depth
3. Depth
12.7.1.4.5
4. Weight per foot
Welds
1. Location, extent (including returns), type
(CJP, PJP, fillet, etc.) and any reinforcement or contouring required
5. Flange thickness
6. Material specification
7. Span-to-depth ratio (for IMF), or link
length (for EBF)
8. Width-to-thickness ratio of cross-section
elements
9. Lateral bracing
10. Other parameters pertinent to the specific
connection under consideration
12.7.1.4.2
3. Attachment details
Column Parameters
1. Cross-section shape: wide flange, box, or
other
2. Cross-section fabrication method: rolled
shape, welded shape or other
3. Column orientation with respect to beam
or link: beam or link is connected to
column flange, beam or link is connected
2. Filler metal classification strength and
notch toughness
3. Details and treatment of weld backing and
weld tabs
4. Weld access holes: size, geometry and
finish
5. Welding quality control and quality
assurance beyond that described in Section
15.9, including NDT method, inspection
frequency, acceptance criteria and
documentation requirements
12.7.1.4.6
Bolts
1. Bolt diameter
2. Bolt grade: ASTM A325, A325M, A490,
A490M or other
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3. Installation requirements: pretensioned,
snug-tight or other
4. Hole type: standard, oversize, short-slot,
long-slot or other
5. Hole fabrication method: drilling,
punching, sub-punching and reaming or
other
6. Other parameters pertinent to the specific
connection under consideration
12.7.1.4.7
Workmanship. All workmanship
parameters that exceed the Code, RCSC and AWS
requirements, pertinent to specific connection under
consideration, as follows:
1. Surface roughness of thermal cut or ground
edges
2. Cutting tolerances
3. Presence of holes, fasteners or welds for
attachments
12.7.1.4.8
Additional Connection Details.
All variables pertinent to the specific connection
under consideration, as established by the CPRP.
12.7.1.5
Design
Procedure.
A
comprehensive design procedure must be available
for a prequalified connection. The design procedure
must address all applicable limit states within the
limits of prequalification.
12.7.1.6
Prequalification Record.
A
prequalified connection shall be provided with a
written prequalification record with the following
information:
1. General description of the prequalified
connection and drawings that clearly
identify key features and components of
the connection
2. Description of the expected behavior of the
connection in the elastic and inelastic
ranges of behavior, intended location(s) of
inelastic action, and a description of limit
states controlling the strength and
deformation capacity of the connection
3. Listing of systems for which connection is
prequalified: IMF or EBF
4. Listing of limits for all prequalification
variables listed in Section 12.7.1.4.
5. Listing of demand critical welds
6. Definition of the region of the connection
that comprises the protected zone
7. Detailed description of the design
procedure for the connection, as required
in Section 12.7.1.5
8. List of references of test reports, research
reports and other publications that
provided the basis for prequalification
9. Summary of quality control and quality
assurance procedures
12.7.2 Cyclic Tests for Qualification of Beamto-Column and Link-to-Column Connections
12.7.2.1
Scope.
This section includes
requirements for qualifying cyclic tests of beam-tocolumn moment connections in special and
intermediate moment frames and link-to-column
connections in eccentrically braced frames, when
required in provisions of this chapter. The purpose
of the testing described in this section is to provide
evidence that a beam-to-column connection or a
link-to-column
connection
satisfies
the
requirements for strength and story drift angle or
link rotation angle in the provisions of this chapter.
Alternative testing requirements are permitted when
approved by the engineer of record and the
authority having jurisdiction.
This section provides minimum recommendaions
for simplified test conditions.
12.7.2.2
Test
Subassemblage
Requirements. The test subassemblage shall
replicate as closely as is practical the conditions that
will occur in the prototype during earthquake
loading. The test subassemblage shall include the
following features:
1. The test specimen shall consist of at least a
single column with beams or links attached
to one or both sides of the column.
2. Points of inflection in the test assemblage
shall coincide approximately with the
anticipated points of inflection in the
prototype under earthquake loading.
3. Lateral bracing of the test subassemblage
is permitted near load application or
reaction points as needed to provide lateral
stability of the test subassemblage.
Additional lateral bracing of the test
subassemblage is not permitted, unless it
replicates lateral bracing to be used in the
prototype.
12.7.2.3
Essential Test Variables. The test
specimen shall replicate as closely as is practical the
pertinent design, detailing, construction features,
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and material properties of the prototype. The
following variables shall be replicated in the test
specimen.
12.7.2.3.1
Sources of Inelastic Rotation.
The inelastic rotation shall be computed based on
an analysis of test specimen deformations. Sources
of inelastic rotation include yielding of members,
yielding of connection elements and connectors,
and slip between members and connection
elements.
For
beam-to-column
moment
connections in special and intermediate moment
frames, inelastic rotation is computed based upon
the assumption that inelastic action is concentrated
at a single point located at the intersection of the
centerline of the beam with the centerline of the
column. For link-to-column connections in
eccentrically braced frames, inelastic rotation shall
be computed based upon the assumption that
inelastic action is concentrated at a single point
located at the inter-section of the centerline of the
link with the face of the column.
Inelastic rotation shall be developed in the test
specimen by inelastic action in the same members
and connection elements as anticipated in the
prototype (in other words, in the beam or link, in the
column panel zone, in the column outside of the
panel zone, or in connection elements) within the
limits described below. The percentage of the total
inelastic rotation in the test specimen that is
developed in each member or connection element
shall be within 25% of the anticipated percentage of
the total inelastic rotation in the prototype that is
developed in the corresponding member or
connection element.
12.7.2.3.2
Size of Members. The size of the
beam or link used in the test specimen shall be
within the following limits:
1. The depth of the test beam or link shall be
no less than 90% of the depth of the
prototype beam or link.
2. The weight per foot of the test beam or link
shall be no less than 75% of the weight per
foot of the prototype beam or link.
The size of the column used in the test specimen
shall properly represent the inelastic action in the
column, as per the requirements in Section
12.7.2.3.1. In addition, the depth of the test column
shall be no less than 90% of the depth of the
prototype column.
Extrapolation beyond the limitations stated in this
section is permitted subject to qualified peer review
and approval by the authority having jurisdiction.
User Note: Based upon the above criteria, beam
or link depth and column depths up to and
including 11% greater than that tested should be
permitted for the prototype. Weight per foot of
the beam or link up to and including 33% greater
than that tested should be permitted for the
prototype.
12.7.2.3.3
Connection
Details.
The
connection details used in the test specimen shall
represent the prototype connection details as closely
as possible. The connection elements used in the
test specimen shall be a full-scale representation of
the connection elements used in the prototype, for
the member sizes being tested.
12.7.2.3.4
Continuity Plates. The size and
connection details of continuity plates used in the
test specimen shall be proportioned to match the
size and connection details of continuity plates used
in the prototype connection as closely as possible.
12.7.2.3.5
Steel Strength. The following
additional requirements shall be satisfied for each
member or connection element of the test specimen
that supplies inelastic rotation by yielding:
1. The yield strength shall be determined as
specified in Section 12.7.2.6.1. The use of
yield stress values that are reported on
certified material test reports in lieu of
physical testing is prohibited for the
purposes of this section.
2. The yield strength of the beam flange as
tested in accordance with Section
12.7.2.6.1 shall not be more than 15%
below RyFy for the grade of steel to be used
for the corresponding elements of the
prototype.
3. The yield strength of the columns and
connection elements shall not be more than
15% above or below RyFy for the grade of
steel to be used for the corre-sponding
elements of the prototype. RyFy shall be
determined in accordance with Section
12.1.2.2.
User Note: Based upon the above criteria, steel
of the specified grade with a specified minimum
yield stress, Fy, of up to and including 1.15 times
the RyFy for the steel tested should be permitted
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shall not exceed that to be used for the
welds on the corresponding prototype. The
tested CVN toughness of the weld as tested
in accordance with Section 12.7.2.6.3 shall
not exceed the minimum CVN toughness
specified for the prototype by more than
50%, nor 34 J, whichever is greater.
in the prototype. In production, this limit should
be checked using the values stated on the steel
manufacturer’s material test reports.
12.7.2.3.6
Welded Joints. Welds on the test
specimen shall satisfy the following requirements:
1. Welding shall be performed in
conformance with Welding Procedure
Specifications (WPS) as required in AWS
D1.1/D1.1M. The WPS essential variables
shall satisfy the requirements in AWS
D1.1/D1.1M and shall be within the
parameters established by the filler-metal
manufacturer. The tensile strength and
Charpy V-notch (CVN) toughness of the
welds used in the test assembly shall be
determined by tests as specified in Section
12.7.2.6.3, made using the same filler
metal classification, manufacturer, brand
or trade name, diameter, and average heat
input for the WPS used on the test
specimen. The use of tensile strength and
CVN toughness values that are reported on
the manufacturer’s typical certificate of
conformance in lieu of physical testing is
prohibited for purposes of this section.
2. The specified minimum tensile strength of
the filler metal used for the test specimen
shall be the same as that to be used for the
welds on the corresponding prototype. The
tensile strength of the deposited weld as
tested in accordance with Section
12.7.2.6.3 shall not exceed the tensile
strength classification of the filler metal
specified for the prototype by more than
172 MPa.
User Note: Based upon the criteria in (3) above,
should the tested CVN tough-ness of the weld
metal in the material test specimen exceed the
specified CVN toughness for the test specimen
by 34 J or 50%, whichever is greater, the
prototype weld should be made with a filler metal
and WPS that will provide a CVN toughness that
is no less than 34 J or 33% lower, whichever is
lower, below the CVN toughness measured in the
weld metal material test plate. When this is the
case, the weld properties resulting from the filler
metal and WPS to be used in the prototype should
be determined using five CVN test specimens.
The test plate is described in AWS D1.8/D1.8M
clause A6 and shown in AWS D1.8/D1.8M
Figure A.1.
4. The welding positions used to make the
welds on the test specimen shall be the
same as those to be used for the prototype
welds.
5. Details of weld backing, weld tabs, access
holes and similar items used for the test
specimen welds shall be the same as those
to be used for the corresponding prototype
welds. Weld backing and weld tabs shall
not be removed from the test specimen
welds unless the corresponding weld
backing and weld tabs are removed from
the prototype welds.
User Note: Based upon the criteria in (2) above,
should the tested tensile strength of the weld
metal exceed 172 MPa above the specified
minimum tensile strength, the prototype weld
should be made with a filler metal and WPS that
will provide a tensile strength no less than 172
MPa below the tensile strength measured in the
material test plate. When this is the case, the
tensile strength of welds resulting from use of the
filler metal and the WPS to be used in the
prototype should be determined by using an allweld-metal tension specimen. The test plate is
described in AWS D1.8/D1.8M clause A6 and
shown in AWS D1.8/D1.8M Figure A.1.
User Note: The filler metal used for production
of the prototype is permitted to be of a different
classification, manufacturer, brand or trade
name, and diameter, provided that Sections
12.7.2.3.6(2) and 12.7.2.3.6(3) are satisfied. To
qualify alternate filler metals, the tests as
prescribed in Section 12.7.2.6.3 should be
conducted.
3. The specified minimum CVN toughness of
the filler metal used for the test spec-imen
12.7.2.3.7
Bolted Joints. The bolted portions
of the test specimen shall replicate the bolted
6. Methods of inspection and nondestructive
testing and standards of acceptance used
for test specimen welds shall be the same
as those to be used for the prototype welds.
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portions of the prototype connection as closely as
possible. Additionally, bolted portions of the test
specimen shall satisfy the following requirements:
1. The bolt grade (for example, ASTM A325,
A325M, ASTM A490, A490M, ASTM
F1852, ASTM F2280) used in the test
specimen shall be the same as that to be
used for the prototype, except that heavy
hex bolts are permitted to be substituted for
twist-off-type tension control bolts of
equal minimum specified tensile strength,
and vice versa.
2. The type and orientation of bolt holes
(standard, oversize, short slot, long slot or
other) used in the test specimen shall be the
same as those to be used for the
corresponding bolt holes in the prototype.
3. When inelastic rotation is to be developed
either by yielding or by slip within a bolted
portion of the connection, the method used
to make the bolt holes (drilling, subpunching and reaming, or other) in the test
specimen shall be the same as that to be
used in the corresponding bolt holes in the
prototype.
4. Bolts in the test specimen shall have the
same installation (pretensioned or other)
and faying surface preparation (no
specified slip resistance, Class A or B slip
resistance, or other) as that to be used for
the corresponding bolts in the prototype.
12.7.2.4
1. 6 cycles at θ = 0.00375 rad
2. 6 cycles at θ = 0.005 rad
3. 6 cycles at θ = 0.0075 rad
4. 4 cycles at θ = 0.01 rad
5. 2 cycles at θ = 0.015 rad
6. 2 cycles at θ = 0.02 rad
7. 2 cycles at θ = 0.03 rad
8. 2 cycles at θ = 0.04 rad
Continue loading at increments of θ = 0.01 rad, with
two cycles of loading at each step.
12.7.2.4.3
Loading Sequence for Link-toColumn Connections. Qualifying cyclic tests of
link-to-column
moment
connections
in
eccentrically braced frames shall be conducted by
controlling the total link rotation angle, total,
imposed on the test specimen, as follows:
1. 6 cycles at total = 0.00375 rad
2. 6 cycles at total = 0.005 rad
3. 6 cycles at total = 0.0075 rad
4. 6 cycles at total = 0.01 rad
5. 4 cycles at total = 0.015 rad
6. 4 cycles at total = 0.02 rad
7. 2 cycles at total = 0.03 rad
8. 1 cycle at total = 0.04 rad
9. 1 cycle at total = 0.05 rad
Loading History
12.7.2.4.1
General Requirements. The test
specimen shall be subjected to cyclic loads in
accordance with the requirements prescribed in
Section 12.7.2.4.2 for beam-to-column moment
connections in special and intermediate moment
frames, and in accordance with the requirements
prescribed in Section 12.7.2.4.3 for link-to-column
connections in eccentrically braced frames.
Loading sequences other than those specified in
Sections 12.7.2.4.2 and 12.7.2.4.3 are permitted to
be used when they are demonstrated to be of
equivalent or greater severity.
12.7.2.4.2
Loading Sequence for Beam-toColumn Moment Connections. Qualifying cyclic
tests of beam-to-column moment connections in
special and intermediate moment frames shall be
conducted by controlling the story drift angle, θ,
imposed on the test specimen, as specified below:
10. 1 cycle at total = 0.07 rad
11. 1 cycle at total = 0.09 rad
Continue loading at increments of total = 0.02 rad,
with one cycle of loading at each step.
12.7.2.5
Instrumentation.
Sufficient
instrumentation shall be provided on the test
specimen to permit measurement or calculation of
the quantities listed in Section 12.7.2.7.
12.7.2.6
Testing
Material Specimens
Requirements
for
12.7.2.6.1
Tension Testing Requirements
for Structural Steel Material Specimens. Tension
testing shall be conducted on samples taken from
material test plates in accordance with Section
12.7.2.6.2. The material test plates shall be taken
from the steel of the same heat as used in the test
specimen. Tension-test results from certified
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
material test reports shall be reported, but shall not
be used in lieu of physical testing for the purposes
of this section. Tension testing shall be conducted
and reported for the following portions of the test
specimen:
1. Flange(s) and web(s) of beams and
columns at standard locations
2. Any element of the connection that
supplies inelastic rotation by yielding
12.7.2.6.2
Methods of Tension Testing for
Structural Steel Material Specimens. Tension
testing shall be conducted in accordance with
ASTM A6/A6M, ASTM A370, and ASTM E8,
with the following exceptions:
1. The yield strength, Fy, that is reported from
the test shall be based upon the yield
strength definition in ASTM A370, using
the offset method at 0.002 strain.
2. The loading rate for the tension test shall
replicate, as closely as practical, the
loading rate to be used for the test
specimen.
12.7.2.6.3
Testing Requirements for Weld
Metal Material Specimens. Weld metal testing
shall be conducted on samples extracted from the
material test plate, made using the same filler metal
classification, manufacturer, brand or trade name
and diameter, and using the same average heat input
as used in the welding of the test specimen. The
tensile strength and CVN toughness of weld
material specimens shall be determined in
accordance with Standard Methods for Mechanical
Testing of Welds (AWS B4.0/B4.0M). The use of
tensile strength and CVN toughness values that are
reported on the manufacturer’s typical certificate of
conformance in lieu of physical testing is prohibited
for use for purposes of this section.
The same WPS shall be used to make the test
specimen and the material test plate. The material
test plate shall use base metal of the same grade and
type as was used for the test specimen, although the
same heat need not be used. If the average heat input
used for making the material test plate is not within
20% of that used for the test specimen, a new
material test plate shall be made and tested.
12.7.2.7
Test Reporting Requirements.
For each test specimen, a written test report meeting
the requirements of the author-ity having
jurisdiction and the requirements of this section
shall be prepared. The report shall thoroughly
document all key features and results of the test.
The report shall include the following information:
1. A drawing or clear description of the test
subassemblage, including key dimensions, boundary conditions at loading and
reaction points, and location of lateral
braces.
2. A drawing of the connection detail
showing member sizes, grades of steel, the
sizes of all connection elements, welding
details including filler metal, the size and
location of bolt holes, the size and grade of
bolts, and all other pertinent details of the
connection.
3. A listing of all other essential variables for
the test specimen, as listed in Section
12.7.2.3.
4. A listing or plot showing the applied load
or displacement history of the test
specimen.
5. A listing of all welds to be designated
demand critical.
6. Definition of the region of the member and
connection to be designated a protected
zone.
7. A plot of the applied load versus the
displacement of the test specimen. The
displacement reported in this plot shall be
measured at or near the point of load
application. The locations on the test
specimen
where
the
loads
and
displacements were measured shall be
clearly indicated.
8. A plot of beam moment versus story drift
angle for beam-to-column moment
connections; or a plot of link shear force
versus link rotation angle for link-tocolumn connections. For beam-to-column
connections, the beam moment and the
story drift angle shall be computed with
respect to the centerline of the column.
9. The story drift angle and the total inelastic
rotation developed by the test specimen.
The components of the test specimen
contributing to the total inelastic rotation
due to yielding or slip shall be identified.
The portion of the total inelastic rotation
contributed by each component of the test
specimen shall be reported. The method
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
used to compute inelastic rotations shall be
clearly shown.
10. A chronological listing of significant test
observations, including observations of
yielding, slip, instability, and rupture of
any portion of the test specimen as
applicable.
11. The controlling failure mode for the test
specimen. If the test is terminated prior to
failure, the reason for terminating the test
shall be clearly indicated.
12. The results of the material specimen tests
specified in Section 12.7.2.6.
13. The welding procedure specifications
(WPS) and welding inspection reports.
14. Additional drawings, data, and discussion
of the test specimen or test results are
permitted to be included in the report.
12.7.2.8
Acceptance Criteria. The test
specimen must satisfy the strength and story drift
angle or link rotation angle requirements of the
provisions of this chapter for the special moment
frame, intermediate moment frame, or eccentrically
braced frame connection, as applicable. The test
specimen must sustain the required story drift angle
or link rotation angle for at least one complete
loading cycle.
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TABLES AND FIGURES OF CHAPTER 12
TABLE 12-1 : Ry AND Rt VALUES FOR STEEL AND STEEL REINFORCEMENT MATERIALS
Application
Hot-rolled structural shapes and bars:
Ry
Rt
• ASTM A36/A36M
1.5
1.2
• ASTM A1043/1043M Gr. 36 (250)
1.3
1.1
• ASTM A572/572M Gr. 50 (345) or 55 (380),
1.1
1.1
• ASTM A1043/A1043M Gr. 50 (345)
1.2
1.1
• ASTM A529 Gr. 50 (345)
1.2
1.2
• ASTM A529 Gr. 55 (380)
1.1
1.2
• ASTM A500/A500M (Gr. B or C), ASTM A501
1.4
1.3
Pipe:
• ASTM A53/A53M
Plates, Strips and Sheets:
1.6
1.2
• ASTM A36/A36M
1.3
1.2
• ASTM A1043/1043M Gr. 36 (250)
1.3
1.1
• A1011/A1011M HSLAS Gr. 55 (380)
1.1
1.1
• ASTM A572/A572M Gr. 42 (290)
1.3
1.0
• ASTM A572/A572M Gr. 50 (345), Gr. 55 (380), ASTM A588/A588M
1.1
1.2
1.2
1.1
1.25
1.25
ASTM A913/A913M Gr. 50 (345), 60 (415), or 65 (450),
ASTM A588/A588M, ASTM A992/A992M
Hollow structural sections (HSS):
• ASTM 1043/1043M Gr. 50 (345)
Steel Reinforcement:
• ASTM A615, ASTM A706
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Unstiffened Elements
TABLE 12-2 : LIMITING WIDTH-TO-THICKNESS RATIOS FOR COMPRESSION ELEMENTS
FOR MODERATELY DUCTILE AND HIGHLY DUCTILE MEMBERS
Limiting Width-to-Thickness
Ratios
𝝀𝒉𝒅
𝝀𝒎𝒅
Highly Ductile
Moderately
Members
Ductile Members
Description of
Elements
Width-toThickness
Ratio
Flanges of rolled or
built-up I-shaped
sections, channels and
tees; legs of single
angle or double angle
members with
separators; outstanding
legs of pairs of angles
in continuous contact
𝑏/𝑡
0.3√𝐸/𝐹𝑦
0.38√𝐸/𝐹𝑦
Flanges of H-pile
sections per section
12.2.5.5
𝑏/𝑡
0.45√𝐸/𝐹𝑦
not Applicable
Stems of tees
𝑑/𝑡
0.3√𝐸/𝐹𝑦
Walls of rectangular
HSS
𝑏/𝑡
Example
[𝑎]
Flanges of boxed Ishaped sections and
built-up box sections
0.38√𝐸/𝐹𝑦
𝑏/𝑡
Stiffened Elements
[𝑏]
Side plates of boxed Ishaped sections and
walls of built-up box
shapes used as diagonal
braces
Webs of rolled or builtup I-shaped sections
used as diagonal braces
ℎ/𝑡
ℎ/𝑡𝑤
[𝑐]
0.55√𝐸/𝐹𝑦
0.64√𝐸/𝐹𝑦
1.49√𝐸/𝐹𝑦
1.49√𝐸/𝐹𝑦
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
Stiffened Elements
TABLE 12-2 (CONTINOUED): LIMITING WIDTH-TO-THICKNESS RATIOS FOR
COMPRESSION ELEMENTS FOR MODERATELY DUCTILE AND HIGHLY DUCTILE
MEMBERS
Description of
Elements
Width-toThickness
Ratio
Webs of rolled or
built-up I-shaped
sections used as
beams or columns [d]
ℎ/𝑡𝑤
Side plates of boxed
I-shaped sections
used as beams or
columns
ℎ/𝑡
Limiting Width-to-Thickness Ratios
𝝀𝒉𝒅
𝝀𝒎𝒅
Highly Ductile
Moderately Ductile
Members
Members
𝑓𝑜𝑟 𝐶𝑎 ≤ 0.125
2.45√𝐸/𝐹𝑦 (1
𝑓𝑜𝑟 𝐶𝑎 ≤ 0.125
− 0.93𝐶𝑎 )
𝑓𝑜𝑟 𝐶𝑎 > 0.125
3.76√𝐸/𝐹𝑦 (1 − 2.75𝐶𝑎 )
0.77√𝐸/𝐹𝑦 (2.93 − 𝐶𝑎 )
𝑓𝑜𝑟 𝐶𝑎 > 0.125
≥ 1.49√𝐸/𝐹𝑦
Example
1.12√𝐸/𝐹𝑦 (2.33 − 𝐶𝑎 )
≥ 1.49√𝐸/𝐹𝑦
where
𝑃𝑢
𝜑𝑐 𝑃𝑦
where
Webs of built-up
box sections used as
beams or column
ℎ/𝑡
Webs of H-pile
sections
ℎ/𝑡𝑤
0.94√𝐸/𝐹𝑦
not Applicable
Walls of round HSS
𝐷/𝑡
0.038𝐸/𝐹𝑦
0.044√𝐸/𝐹𝑦
Walls of rectangular
filled composite
members
𝑏/𝑡
1.4√𝐸/𝐹𝑦
2.26√𝐸/𝐹𝑦
Walls of round filled
composite members
𝐷/𝑡
0.076𝐸/𝐹𝑦
0.15𝐸/𝐹𝑦
𝐶𝑎 =
𝐶𝑎 =
𝑃𝑢
𝜑𝑐 𝑃𝑦
Composite Elements
[𝑎]
[a] for tee shaped compression members, the limiting width-to-thickness ratio for highly ductile members for the stem of the tee can be increased to
0.38√𝐸/𝐹𝑦 if either of the following conditions are satisfied:
(1) bukling of the compression member occurs about the plane of the stem
(2) the axial compression is transferred at end connections to only the outside face of the flange of the tee resulting in an eccentric connection that
reduces the compression stresses at the tip of the stem
[b] the limiting width-to-thickness ratio of flanges of boxed I-shaped sections and built-up box sections of columns in SMF systems shall not exceed
0.6√𝐸/𝐹𝑦 .
[c] the limiting width-to thickness ratio of walls of rectangular HSS members, flanges of boxed I-shaped sections and falnges of built-up box sections
used as beams or columns shall not exceed 1.12√𝐸/𝐹𝑦 .
[d] for I-shaped beams in SMF systems, where Ca is less than or equal to 0.125, the limiting ratio ℎ/𝑡𝑤 shall not exceed 2.45√𝐸/𝐹𝑦 . For I-shaped
beams in IMF systems, where Ca is less than or equal to 0.125, the limiting width-to-thickness ratio shall not exceed 3.76√𝐸/𝐹𝑦 .
[e] the limiting diameter-to-thickness ratio of round HSS members used as beams or column shall not exceed 0.07 𝐸/𝐹𝑦 .
SBC 306-CR-18
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CHAPTER 12—SEISMIC PROVISIONS FOR STRUCTURAL STEEL BUILDINGS
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SBC 306-CR-18
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CHAPTER 13—DESIGN FOR SERVICEABLILITY
CHAPTER 13—DESIGN FOR SERVICEABLILITY
This chapter addresses serviceability design
requirements. The chapter is organized as follows:
13.1 —General Provisions
13.2 —Camber
13.3 —Deflection
13.3—Deflection
Deflections in structural members and structural
systems
under
appropriate
service
load
combinations shall not impair the serviceability of
the structure.
User Note: Conditions to be considered
include levelness of floors, alignment of
structural members, integrity of building
finishes, and other factors that affect the
normal usage and function of the structure.
For composite members, the additional
deflections due to the shrinkage and creep of
the concrete should be considered.
13.4 —Drift
13.5 —Vibration
13.6 —Wind-Induced Motion
13.7 —Expansion and Contraction
13.8 —Connection Slip
13.1—General Provisions
Serviceability is a state in which the function of a
building, its appearance, maintainability, durability
and comfort of its occupants are preserved under
normal usage. Limiting values of structural
behavior for serviceability (such as maximum
deflections and accelerations) shall be chosen with
due regard to the intended function of the structure.
Serviceability shall be evaluated using appropriate
load combinations for the serviceability limit states
identified.
13.4—Drift
Drift of a structure shall be evaluated under service
loads to provide for serviceability of the structure,
including the integrity of interior partitions and
exterior cladding. Drift under strength load
combinations shall not cause collision with adjacent
structures or exceed the limiting values of such
drifts that may be specified by the applicable Saudi
building code.
13.5—Vibration
User Note: Serviceability limit states, service
loads, and appropriate load combinations for
serviceability requirements can be found in SBC
301, Appendix C and Commentary to Appendix
C. The performance requirements for
serviceability in this chapter are consistent with
those requirements. Service loads, as stipulated
herein, are those that act on the structure at an
arbitrary point in time and are not usually taken
as the nominal loads.
The effect of vibration on the comfort of the
occupants and the function of the structure shall be
considered. The sources of vibration to be
considered include pedestrian loading, vibrating
machinery and others identified for the structure.
13.6—Wind-Induced Motion
The effect of wind-induced motion of buildings on
the comfort of occupants shall be considered.
13.7—Expansion and Contraction
13.2—Camber
Where camber is used to achieve proper position
and location of the structure, the magnitude,
direction and location of camber shall be specified
in the structural drawings.
The effects of thermal expansion and contraction of
a building shall be considered. Damage to building
cladding can cause water penetration and may lead
to corrosion.
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CHAPTER 13—DESIGN FOR SERVICEABLILITY
13.8—Connection Slip
The effects of connection slip shall be included in
the design where slip at bolted connections may
cause deformations that impair the serviceability of
the structure. Where appropriate, the connection
shall be designed to preclude slip.
User Note: For the design of slip-critical
connections, see Sections 10.3.8 and 10.3.9 .
For more information on connection slip, refer
to the RCSC Specification for Structural Joints
Using High-Strength Bolts.
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CHAPTER 13—DESIGN FOR SERVICEABLILITY
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CHAPTER 14—FABRICATION AND ERECTION
CHAPTER 14—FABRICATION AND ERECTION
This chapter addresses requirements for shop
drawings, fabrication, shop painting and erection.
The chapter is organized as follows:
14.1
—Shop and Erection Drawings
14.2
—Fabrication
14.3
—Shop Painting
14.4
—Erection
14.1—Shop and Erection Drawings
Shop and erection drawings are permitted to be
prepared in stages. Shop drawings shall be
prepared in advance of fabrication and give
complete information necessary for the fabrication
of the component parts of the structure, including
the location, type and size of welds and bolts.
Erection drawings shall be prepared in advance of
erection and give information necessary for erection
of the structure. Shop and erection drawings shall
clearly distinguish between shop and field welds
and bolts and shall clearly identify pretensioned
and slip-critical high-strength bolted connections.
Shop and erection drawings shall be made with due
regard to speed and economy in fabrication and
erection.
14.2—Fabrication
14.2.1 Cambering, Curving and Straightening.
Local application of heat or mechanical means is
permitted to be used to introduce or correct camber,
curvature and straightness. The temperature of
heated areas shall not exceed 593 C for ASTM
A514/A514M and ASTM A852/A852M steel nor
649 C for other steels.
14.2.2 Thermal Cutting. Thermally cut edges
shall meet the requirements of AWS D1.1/D1.1M,
sub clauses 5.15.1.2, 5.15.4.3 and 5.15.4.4 with the
exception that thermally cut free edges that will not
be subject to fatigue shall be free of round-bottom
gouges greater than 5 mm deep and sharp V-shaped
notches. Gouges deeper than 5 mm and notches
shall be removed by grinding or repaired by
welding.
Reentrant corners shall be formed with a curved
transition. The radius need not exceed that
required to fit the connection. The surface
resulting from two straight torch cuts meeting at a
point is not considered to be curved. Discontinuous
corners are permitted where the material on both
sides of the discontinuous reentrant corner are
connected to a mating piece to prevent
deformation and associated stress concentration at
the corner.
User Note: Reentrant corners with a radius of
13 to 10 mm are acceptable for statically loaded
work. Where pieces need to fit tightly together, a
discontinuous reentrant corner is acceptable if
the pieces are connected close to the corner on
both sides of the discontinuous corner. Slots in
HSS for gussets may be made with semicircular
ends or with curved corners. Square ends are
acceptable provided the edge of the gusset is
welded to the HSS.
Weld access holes shall meet the geometrical
requirements of Section 10.1.6 . Beam copes and
weld access holes in shapes that are to be
galvanized shall be ground to bright metal. For
shapes with a flange thickness not exceeding 50
mm, the roughness of thermally cut surfaces of
copes shall be no greater than a surface roughness
value of 50 m as defined in ASME B46.1. For
beam copes and weld access holes in which the
curved part of the access hole is thermally cut in
ASTM A6/A6M hot-rolled shapes with a flange
thickness exceeding 50 mm and welded built-up
shapes with material thickness greater than 50 mm,
a preheat temperature of not less than 66 C shall
be applied prior to thermal cutting. The thermally
cut surface of access holes in ASTM A6/A6M
hot-rolled shapes with a flange thickness exceeding
50 mm and built-up shapes with a material
thickness greater than 50 mm shall be ground.
User Note: The AWS Surface Roughness Guide
for Oxygen Cutting (AWS C4.1-77) Sample 2
may be used as a guide for evaluating the surface
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CHAPTER 14—FABRICATION AND ERECTION
roughness of copes in shapes with flanges not
exceeding 50 mm thick.
14.2.3 Planning of Edges. Planning or finishing
of sheared or thermally cut edges of plates or
shapes is not required unless specifically called for
in the construction documents or included in a
stipulated edge preparation for welding.
14.2.4 Welded Construction. The technique of
welding, the workmanship, appearance, and quality
of welds, and the methods used in correcting
nonconforming work shall be in accordance with
AWS D1.1/D1.1M except as modified in Section
10.2.
14.2.5 Bolted Construction. Parts of bolted
members shall be pinned or bolted and rigidly held
together during assembly. Use of a drift pin in bolt
holes during assembly shall not distort the metal or
enlarge the holes. Poor matching of holes shall be
cause for rejection.
Bolt holes shall comply with the provisions of the
RCSC Specification for Structural Joints Using
High-Strength Bolts, hereafter referred to as the
RCSC Specification, Section 3.3 except that
thermally cut holes are permitted with a surface
roughness profile not exceeding 25 m as defined
in ASME B46.1. Gouges shall not exceed a depth
of 2 mm. Water jet cut holes are also permitted.
User Note: The AWS Surface Roughness
Guide for Oxygen Cutting (AWS C4.1- 77)
sample 3 may be used as a guide for
evaluating the surface roughness of thermally
cut holes.
Fully inserted finger shims, with a total thickness
of not more than 6 mm within a joint, are permitted
without changing the strength (based upon hole
type) for the design of connections. The orientation
of such shims is independent of the direction of
application of the load.
The use of high-strength bolts shall conform to
the requirements of the RCSC Specification,
except as modified in Section 10.3.
14.2.6 Compression Joints. Compression joints
that depend on contact bearing as part of the splice
strength shall have the bearing surfaces of
individual fabricated pieces prepared by milling,
sawing or other suitable means.
14.2.7 Dimensional Tolerances. Dimensional
tolerances shall be in accordance with Chapter 6 of
the AISC Code of Standard Practice for Steel
Buildings and Bridges, hereafter referred to as the
Code of Standard Practice, AISC 303-10 (2010).
14.2.8 Finish of Column Bases. Column bases
and base plates shall be finished in accordance
with the following requirements:
1. Steel bearing plates 50 mm or less in
thickness are permitted without milling
provided a satisfactory contact bearing is
obtained. Steel bearing plates over 50 mm
but not over 100 mm in thickness are
permitted to be straightened by pressing
or, if presses are not available, by milling
for bearing surfaces, except as noted in
subparagraphs 2 and 3 of this section,
to obtain a satisfactory contact bearing.
Steel bearing plates over 100 mm in
thickness shall be milled for bearing
surfaces, except as noted in subparagraphs
2 and 3 of this section.
2. Bottom surfaces of bearing plates and
column bases that are grouted to ensure
full bearing contact on foundations need
not be milled.
3. Top surfaces of bearing plates need not be
milled when complete-joint-penetration
groove welds are provided between the
column and the bearing plate.
14.2.9 Holes for Anchor Rods. Holes for anchor
rods are permitted to be thermally cut in
accordance with the provisions of Section 14.2.2 .
14.2.10 Drain Holes. When water can collect
inside HSS or box members, either during
construction or during service, the member shall be
sealed, provided with a drain hole at the base, or
protected by other suitable means.
14.2.11 Requirements for Galvanized Members.
Members and parts to be galvanized shall be
designed, detailed and fabricated to provide for flow
and drainage of pickling fluids and zinc and to
prevent pressure buildup in enclosed parts.
User Note: See The Design of Products to be
Hot-Dip
Galvanized After
Fabrication,
American Galvanizer’s Association, and
ASTM A123, A153, A384 and A780 for useful
information on design and detailing of
galvanized members. See Section 14.2 for
requirements for copes of members to be
galvanized.
SBC 306-CR-18
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CHAPTER 14—FABRICATION AND ERECTION
14.3—Shop Painting
14.3.1 General Requirements. Shop painting
and surface preparation shall be in accordance with
the provisions in Chapter 6 of the Code of Standard
Practice, AISC 303-10 (2010).
Shop paint is not required unless specified by the
contract documents.
14.3.2 Inaccessible Surfaces. Except for contact
surfaces, surfaces inaccessible after shop assembly
shall be cleaned and painted prior to assembly, if
required by the construction documents.
14.3.3 Contact Surfaces. Paint is permitted in
bearing-type connections. For slip-critical
connections, the faying surface requirements shall
be in accordance with the RCSC Specification,
Section 3.2.2.2 .
14.3.4 Finished Surfaces.
Machine-finished
surfaces shall be protected against corrosion by a
rust inhibitive coating that can be removed prior to
erection, or which has characteristics that make
removal prior to erection unnecessary.
14.4.4 Fit of Column Compression Joints and
Base Plates. Lack of contact bearing not exceeding
a gap of 2 mm, regardless of the type of splice used
(partial-joint-penetration groove welded or bolted),
is permitted. If the gap exceeds 2 mm, but is equal
to or less than 6 mm, and if an engineering
investigation shows that sufficient contact area
does not exist, the gap shall be packed out with
nontapered steel shims. Shims need not be other
than mild steel, regardless of the grade of the main
material.
14.4.5 Field Welding. Surfaces in and adjacent
to joints to be field welded shall be prepared as
necessary to assure weld quality. This preparation
shall include surface preparation necessary to
correct for damage or contamination occurring
subsequent to fabrication.
14.4.6 Field Painting. Responsibility for touchup painting, cleaning and field painting shall be
allocated in accordance with accepted local
practices, and this allocation shall be set forth
explicitly in the contract documents.
14.3.5 Surfaces Adjacent to Field Welds.
Unless otherwise specified in the design
documents, surfaces within 50 mm of any field
weld location shall be free of materials that would
prevent proper welding or produce objectionable
fumes during welding.
14.4—Erection
14.4.1 Column Base Setting. Column bases shall
be set level and to correct elevation with full bearing
on concrete or masonry as defined in Chapter 7 of
the AISC Code of Standard Practice.
14.4.2 Stability and Connections. The frame of
structural steel buildings shall be carried up true
and plumb within the limits defined in Chapter 7 of
the AISC Code of Standard Practice. As erection
progresses, the structure shall be secured to support
dead, erection and other loads anticipated to occur
during the period of erection. Temporary bracing
shall be provided, in accordance with the
requirements of the AISC Code of Standard
Practice, wherever necessary to support the loads
to which the structure may be subjected,
including equipment and the operation of same.
Such bracing shall be left in place as long as
required for safety.
14.4.3 Alignment. No permanent bolting or
welding shall be performed until the adjacent
affected portions of the structure have been properly
aligned.
SBC 306-CR-18
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CHAPTER 14—FABRICATION AND ERECTION
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SBC 306-CR-18
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CHAPTER 15—QUALITY CONTROL AND QUALITY ASSURANCE
CHAPTER 15—QUALITY CONTROL AND QUALITY ASSURANCE
This chapter addresses minimum requirements for
quality
control,
quality
assurance
and
nondestructive testing for structural steel systems
and composite members for buildings and other
structures.
User Note: This chapter does not address
quality control or quality assurance for surface
preparation or coatings.
User Note: The inspection of steel (open-web)
joists and joist girders, tanks, pressure vessels,
cables, cold-formed steel products, or gage
metal products is not addressed in this Code.
User Note: The QA/QC requirements in
Chapter 15 are considered adequate and
effective for most steel structures and are
strongly encouraged without modification.
When the ABC and AHJ requires the use of
a quality assurance plan, this chapter outlines
the minimum requirements deemed effective
to provide satisfactory results in steel building
construction. There may be cases where
supplemental inspections are advisable.
Additionally, where the contractor’s quality
control program has demonstrated the
capability to perform some tasks this plan has
assigned to quality assurance, modification of
the plan could be considered.
The Chapter is organized as follows:
15.1 —Scope
15.2—Fabricator and Erector Quality Control
Program
15.3 —Fabricator and Erector Documents
15.4 —Inspection and Nondestrective Testing
Personnel
15.5 —Minimum
Requirements
for
Inspection of Structural Steel Bulidings
15.6 —Minimum
Requirements
for
Inspection of Composite Construction
15.7 —Approved Fabricators and Erectors
15.8 —Nonconforming
Workmanship
Material
and
15.1—Scope
Quality control (QC) as specified in this chapter
shall be provided by the fabricator and erector.
Quality assurance (QA) as specified in this chapter
shall be provided by others when required by the
authority having jurisdiction (AHJ), applicable
building code (ABC), purchaser, owner, or engineer
of record (EOR). Nondestructive testing (NDT)
shall be performed by the agency or firm
responsible for quality assurance, except as
permitted in accordance with Section 15.7.
User Note: The producers of materials
manufactured in accordance with standard
specifications referenced in Section 1.3 in this
Code, and steel deck manufacturers, are not
considered to be fabricators or erectors.
15.2—Fabricator and Erector Quality
Control Program
The fabricator and erector shall establish and
maintain quality control procedures and perform
inspections to ensure that their work is performed
in accordance with this Specification and the
construction documents.
Material identification procedures shall comply
with Section 15.2.1 and shall be monitored by the
fabricator’s quality control inspector (QCI).
The fabricator’s QCI shall inspect the following as
a minimum, as applicable:
1. Shop welding, high-strength bolting, and
details in accordance with Section 15.5.
2. Shop cut and finished surfaces in
accordance with Section 14.2.
3. Shop
heating
for
straightening,
cambering and curving in accordance
with Section 14.2.1 .
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CHAPTER 15—QUALITY CONTROL AND QUALITY ASSURANCE
4. Tolerances for shop fabrication in
accordance with Section 6 of the Code
of Standard Practice, AISC 303-10.
The erector’s QCI shall inspect the following as a
minimum, as applicable:
1. Field welding, high-strength bolting, and
details in accordance with Section 15.5.
2. Steel deck and headed steel stud anchor
placement and attachment in accordance
with Section 15.6.
3. Field cut surfaces in accordance with
Section 14.2.2 .
4. Field heating for straightening
accordance with Section 14.2.1 .
in
5. Tolerances for field erection in
accordance with Section 7.13 of the
Code of Standard Practice, AISC 303-10 .
15.2.1 Identification of Steel. The fabricator
shall be able to demonstrate by written procedure
and actual practice a method of material
identification, visible up to the point of assembling
members. Identification procedures shall comply
with the requirements of Section 6.16.1 of the Code
of Standard Practice, AISC 303-10.
15.3—Fabricator and Erector
Documents
5. For demand critical welds, applicable
manufacturer’s certifications that the filler
metal meets the supplemental notch
toughness requirements, as applicable.
Should the filler metal manufacturer not
supply such supplemental certifications,
the fabricator or erector, as applicable,
shall have the necessary testing performed
and provide the applicable test reports
6. Manufacturer’s product data sheets or
catalog data for shielded metal arc welding
(SMAW), flux cored arc welding (FCAW)
and gas metal arc welding (GMAW)
composite (cored) filler metals to be used
7. Bolt installation procedures
8. Specific assembly order, welding
sequence, welding technique, or other
special precautions for joints or groups of
joints where such items are designated to
be submitted to the engineer of record
For composite construction, the following
documents shall be submitted by the responsible
contractor for review by the EOR or the EOR’s
designee, prior to concrete production or placement,
as applicable:
1. Concrete mix design and test reports for
the mix design
2. Reinforcing steel shop drawings
15.3.1 Submittals for Steel Construction. The
fabricator or erector shall submit the following
documents for review by the engineer of record
(EOR) or the EOR’s designee, in accordance with
Section 4 or A4.4 of the Code of Standard Practice,
AISC 303-10, prior to fabrication or erection, as
applicable:
1. Shop drawings, unless shop drawings have
been furnished by others
3. Concrete placement sequences, techniques
and restriction
15.3.2 Available
Documents
for
Steel
Construction. The following documents shall be
available in electronic or printed form for review
by the EOR or the EOR’s designee prior to
fabrication or erection, as applicable, unless
otherwise required in the contract documents to be
submitted:
2. Erection drawings, unless erection
drawings have been furnished by others
1. For main structural steel elements, copies
of material test reports in accordance with
Section 1.3.1 .
For seismic force resisting systems, the following
additional documents shall be submitted, as
applicable:
2. For steel castings and forgings, copies of
material test reports in accordance with
Section 1.3.2 .
3. Welding procedure specifications (WPS)
3. For fasteners, copies of manufacturer’s
certifications in accordance with Section
1.3.3 .
4. Copies of the manufacturer’s typical
certificate of conformance for all
electrodes, fluxes and shielding gasses to
be used
4. For
deck
fasteners,
copies
of
manufacturer’s product data sheets or
catalog data. The data sheets shall describe
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CHAPTER 15—QUALITY CONTROL AND QUALITY ASSURANCE
the product, limitations of use, and
recommended or typical installation
instructions.
5. For anchor rods and threaded rods, copies
of material test reports in accordance with
Section 1.3.4 .
6. For welding consumables, copies of
manufacturer’s
certifications
in
accordance with Section 1.3.5 .
7. For headed stud anchors, copies of
manufacturer’s
certifications
in
accordance with Section 1.3.6 .
8. Manufacturer’s product data sheets or
catalog data for welding filler metals and
fluxes to be used. The data sheets shall
describe the product, limitations of use,
recommended
or
typical
welding
parameters, and storage and exposure
requirements, including baking, if
applicable.
9. Welding procedure specifications (WPSs).
10. Procedure qualification records (PQRs)
for WPSs that are not prequalified in
accordance with AWS D1.1/D1.1M or
AWS D1.3/D1.3M, as applicable.
11. Welding
personnel
qualification records
continuity records.
performance
(WPQR) and
12. Fabricator’s or erector’s, as applicable,
written quality control manual that shall
include, as a minimum:
Material control procedures
Inspection procedures
Nonconformance procedures
13. Fabricator’s or erector’s, as applicable, QC
inspector qualifications.
15.3.3 Submittals for Composite Construction.
For composite construction, the following
documents shall be submitted by the responsible
contractor for review by the EOR or the EOR’s
designee, prior to concrete production or placement,
as applicable:
1. Concrete mix design and test reports for
the mix design
2. Reinforcing steel shop drawings
3. Concrete placement sequences, techniques
and restriction
15.3.4 Available Documents for Composite
Construction. For composite construction, the
following documents shall be available from the
responsible contractor for review by the EOR or the
EOR’s designee prior to fabrication or erection, as
applicable, unless specified to be submitted:
1. Material test reports for reinforcing steel
2. Inspection procedures
3. Nonconformance procedure
4. Material control procedure
5. Welder performance qualification records
(WPQR) as required by AWS D1.4/D1.4M.
6. QC Inspector qualifications
The responsible contractor shall retain their
document(s) for at least one year after substantial
completion of construction.
15.4—Inspection and Nondestrective
Testing Personnel
15.4.1 Quality
Control
Inspector
Qualifications. Quality control (QC) welding
inspection personnel shall be qualified to the
satisfaction of the fabricator’s or erector’s QC
program, as applicable, and in accordance with
either of the following:
(a) Associate welding inspectors (AWI) or higher
as defined in AWS B5.1, Standard for the
Qualification of Welding Inspectors, or
(b) Qualified under the provisions of AWS
D1.1/D1.1M sub clause 6.1.4
QC bolting
inspection personnel shall be qualified on the
basis of documented training and experience in
structural bolting inspection.
15.4.2 Quality
Assurance
Inspector
Qualifications. Quality assurance (QA) welding
inspectors shall be qualified to the satisfaction of
the QA agency’s written practice, and in accordance
with either of the following:
(a) Welding inspectors (WIs) or senior welding
inspectors (SWIs), as defined in AWS B5.1,
Standard for the Qualification of Welding
Inspectors, except associate welding inspectors
(AWIs) are permitted to be used under the
direct supervision of WIs, who are on the
premises and available when weld inspection
is being conducted, or
(b) Qualified under the provisions of AWS
D1.1/D1.1M, sub clause 6.1.4. QA bolting
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CHAPTER 15—QUALITY CONTROL AND QUALITY ASSURANCE
inspection personnel shall be qualified on the
basis of documented training and experience in
structural bolting inspection.
15.4.3 NDT
Personnel
Qualifications.
Nondestructive testing personnel, for NDT other
than visual, shall be qualified in accordance with
their employer’s written practice, which shall meet
or exceed the criteria of AWS D1.1/D1.1M
Structural Welding Code—Steel, sub clause 6.14.6,
and:
(a) American Society for Nondestructive Testing
(ASNT) SNT-TC-1A, Recommended Practice
for the Qualification and Certification of
Nondestructive Testing Personnel, or
(b) ASNT CP-189, Standard for the Qualification
and Certification of Nondestructive Testing
Personnel.
15.4.4.2
Inspection and Nondestructive
Testing Personnel. In addition to the requirements
of Sections 15.4.1 and 15.4.2, visual welding
inspection and non-destructive testing (NDT) shall
be conducted by personnel qualified in accordance
with AWS D1.1/D1.1M clause 7.2. In addition to the
requirements of Section 15.4.3, ultrasonic testing
technicians shall be qualified in accordance with
AWS D1.1/D1.1M clause 7.2.4.
User Note: The recommendations of the
International Code Council Model Program for
Special Inspection should be considered a
minimum requirement to establish the
qualifications of a bolting inspector.
15.4.4 Additional Requirements for Seismic
Force Resisting Systems (SFRS)
15.5—Minimum Requirements for
Inspection of Structural Steel
Bulidings
15.4.4.1 Quality
Assurance
Agency
Documents. The agency responsible for quality
assurance shall submit the following documents to
the authority having jurisdiction, the engineer of
record, and the owner or owner’s designee:
15.5.1 Quality Control. QC inspection tasks
shall be performed by the fabricator’s or erector’s
quality control inspector (QCI), as applicable, in
accordance with Sections 15.5.4 , 15.5.5, 15.5.6
and 15.5.7 .
1. QA agency’s written practices for the
monitoring and control of the agency’s
operations. The written practice shall
include:
Tasks in TABLE 15-1 through TABLE 15-3 and
TABLE 15-4 through TABLE 15-6 listed for QC
are those inspections performed by the QCI to
ensure that the work is performed in accordance
with the construction documents.
The agency’s procedures for the
selection and administration of
inspection personnel, describing the
training, experience and examination
requirements for qualification and
certification of inspection personnel,
and
The agency’s inspection procedures,
including general inspection, material
controls, and visual welding inspection
2. Qualifications of management and QA
personnel designated for the project
3. Qualification records for inspectors and
NDT technicians designated for the project
4. NDT
procedures
and
equipment
calibration records for NDT to be
performed and equipment to be used for
the project
5.
For composite construction, concrete
testing procedures and equipment
For QC inspection, the applicable construction
documents are the shop drawings and the erection
drawings, and the applicable referenced
specifications, codes and standards.
15.5.2 Quality Assurance. Quality assurance
(QA) inspection of fabricated items shall be made
at the fabricator’s plant. The quality assurance
inspector (QAI) shall schedule this work to
minimize interruption to the work of the fabricator.
QA inspection of the erected steel system shall be
made at the project site. The QAI shall schedule this
work to minimize interruption to the work of the
erector.
The QAI shall review the material test reports and
certifications as listed in Section 15.3.2 for
compliance with the construction documents.
QA inspection tasks shall be performed by the
QAI, in accordance with Sections 15.5.4 , 15.5.5,
15.5.6 and 15.5.7 .
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User Note: The QCI need not refer to the design
drawings and project specifications. The Code
of Standard Practice for Steel Buildings and
Bridges, AISC 303-10, Section 4.2(a), requires
the transfer of information from the Contract
Documents (design drawings and project
specification) into accurate and complete shop
and erection drawings, allowing QC inspection
to be based upon shop and erection drawings
alone.
Tasks in TABLE 15-1 through TABLE 15-3 and
TABLE 15-4 through TABLE 15-6 listed for QA
are those inspections performed by the QAI to
ensure that the work is performed in accordance
with the construction documents.
Concurrent with the submittal of such reports to
the AHJ, EOR or owner, the QA agency shall
submit to the fabricator and erector:
1. Inspection reports
2. Nondestructive testing reports
15.5.3 Coordinated Inspection. Where a task is
noted to be performed by both QC and QA, it is
permitted to coordinate the inspection function
between the QCI and QAI so that the inspection
functions are performed by only one party. Where
QA relies upon inspection functions performed by
QC, the approval of the engineer of record and
the authority having jurisdiction is required.
15.5.4 Welding Inspection and Nondestructive
Testing
15.5.4.1
Visual Welding Inspection.
Observation of welding operations and visual
inspection of in-process and completed welds shall
be the primary method to confirm that the
materials, procedures and workmanship are in
conformance with the construction documents. For
structural steel, all provisions of AWS
D1.1/D1.1M Structural Welding Code—Steel for
statically loaded structures shall apply.
User Note: Section 10.2 of this Code contains
exceptions to AWS D1.1/D1.1M.
As a minimum, welding inspection tasks shall be in
accordance with TABLE 15-1, TABLE 15-2 and
TABLE 15-3. In these tables, the inspection tasks
are as follows:
O – Observe these items on a random basis.
Operations need not be delayed pending these
inspections.
P – Perform these tasks for each welded joint or
member.
15.5.4.2
Nondestructive
Welded Joints
Testing
of
15.5.4.2.1
Procedures. Ultrasonic testing
(UT), magnetic particle testing (MT), penetrant
testing (PT) and radiographic testing (RT), where
required, shall be performed by QA in accordance
with AWS D1.1/D1.1M. Acceptance criteria shall
be in accordance with AWS D1.1/D1.1M for
statically loaded structures, unless otherwise
designated in the design drawings or project
specifications.
15.5.4.2.2
CJP Groove Weld NDT. For
structures in Risk Category III or IV of Table 1-1,
Risk Category of Buildings and Other Structures
for Flood, Wind and Earthquake Loads, of SBC
301, UT shall be performed by QA on all CJP
groove welds subject to transversely applied
tension loading in butt, T- and corner joints, in
materials 8 mm thick or greater. For structures in
Risk Category II, UT shall be performed by QA on
10% of CJP groove welds in butt, T- and corner
joints subject to transversely applied tension
loading, in materials 8 mm thick or greater.
User Note: For structures in Risk Category I,
NDT of CJP groove welds is not required. For
all structures in all Risk Categories, NDT of CJP
groove welds in materials less than 8 mm thick
is not required.
15.5.4.2.3
Access Hole NDT. Thermally cut
surfaces of access holes shall be tested by QA using
MT or PT, when the flange thickness exceeds 50
mm for rolled shapes, or when the web thickness
exceeds 50 mm for built-up shapes. Any crack
shall be deemed unacceptable regardless of size or
location.
15.5.4.2.4
Welded Joints Subjected to
Fatigue. When required by Appendix C, TABLE
C-1, welded joints requiring weld soundness to be
established by radiographic or ultrasonic
inspection shall be tested by QA as prescribed.
Reduction in the rate of UT is prohibited.
15.5.4.2.5
Reduction of Rate of Ultrasonic
Testing. The rate of UT is permitted to be reduced
if approved by the EOR and the AHJ. Where the
initial rate for UT is 100%, the NDT rate for an
individual welder or welding operator is permitted
to be reduced to 25%, provided the reject rate, the
number of welds containing unacceptable defects
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divided by the number of welds completed, is
demonstrated to be 5% or less of the welds tested
for the welder or welding operator. A sampling
of at least 40 completed welds for a job shall be
made for such reduction evaluation. For
evaluating the reject rate of continuous welds over
1 m in length where the effective throat is 25 mm
or less, each 300 mm increment or fraction thereof
shall be considered as one weld. For evaluating the
reject rate on continuous welds over 1 m in length
where the effective throat is greater than 25 mm,
each 150 mm of length or fraction thereof shall be
considered one weld.
15.5.4.2.6
Increase in Rate of Ultrasonic
Testing. For structures in Risk Category II, where
the initial rate for UT is 10%, the NDT rate for an
individual welder or welding operator shall be
increased to 100% should the reject rate, the
number of welds containing unacceptable defects
divided by the number of welds completed, exceeds
5% of the welds tested for the welder or welding
operator. A sampling of at least 20 completed
welds for a job shall be made prior to
implementing such an increase. When the reject
rate for the welder or welding operator, after a
sampling of at least 40 completed welds, has fallen
to 5% or less, the rate of UT shall be returned to
10%. For evaluating the reject rate of continuous
welds over 1 m in length where the effective throat
is 25 mm or less, each 300 mm increment or
fraction thereof shall be considered as one weld.
For evaluating the reject rate on continuous welds
over 1 m in length where the effective throat is
greater than 25 mm, each 150 mm of length or
fraction thereof shall be considered one weld.
15.5.4.2.7
Documentation.
All
NDT
performed shall be documented. For shop
fabrication, the NDT report shall identify the tested
weld by piece mark and location in the piece. For
field work, the NDT report shall identify the tested
weld by location in the structure, piece mark, and
location in the piece.
When a weld is rejected on the basis of NDT, the
NDT record shall indicate the location of the defect
and the basis of rejection.
15.5.5 Additional Requirements for Seismic
Force Resisting Systems (SFRS).
Welding
inspection and nondestructive testing shall satisfy
the requirements of Section 15.5.4, this Section and
AWS D1.1/D1.1M.
the welding of seismic force resisting systems,
and has been coordinated when possible with
these
provisions.
AWS
D1.1/D1.1M
requirements related to inspection and nondestructive testing are organized as follows,
including normative (mandatory) annexes:
1. General Requirements
7. Inspection
Annex F. Supplemental Ultrasonic Technician
Testing
Annex G. Supplemental Magnetic Particle
Testing Procedures
Annex H. Flaw Sizing by Ultrasonic Testing
15.5.5.1
Visual Welding Inspection. All
requirements of the Section 15.5.4.1 shall apply,
except as specifically modified by
AWS
D1.1/D1.1M.
Visual welding inspection shall be performed by
both quality control and quality assurance
personnel. As a minimum, tasks shall be as listed
in TABLE 15-1, TABLE 15-2 and TABLE 15-3.
15.5.5.2
NDT of Welded Joints.
In
addition to the requirements of Section 15.5.4.2,
nondestructive testing of welded joints shall be as
required in this section:
15.5.5.2.1
k-Area NDT. Where welding of
doubler plates, continuity plates or stiffeners has
been performed in the k-area, the web shall be tested
for cracks using magnetic particle testing (MT). The
MT inspection area shall include the k-area base
metal within 75 mm of the weld. The MT shall be
performed no sooner than 48 hours following
completion of the welding.
15.5.5.2.2
CJP Groove Weld NDT .
Ultrasonic testing (UT) shall be performed on 100%
of CJP groove welds in materials 8 mm thick or
greater. Ultrasonic testing in materials less than 8
mm thick is not required. Weld discontinuities shall
be accepted or rejected on the basis of criteria of
AWS D1.1/D1.1M Table 6.2. Magnetic particle
testing shall be performed on 25% of all beam-tocolumn CJP groove welds. The rate of UT and MT
is permitted to be reduced in accordance with
Sections 15.5.5.2.7 and 15.5.5.2.8, respectively.
Exception: For ordinary moment frames, UT and
MT of CJP groove welds are required only for
demand critical welds.
User Note: AWS D1.1/D1.1M was specifically
written to provide additional requirements for
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15.5.5.2.3
Base Metal NDT for Lamellar
Tearing and Laminations. After joint completion,
base metal thicker than 38 mm loaded in tension in
the through-thickness direction in tee and corner
joints, where the connected material is greater than
19 mm and contains CJP groove welds, shall be
ultrasonically tested for discontinuities behind and
adjacent to the fusion line of such welds. Any base
metal discontinuities found within t/4 of the steel
surface shall be accepted or rejected on the basis of
criteria of AWS D1.1/D1.1M Table 6.2, where t is
the thickness of the part subjected to the throughthickness strain.
15.5.5.2.4
Beam Cope and Access Hole
NDT. At welded splices and connections, thermally
cut surfaces of beam copes and access holes shall
be tested using magnetic particle testing or
penetrant testing, when the flange thickness
exceeds 38 mm for rolled shapes, or when the web
thickness exceeds 38 mm for built-up shapes.
15.5.5.2.5
Reduced Beam Section Repair
NDT. Magnetic particle testing shall be performed
on any weld and adjacent area of the reduced beam
section (RBS) cut surface that has been repaired by
welding, or on the base metal of the RBS cut surface
if a sharp notch has been removed by grinding.
15.5.5.2.6
Weld Tab Removal Sites. At the
end of welds where weld tabs have been removed,
magnetic particle testing shall be performed on the
same beam-to-column joints receiving UT as
required under Section 15.5.5.2.2 . The rate of MT
is permitted to be reduced in accordance with
Section 15.5.5.2.8 . MT of continuity plate weld
tabs removal sites is not required.
15.5.5.2.7
Reduction of Percentage of
Ultrasonic Testing. The reduction of percentage of
UT is permitted to be reduced in accordance with
Section 15.5.4.2.5, except no reduction is permitted
for demand critical welds.
15.5.5.2.8
Reduction of Percentage of
Magnetic Particle Testing. The amount of MT on
CJP groove welds is permitted to be reduced if
approved by the engineer of record and the
authority having jurisdiction. The MT rate for an
individual welder or welding operator is permitted
to be reduced to 10%, provided the reject rate is
demonstrated to be 5% or less of the welds tested
for the welder or welding operator. A sampling of
at least 20 completed welds for a job shall be made
for such reduction evaluation. Reject rate is the
number of welds containing rejectable defects
divided by the number of welds completed. This
reduction is prohibited on welds in the k-area, at
repair sites, backing removal sites, and access holes.
15.5.6 Inspection of High-Strength Bolting.
Observation of bolting operations shall be the
primary method used to confirm that the
materials,
procedures
and
workmanship
incorporated in construction are in conformance
with the construction documents and the
provisions of the RCSC Specification.
1. For snug-tight joints, pre-installation
verification testing as specified in TABLE
15-4 and monitoring of the installation
procedures as specified in TABLE 15-5
are not applicable. The QCI and QAI
need not be present during the installation
of fasteners in snug-tight joints.
2. For pretensioned joints and slip-critical
joints, when the installer is using the
turn-of-nut method with match marking
techniques, the direct-tension-indicator
method, or the twist-off-type tension
control bolt method, monitoring of bolt
pretensioning procedures shall be as
specified in TABLE 15-5. The QCI and
QAI need not be present during the
installation of fasteners when these
methods are used by the installer.
3. For pretensioned joints and slip-critical
joints, when the installer is using the
calibrated wrench method or the turn-ofnut method without match marking,
monitoring
of
bolt
pretensioning
procedures shall be as specified in
TABLE 15-5. The QCI and QAI shall be
engaged in their assigned inspection
duties during installation of fasteners
when these methods are used by the
installer.
As a minimum, bolting inspection tasks shall be in
accordance with TABLE 15-4, TABLE 15-5 and
TABLE 15-6. In these tables, the inspection tasks
are as follows:
O – Observe these items on a random basis.
Operations need not be delayed pending these
inspections.
P – Perform these tasks for each bolted connection.
15.5.7 Other Inspection Tasks. The fabricator’s
QCI shall inspect the fabricated steel to verify
compliance with the details shown on the shop
drawings, such as proper application of joint details
at each connection. The erector’s QCI shall inspect
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the erected steel frame to verify compliance with
the details shown on the erection drawings, such
as braces, stiffeners, member locations and proper
application of joint details at each connection.
The QAI shall be on the premises for inspection
during the placement of anchor rods and other
embedments supporting structural steel for
compliance with the construction documents. As a
minimum, the diameter, grade, type and length of
the anchor rod or embedded item, and the extent or
depth of embedment into the concrete, shall be
verified prior to placement of concrete.
The QAI shall inspect the fabricated steel or
erected steel frame, as appropriate, to verify
compliance with the details shown on the
construction documents, such as braces, stiffeners,
member locations and proper application of joint
details at each connection.
For SFRS, where applicable, the inspection tasks
listed in TABLE 15-7 shall be performed.
15.6—Minimum Requirements for
Inspection of Composite Construction
Inspection of structural steel and steel deck used
in composite construction shall comply with the
requirements of this Chapter.
For welding of steel headed stud anchors, the
provisions of AWS D1.1/D1.1M, Structural
Welding Code—Steel, apply.
For welding of steel deck, observation of welding
operations and visual inspection of in-process and
completed welds shall be the primary method to
confirm that the materials, procedures and
workmanship are in conformance with the
construction documents. All applicable provisions
of AWS D1.3/D1.3M, Structural Welding Code—
Sheet Steel, shall apply. Deck welding inspection
shall include verification of the welding
consumables, welding procedure specifications
and qualifications of welding personnel prior to the
start of the work, observations of the work in
progress, and a visual inspection of all completed
welds. For steel deck attached by fastening systems
other than welding, inspection shall include
verification of the fasteners to be used prior to the
start of the work, observations of the work in
progress to confirm installation in conformance
with the manufacturer’s recommendations, and a
visual inspection of the completed installation.
For those items for quality control (QC) in TABLE
15-8 that contain an observe designation, the QC
inspection shall be performed by the erector’s
quality control inspector (QCI). In TABLE 15-8,
the inspection tasks are as follows:
O – Observe these items on a random basis.
Operations need not be delayed pending these
inspections.
P – Perform these tasks for each steel element.
Where applicable, inspections of the composite
structures shall satisfy the requirements of this
Section. These inspections shall be performed by the
responsible contractor’s quality control personnel
and by quality assurance personnel.
Where applicable, inspection of reinforced concrete
shall comply with the requirements of SBC 304, and
inspection of welded reinforcing steel shall comply
with the applicable requirements of Section 15.4.
Where applicable to the type of composite
construction, the minimum inspection tasks shall be
as listed in Table 15-9, TABLE 15-10, and TABLE
15-11.
15.7—Approved Fabricators and
Erectors
Quality assurance (QA) inspections, except
nondestructive testing (NDT), may be waived
when the work is performed in a fabricating shop
or by an erector approved by the authority having
jurisdiction (AHJ) to perform the work without QA.
NDT of welds completed in an approved
fabricator’s shop may be performed by that
fabricator when approved by the AHJ. When the
fabricator performs the NDT, the QA agency shall
review the fabricator’s NDT reports.
At completion of fabrication, the approved
fabricator shall submit a certificate of compliance
to the AHJ stating that the materials supplied and
work performed by the fabricator are in accordance
with the construction documents. At completion of
erection, the approved erector shall submit a
certificate of compliance to the AHJ stating that the
materials supplied and work performed by the
erector are in accordance with the construction
documents.
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15.8—Nonconforming Material and
Workmanship
Identification and rejection of material or
workmanship that is not in conformance with the
construction documents shall be permitted at any
time during the progress of the work. However,
this provision shall not relieve the owner or the
inspector of the obligation for timely, insequence inspections. Nonconforming material
and
workmanship shall be brought to the
immediate attention of the fabricator or erector, as
applicable.
Nonconforming material or workmanship shall be
brought into conformance, or made suitable for its
intended purpose as determined by the engineer of
record.
Concurrent with the submittal of such reports to
the AHJ, EOR or owner, the QA agency shall
submit to the fabricator and erector:
1. Nonconformance reports
2. Reports of repair, replacement
acceptance of nonconforming items
or
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TABLES AND FIGURES OF CHAPTER 15
TABLE 15-1 : INSPECTION TASKS PRIOR TO WELDING
Inspection Tasks Prior to Welding
QC
QA
Welding procedure specifications (WPSs) available
P
P
Manufacturer certifications for welding consumables available
P
P
Material identification (type/grade)
O
O
Welder identification system1
O
O
O
(P/O for
SFRS)**
O
O
O
O
(P/O for
SFRS)**
O
O
—
Fit-up of groove welds (including joint geometry)
• Joint preparation
• Dimensions (alignment, root opening, root face, bevel)
• Cleanliness (condition of steel surfaces)
• Tacking (tack weld quality and location)
• Backing type and fit (if applicable)
Configuration and finish of access holes
Fit-up of fillet welds
• Dimensions (alignment, gaps at root)
• Cleanliness (condition of steel surfaces)
• Tacking (tack weld quality and location)
Check welding equipment
1
The fabricator or erector, as applicable, shall maintain a system by which a welder who has welded a joint or member
can be identified. Stamps, if used, shall be the low-stress type.
** Following performance of this inspection task for ten welds to be made by a given welder, with the welder
demonstrating understanding of requirements and possession of skills and tools to verify these items, the Perform
designation of this task shall be reduced to Observe, and the welder shall perform this task. Should the inspector
determine that the welder has discontinued performance of this task, the task shall be returned to Perform until such
time as the Inspector has re-established adequate assurance that the welder will perform the inspection tasks listed.
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TABLE 15-2 : INSPECTION TASKS DURING WELDING
Inspection Tasks During Welding
QC
QA
Use of qualified welders
O
O
O
O
O
O
O
O
O
O
O
O
Control and handling of welding consumables
• Packaging
• Exposure control
No welding over cracked tack welds
Environmental conditions
• Wind speed within limits
• Precipitation and temperature
WPS followed
• Settings on welding equipment
• Travel speed
• Selected welding materials
• Shielding gas type/flow rate
• Preheat applied
• Interpass temperature maintained (min./max.)
• Proper position (F, V, H, OH)
Welding techniques
• Interpass and final cleaning
• Each pass within profile limitations
• Each pass meets quality requirements
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TABLE 15-3 : INSPECTION TASKS AFTER WELDING
Inspection Tasks After Welding
QC
QA
Welds cleaned
O
O
Size, length and location of welds
P
P
P
P
Arc strikes
P
P
k-area1
P
P
Placement of reinforcing or contouring fillet welds (if required)2
P**
P**
Backing removed and weld tabs removed (if required)
P**
P**
Repair activities
P
P**
Document acceptance or rejection of welded joint or member
P
P
Welds meet visual acceptance criteria
• Crack prohibition
• Weld/base-metal fusion
• Crater cross section
• Weld profiles
• Weld size
• Undercut
• Porosity
1
When welding of doubler plates, continuity plates or stiffeners has been performed in the k-area, visually inspect
the web k-area for cracks within 75 mm of the weld.
2
Apply only for SFRS
**
For SFRS, the inspector shall prepare reports indicating that the work has been performed in accordance with the
contract documents. The report need not provide detailed measurements for joint fit-up, WPS settings, completed
welds, or other individual items listed in the table. For shop fabrication, the report shall indicate the piece mark of the
piece inspected. For field work, the report shall indicate the reference grid lines and floor or elevation inspected.
Work not in compliance with the contract documents and whether the noncompliance has been satisfactorily repaired
shall be noted in the inspection report.
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TABLE 15-4 : INSPECTION TASKS PRIOR TO BOLTING
Inspection Tasks Prior to Bolting
QC
QA
Manufacturer’s certifications available for fastener materials
O
P
Fasteners marked in accordance with ASTM requirements
O
O
Proper fasteners selected for the joint detail (grade, type, bolt length if threads are to be
excluded from shear plane)
O
O
Proper bolting procedure selected for joint detail
O
O
Connecting elements, including the appropriate faying surface condition and hole
preparation, if specified, meet applicable requirements
O
O
Pre-installation verification testing by installation personnel observed and documented
for fastener assemblies and methods used
P**
O**
Proper storage provided for bolts, nuts, washers and other fastener components
O
O
** For SFRS, the inspector shall prepare reports indicating that the work has been performed in accordance with the
contract documents. For shop fabrication, the report shall indicate the piece mark of the piece inspected. For field work,
the report shall indicate the reference grid lines and floor or elevation inspected. Work not in compliance with the
contract documents and whether the noncompliance has been satisfactorily repaired shall be noted in the inspection
report.
TABLE 15-5 : INSPECTION TASKS DURING BOLTING
Inspection Tasks During Bolting
QC
QA
Fastener assemblies, of suitable condition, placed in all holes and washers (if required)
are positioned as required
O
O
Joint brought to the snug-tight condition prior to the pretensioning operation
O
O
Fastener component not turned by the wrench prevented from rotating
O
O
Fasteners are pretensioned in accordance with the RCSC Specification, progressing
systematically from the most rigid point toward the
free edges
O
O
TABLE 15-6 : INSPECTION TASKS AFTER BOLTING
Inspection Tasks After Bolting
QC
QA
Document acceptance or rejection of bolted connections
**
P**
P
** For SFRS, the inspector shall prepare report indicating that the work has been performed in accordance with the
contract documents. For shop fabrication, the report shall indicate the piece mark of the piece inspected. For field work,
the report shall indicate the reference grid lines and floor or elevation inspected. Work not in compliance with the contract
documents and whether the noncompliance has been satisfactorily repaired shall be noted in the inspection report.
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TABLE 15-7 : OTHER INSPECTION TASKS FOR SFRS
Other Inspection Tasks
RBS requirements, if applicable
– Contour and finish
– Dimensional tolerances
QC
QA
P**
P**
Protected zone—no holes and unapproved attachments made by fabricator or erector, as applicable
P**
P**
** The inspector shall prepare reports indicating that the work has been performed in accordance with the contract
documents. For shop fabrication, the report shall indicate the piece mark of the piece inspected. For field work, the report
shall indicate the reference grid lines and floor or elevation inspected. Work not in compliance with the contract
documents and whether the noncompliance has been satisfactorily repaired shall be noted in the inspection report.
TABLE 15-8 : INSPECTION OF STEEL ELEMENTS OF COMPOSITE CONSTRUCTION PRIOR
TO CONCRETE PLACEMENT
Inspection of Steel Elements of Composite Construction Prior to Concrete
Placement
QC
QA
Placement and installation of steel deck
P
P
Placement and installation of steel headed stud anchors
P
P
Document acceptance or rejection of steel elements
P
P
Table 15-9 Inspection of Composite Structures Prior to Concrete Placement
Inspection of Composite Structures Prior to Concrete Placement
QC QA
Material identification of reinforcing steel (Type/Grade)
O
O
Determination of carbon equivalent for reinforcing steel other than ASTM A706
O
O
Proper reinforcing steel size, spacing and orientation
O
O
Reinforcing steel has not been rebent in the field
O
O
Reinforcing steel has been tied and supported as required
O
O
Required reinforcing steel clearances have been provided
O
O
Composite member has required size
O
O
SBC 306-CR-18
201
CHAPTER 15—QUALITY CONTROL AND QUALITY ASSURANCE
TABLE 15-10 : INSPECTION OF COMPOSITE STRUCTURES DURING CONCRETE
PLACEMENT
Inspection of Composite Structures during Concrete Placement
QC
QA
Concrete: Material identification (mix design, compressive strength, maximum large
aggregate size, maximum slump)
O**
O**
Limits on water added at the truck or pump
O**
O**
Proper placement techniques to limit segregation
O
O
** The inspector shall prepare reports indicating that the work has been performed in accordance with the contract
documents. Work not in compliance with the contract documents and whether the noncompliance has been satisfactorily
repaired shall be noted in the inspection report.
TABLE 15-11 : INSPECTION OF COMPOSITE STRUCTURES AFTER CONCRETE PLACEMENT
Inspection of Composite Structures After Concrete Placement
QC
QA
Achievement of minimum specified concrete compressive strength at specified age
-**
-**
** The inspector shall prepare reports indicating that the work has been performed in accordance with the contract
documents. Work not in compliance with the contract documents and whether the noncompliance has been
satisfactorily repaired shall be noted in the inspection report.
P
SBC 306-CR-18
202
CHAPTER 15—QUALITY CONTROL AND QUALITY ASSURANCE
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SBC 306-CR-18
203
CHAPTER 16—EVALUATION OF EXISTING STRUCTURES
CHAPTER 16—EVALUATION OF EXISTING STRUCTURES
This chapter applies to the evaluation of the
strength and stiffness under static vertical (gravity)
loads of existing structures by structural analysis,
by load tests or by a combination of structural
analysis and load tests when specified by the
engineer of record or in the contract documents.
For such evaluation, the steel grades are not limited
to those listed in Section 1.3.1 . This chapter does
not address load testing for the effects of seismic
loads or moving loads (vibrations).
The chapter is organized as follows:
16.1 —General Provisions
16.2 —Material Properties
16.3 —Evaluation by Structural Analysis
16.4 —Evaluation by Load Tests
16.5 —Evaluation Report
16.1—General Provisions
These provisions shall be applicable when the
evaluation of an existing steel structure is
specified for (a) verification of a specific set of
design loadings or (b) determination of the design
strength of a force resisting member or system. The
evaluation shall be performed by structural
analysis (Section 16.3), by load tests (Section
16.4), or by a combination of structural analysis and
load tests, as specified in the contract documents.
Where load tests are used, the engineer of record
shall first analyze the applicable parts of the
structure, prepare a testing plan, and develop a
written procedure to prevent excessive permanent
deformation or catastrophic collapse during testing.
16.2—Material Properties
16.2.1 Determination of Required Tests. The
engineer of record shall determine the specific
tests that are required from Sections 16.2.2
through 16.2.6 and specify the locations where
they are required. Where available, the use of
applicable project records shall be permitted to
reduce or eliminate the need for testing.
16.2.2 Tensile Properties. Tensile properties of
members shall be considered in evaluation by
structural analysis (Section 16.3) or load tests
(Section 16.4). Such properties shall include the
yield stress, tensile strength and percent
elongation. Where available, certified material test
reports or certified reports of tests made by the
fabricator or a testing laboratory in accordance with
ASTM A6/A6M or A568/A568M, as applicable,
shall be permitted for this purpose. Otherwise,
tensile tests shall be conducted in accordance with
ASTM A370 from samples cut from components of
the structure.
16.2.3 Chemical Composition. Where welding
is anticipated for repair or modification of existing
structures, the chemical composition of the steel
shall be determined for use in preparing a welding
procedure specification (WPS). Where available,
results from certified material test reports or
certified reports of tests made by the fabricator or
a testing laboratory in accordance with ASTM
procedures shall be permitted for this purpose.
Otherwise, analyses shall be conducted in
accordance with ASTM A751 from the samples
used to determine tensile properties, or from
samples taken from the same locations.
16.2.4 Base Metal Notch Toughness. Where
welded tension splices in heavy shapes and plates as
defined in Section 1.3.1.4 are critical to the
performance of the structure, the Charpy V-notch
toughness shall be determined in accordance with
the provisions of Section 1.3.1.4. If the notch
toughness so determined does not meet the
provisions of Section 1.3.1.4, the engineer of record
shall determine if remedial actions are required.
16.2.5 Weld
Metal.
Where
structural
performance is dependent on existing welded
connections, representative samples of weld metal
shall be obtained. Chemical analysis and
mechanical tests shall be made to characterize the
weld metal. A determination shall be made of the
magnitude and consequences of imperfections. If
the requirements of AWS D1.1/D1.1M are not
met, the engineer of record shall determine if
remedial actions are required.
16.2.6 Bolts and Rivets. Representative samples
of bolts shall be inspected to determine markings
and classifications. Where bolts cannot be properly
identified visually, representative samples shall
be removed and tested to determine tensile
SBC 306-CR-18
204
CHAPTER 16—EVALUATION OF EXISTING STRUCTURES
strength in accordance with ASTM F606 or
ASTM F606M and the bolt classified
accordingly. Alternatively, the assumption that
the bolts are ASTM A307 shall be permitted.
Rivets shall be assumed to be ASTM A502, Grade
1, unless a higher grade is established through
documentation or testing.
16.3—Evaluation b y Structural
Analysis
16.3.1 Dimensional Data. All dimensions used
in the evaluation, such as spans, column heights,
member spacings, bracing locations, cross section
dimensions, thicknesses, and connection details,
shall be determined from a field survey.
Alternatively, when available, it shall be permitted
to determine such dimensions from applicable
project design or shop drawings with field
verification of critical values.
16.3.2 Strength Evaluation. Forces (load effects)
in members and connections shall be determined
by structural analysis applicable to the type of
structure evaluated. The load effects shall be
determined for the static vertical (gravity) loads
and factored load combinations stipulated in
Section 2.2.
The design strength of members and connections
shall be determined from applicable provisions of
Chapters 2 through 10 of this Code.
16.3.3 Serviceability Evaluation.
Where
required, the deformations at service loads shall be
calculated and reported.
16.4—Evaluation by Load Tests
16.4.1 Determination of Load Rating by
Testing. To determine the load rating of an existing
floor or roof structure by testing, a test load shall
be applied incrementally in accordance with the
engineer of record’s plan. The structure shall be
visually inspected for signs of distress or imminent
failure at each load level. Appropriate measures
shall be taken if these or any other unusual
conditions are encountered.
The tested strength of the structure shall be taken as
the maximum applied test load plus the in-situ
dead load. The live load rating of a floor structure
shall be determined by setting the tested strength
equal to 1.2D 1.6L, where D is the nominal dead
load and L is the nominal live load rating for the
structure. The nominal live load rating of the floor
structure shall not exceed that which can be
calculated using applicable provisions of the
specification. For roof structures, Lr or R as defined
in SBC 301, shall be substituted for L. More severe
load combinations shall be used where required
by applicable Saudi building codes.
Periodic unloading shall be considered once the
service load level is attained and after the onset
of inelastic structural behavior is identified to
document the amount of permanent set and the
magnitude of the inelastic deformations.
Deformations of the structure, such as member
deflections, shall be monitored at critical locations
during the test, referenced to the initial position
before loading. It shall be demonstrated that the
deformation of the structure does not increase by
more than 10% during a one-hour holding period
under sustained, maximum test load. It is
permissible to repeat the sequence if necessary to
demonstrate compliance.
Deformations of the structure shall also be recorded
24 hours after the test loading is removed to
determine the amount of permanent set. Because
the amount of acceptable permanent deformation
depends on the specific structure, no limit is
specified for permanent deformation at maximum
loading. Where it is not feasible to load test the
entire structure, a segment or zone of not less than
one complete bay, representative of the most critical
conditions, shall be selected.
16.4.2 Serviceability Evaluation. When load
tests are prescribed, the structure shall be loaded
incrementally to the service load level.
Deformations shall be monitored during a one hour
holding period under sustained service test load.
The structure shall then be unloaded and the
deformation recorded.
16.5—Evaluation Report
After the evaluation of an existing structure has
been completed, the engineer of record shall
prepare a report documenting the evaluation. The
report shall indicate whether the evaluation was
performed by structural analysis, by load testing,
or by a combination of structural analysis and load
testing. Furthermore, when testing is performed,
the report shall include the loads and load
combination used and the load- deformation and
time-deformation relationships observed. All
relevant information obtained from design
drawings, material test reports, and auxiliary
material testing shall also be reported. Finally, the
report shall indicate whether the structure, including
all members and connections, is adequate to
withstand the load effects.
SBC 306-CR-18
205
CHAPTER 16—EVALUATION OF EXISTING STRUCTURES
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SBC 306-CR-18
206
APPENDIX A —DESIGN BY INELASTIC ANALYSIS
APPENDIX A—Design by Inelastic Analysis
This appendix addresses design by inelastic
analysis, in which consideration of the
redistribution of member and connection forces
and moments as a result of localized yielding is
permitted.
The appendix is organized as follows:
A.1
— General Requirements
A.2
— Ductility Requirements
A.3
— Analysis Requirements.
ductility consistent with the intended behavior of
the structural system. Force redistribution due to
rupture of a member or connection is not permitted.
Any method that uses inelastic analysis to
proportion members and connections to satisfy
these general requirements is permitted. A design
method based on inelastic analysis that meets the
above strength requirements, the ductility
requirements of Section A.2 , and the analysis
requirements of Section A.3 satisfies these
general requirements.
A.1— General Requirements
A.2— Ductility Requirements.
Design by inelastic analysis shall be conducted in
accordance with Section 2.3.3 using load and
resistance factor design (LRFD). The design
strength of the structural system and its members
and connections shall equal or exceed the required
strength as determined by the inelastic analysis. The
provisions of this Appendix do not apply to seismic
design.
Members and connections with elements subject
to yielding, shall be proportioned such that all
inelastic deformation demands are less than or
equal to their inelastic deformation capacities. In
lieu of explicitly, ensuring that the inelastic
deformation demands are less than or equal to their
inelastic deformation capacities. The following
requirements shall be satisfied for steel members
subject to plastic hinging.
The inelastic analysis shall take into account: (1)
flexural, shear and axial member deformations,
and all other component and connection
deformations that contribute to the displacements
of the structure; (2) second-order effects
(including P -Δ and P-effects); (3) geometric
imperfections; (4) stiffness reductions due to
inelasticity, including the effect of residual stresses
and partial yielding of the cross section; and (5)
uncertainty in system, member, and connection
strength and stiffness.
Strength limit states detected by an inelastic
analysis that incorporates all of the above
requirements are not subject to the corresponding
provisions of the Code when a comparable or
higher level of reliability is provided by the
analysis. Strength limit states not detected by the
inelastic analysis shall be evaluated using the
corresponding provisions of Chapters 4, 5, 6, 7, 8,
9, 10 and 11. Connections shall meet the
requirements of Section 2.3.6 .
A.2.1 Material. The specified minimum yield
stress, Fy, of members subject to plastic hinging
shall not exceed 450 MPa.
A.2.2 Cross Section. The cross section of
members at plastic hinge locations shall be doubly
symmetric with width-to-thickness ratios of their
compression elements not exceeding pd, where
pd is equal to p from Table 2-2 except as modified
below:
(a) For the width-to-thickness ratio, h/tw, of webs
of I-shaped sections, rectangular HSS, and boxshaped sections subject to combined flexure
and compression
When Pu /cPy 0.125
𝜆𝑝𝑑 = 3.76√
𝐸
2.75𝑃𝑢
(1 −
)
𝐹𝑦
𝜑𝑐 𝑃𝑦
(A-1)
When Pu /cPy 0.125
Members and connections subject to inelastic
deformations, shall be shown to have adequate
SBC 306-CR-18
207
APPENDIX A —DESIGN BY INELASTIC ANALYSIS
𝜆𝑝𝑑 = 1.12√
𝐸
𝑃𝑢
𝐸
(2.33 −
) ≥ 1.49√
𝐹𝑦
𝜑𝑐 𝑃𝑦
𝐹𝑦
When the magnitude of the bending
moment at any location within the unbraced
length exceeds M2
(A-2)
where
𝑀1′ ⁄𝑀2 = +1
h
as defined in section 2.4.1 , mm
tw
web thickness, mm
Pu
required axial strength in compression, N
Py
FyAg axial yield strength, N
c
resistance factor for compression 0.85
(A-6)
Otherwise:
(b) For the width-to-thickness ratio, b/t, of flanges
of rectangular HSS and box-shaped sections,
and for flange cover plates, and diaphragm
plates between lines of fasteners or welds
When 𝑀𝑚𝑖𝑑 ≤
𝑀1 +𝑀2
2
𝑀1′ = 𝑀1
When 𝑀𝑚𝑖𝑑 >
(A-7)
𝑀1 +𝑀2
2
𝑀1′ = 2𝑀𝑚𝑖𝑑 − 𝑀2 < 𝑀2
(A-8)
where
M1
= smaller moment at end of unbraced
length, N-mm
(A-3)
M2
= larger moment at end of unbraced length,
N-mm. M2 shall be taken as positive in
all cases.
b
as defined in section 2.4.1 , mm
Mmid
t
as defined in section 2.4.1 , mm
= moment at middle of unbraced length, Nmm
M1
= effective moment at end of unbraced
length opposite from M2, N-mm
𝜆𝑝𝑑 = 0.94√𝐸 ⁄𝐹𝑦
where
(c) For the diameter-to-thickness ratio, D/t, of
circular HSS in flexure
𝜆𝑝𝑑 = 0.045 𝐸 ⁄𝐹𝑦
(A-4)
where
outside diameter of round HSS, mm
D
A.2.3 Unbraced Length. In prismatic member
segments that contain plastic hinges, the laterally
unbraced length, Lb, shall not exceed Lpd,
determined as follows. For members subject to
flexure only, or to flexure and axial tension, Lb
shall be taken as the length between points braced
against lateral displacement of the compression
flange, or between points braced to prevent twist
of the cross section. For members subject to
flexure and axial compression, Lb shall be taken as
the length between points braced against both
lateral displacement in the minor axis direction and
twist of the cross section.
(a) For I-shaped members bent about their major
axis:
𝐿𝑝𝑑 = [0.12 − 0.076
𝑀1′ 𝐸
] 𝑟
𝑀2 𝐹𝑦 𝑦
(A-5)
where
ry
radius of gyration about minor axis, mm.
The moments M1 and Mmid are individually taken as
positive when they cause compression in the same
flange as the moment M2 and negative otherwise.
(b) For solid rectangular bars and for rectangular
HSS and box-shaped members bent about their
major axis
𝐿𝑝𝑑 = [0.17 − 0.10
𝑀1′ 𝐸
𝐸
] 𝑟𝑦 ≥ 0.10 𝑟𝑦 (A-9)
𝑀2 𝐹𝑦
𝐹𝑦
For all types of members subject to axial
compression and containing plastic hinges, the
laterally unbraced lengths about the cross section
major and minor axes shall not exceed
4.71 𝑟𝑥 √𝐸 ⁄𝐹𝑦 and 4.71 𝑟𝑦 √𝐸 ⁄𝐹𝑦 , respectively.
There is no Lpd limit for member segments
containing plastic hinges in the following cases:
1. Members with circular or square cross
sections subject only to flexure or to
combined flexure and tension
2. Members subject only to flexure about
their minor axis or combined tension and
flexure about their minor axis
3. Members subject only to tension
SBC 306-CR-18
208
APPENDIX A —DESIGN BY INELASTIC ANALYSIS
A.2.4 Axial Force. To assure adequate ductility
in compression members with plastic hinges,
the design strength in compression shall not exceed
0.75𝐹𝑦 𝐴𝑔 .
A.3— Analysis Requirements.
2. The
elastic-perfectly-plastic
yield
criterion, expressed in terms of the axial
force, major axis bending moment, and
minor axis bending moment, shall satisfy
the cross section strength limit defined
by Eqs. (8-1) and (8-2) using 𝑃𝑐 = 0.9𝑃𝑦 ,
𝑀𝑐𝑥 = 0.9𝑀𝑝𝑥 and 𝑀𝑐𝑦 = 0.9𝑀𝑝𝑦 .
The structural analysis shall satisfy the general
requirements of Section A.1. These requirements
are permitted to be satisfied by a second-order
inelastic analysis meeting the requirements of this
Section.
Exception:
For continuous beams not subject to axial
compression, a first-order inelastic or plastic
analysis is permitted and the requirements of
Sections A.3.2 and A.3.3 are waived.
A.3.1 Material Properties and Yield Criteria.
The specified minimum yield stress, Fy, and the
stiffness of all steel members and connections shall
be reduced by a factor of 0.90 for the analysis,
except as noted below in Section A.3.3.
The influence of axial force, major axis bending
moment, and minor axis bending moment shall be
included in the calculation of the inelastic response.
The plastic strength of the member cross section
shall be represented in the analysis either by an
elastic-perfectly-plastic yield criterion expressed
in terms of the axial force, major axis bending
moment, and minor axis bending moment, or by
explicit modeling of the material stress-strain
response as elastic-perfectly-plastic.
A.3.2 Geometric Imperfections. The analysis
shall include the effects of initial geometric
imperfections. This shall be done by explicitly
modeling the imperfections as specified in Section
3.2.2.1 or by the equivalent notional loads as
specified in Section 3.2.2.2 .
A.3.3 Residual Stress and Partial Yielding
Effects. The analysis shall include the influence of
residual stresses and partial yielding. This shall be
done by explicitly modeling these effects in the
analysis or by reducing the stiffness of all structural
components as specified in Section 3.2.3 .
If the provisions of Section 3.2.3 are used, then:
1. The 0.9 stiffness reduction factor specified
in Section A.3.1 shall be replaced by the
reduction of the elastic modulus E by 0.8
as specified in Section 3.2.3 , and
SBC 306-CR-18
209
APPENDIX A —DESIGN BY INELASTIC ANALYSIS
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SBC 306-CR-18
210
APPENDIX B —DESIGN FOR PONDING
APPENDIX B—Design for Ponding
This appendix provides methods for determining
whether a roof system has adequate strength and
stiffness to resist ponding.
A steel deck shall be considered a secondary
member when it is directly supported by the
primary members.
The appendix is organized as follows:
B.1
—Simplified Design for Ponding
B.2— Improved Design for Ponding
B.2
— Improved Design for Ponding
The provisions given below are to be used when a
more accurate evaluation of framing stiffness is
needed than that given by Eqs. (B-1) and (B-2).
B.1—Simplified Design for Ponding
Define the stress indexes
The roof system shall be considered stable for
ponding and no further investigation is needed if
both of the following two conditions are met:
𝐶𝑝 + 0.9𝐶𝑠 ≤ 0.25
𝐼𝑑 ≥ 3,940𝑆 4
(B-1)
(B-2)
(B-5)
0.8𝐹𝑦 − 𝑓𝑜
𝑈𝑠 = (
)
𝑓𝑜
𝑠
(B-6)
where
where
504𝐿𝑠 𝐿4𝑝
𝐼𝑝
504𝑆𝐿4𝑠
𝐶𝑠 =
𝐼𝑠
𝐶𝑝 =
(B-3)
(B-4)
Id = moment of inertia of the steel deck
supported on secondary members, mm4
per m
Ip = moment of inertia of primary members,
mm4
Is
0.8𝐹𝑦 − 𝑓𝑜
𝑈𝑝 = (
)
𝑓𝑜
𝑝
= moment of inertia of secondary members,
mm4
Lp = length of primary members, m
Ls = length of secondary members, m
S = spacing of secondary members, m
For trusses and steel joists, the calculation of the
moments of inertia, Ip and Is, shall include the
effects of web member strain when used in the
above equation.
User Note: When the moment of inertia is
calculated using only the truss or joist chord
areas, the reduction in the moment of inertia due
to web strain can typically be taken as 15%.
Up = stress index for the primary member
Us = stress index for the secondary member
fo =stress due to D R (D nominal dead load,
R nominal load due to rainwater
exclusive of the ponding contribution),
MPa.
For roof framing consisting of primary and
secondary members, evaluate the combined
stiffness as follows. Enter FIGURE B-1 at the
level of the computed stress index, U p, determined
for the primary beam; move horizontally to the
computed Cs value of the secondary beams and
then downward to the abscissa scale. The
combined stiffness of the primary and secondary
framing is sufficient to prevent ponding if the
flexibility coefficient read from this latter scale is
more than the value of Cp computed for the given
primary member; if not, a stiffer primary or
secondary beam, or combination of both, is
required.
A similar procedure must be followed FIGURE
B-2.
For roof framing consisting of a series of equally
spaced wall bearing beams, evaluate the stiffness as
follows. The beams are considered as secondary
members supported on an infinitely stiff primary
SBC 306-CR-18
211
APPENDIX B —DESIGN FOR PONDING
member. For this case, enter FIGURE B-2. with
the computed stress index, Us. The limiting value
of Cs is determined by the intercept of a horizontal
line representing the Us value and the curve for Cp
0.
User Note: The ponding deflection contributed
by a metal deck is usually such a small part of
the total ponding deflection of a roof panel that it
is sufficient merely to limit its moment of inertia
[per meter of width normal to its span] to 3940
times the fourth power of its span length.
Evaluate the stability against ponding of a roof
consisting of a metal roof deck of relatively slender
depth-to-span ratio, spanning between beams
supported directly on columns, as follows. Use
FIGURE B-1 or FIGURE B-2, using as Cs the
flexibility coefficient for a one-meter width of the
roof deck (S 1.0).
SBC 306-CR-18
212
APPENDIX B —DESIGN FOR PONDING
TABLES AND FIGURES OF APPENDIX B
Upper Limit
ofLimit
Flexibility
coefficient Cp
Upper
of Flexibility
Coefficient C
FIGURE B-1. LIMITING FLEXIBILITY COEFFICIENT FOR THE PRIMARY SYSTEMS
SBC 306-CR-18
213
APPENDIX B —DESIGN FOR PONDING
Upper Upper
Limit ofLimit
Flexibility
coefficient Cs
of Flexibility
Coefficient C
FIGURE B-2. LIMITING FLEXIBILITY COEFFICIENT FOR THE SECONDARY SYSTEMS
SBC 306-CR-18
214
APPENDIX B —DESIGN FOR PONDING
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SBC 306-CR-18
215
APPENDIX C —DESIGN FOR FATIGUE
APPENDIX C—DESIGN FOR FATIGUE
This appendix applies to members and connections
subject to high cycle loading within the elastic
range of stresses of frequency and magnitude
sufficient to initiate cracking and progressive
failure, which defines the limit state of fatigue.
The appendix is organized as follows:
C.1— General Provisions
C.2
— Calculation of Maximum Stresses and Stress
Ranges
C.3— Design Stress Range
C.4—
Special Fabrication
Requirements
and
Erection
structures subject to code mandated wind loads is
required.
The cyclic load resistance determined by the
provisions of this Appendix is applicable to
structures with suitable corrosion protection or
subject only to mildly corrosive atmospheres,
such as normal atmospheric conditions.
The cyclic load resistance determined by the
provisions of this Appendix is applicable only to
structures subject to temperatures not exceeding
150 C.
The engineer of record shall provide either
complete details including weld sizes or shall
specify the planned cycle life and the maximum
range of moments, shears and reactions for the
connections.
C.1— General Provisions
The provisions of this Appendix apply to stresses
calculated on the basis of service loads. The
maximum permitted stress due to service loads is
0.66Fy .
Stress range is defined as the magnitude of the
change in stress due to the application or removal
of the service live load. In the case of a stress
reversal, the stress range shall be computed as the
numerical sum of maximum repeated tensile and
compressive stresses or the numerical sum of
maximum shearing stresses of opposite direction at
the point of probable crack initiation.
C.2— Calculation of Maximum Stresses
and Stress Ranges
Calculated stresses shall be based upon elastic
analysis. Stresses shall not be amplified by stress
concentration
factors
for
geometrical
discontinuities.
For bolts and threaded rods subject to axial
tension, the calculated stresses shall include the
effects of prying action, if any. In the case of axial
stress combined with bending, the maximum
stresses, of each kind, shall be those determined for
concurrent arrangements of the applied load.
In the case of complete-joint-penetration groove
welds, the maximum allowable stress range
calculated by Eq. (C-1) applies only to welds
that have been ultrasonically or radiographically
tested and meet the acceptance requirements of
Sections 6.12.2 or 6.13.2 of AWS D1.1/D1.1M.
For members having symmetric cross sections,
the fasteners and welds shall be arranged
symmetrically about the axis of the member, or the
total stresses including those due to eccentricity
shall be included in the calculation of the stress
range.
No evaluation of fatigue resistance is required if the
live load stress range is less than the threshold
allowable stress range, FTH. See TABLE C-1.
For axially loaded angle members where the
center of gravity of the connecting welds lies
between the line of the center of gravity of the angle
cross section and the center of the connected leg,
the effects of eccentricity shall be ignored. If the
center of gravity of the connecting welds lies
outside this zone, the total stresses, including those
due to joint eccentricity, shall be included in the
calculation of stress range.
No evaluation of fatigue resistance of members
consisting of shapes or plate is required if the
number of cycles of application of live load is less
than 20,000. No evaluation of fatigue resistance of
members consisting of HSS in building-type
SBC 306-CR-18
216
APPENDIX C —DESIGN FOR FATIGUE
C.3— Design Stress Range
The range of stress at service loads shall not
exceed the stress range as given in Sections C.3.1
and C.3.2.
C.3.1
Plain Material and Welded Joints.
(a) For stress categories A, B, B, C, D, E and Ethe
allowable stress range, FSR, shall be determined
as follows:
𝐶𝑓 329 0.333
)
𝐹𝑆𝑅 = (
≥ 𝐹𝑇𝐻
𝑛𝑆𝑅
(C-1)
FSR = allowable stress range, MPa
=
threshold allowable stress range,
maximum stress range for indefinite
design life from TABLE C-1, MPa
nSR = number of stress range fluctuations in
design life
RPJP, the reduction factor for reinforced or nonreinforced transverse PJP groove welds, is
determined as follows;
tp
14.41011
𝐹𝑆𝑅 = (
)
𝑛𝑆𝑅
= thickness of tension loaded plate, mm
Based upon crack initiation from the roots of
a pair of transverse fillet welds on opposite
sides of the tension loaded plate element, the
allowable stress range, FSR, on the cross
section at the root of the welds shall be
determined by Eq. (C-6) for stress category
Cas follows:
(C-2)
Based upon crack initiation from the toe of the
weld on the tension loaded plate element (i.e.,
when RPJP = 1.0), the allowable stress range,
FSR, shall be determined by Eq. (C-3) for
stress category C as follows:
(C-5)
w = leg size of the reinforcing or contouring
fillet, if any, in the direction of the
thickness of the tension-loaded plate, mm
0.167
(c) For tension-loaded plate elements connected
at their end by cruciform, T or corner details
with complete-joint-penetration (CJP) groove
welds or partial-joint-penetration (PJP) groove
welds, fillet welds, or combinations of the
preceding, transverse to the direction of stress,
the allowable stress range on the cross section
of the tension-loaded plate element shall be
determined as follows:
) ≤ 1.0
2a = length of the non-welded root face in the
direction of the thickness of the tensionloaded plate, mm
(b) For stress category F, the allowable stress
range, FSR, shall be determined as follows:
≥ 𝐹𝑇𝐻
2𝑎
𝑤
)+1.24( )
𝑡𝑝
𝑡𝑝
𝑡𝑝0.167
If RPJP 1.0, use stress category C.
= number of stress range fluctuations per
day 365 years of design life
𝐶𝑓 11104
𝐹𝑆𝑅 = (
)
𝑛𝑆𝑅
(C-4)
where
𝑅𝑃𝐽𝑃 = (
= constant from TABLE C-1 for the fatigue
category
FTH
0.333
14.41011
𝐹𝑆𝑅 = 𝑅𝑃𝐽𝑃 (
)
𝑛𝑆𝑅
1.12−1.01(
where
Cf
section at the root of the weld shall be
determined by Eq. (C-4), for stress category
Cas follows:
0.333
14.41011
𝐹𝑆𝑅 = 𝑅𝐹𝐼𝐿 (
)
𝑛𝑆𝑅
(C-6)
where
RFIL is the reduction factor for joints using a pair of
transverse fillet welds only.
𝑤
0.10 + 1.24 ( )
𝑡𝑝
𝑅𝐹𝐼𝐿 = (
) ≤ 1.0
𝑡𝑝0.167
(C-7)
If RFIL = 1.0, use stress category C.
0.333
≥ 68.9
(C-3)
Based upon crack initiation from the root of
the weld on the tension loaded plate element
using transverse PJP groove welds, with or
without reinforcing or contouring fillet welds,
the allowable stress range on the cross
C.3.2 Bolts and Threaded Parts. In bolts and
threaded parts, the range of stress at service loads
shall not exceed the allowable stress range
computed as follows:
(a) For mechanically fastened connections loaded
in shear, the maximum range of stress in the
connected material at service loads shall not
SBC 306-CR-18
217
APPENDIX C —DESIGN FOR FATIGUE
exceed the allowable stress range computed
using Eq. (C-1) where Cf and FTH are taken from
Section 2 of TABLE C-1.
(b) For high-strength bolts, common bolts and
threaded anchor rods with cut, ground or rolled
threads, the maximum range of tensile stress on
the net tensile area from applied axial load and
moment plus load due to prying action shall not
exceed the allowable stress range computed
using Eq. (C-8) (stress category G). The net
area in tension, At , is given by Eq. (C-9).
In transverse joints subject to tension, backing bars,
if used, shall be removed and the joint back gouged
and welded.
0.333
User Note: AWS C4.1 Sample 3 may be used
to evaluate compliance with this requirement.
1.281011
𝐹𝑆𝑅 = (
)
≥ 48
𝑛𝑆𝑅
𝜋
𝐴𝑡 = (𝑑𝑏 − 0.9382𝑝)2
4
where
(C-8)
(C-9)
db = the nominal diameter (body or shank
diameter), mm
p = pitch (mm per thread)
For joints in which the material within the grip is
not limited to steel or joints which are not tensioned
to the requirements of TABLE 10-6, all axial load
and moment applied to the joint plus effects of any
prying action shall be assumed to be carried
exclusively by the bolts or rods.
For joints in which the material within the grip is
limited to steel and which are pretensioned to the
requirements of TABLE 10-6, an analysis of the
relative stiffness of the connected parts and bolts
shall be permitted to be used to determine the
tensile stress range in the pretensioned bolts due to
the total service live load and moment plus effects
of any prying action. Alternatively, the stress range
in the bolts shall be assumed to be equal to the stress
on the net tensile area due to 20% of the absolute
value of the service load axial load and moment
from dead, live and other loads.
In transverse complete-joint-penetration T and
corner joints, a reinforcing fillet weld, not less than
6 mm in size shall be added at reentrant corners.
The surface roughness of thermally cut edges
subject to cyclic stress ranges, that include tension,
shall not exceed 25 m, where ASME B46.1 is the
reference standard.
Reentrant corners at cuts, copes and weld access
holes shall form a radius of not less than 10 mm by
predrilling or subpunching and reaming a hole, or
by thermal cutting to form the radius of the cut. If
the radius portion is formed by thermal cutting, the
cut surface shall be ground to a bright metal surface.
For transverse butt joints in regions of tensile stress,
weld tabs shall be used to provide for cascading the
weld termination outside the finished joint. End
dams shall not be used. Run-off tabs shall be
removed and the end of the weld finished flush
with the edge of the member.
See Section 10.2.2.2 for requirements for end
returns on certain fillet welds subject to cyclic
service loading.
C.4— Special Fabrication and Erection
Requirements
Longitudinal backing bars are permitted to remain
in place, and if used, shall be continuous. If splicing
is necessary for long joints, the bar shall be joined
with complete penetration butt joints and the
reinforcement ground prior to assembly in the
joint. Longitudinal backing, if left in place, shall be
attached with continuous fillet welds.
SBC 306-CR-18
218
APPENDIX C —DESIGN FOR FATIGUE
TABLES AND FIGURES OF APPENDIX C
TABLE C-1: FATIGUE DESIGN PARAMETERS
Threshold
FTH
(MPa)
SECTION 1 – PLAIN MATERIAL AWAY FROM ANY WELDING
Description
Stress
Category
Constant
Cf
1.1 Base metal, except noncoated
weathering steel, with rolled or cleaned
surface. Flame-cut edges with surface
roughness value of 25 μm or less, but
without reentrant corners.
A
250 x 108
165
Away from all welds
or structural
connections
1.2 Noncoated weathering steel base
metal with rolled or cleaned surface.
Flame-cut edges with surface
roughness value of 25 μm or less, but
without reentrant corners.
B
120 x 108
110
Away from all welds
or structural
connections
1.3 Member with drilled or reamed
holes. Member with re-entrant corners
at copes, cuts, block-outs or other
geometrical discontinuities made to
requirements of t h i s Appendix,
Section C.4, except weld access holes.
B
120 x 108
110
At any external edge
or at hole perimeter
69
At reentrant corner of
weld access hole or at
any small hole (may
contain bolt for
minor connections)
1.4 Rolled cross sections with weld
access holes made to requirements
of Section 10.1.6 and this Appendix,
Section C.4. Members with drilled or
reamed holes containing bolts for
attachment of light bracing where there
is a small longitudinal component of
brace force.
C
44 x 108
Potential Crack
Initiation Point
SECTION 2 – CONNECTED MATERIAL IN MECHANICALLY FASTENED JOINTS
2.1 Gross area of base metal in lap
joints connected by high-strength bolts
in joints satisfying all requirements
for slip-critical connections.
B
120 x 108
Through gross section
near hole
110
2.2 Base metal at net section of highstrength bolted joints, designed on the
basis of bearing resistance, but
fabricated and installed to all
requirements for slip-critical
connections.
B
120 x 108
110
2.3 Base metal at the net section of
other mechanically fastened joints
except eye bars and pin plates.
D
22 x 108
48
In net section
originating at side of
hole
E
8
31
In net section
originating at side of
hole
2.4 Base metal at net section of eyebar
head or pin plate.
11 x 10
SBC 306-CR-18
In net section
originating at side of
hole
219
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Illustrative Typical Examples
SECTION 1 – PLAIN MATERIAL AWAY FROM ANY WELDING
1.1 and 1.2
1.3
1.4
SECTION 2 – CONNECTED MATERIAL IN MECHANICALLY FASTENED JOINTS
2.1
(Note: figures are for slip-critical bolted connections)
2.2
(Note: figures are for bolted connections designed to bear, meeting the requirements of slip-critical connections)
2.3
(Note: figures are for snug-tightened bolts, rivets, or other mechanical fasteners)
2.4
SBC 306-CR-18
220
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Threshold
Potential Crack
FTH
Initiation Point
(MPa)
SECTION 3 – WELDED JOINTS JOINING COMPONENTS OF BUILT-UP MEMBERS
Description
3.1 Base metal and weld metal in
members without attachments built up of
plates or shapes connected by
continuous longitudinal complete-jointpenetration groove welds, back gouged
and welded from second side, or by
continuous fillet welds.
3.2 Base metal and weld metal in
members without attachments built up of
plates or shapes, connected by
continuous longitudinal complete-jointpenetration groove welds with backing
bars not removed, or by continuous
partial- joint-penetration groove welds.
3.3 Base metal at weld metal
terminations of longitudinal welds at weld
access holes in connected built-up
members.
3.4 Base metal at ends of longitudinal
intermittent fillet weld segments.
Stress
Category
B
Constant
Cf
120 x 108
110
Flange thickness (tf) > 20 mm
3.6 Base metal at ends of partial length
welded coverplates wider than the flange
without welds across the ends.
From surface or
internal discontinuities
in weld, including weld
attaching backing bars
B’
61 x 108
83
D
8
48
From the weld
termination into the
web or flange
31
In connected mate rial
at start and stop
locations of any weld
deposit
E
22 x 10
11 x 108
3.5 Base metal at ends of partial length
welded coverplates narrower than the
flange having square or tapered ends, with
or without welds across the ends; and
coverplates wider than the flange with
welds across the ends.
Flange thickness (tf) ≤ 20 mm
From surface or
internal discontinuities
in weld away from
end of weld
In flange at toe of
end weld or in flange
at termination of
longitudinal weld or in
edge of flange with
wide coverplates
11 x 108
E
E’
8
3.9 x 10
31
18
E’
3.9 x 108
18
In edge of flange at
end of cover- plate
weld
SECTION 4 – LONGITUDINAL FILLET WELDED END CONNECTIONS
4.1 Base metal at junction of axially
loaded members with longitudinally
welded end connections. Welds shall be
on each side of the axis of the member to
balance weld stresses.
T ≤ 12 mm
T > 12 mm
Initiating from end
of any weld termination extending
into the base metal
E
E’
11 x 108
3.9 x 108
SBC 306-CR-18
31
18
221
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Illustrative Typical Examples
SECTION 3 – WELDED JOINTS JOINING COMPONENTS OF BUILT-UP MEMBERS
3.1
3.2
3.3
3.4
3.5
3.6
SECTION 4 – LONGITUDINAL FILLET WELDED END CONNECTIONS
4.1
SBC 306-CR-18
222
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Threshold
Potential Crack
FTH
Initiation Point
(MPa)
SECTION 5 – WELDED JOINTS TRANSVERSE TO DIRECTION OF STRESS
Description
5.1 Weld metal and base metal in or
adjacent to complete-joint-penetration
groove welded splices in rolled or
welded cross sections with welds
ground essentially parallel to the
direction of stress and with soundness
established by radiographic or
ultrasonic inspection in accordance
with the requirements of subclauses
6.12 or 6.13 of AWS D1.1/D1.1M.
6.13 of AWS D1.1/D1.1M.
Stress
Category
Constant
Cf
From internal discontinuities in weld
metal or along the
fusion boundary
B
120 x 108
110
5.2 Weld metal and base metal in or
adjacent to complete-joint-penetration
groove welded splices with welds ground
essentially parallel to the direction of stress
at transitions in thickness or width made
on a slope no greater than 1:21/2 and with
weld soundness established by
radiographic or ultrasonic inspection in
accordance with the requirements of
subclauses 6.12 or 6.13 of AWS
D1.1/D1.1M.
Fy < 620 MPa
Fy ≥ 620 MPa
5.3 Base metal with Fy equal to or
greater than 620 MPa and weld metal
in or adjacent to complete-jointpenetration groove welded splices
with welds ground essentially parallel
to the direction of stress at transitions
in width made on a radius of not less than
600 mm with the point of tangency at the
end of the groove weld and with weld
sound- ness established by
radiographic or ultrasonic inspection
in accordance with the requirements of
subclauses 6.12 or 6.13 of AWS
D1.1/D1.1M.
5.4 Weld metal and base metal in or
adjacent to the toe of complete-jointpenetration groove welds in T or
corner joints or splices, with or
without transitions in thickness having
slopes no greater than 1:21/2, when
weld reinforcement is not removed and
with weld soundness established by
radiographic or ultrasonic inspection in
accordance with the requirements of
subclauses 6.12 or 6.13 of AWS
D1.1/D1.1M.
From internal
discontinuities in
filler metal or along
fusion boundary or at
start of transition
when Fy ≥ 620 MPa
B
B’
120 x 108
61 x 108
110
83
From internal discontinuities in filler
metal or
discontinuities along
the fusion boundary
B
120 x 108
110
From surface discontinuity at toe of
weld extending into
base metal or into
weld metal.
C
44 x 108
SBC 306-CR-18
69
223
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Illustrative Typical Examples
SECTION 5 – WELDED JOINTS TRANSVERSE TO DIRECTION OF STRESS
5.1
5.2
5.3
5.4
SBC 306-CR-18
224
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Threshold
Potential Crack
FTH
Initiation Point
(MPa)
SECTION 5 – WELDED JOINTS TRANSVERSE TO DIRECTION OF STRESS (continued)
Initiating
from
5.5 Base metal and weld metal at
transverse end connections of tensiongeometrical
loaded plate elements using partialdiscontinuity at toe of
joint-penetration groove welds in butt
weld extending into
or T- or corner joints, with reinforcing
base metal.
or contouring fillets, FSR shall be the
smaller of the toe crack or root crack
allowable stress range.
C
44 x 108
Crack initiating from weld toe:
69
Description
Crack initiating from weld root:
5.6 Base metal and weld metal at
transverse
end
connections
of
tension-loaded plate elements using a
pair of fillet welds on opposite sides of
the plate. FSR shall be the smaller of the
toe crack or root crack allowable stress
range.
Crack initiating from weld toe:
Crack initiating from weld root:
5.7 Base metal of tension loaded plate
elements and on girders and rolled
beam webs or flanges at toe of
transverse fillet welds adjacent to
welded transverse stiffeners.
Stress
Category
C’
Constant
Cf
Eqn. (C-4)
None provided
Initiating at weld
root
subject
to
tension
extending
into and through
weld.
Initiating
from
geometrical
discontinuity at toe of
weld extending into
base metal.
C
C’’
C
44 x 108
Eqn.(C-6)
44 x 108
SBC 306-CR-18
69
None provided
69
Initiating at weld
root
subject
to
tension
extending
into and through
weld
From
geometrical
discontinuity at toe
of fillet extending
into base metal
225
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Illustrative Typical Examples
SECTION 5 – WELDED JOINTS TRANSVERSE TO DIRECTION OF STRESS (continued)
5.5
5.6
5.7
SBC 306-CR-18
226
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Threshold
Potential Crack
FTH
Initiation Point
(MPa)
SECTION 6 – BASE METAL AT WELDED TRANSVERSE MEMBER CONNECTIONS
Description
Stress
Category
Constant
Cf
Near
point
of
tangency of radius at
edge of member
6.1 Base metal at details attached by
complete-joint-penetration groove welds
subject to longitudinal loading only
when the detail embodies a transition
radius, R, with the weld termination
ground smooth and with weld soundness
established
by
radiographic or
ultrasonic inspection in accordance with
the requirements of subclauses 6.12 or
6.13 of AWS D1.1/D1.1M.
R ≥ 600 mm
600 mm > R ≥ 150 mm
B
120 x 108
C
8
150 mm > R ≥ 50 mm
D
44 x 10
22 x 108
110
69
48
E
11 x 108
31
B
120 x 108
110
C
44 x 10
8
69
150 mm > R ≥ 50 mm
D
22 x 10
8
48
50 mm > R
E
11 x 108
31
When weld reinforcement is not
removed: R ≥ 600 mm
C
44 x 108
69
600 mm > R ≥ 150 mm
C
44 x 108
69
150 mm > R ≥ 50 mm
D
22 x 108
48
E
11 x 108
31
50 mm > R
6.2 Base metal at details of equal
thickness attached by complete-jointpenetration groove welds subject to
transverse loading with or without
longitudinal loading when the detail
embodies a transition radius, R, with the
weld termination ground smooth and with
weld
soundness
established
by
radiographic or ultrasonic inspection in
accordance with the requirements of
subclauses 6.12 or 6.13 of AWS
D1.1/D1.1M: When weld reinforcement is
removed:
R ≥ 600 mm
600 mm > R ≥ 150 mm
50 mm > R
SBC 306-CR-18
Near
points
of
tangency of radius or
in the weld or at
fusion boundary or
member or attachment
At toe of the weld
either along edge of
member
or
the
attachment
227
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Illustrative Typical Examples
SECTION 6 – BASE METAL AT WELDED TRANSVERSE MEMBER CONNECTIONS
6.1
6.2
SBC 306-CR-18
228
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Description
Stress
Category
Constant
Cf
Threshold
FTH
(MPa)
Potential Crack
Initiation Point
SECTION 6 – BASE METAL AT WELDED TRANSVERSE MEMBER CONNECTIONS (cont’d)
6.3 Base metal at details of unequal
thickness attached by complete-jointpenetration groove welds subject to
transverse loading with or without
longitudinal loading when the detail
embodies a transition radius, R, with
the weld termination ground smooth
and with weld soundness established
by radiographic or
ultrasonic
inspection in accordance with the
requirements of subclauses 6.12 or
6.13 of AWS D1.1/D1.1M. When
weld reinforcement is removed:
R > 50 mm
D
22 x 108
48
R ≤ 50 mm
E
11 x 108
31
When reinforcement is not removed:
Any radius
E
11 x 108
31
6.4 Base metal subject to longitudinal
stress at transverse members, with or
without transverse stress, attached by
fillet
or
partial-joint-penetration
groove welds parallel to direction of
stress when the detail embodies a
transition radius, R, with weld
termination ground smooth:
R > 50 mm
R ≤ 50 mm
At toe of weld along
edge
of
thinner
material In weld
termination in small
radius.
At toe of weld along
edge of thinner
material
Initiating in base
metal at the weld
termination or at
the toe of the weld
extending into the
base metal
D
22 x 108
48
E
8
31
11 x 10
SBC 306-CR-18
229
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Illustrative Typical Examples
SECTION 6 – BASE METAL AT WELDED TRANSVERSE MEMBER CONNECTIONS
6.3
6.4
SBC 306-CR-18
230
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Description
Stress
Category
Constant
Cf
Threshold
FTH
(MPa)
Potential Crack
Initiation Point
SECTION 7 – BASE METAL AT SHORT ATTACHMENTS1
7.1 Base metal subject to longitudinal
loading at details with welds parallel or
transverse to the direction of stress
where the detail embodies no
transition radius and with detail length
in direction of stress, a, and thickness
of the attachment, b:
a < 50 mm
50 mm ≤ a ≤ lesser of 12b or 100 mm
a > 100 mm
when b > 20 mm
a > lesser of 12b or 100 mm
when b ≤ 20 mm
Initiating in base
metal at the weld
termination or at the
toe of the weld
extending into the
base metal.
C
44 x 108
D
22 x 10
8
E
11 x 108
31
E’
3.9 x 108
18
69
48
7.2 Base metal subject to longitudinal
stress at details attached by fillet or
partial-joint-penetration groove welds,
with or without transverse load on
detail, when the detail embodies a
transition radius, R, with weld
termination ground smooth:
R > 50 mm
Initiating in base
metal at the weld
termination,
extending into the
base metal
D
22 x 108
48
R ≤ 50 mm
E
11 x 108
31
1
“Attachment” as used herein is defined as any steel detail welded to a member by its mere presence and independent
of its loading, causes a discontinuity in the stress flow in the member and thus reduces the fatigue resistance.
SBC 306-CR-18
231
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Illustrative Typical Examples
SECTION 7 – BASE METAL AT SHORT ATTACHMENTS1
7.1
7.2
SBC 306-CR-18
232
APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Description
Stress
Category
Constant
Cf
Threshold
FTH
(MPa)
Potential Crack
Initiation Point
69
At toe of weld in
base metal
55
Initiating at the root
of the fillet weld,
extending into the
weld
31
Initiating in the base
metal at the end of
the plug or slot
weld, extending into
the base metal
55
Initiating in the
weld at the faying
surface, extending
into the weld
48
Initiating at the root
of
the
threads,
extending into the
fastener
SECTION 8 - MISCELLANEOUS
8.1 Base metal at steel headed stud
anchors attached by fillet or
automatic stud welding.
8.2 Shear on throat of continuous or
intermittent longitudinal or transverse
fillet welds.
8.3 Base metal at plug or slot welds.
8.4 Shear on plug or slot welds.
8.5 Snug-tightened high-strength bolts,
common bolts, threaded anchor rods,
and hanger rods with cut, ground or
rolled threads. Stress range on tensile
stress area due to live load plus prying
action when applicable.
C
44 x 108
F
150 x 1010
Eqn. (C-2)
E
120 x 108
F
150 x 1010
Eqn. (C-2)
G
3.9 x 108
SBC 306-CR-18
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APPENDIX C —DESIGN FOR FATIGUE
TABLE C-1 (CONTINUED): FATIGUE DESIGN PARAMETERS
Illustrative Typical Examples
SECTION 8 - MISCELLANEOUS
8.1
8.2
8.3
8.4
8.5
SBC 306-CR-18
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APPENDIX C —DESIGN FOR FATIGUE
FIGURE CC-1. FATIGUE RESISTANCE CURVES.
SBC 306-CR-18
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APPENDIX C —DESIGN FOR FATIGUE
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APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS
APPENDIX D—STRUCTURAL DESIGN FOR FIRE CONDITIONS
This appendix provides criteria for the design and
evaluation of structural steel components, systems
and frames for fire conditions. These criteria
provide for the determination of the heat input,
thermal expansion and degradation in mechanical
properties of materials at elevated temperatures that
cause progressive decrease in strength and stiffness
of structural components and systems at elevated
temperatures.
The appendix is organized as follows:
D.1
— General Provisions
D.2
— Structural Design for Fire Conditions
by Analysis
D.3
— Design by Qualification Testing
alternative material or method, as permitted by the
applicable Saudi building code.
Structural design for fire conditions using Section
D.2 shall be performed using the load and resistance
factor design method in accordance with the
provisions of Section 2.3.3 .
D.1.3 Design by Qualification Testing. The
qualification testing methods in Section D.3 are
permitted to be used to document the fire resistance
of steel framing subject to the standardized fire
testing protocols required by the applicable Saudi
building code.
D.1.4 Load Combinations and Required
Strength. The required strength of the structure
and its elements shall be determined from the
gravity load combination as follows:
[0.9 or 1.2] 𝐷 + 𝑇 + 0.5𝐿
D.1— General Provisions
The methods contained in this appendix provide
regulatory evidence of compliance in accordance
with the design applications outlined in this section.
D.1.1 Performance Objective.
Structural
components, members and building frame systems
shall be designed so as to maintain their loadbearing function during the design-basis fire and to
satisfy other performance requirements specified
for the building occupancy.
Deformation criteria shall be applied where the
means of providing structural fire resistance, or the
design criteria for fire barriers, requires
consideration of the deformation of the loadcarrying structure.
Within the compartment of fire origin, forces and
deformations from the design-basis fire shall not
cause a breach of horizontal or vertical.
D.1.2 Design by Engineering Analysis. The
analysis methods in Section D.2 are permitted to be
used to document the anticipated performance of
steel framing when subjected to design-basis fire
scenarios. Methods in Section D.2 provide evidence
of compliance with performance objectives
established in Section D.1.1.
The analysis methods in Section D.2 are permitted
to be used to demonstrate an equivalency for an
(D-1)
where
D
= nominal dead load
L
= nominal occupancy live load
T
= nominal forces and deformations due to
the design-basis fire defined in Section
D.2.1
A notional load, Ni = 0.002Yi, as defined in Section
3.2.2 , where Ni = notional load applied at framing
level i and Yi = gravity load from combination D.1
acting on framing level i, shall be applied in
combination with the loads stipulated in Eq. (D-1).
D.2— Structural Design for Fire
Conditions by Analysis
It is permitted to design structural members,
components and building frames for elevated
temperatures in accordance with the requirements
of this section.
D.2.1 Design-Basis Fire. A design-basis fire
shall be identified to describe the heating conditions
for the structure. These heating conditions shall
relate to the fuel commodities and compartment
characteristics present in the assumed fire area. The
fuel load density based on the occupancy of the
SBC 306-CR-18
237
APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS
space shall be considered when determining the
total fuel load. Heating conditions shall be specified
either in terms of a heat flux or temperature of the
upper gas layer created by the fire. The variation of
the heating conditions with time shall be
determined for the duration of the fire.
When the analysis methods in this Section are used
to demonstrate an equivalency as an alternative
material or method as permitted by the applicable
Saudi building code, the design-basis fire shall be
determined in accordance with ASTM E119.
D2.1.1 Localized Fire. Where the heat release
rate from the fire is insufficient to cause flashover,
a localized fire exposure shall be assumed. In such
cases, the fuel composition, arrangement of the fuel
array and floor area occupied by the fuel shall be
used to determine the radiant heat flux from the
flame and smoke plume to the structure.
D2.1.2 Post-Flashover Compartment Fires.
Where the heat release rate from the fire is sufficient
to cause flashover, a post-flashover compartment
fire shall be assumed. The determination of the
temperature versus time profile resulting from the
fire shall include fuel load, ventilation
characteristics of the space (natural and
mechanical), compartment dimensions and thermal
characteristics of the compartment boundary.
The fire duration in a particular area shall be
determined by considering the total combustible
mass, or fuel load available in the space. In the case
of either a localized fire or a post-flashover
compartment fire, the fire duration shall be
determined as the total combustible mass divided
by the mass loss rate.
D2.1.3 Exterior Fires. The exposure of exterior
structure to flames projecting from windows or
other wall openings as a result of a post-flashover
compartment fire shall be considered along with the
radiation from the interior fire through the opening.
The shape and length of the flame projection shall
be used along with the distance between the flame
and the exterior steelwork to determine the heat flux
to the steel. The method identified in Section D2.1.2
shall be used for describing the characteristics of the
interior compartment fire.
D2.1.4 Active Fire Protection Systems. The
effects of active fire protection systems shall be
considered when describing the design-basis fire.
Where automatic smoke and heat vents are installed
in non-sprinklered spaces, the resulting smoke
temperature shall be determined from calculation.
D.2.2 Temperatures in Structural Systems
under Fire Conditions. Temperatures within
structural members, components and frames due to
the heating conditions posed by the design-basis
fire shall be determined by a heat transfer analysis.
D.2.3 Material
Strengths
at
Elevated
Temperatures. Material properties at elevated
temperatures shall be determined from test data. In
the absence of such data, it is permitted to use the
material properties stipulated in this section. These
relationships do not apply for steels with yield
strengths in excess of 450 MPa or concretes with
specified compression strength in excess of 55
MPa.
D2.3.1 Thermal Elongation. The coefficients of
expansion shall be taken as follows:
(a) For structural and reinforcing steels: For
calculations at temperatures above 65 °C, the
coefficient of thermal expansion shall be 1.4
x10-5/oC.
(b) For normal weight concrete: For calculations at
temperatures above 65 °C, the coefficient of
thermal expansion shall be 1.8 x 10-5/oC.
(c) For lightweight concrete: For calculations at
temperatures above 65 °C, the coefficient of
thermal expansion shall be 7.9 x10-6/oC.
D2.3.2 Mechanical Properties at Elevated
Temperatures. The deterioration in strength and
stiffness of structural members, components and
systems shall be taken into account in the structural
analysis of the frame. The values Fy (T), Fp (T), Fu
(T), E(T), G(T), fc’(T), Ec (T) and cu(T) at elevated
temperature to be used in structural analysis,
expressed as the ratio with respect to the property at
ambient, assumed to be 20 °C, shall be defined as
in TABLE D-1 and TABLE D-2. Fp(T) is the
proportional limit at elevated temperatures, which
is calculated as a ratio to yield strength as specified
in TABLE D-1. It is permitted to interpolate
between these values.
For lightweight concrete, values of cu shall be
obtained from tests.
D.2.4
Structural Design Requirements
D2.4.1 General Structural Integrity.
The
structural frame shall be capable of providing
adequate strength and deformation capacity to
withstand, as a system, the structural actions
developed during the fire within the prescribed
limits of deformation. The structural system shall
SBC 306-CR-18
238
APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS
be designed to sustain local damage with the
structural system, as a whole, remaining stable.
represent the proposed structural design. Material
properties shall be defined as per Section D.2.3.
Continuous load paths shall be provided to transfer
all forces from the exposed region to the final point
of resistance. The foundation shall be designed to
resist the forces and to accommodate the
deformations developed during the design- basis
fire.
The resulting analysis shall consider all relevant
limit states, such as excessive deflections,
connection fractures, and overall or local buckling.
D2.4.2 Strength Requirements and Deformation
Limits. Conformance of the structural system to
these requirements shall be demonstrated by
constructing a mathematical model of the structure
based on principles of structural mechanics and
evaluating this model for the internal forces and
deformations in the members of the structure
developed by the temperatures from the designbasis fire.
Individual members shall be provided with
adequate strength to resist the shears, axial forces
and moments determined in accordance with these
provisions.
Connections shall develop the strength of the
connected members or the forces indicated above.
Where the means of providing fire resistance
requires the consideration of deformation criteria,
the deformation of the structural system, or
members thereof, under the design-basis fire shall
not exceed the prescribed limits.
D2.4.3 Methods of Analysis
D.2.4.3.1 Advanced Methods of Analysis. The
methods of analysis in this section are permitted for
the design of all steel building structures for fire
conditions. The design-basis fire exposure shall be
that determined in Section D.2.1. The analysis shall
include both a thermal response and the mechanical
response to the design-basis fire.
The thermal response shall produce a temperature
field in each structural element as a result of the
design-basis fire and shall incorporate temperaturedependent thermal properties of the structural
elements and fire-resistive materials, as per Section
D.2.2.
The mechanical response results in forces and
deformations in the structural system subjected to
the thermal response calculated from the designbasis fire. The mechanical response shall take into
account explicitly the deterioration in strength and
stiffness with increasing temperature, the effects of
thermal expansions, and large deformations.
Boundary conditions and connection fixity must
D.2.4.3.2 Simple Methods of Analysis. The
methods of analysis in this section are permitted to
be used for the evaluation of the performance of
individual members at elevated temperatures
during exposure to fire.
The support and restraint conditions (forces,
moments and boundary conditions) applicable at
normal temperatures are permitted to be assumed to
remain unchanged throughout the fire exposure.
For steel temperatures less than or equal to 200 oC,
the member and connection design strengths shall
be determined without consideration of temperature
effects.
User Note: At temperatures below 200 C, the
degradation in steel properties need not be
considered in calculating member strengths for
the simple method of analysis; however, forces
and deformations induced by elevated
temperatures must be considered.
1. Tension Members
It is permitted to model the thermal response of a
tension element using a one- dimensional heat
transfer equation with heat input as determined by
the design-basis fire defined in Section D.2.1.
The design strength of a tension member shall be
determined using the provisions of Chapter 4, with
steel properties as stipulated in Section D.2.3 and
assuming a uniform temperature over the cross
section using the temperature equal to the
maximum steel temperature.
2. Compression Members
It is permitted to model the thermal response of a
compression element using a one-dimensional heat
transfer equation with heat input as determined by
the design-basis fire defined in Section D.2.1.
The design strength of a compression member shall
be determined using the provisions of Chapter 5
with steel properties as stipulated in Section D2.3.2
and Eq. (D-2) used in lieu of Eqs. (5-2) and (5-3) in
Chapter 5 to calculate the nominal compressive
strength for flexural buckling:
SBC 306-CR-18
239
APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS
𝐹𝑐𝑟 (𝑇) = [0.42
𝐹 (𝑇)
√ 𝑦
𝐹𝑒 (𝑇)
] 𝐹𝑦 (𝑇)
(D-2)
4. Composite Floor Members
Where Fy (T) is the yield stress at elevated
temperature and Fe (T) is the critical elastic
buckling stress calculated from Eq. (5-4) in Chapter
5 with the elastic modulus E(T) at elevated
temperature. Fy (T) and E(T) are obtained using
coefficients from TABLE D-1.
3. Flexural Members
It is permitted to model the thermal response of
flexural elements using a one-dimensional heat
transfer equation to calculate bottom flange
temperature and to assume that this bottom flange
temperature is constant over the depth of the
member.
The design strength of a flexural member shall be
determined using the provisions of Chapter 6 with
steel properties as stipulated in Section D2.3.2 and
Eqs. (D-3) through (D-10) used in lieu of Eqs. (6-3)
through (6-7) in CHAPTER 6 to calculate the
nominal flexural strength for lateral-torsional
buckling of laterally unbraced doubly symmetric
members:
(a) When 𝐿𝑏 ≤ 𝐿𝑟 (𝑇)
𝑀𝑛 (𝑇) = 𝐶𝑏 [𝑀𝑟 (𝑇) + {𝑀𝑝 (𝑇) −
𝐿
𝑀𝑟 (𝑇)}[1 − 𝑏 ]𝐶𝑥
(D-3)
𝐿𝑟 (𝑇)
(d) When 𝐿𝑏 > 𝐿𝑟 (𝑇)
𝑀𝑛 (𝑇) = 𝐹𝑐𝑟 (𝑇)𝑆𝑥
(D-4)
where
𝐹𝑐𝑟 (𝑇) =
𝐶𝑏 𝜋2 𝐸(𝑇)
𝐿
𝑟𝑡𝑠
( 𝑏 )2
𝐿𝑟 (𝑇) = 1.95𝑟𝑡𝑠
𝐽𝑐
𝐿
𝑥 𝑜
𝑡𝑠
𝑏
√1 + 0.078 𝑆 ℎ (𝑟 )2
𝐸(𝑇)
𝐹𝐿 (𝑇)
calculated in accordance with TABLE D-1, and
other terms are as defined in Chapter 6.
(D-5)
√𝐴 + √(𝐴)2 + 6.76(𝐵)2 (D-6)
Where,
𝐽𝑐
𝑆𝑥 ℎ𝑜
𝐹𝐿 (𝑇)
𝐵=
𝐸(𝑇)
𝑀𝑟 (𝑇) = 𝑆𝑥 𝐹𝐿 (𝑇)
𝐹𝐿 (𝑇) = 𝐹𝑦 (𝑘𝑝 − 0.3𝑘𝑦 )
𝑀𝑝 (𝑇) = 𝑍𝑥 𝐹𝑦 (𝑇)
𝐴=
(D-7)
(D-8)
(D-9)
𝑇
𝑐𝑥 = 0.6 +
≤ 3.0 where T is in C° (D-10)
250
The material properties at elevated temperatures,
𝐸(𝑇) and 𝐹𝑦 (𝑇), and the kp and ky coefficients are
It is permitted to model the thermal response of
flexural elements supporting a concrete slab using a
one-dimensional heat transfer equation to calculate
bottom flange temperature. That temperature shall
be taken as constant between the bottom flange and
mid-depth of the web and shall decrease linearly by
no more than 25% from the mid-depth of the web
to the top flange of the beam.
The design strength of a composite flexural member
shall be determined using the provisions of Chapter
9, with reduced yield stresses in the steel consistent
with the temperature variation described under
thermal response.
D2.4.4 Design Strength. The design strength shall
be determined as in Section 2.3.3 in Chapter 2. The
nominal strength, Rn, shall be calculated using
material properties, as provided in Section D.2.3, at
the temperature developed by the design-basis fire,
and as stipulated in this appendix.
D.3— Design by Qualification Testing
D.3.1 Qualification Standards.
Structural
members and components in steel buildings shall be
qualified for the rating period in conformance with
ASTM E119. Demonstration of compliance with
these requirements using the procedures specified
for steel construction in Chapter 5 of
SEI/ASCE/SFPE Standard 29-05, Standard
Calculation Methods for Structural Fire
Protection, is permitted.
D.3.2 Restrained Construction. For floor and
roof assemblies and individual beams in buildings,
a restrained condition exists when the surrounding
or supporting structure is capable of resisting forces
and accommodating deformations caused by
thermal expansion throughout the range of
anticipated elevated temperatures.
Steel beams, girders and frames supporting
concrete slabs that are welded or bolted to integral
framing members shall be considered restrained
construction.
D.3.3 Unrestrained Construction. Steel beams,
girders and frames that do not support a concrete
slab shall be considered unrestrained unless the
members are bolted or welded to surrounding
construction that has been specifically designed and
detailed to resist effects of elevated temperatures.
SBC 306-CR-18
240
APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS
A steel member bearing on a wall in a single span
or at the end span of multiple spans shall be
considered unrestrained unless the wall has been
designed and detailed to resist effects of thermal
expansion.
SBC 306-CR-18
241
APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS
BIBLIOGRAPHY
The following references provide further
information on key issues related to fire-resistant
design of steel building systems and components,
and are representative of the extensive literature on
the topic. The references were selected because they
are archival in nature or otherwise easily accessible
by engineers seeking to design fire-resistance into
building structures.
AISI (1980), Designing Fire Protection for Steel
Columns, American Iron and Steel Institute,
Washington, DC.
Bailey, C.G. (2000), “The Influence of the Thermal
Expansion of Beams on the Structural Behavior of
Columns in Steel-Framed Structures During a
Fire,” Engineering Structures, Vol. 22, No. 7, pp.
755–768.
Bennetts, I.D. and Thomas, I.R. (2002), “Design of
Steel Structures under Fire Conditions,”
Progress in Structural Engineering and Materials,
Vol. 4, No. 1, pp. 6–17.
Boring, D.F., Spence, J.C. and Wells, W.G. (1981),
Fire Protection Through Modern Building Codes,
5th Ed., American Iron and Steel Institute,
Washington, DC.
Brozzetti, J., Law, M., Pettersson, O. and
Witteveen, J. (1983), “Safety Concepts and Design
for Fire Resistance of Steel Structures,” IABSE
Surveys S-22/83, IABSE Periodica 1/1983, ETHHonggerberg, Zurich, Switzerland.
Chalk, P.L. and Corotis, R.B. (1980), “Probability
Model for Design Live Loads,” Journal of the
Structures Division, ASCE, Vol. 106, No. ST10, pp.
2,017–2,033.
Chan, S.L. and Chan, B.H.M. (2001), “Refined
Plastic Hinge Analysis of Steel Frames under Fire,”
Steel and Composite Structures, Vol. 1, No. 1, pp.
111–130.
CIB W14 (1983), “A Conceptual Approach
Towards a Probability Based Design Guide on
Structural Fire Safety,” Fire Safety Journal, Vol. 6,
No. 1, pp. 1–79.
CIB W14 (2001), “Rational Safety Engineering
Approach to Fire Resistance of Buildings,” CIB
Report No. 269, International Council for Research
and Innovation in Building and Construction,
Rotterdam, the Netherlands.
Culver, C.G. (1978), “Characteristics of Fire Loads
in Office Buildings,” Fire Technology, Vol. 1,491,
pp. 51–60.
Huang, Z., Burgess, I.W. and Plank, R.J. (2000),
“Three-Dimensional Analysis of Composite SteelFramed Buildings in Fire,” Journal of Structural
Engineering, ASCE, Vol. 126, No. 3, pp. 389–397.
Jeanes, D.C. (1985), “Application of the Computer
in Modeling Fire Endurance of Structural Steel
Floor Systems,” Fire Safety Journal, Vol. 9, pp.
119–135.
Kruppa, J. (2000), “Recent Developments in Fire
Design,” Progress in Structures Engineering and
Materials, Vol. 2, No. 1, pp. 6–15.
Lane, B. (2000), “Performance-Based Design for
Fire Resistance,” Modern Steel Construction,
AISC, December, pp. 54–61.
Lawson, R.M. (2001), “Fire Engineering Design of
Steel and Composite Buildings,”Journal of
Constructional Steel Research, Vol. 57, pp. 1,233–
1,247.
Lie, T.T. (1978), “Fire Resistance of Structural
Steel,” Engineering Journal, AISC, Vol. 15, No. 4,
pp. 116–125.
Lie, T.T. and Almand, K.H. (1990), “A Method to
Predict the Fire Resistance of Steel Building
Columns,” Engineering Journal, AISC, Vol. 27, pp.
158–167.
Magnusson, S.E. and Thelandersson, S. (1974), “A
Discussion of Compartment Fires,” Fire
Technology, Vol. 10, No. 4, pp. 228–246.
Milke, J.A. (1985), “Overview of Existing
Analytical Methods for the Determination of Fire
Resistance,” Fire Technology, Vol. 21, No. 1, pp.
59–65.
Milke, J.A. (1992), “Software Review:
Temperature Analysis of Structures Exposed to
Fire,” Fire Technology, Vol. 28, No. 2, pp. 184–
189.
Newman, G. (1999), “The Cardington Fire Tests,”
Proceedings of the North American Steel
Construction Conference, Toronto, Canada, AISC,
Chicago, IL, pp. 28.1–28.22.
Nwosu, D.I. and Kodur, V.K.R. (1999), “Behavior
of Steel Frames Under Fire Conditions,”Canadian
Journal of Civil Engineering, Vol. 26, pp. 156–167.
Sakumoto,
Properties
SBC 306-CR-18
Y.
of
(1992), “High-Temperature
Fire-Resistant
Steel
for
242
APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS
Buildings,”Journal of Structural Engineering,
ASCE, Vol. 18, No. 2, pp. 392–407.
Sakumoto, Y. (1999), “Research on New FireProtection Materials and Fire-Safe Design,”Journal
of Structural Engineering, ASCE, Vol. 125, No. 12,
pp. 1,415–1,422.
Toh, W.S., Tan, K.H. and Fung, T.C. (2001),
“Strength and Stability of Steel Frames in Fire:
Rankine Approach,” Journal of Structural
Engineering, ASCE, Vol. 127, No. 4, pp. 461–468.
Usmani, A.S., Rotter, J.M., Lamont, S., Sanad,
A.M. and Gillie, M. (2001), “Fundamental
Principles of Structural Behavior under Thermal
Effects,” Fire Safety Journal, Vol. 36, No. 8.
Wang, Y.C. and Moore, D.B. (1995), “Steel Frames
in Fire: Analysis,” Engineering Structures, Vol. 17,
No. 6, pp. 462–472.
Wang, Y.C. and Kodur, V.K.R. (2000), “Research
Toward Use of Unprotected Steel Structures,”
Journal of Structural Engineering, ASCE, Vol.
120, No. 12, pp. 1,442–1,450.
Wang, Y.C. (2000), “An Analysis of the Global
Structural Behavior of the Cardington SteelFramed Building during the Two BRE Fire Tests,”
Engineering Structures, Vol. 22, pp. 401–412.
SBC 306-CR-18
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APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS
TABLES AND FIGURES OF APPENDIX D
TABLE D-1: PROPERTIES OF STEEL AT ELEVATED TEMPERATURES
Steel Temperature, °C
20
100
200
300
400
500
600
700
800
900
1000
1100
1200
kE = E (T)/E
= G (T)/G
1.00
1.00
0.90
0.80
0.70
0.60
0.31
0.13
0.09
0.0675
0.045
0.0225
0.00
kp= Fp (T)/Fy
ky = Fy (T)/Fy
ku= Fu (T)/Fy
1.00
1.00
0.807
0.613
0.42
0.36
0.18
0.075
0.05
0.0375
0.025
0.0125
0.00
1.00
1.00
1.00
1.00
1.00
0.78
0.47
0.23
0.11
0.06
0.04
0.02
0.00
1.25
1.25
1.25
1.25
1.00
0.78
0.47
0.23
0.11
0.06
0.04
0.02
0.00
TABLE D-2: PROPERTIES OF CONCRETE AT ELEVATED TEMPERATURES
Concrete
Temperature
°C
20
100
200
300
400
500
600
700
800
900
1000
1100
1200
kc = fc’ (T )/fc’
Normal weight
Lightweight
concrete
concrete
1.00
1.00
1.00
1.00
0.95
1.00
0.85
1.00
0.75
0.88
0.60
0.76
0.45
0.64
0.30
0.52
0.15
0.40
0.08
0.28
0.04
0.16
0.01
0.04
0.00
0.00
Ec (T )/Ec
cu (T ), % Normal
weight concrete
1.00
0.92
0.76
0.59
0.43
0.26
0.14
0.083
0.067
0.050
0.033
0.017
0.000
0.25
0.40
0.55
0.70
1.0
1.5
2.5
2.5
2.5
2.5
2.5
2.5
0.00
TABLE CD-1: GUIDELINES FOR ESTIMATING F
Type of Assembly
Column, exposed on all sides
Floor beam: Embedded in concrete floor slab, with only bottom flange of beam exposed to
fire
Floor beam, with concrete slab resting on top flange of beam
Flange width-to-beam depth ratio ≥ 0.5
Flange width-to-beam depth ratio < 0.5
Box girder and lattice girder
SBC 306-CR-18
F
0.7
0.5
0.5
0.7
0.7
244
APPENDIX D —STRUCTURAL DESIGN FOR FIRE CONDITIONS
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SBC 306-CR-18
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APPENDIX E —STABILITY BRACING FOR COLUMNS AND BEAMS
APPENDIX E—Stability Bracing for Columns and Beams
This appendix addresses the minimum strength and
stiffness necessary to provide a braced point in a
column, beam or beam-column.
The appendix is organized as follows:
E.1
— General Provisions
E.2
— Column Bracing
E.3
— Beam Bracing
E.4
— Beam-Column Bracing
User Note: The stability requirements for
braced-frame systems are provided in Chapter
3. The provisions in this appendix apply to
bracing that is provided to stabilize individual
columns, beams and beam-columns.
A relative brace controls the movement of the
braced point with respect to adjacent braced
points. A nodal brace controls the movement at
the braced point without direct interaction with
adjacent braced points. A continuous bracing
system consists of bracing that is attached along
the entire member length; however, nodal
bracing systems with a regular spacing can also
be modeled as a continuous system.
The design strength and stiffness of the bracing
members and connections shall equal or exceed the
required strength and stiffness, respectively, unless
analysis indicates that smaller values are justified.
A second-order analysis that includes the initial
out-of-straightness of the member to obtain brace
strength and stiffness requirements is permitted in
lieu of the requirements of this appendix.
E.1— General Provisions
E.2— Column Bracing
Columns with end and intermediate braced points
designed to meet the requirements in Section E.2
are permitted to be designed based on the unbraced
length, L, between the braced points with an
effective length factor, K= 1.0. Beams with
intermediate braced points designed to meet the
requirements in Section E.3 are permitted to be
designed based on the unbraced length, Lb, between
the braced points.
It is permitted to brace an individual column at end
and intermediate points along the length using
either relative or nodal bracing.
When bracing is perpendicular to the members to
be braced, the equations in Sections E.2 and E.3
shall be used directly. When bracing is oriented at
an angle to the member to be braced, these
equations shall be adjusted for the angle of
inclination. The evaluation of the stiffness furnished
by a brace shall include its member and geometric
properties, as well as the effects of connections and
anchoring details.
User Note: In this appendix, relative and nodal
bracing systems are addressed for columns and
for beams with lateral bracing. For beams with
torsional bracing, nodal and continuous bracing
systems are addressed.
E.2.1
Relative Bracing. The required strength is
𝑃𝑟𝑏 = 0.004𝑃𝑟
(E-1)
The required stiffness is
𝛽𝑏𝑟 =
1 2𝑃𝑟
( )
𝜑 𝐿𝑏
(E-2)
where
𝜑
= 0.75
Lb
= unbraced length, mm
Pr
= required strength in axial compression, N
E.2.2
Nodal Bracing. The required strength is
𝑃𝑟𝑏 = 0.01𝑃𝑟
(E-3)
The required stiffness is
𝛽𝑏𝑟 =
SBC 306-CR-18
1 8𝑃𝑟
( )
𝜑 𝐿𝑏
(E-4)
246
APPENDIX E —STABILITY BRACING FOR COLUMNS AND BEAMS
User Note: These equations correspond to
the assumption that nodal braces are
equally spaced along the column.
where
𝜑
= 0.75
Lb
= unbraced length, mm
Pr
= required strength in axial compression,
N
= 2.0 for the brace closest to the inflection
point in a beam subject to double
curvature bending
ho
= distance between flange centroids, mm
Mr
= required flexural strength, N-mm
E3.1.2 Nodal Bracing. The required strength is
In Eq. (E-4), Lb need not be taken less than the
maximum effective length, KL, permitted for the
column based upon the required axial strength, Pr .
𝑃𝑟𝑏 = 0.02𝑀𝑟 𝐶𝑑 /ℎ0
(E-7)
The required stiffness is
𝛽𝑏𝑟 =
1 10𝑀𝑟 𝐶𝑑
(
)
𝜑 𝐿𝑏 ℎ𝑜
(E-8)
where
𝜑
= 0.75
E.3— Beam Bracing
Mr
= required flexural strength, N-mm
Beams and trusses shall be restrained against
rotation about their longitudinal axis at points of
support. When a braced point is assumed in the
design between points of support, lateral bracing,
torsional bracing, or a combination of the two shall
be provided to prevent the relative displacement
of the top and bottom flanges (i.e., to prevent
twist). In members subject to double curvature
bending, the inflection point shall not be considered
a braced point unless bracing is provided at that
location.
In Eq. (E-8), Lb need not be taken less than the
maximum unbraced length permitted for the beam
based upon the flexural required strength, Mr.
E.3.1 Lateral Bracing. Lateral bracing shall be
attached at or near the beam compression flange,
except as follows:
1. At the free end of a cantilevered beam,
lateral bracing shall be attached at or near
the top (tension) flange.
2. For braced beams subject to double
curvature bending, lateral bracing shall be
attached to both flanges at the braced point
nearest the inflection point.
E.3.2 Torsional Bracing. It is permitted to
attach torsional bracing at any cross-sectional
location, and it need not be attached near the
compression flange.
User Note: Torsional bracing can be provided
with a moment-connected beam, cross-frame,
or other diaphragm element.
E3.2.1 Nodal Bracing. The required strength is
𝑀𝑟𝑏 =
1 4𝑀𝑟 𝐶𝑑
(
)
𝜑 𝐿𝑏 ℎ𝑜
𝛽𝑇 =
𝛽𝑠𝑒𝑐 =
where
𝜑
= 0.75
Cd
= 1.0 except in the following case;
(E-10)
1 2.4𝐿𝑀𝑟2
(
)
𝜑 𝑛𝐸𝐼𝑦 𝐶𝑏2
(E-11)
where
(E-5)
(E-6)
𝛽𝑇
𝛽
(1 − 𝑇 )
𝛽𝑠𝑒𝑐
𝛽𝑇𝑏 =
The required stiffness is
𝛽𝑏𝑟 =
(E-9)
The required stiffness of the brace is
E3.1.1 Relative Bracing. The required strength is
𝑃𝑟𝑏 = 0.008𝑀𝑟 𝐶𝑑 /ℎ0
0.024𝑀𝑟 𝐿
𝑛𝐶𝑏 𝐿𝑏
3
3.3𝐸 1.5 ℎ0 𝑡𝑤
ℎ0
(
12
𝑡 𝑏3
+ 𝑠𝑡 𝑠 )
12
(E-12)
Cb
= modification factor defined in Chapter 6
E
= modulus of elasticity of steel = 200 000
MPa
Iy
= out-of-plane moment of inertia, mm
L
= length of span, mm
SBC 306-CR-18
4
247
APPENDIX E —STABILITY BRACING FOR COLUMNS AND BEAMS
bs
= stiffener width for one-sided stiffeners,
mm
= twice the individual stiffener width for
pairs of stiffeners, mm
n
= number of nodal braced points within the
span
tw
= thickness of beam web, mm
tst
= thickness of web stiffener, mm
𝛽𝑇
= overall brace system stiffness, N-mm/rad
𝛽𝑠𝑒𝑐
= web distortional stiffness, including the
effect of web transverse stiffeners, if
any, N-mm/rad
User Note: If sec T, Eq. (E-10) is negative,
which indicates that torsional beam bracing
will not be effective due to inadequate web
distortional stiffness.
Mr = required flexural strength, N-mm
When required, the web stiffener shall extend the
full depth of the braced member and shall be
attached to the flange if the torsional brace is also
attached to the flange. Alternatively, it shall be
permissible to stop the stiffener short by a distance
equal to 4tw from any beam flange that is not
directly attached to the torsional brace.
as specified in Section E.2, and the required
strength and stiffness for the flexure shall be
determined as specified in Section E.3. The values
so determined shall be combined as follows:
(a) When relative lateral bracing is used, the
required strength shall be taken as the sum of
the values determined using Eqs. (E-1) and
(E-5), and the required stiffness shall be
taken as the sum of the values determined
using Eqs. (E-2) and (E-6).
(b) When nodal lateral bracing is used, the
required strength shall be taken as the sum of
the values determined using Eqs. (E-3) and
(E-7), and the required stiffness shall be
taken as the sum of the values determined
using Eqs. (E-4) and (E-8). In Eqs. (E-4) and
(E-8), Lb for beam- columns shall be taken as
the actual unbraced length; the provisions in
Sections E.2.2 and E3.1.2 that Lb need not be
taken less than the maximum permitted
effective length based upon Pr and Mr shall not
be applied.
(c) When torsional bracing is provided for flexure
in combination with relative or nodal bracing
for the axial force, the required strength and
stiffness shall be combined or distributed in a
manner that is consistent with the resistance
provided by the element(s) of the actual bracing
details.
In Eq. (E-9), Lb need not be taken less than the
maximum unbraced length permitted for the beam
based upon the required flexural strength, Mr.
E3.2.2 Continuous Bracing. For continuous
bracing, Eqs. (E-9) and (E-10) shall be used with
the following modifications:
1. L/n = 1.0
2. Lb shall be taken equal to the maximum
unbraced length permitted for the beam
based upon the required flexural strength,
Mr
3. The web distortional stiffness shall be
taken as:
𝛽𝑠𝑒𝑐 =
3
3.3𝐸𝑡𝑤
12ℎ0
(E-13)
E.4— Beam-Column Bracing
For bracing of beam-columns, the required strength
and stiffness for the axial force shall be determined
SBC 306-CR-18
248
APPENDIX E —STABILITY BRACING FOR COLUMNS AND BEAMS
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SBC 306-CR-18
249
APPENDIX F —ALTERNATIVE METHODS OF DESIGN FOR STABILITY
APPENDIX F—ALTERNATIVE METHODS OF DESIGN FOR
STABILITY
This appendix presents alternatives to the direct
analysis method of design for stability defined in
Chapter 3. The two alternative methods covered are
the effective length method and the first-order
analysis method.
of Section 3.2.1 , except that the stiffness
reduction indicated in Section 3.2.3 shall not be
applied; the nominal stiffnesses of all structural
steel components shall be used. Notional loads
shall be applied in the analysis in accordance with
Section 3.2.2.2 .
The appendix is organized as follows:
F.1
— General Stability Requirements
F.2
— Effective Length Method
F.3
— First-Order Analysis Method
User Note: Since the condition specified in
Section 3.2.2.2 (4) will be satisfied in all cases
where the effective length method is
applicable, the notional load need only be
applied in gravity-only load cases.
F.1— General Stability Requirements
The general requirements of Section 3.1 shall
apply. As an alternative to the direct analysis
method (defined in Sections 3.1 and 3.2), it is
permissible to design structures for stability in
accordance with either the effective length method,
specified in Section F.2, or the first-order analysis
method, specified in Section F.3, subject to the
limitations indicated in those sections.
F.2— Effective Length Method
F.2.1 Limitations. The use of the effective length
method shall be limited to the following conditions:
1. The structure supports gravity loads
primarily through nominally vertical
columns, walls or frames.
2. The ratio of maximum second-order drift
to maximum first-order drift (both
determined for LRFD load combinations,
based on nominal unreduced stiffnesses) in
all stories is equal to or less than 1.5.
User Note: The ratio of second-order drift
to first-order drift in a story may be taken
as the B2 multiplier, calculated as specified
in Appendix G.
F.2.2 Required Strengths.
The required
strengths of components shall be determined from
structural analysis conforming to the requirements
F.2.3 Design Strengths. The design strengths of
members and connections shall be calculated in
accordance with the provisions of Chapter 4,
Chapter 5, Chapter 6, Chapter 7, Chapter 8, Chapter
9, Chapter 10 and Chapter 11, as applicable.
The effective length factor, K, of members subject
to compression shall be taken as specified in (a) or
(b), below, as applicable.
(a) In braced frame systems, shear wall
systems, and other structural systems where
lateral stability and resistance to lateral loads
does not rely on the flexural stiffness of
columns, the effective length factor, K, of
members subject to compression shall be
taken as 1.0, unless rational analysis indicates
that a lower value is appropriate.
(b) In moment frame systems and other structural
systems in which the flexural stiffnesses of
columns are considered to contribute to lateral
stability and resistance to lateral loads, the
effective length factor, K, or elastic critical
buckling stress, Fe, of those columns whose
flexural stiffnesses are considered to contribute
to lateral stability and resistance to lateral
loads shall be determined from a sidesway
buckling analysis of the structure; K shall be
taken as 1.0 for columns whose flexural
stiffnesses are not considered to contribute to
lateral stability and resistance to lateral loads
such as leaning columns.
Exception: It is permitted to use K 1.0 in the
design of all columns if the ratio of maximum
SBC 306-CR-18
250
APPENDIX F —ALTERNATIVE METHODS OF DESIGN FOR STABILITY
second-order drift to maximum first-order drift
(both determined for LRFD load combinations,
based on nominal unreduced stiffnesses) in all
stories is equal to or less than 1.1.
all other deformations that
displacements of the structure.
contribute
to
1. All load combinations shall include an
additional lateral load, Ni, applied in
combination with other loads at each level
of the structure:
Bracing intended to define the unbraced lengths
of members shall have sufficient stiffness and
strength to control member movement at the braced
points.
𝑁𝑖 = 2.1(𝛥⁄𝐿)𝑌𝑖 ≥ 0.0042 𝑌𝑖
(F-2)
where
User Note: Methods of satisfying the bracing
requirement are provided in Appendix E. The
requirements of Appendix E are not applicable
to bracing that is included in the analysis of the
overall structure as part of the overall forceresisting system.
Yi
gravity load applied at level i from
the LRFD load combinations, as
applicable, N
/L
maximum ratio of to L for all stories in
the structure
first-order interstory drift due to the LRFD
combination, mm. Where varies over
the plan area of the structure, shall be
the average drift weighted in proportion to
vertical load or, alternatively, the
maximum drift.
L
height of story, mm
F.3— First-Order Analysis Method
F.3.1 Limitations. The use of the first-order
analysis method shall be limited to the following
conditions:
1. The structure supports gravity loads
primarily through nominally vertical
columns, walls or frames.
2. The ratio of maximum second-order drift
to maximum first-order drift (both
determined for LRFD load combinations,
based on nominal unreduced stiffnesses) in
all stories is equal to or less than 1.5.
User Note: The ratio of second-order drift to
first-order drift in a story may be taken as the
B2 multiplier, calculated as specified in
Appendix G.
3. The required axial compressive strengths
of all members whose flexural stiffnesses
are considered to contribute to the lateral
stability of the structure satisfy the
limitation:
𝑃𝑟 ≤ 0.5𝑃𝑦
The additional lateral load at any level, Ni, shall be
distributed over that level in the same manner as the
gravity load at the level. The additional lateral loads
shall be applied in the direction that provides the
greatest destabilizing effect.
User Note: For most building structures, the
requirement regarding the direction of Ni may
be satisfied as follows: For load combinations
that do not include lateral loading, consider two
alternative orthogonal directions for the
additional lateral load, in a positive and a
negative sense in each of the two directions,
same direction at all levels; for load
combinations that include lateral loading, apply
all the additional lateral loads in the direction
of the resultant of all lateral loads in the
combination.
(F-1)
where
Pr
required axial compressive strength
under LRFD load combinations.
Py
Fy A axial yield strength.
F.3.2 Required Strength.
The required
strengths of components shall be determined from
a first-order analysis, with additional requirements
(1) and (2) below. The analysis shall consider
flexural, shear and axial member deformations, and
2. The nonsway amplification of beamcolumn moments shall be considered by
applying the B1 amplifier of Appendix G to
the total member moments.
F.3.3 Design Strengths. The design strengths of
members and connections shall be calculated in
accordance with the provisions of Chapters 4, 5, 6,
7, 8, 9, 10 and 11, as applicable.
The effective length factor, K, of all members shall
be taken as unity.
SBC 306-CR-18
251
APPENDIX F —ALTERNATIVE METHODS OF DESIGN FOR STABILITY
Bracing intended to define the unbraced lengths
of members shall have sufficient stiffness and
strength to control member movement at the braced
points.
User Note: Methods of satisfying this
requirement are provided in Appendix E. The
requirements of Appendix E are not applicable
to bracing that is included in the analysis of
the overall structure as part of the overall
force-resisting system.
SBC 306-CR-18
252
APPENDIX F —ALTERNATIVE METHODS OF DESIGN FOR STABILITY
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SBC 306-CR-18
253
APPENDIX G —APPROXIMATE SECOND-ORDER ANALYSIS
APPENDIX G—APPROXIMATE SECOND-ORDER ANALYSIS
This appendix provides, as an alternative to a
rigorous second-order analysis, a procedure to
account for second-order effects in structures by
amplifying the required strengths indicated by a
first-order analysis.
The appendix is organized as follows:
G.1
— Limitations
G.2
— Calculation Procedure
Mnt
= first-order moment using LRFD load
combinations, with the structure
restrained against lateral translation.
Mr
= required second-order flexural strength
using LRFD load combinations
Plt
= first-order axial force using LRFD load
combinations, due to lateral translation
of the structure only.
Pnt
= first-order axial force using LRFD load
combinations,
with
the structure
restrained against lateral translation.
Pr
= required second-order axial strength
using LRFD load combinations.
G.1— Limitations
The use of this procedure is limited to structures that
support gravity loads primarily through nominally
vertical columns, walls or frames, except that it is
permissible to use the procedure specified for
determining P-effects for any individual
compression member.
G.2— Calculation Procedure
The required second-order flexural strength, Mr,
and axial strength, Pr, of all members shall be
determined as follows:
𝑀𝑟 = 𝐵1 𝑀𝑛𝑡 + 𝐵2 𝑀𝑙𝑡
𝑃𝑟 = 𝑃𝑛𝑡 + 𝐵2 𝑃𝑙𝑡
(G-1)
(G-2)
where
B1
B2
Mlt
= multiplier to account for P-effects,
determined for each member subject to
compression and flexure, and each
direction of bending of the member in
accordance with Section G.2.1. B1 shall
be taken as 1.0 for members not subject
to compression.
= multiplier to account for P-effects,
determined for each story of the
structure and each direction of lateral
translation of the story in accordance
with Section G.2.2.
= first-order moment using LRFD load
combinations, due to lateral translation
of the structure only.
User Note: Eqs. (G-1) and (G-2) are applicable
to all members in all structures. It should be
noted that B1 values other than unity apply
only to moments in beam-columns; B2 applies
to moments and axial forces in components of
the lateral force resisting system (including
columns, beams, bracing members and
shear walls).
G.2.1 Multiplier B1 for P-Effects. The B1
multiplier for each member subject to
compression and each direction of bending of the
member is calculated as follows:
𝐵1 =
𝐶𝑚
≥ 1
(1 − 𝑃𝑟 /𝑃𝑒1 )
(G-3)
where
Cm
coefficient assuming no lateral translation
of the frame determined as follows:
(a) For beam-columns not subject to transverse
loading between supports in the plane of
bending
𝐶𝑚 = 0.6 − 0.4(𝑀1 ⁄𝑀2 )
(G-4)
where M1 and M2, calculated from a first-order
analysis, are the smaller and larger moments,
respectively, at the ends of that portion of the
member unbraced in the plane of bending under
consideration. M1/M2 is positive when the member
SBC 306-CR-18
254
APPENDIX G —APPROXIMATE SECOND-ORDER ANALYSIS
is bent in reverse curvature, and negative when
bent in single curvature.
(b) For beam-columns subject to transverse
loading between supports, the value of Cm
shall be determined either by analysis or
conservatively taken as 1.0 for all cases.
Pe1 = elastic critical buckling strength of the
member in the plane of bending, calculated
based on the assumption of no lateral
translation at the member ends, N
𝑃𝑒1 =
𝜋 2 𝐸𝐼 ∗
(𝐾1 𝐿)2
(G-5)
Pe story = elastic critical buckling strength for the
story in the direction of translation being
considered, N , determined by sidesway
buckling analysis or as:
𝑅𝑀 = 1 − 0.15
Pmf
total vertical load in columns in the story
that are part of moment frames, if any, in
the direction of translation being
considered (= 0 for braced frame
systems), N
H
first-order interstory drift, in the
direction of translation being considered,
due to lateral forces, mm, computed
using the stiffness required to be used in
the analysis. Where H varies over the
plan area of the structure, it shall be the
average drift weighted in proportion to
vertical load or, alternatively, the
maximum drift.
H
story shear, in the direction of translation
being considered, produced by the lateral
forces used to compute H , N
modulus of elasticity of steel
200000 MPa
I
moment of inertia in the plane of
bending, mm4
L
=length of member, mm
K1
effective length factor in the plane of
bending, calculated based on the
assumption of no lateral translation at the
member ends, set equal to 1.0 unless
analysis justifies a smaller value
(G-8)
height of story, mm
EI for the effective length and first-order
analysis methods)
E
𝑃𝑚𝑓
𝑃𝑠𝑡𝑜𝑟𝑦
L
flexural rigidity required to be used in the
analysis
= 0.8𝜏𝑏 𝐸𝐼 when used in the direct
analysis method where b is as defined in
Chapter 3;
(G-7)
where
where
EI*
𝐻𝐿
𝛥𝐻
𝑃𝑒−𝑠𝑡𝑜𝑟𝑦 = 𝑅𝑀
User Note: H and H in Eq. (G-7) may be
based on any lateral loading that provides a
representative value of story lateral stiffness,
H/H.
It is permitted to use the first-order estimate of Pr
(i.e., 𝑃𝑟 = 𝑃𝑛𝑡 + 𝑃𝑙𝑡 ) in Eq. (G-3).
G.2.2 Multiplier B2 for P-Effects. The B2
multiplier for each story and each direction of lateral
translation is calculated as follows:
𝐵2 =
1
𝑃𝑠𝑡𝑜𝑟𝑦
1−
𝑃𝑒−𝑠𝑡𝑜𝑟𝑦
(G-6)
where
Pstory
= total vertical load supported by the story
using LRFD load combinations, including
loads in columns that are not part of the
lateral force resisting system, N
SBC 306-CR-18
255
APPENDIX G —APPROXIMATE SECOND-ORDER ANALYSIS
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SBC 306-CR-18
256
REFERENCES
REFERENCES
AASHTO (2002), Standard Specifications for
Highway Bridges, 17th Ed., American
Association of State Highway and
Transportation Officials, Washington, DC.
AASHTO (2010), LRFD Bridge Design
Specifications,
5th
Ed., American
Association of State Highway and
Transportation Officials, Washington, DC.
ACI (1997), Prediction of Creep, Shrinkage and
Temperature Effects in Concrete Structures,
ACI 209R-92, American Concrete
Institute, Farmington Hills, MI.
ACI (1999), “Details and Detailing of Concrete
Reinforcement,” ACI 315-99, contained
within ACI Detailing Manual, SP-66(04),
American
Concrete
Institute,
FarmingtonHills, MI.
ACI (2001), Code Requirements for Nuclear
Safety Related Concrete Structures, ACI
349- 01, American Concrete Institute,
Farmington Hills, MI.
ACI (2002), Building Code Requirements for
Structural Concrete, ACI 318-02 and ACI
318M-02, American Concrete Institute,
Farmington Hills, MI.
ACI (2002), “Recommendations for the
Design of Beam Column Joints in
Monolithic Concrete Structures,” ACI
352R-02, American Concrete Institute,
Farmington Hills, MI.
ACI (2004a), Manual of Structural and
Placing Drawings for Reinforced Concrete
Structures, ACI 315R-04, contained within
ACI Detailing Manual, SP-66(04),
AmericanConcrete Institute, Farmington
Hills, MI.
ACI (2004b) ACI Detailing Manual, ACI SP66(04),
American
Concrete
Institute,Farmington Hills, MI.
ACI (2005), Specification for Structural
Concrete, ACI 301-05, American Concrete
Institute, Farmington Hills, MI.
ACI (2006), Code Requirements for Nuclear
Safety-Related
Concrete
Structures
&Commentary, ACI 349-06, American
Concrete Institute, Farmington Hills, MI.
ACI (2006), Specifications for Tolerances for
Concrete Construction and Materials, ACI
117-06, American Concrete Institute,
Farmington Hills, MI.
ACI (2008), Building Code Requirements for
Structural Concrete, ACI 318-08 and ACI
318M-08, American Concrete Institute,
Farmington Hills, MI.
AISC (1969), Specification for the Design,
Fabrication, and Erection of Structural
Steel for Buildings, American Institute of
Steel Construction, Chicago, IL.
AISC (1973), “Commentary on Highly
Restrained
Welded
Connections,”
Engineering Journal, American Institute of
Steel Construction, Vol. 10, No. 3, 3rd
Quarter, pp. 61–73.
AISC (1975), Australian Standard AS1250,
Australian Institute of Steel Construction,
Sydney, Australia.
AISC (1978), Specification for the Design,
Fabrication, and Erection of Structural
Steel for Buildings, American Institute of
Steel Construction, Chicago, IL.
AISC (1986), Load and Resistance Factor
Design Specification for Structural Steel
Buildings, American Institute of Steel
Construction, Chicago, IL.
AISC (1989), Specification for Structural
Steel Buildings—Allowable Stress Design
and Plastic Design, American Institute of
Steel Construction, Chicago, IL.
AISC (1993), Load and Resistance Factor
Design Specification for Structural Steel
Buildings, American Institute of Steel
Construction, Chicago, IL.
SBC 306-CR-18
257
REFERENCES
AISC (1997a), A Guide to Engineering and
Quality Criteria for Steel Structures,
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