2022 Interim Revisions to the
LRFD Specifications for Structural
Supports for Highway Signs,
Luminaires, and Traffic Signals
First Edition 2015
Publication Code LRFDLTS-1-I5
ISBN 978-1-56051-777-1
American Association of State Highway and Transportation Officials
555 12th Street NW, Suite 1000
Washington, DC 20004
202-624-5800 phone/202-624-5806 fax
www.transportation.org
© 2022 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is
a violation of applicable law.
ISBN: 978-1-56051-777-1
Pub Code: LRFDLTS-1-I5
© 2022 by the American Association of State Highway and Transportation Officials.
All rights reserved. Duplication is a violation of applicable law.
INSTRUCTIONS AND INFORMATION
2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR STRUCTURAL SUPPORTS
FOR HIGHWAY SIGNS, LUMINAIRES AND TRAFFIC SIGNALS, FIRST EDITION
2022 INTERIM REVISIONS
INSTRUCTIONS AND INFORMATION
General
AASHTO has issued proposed interim revisions to the LRFD Specifications for Structural Supports for Highway
Signs, Luminaires and Traffic Signals, First Edition (2015). This packet contains the revised pages. They are designed to
replace the corresponding pages in the book.
Affected Articles
Underlined text indicates revisions that were approved in 2021 by the AASHTO Committee on Bridges and
Structures. Strikethrough text indicates any deletions that were likewise approved by the Committee. A list of affected
articles is included below.
All interim pages are displayed on a purple background to make the changes stand out when inserted in the first
edition binder, and to differentiate them from earlier interims. They also have a page header displaying the interim
publication year. Please note that these pages may also contain nontechnical (i.e., editorial) changes made by AASHTO
publications staff; any changes of this type will not be marked in any way so as not to distract the reader from the
technical changes.
2022 Changed Articles
SECTION 5: STEEL DESIGN
5.5.3.2
SECTION 6: ALUMINUM DESIGN
Section has been replaced in its entirety.
SECTION 14: FABRICATION, MATERIALS, AND DETAILING
14.5
14.9
SECTION 15: CONSTRUCTION
15.9
APPENDIX C: ALTERNATE METHODS FOR FATIGUE DESIGN
C.1
iii
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INSTRUCTIONS AND INFORMATION
2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR STRUCTURAL SUPPORTS
FOR HIGHWAY SIGNS, LUMINAIRES AND TRAFFIC SIGNALS, FIRST EDITION
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iv
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2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR STRUCTURAL
SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
SECTION 5: STEEL DESIGN
= connection eccentricity (in.) (5.9.3)
= plastic section modulus (5.8.7.1)
= plastic section modulus about the x axis (in.3) (5.8.2) (5.8.3.1.1) (5.8.3.1.3) (C5.8.3.1.3) (5.8.3.2.1) (5.8.4.3)
(C5.12.2)
Zy = plastic section modulus about the y axis (in.3) (5.8.5.1)
λ
= width–thickness ratio of the element (5.8.2) (5.8.3.1.2) (C5.8.3.2) (5.8.3.2.1) (5.8.3.2.2) (5.8.3.2.3) (5.8.4.2)
(5.8.4.3) (5.8.5.2) (5.10.2.1) (5.10.2.2) (5.10.2.3) (5.12.2)
λmax = maximum width–thickness ratio (C5.7.1) (5.7.2) (5.7.3) (C5.11.3.1.2) (5.12.2)
λp = width–thickness ratio at the compact limit (5.7.1) (C5.7.1) (5.7.2) (5.7.3) (5.8.2) (5.8.3.1.2) (5.8.3.2.1) (5.8.3.2.2)
(5.8.3.2.3) (5.8.4.2) (5.8.4.3) (5.8.5.2)
λr
= width–thickness ratio at the noncompact limit (5.7.1) (C5.7.1) (5.7.2) (5.7.3) (5.8.2) (5.8.3.1.2) (C5.8.3.2)
(5.8.3.2.1) (5.8.3.2.3) (5.8.5.2) (5.10.2.1) (5.10.2.2) (5.10.2.3) (5.12.2)
x
Z
Zx
θ
= angle of the sound beam for ultrasonic inspection of groove welds (degrees) (5.5.3.2) (5.6.5)
φc
= resistance factor for compression (5.5.3.2) (5.10.1) (5.12.1)
φf
= resistance factor for flexure (5.5.3.2) (5.8.1) (5.12.2)
φrt
= resistance factor for cables (5.13)
φT
= resistance factor for torsion (5.5.3.2)
φt
= resistance factor for bolt tension (5.11.1) (5.12.1)
φu
= resistance factor for tension fracture (5.5.3.2) (5.9.1)
φv
= resistance factor for shear (5.5.3.2) (5.11.1)
φy
= resistance factor for tension yield (5.5.3.2) (5.9.1)
5.4—MATERIAL
C5.4
Grades of steel listed in the AASHTO LRFD
Bridge Design Specifications (LRFD Design) are
Steel other than that listed may be used with
permission from the Owner.
applicable for welded structural supports for highway
signs, luminaires, and traffic signals.
Typical steel materials used in structural supports
for highway signs, luminaires, and traffic signals are:
For steels not generally addressed by LRFD
Design, but having a specified yield strength acceptable
to the Owner, the LRFD limit state design criteria shall
be derived by applying the general equations given in
LRFD Design except as indicated by this Section.
All steels greater than 0.5 in. in thickness, used for
structural supports for highway signs, luminaires, and
traffic signals, that are main load carrying tension
members shall meet the current Charpy V-Notch
impact requirements in LRFD Design.
•
ASTM A595 Grade A, B, and C
•
ASTM A572 Grade 42, 50, 55, 60, and 65
•
ASTM A1011
•
ASTM F1554 Grade 36, 55, and 105 Anchor Bolts
Generally, the Specification indicated in this Section
applies.
Although the structural supports addressed by these
Specifications are not subjected to high-impact loadings,
steel members greater than 0.5 in. in thickness should
meet a general notch toughness requirement to avoid
brittle fracture. The non-fracture critical values may be
used.
5-5
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2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR STRUCTURAL
SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
5-6
5.5—DESIGN LIMIT STATES
5.5.1—General
Structural components and connections shall be
proportioned to satisfy the requirements at strength,
extreme event, service, and fatigue limit states.
5.5.2—Service Limit State
General service requirements are provided in
Section 10.
5.5.3—Strength Limit State
5.5.3.1—General
C5.5.3.1
Strength and stability shall be considered using the
applicable strength load combinations specified in
Table 3.4-1.
5.5.3.2—Resistance Factors
Resistance factors, , for the strength limit states
shall be taken as follows:

Flexure f = 0.90

Shear v = 0.90

Torsion T = 0.95

Axial compression, c = 0.90

Tension, fracture in net section u = 0.75

Tension, yielding in gross section y = 0.90

Resistance factor for cables and associated
connections rt = 0.65
NCHRP project 10-80 developed specific LRFD
load and resistance factors using ASCE/SEI 07-2010
loading.
C5.5.3.2
NCHRP Project Report 796 determined resistance
factors specifically for signs, luminaires, and traffic
signal supports and these may differ from other
specifications. (Puckett et al., 2014)
5.5.4—Extreme Limit State
C5.5.4
All applicable load combinations in Table 3.4-1 for
the extreme event limit state shall be investigated.
The resistance factors for the extreme event shall
be as defined in the strength limit state in Article 5.5.3.
The ASCE 7-10 wind maps were generated using a
wind load factor of unity. These specifications use a
similar approach and therefore include wind in
combination with other loads to be addressed as an
extreme event.
5.5.5—Fatigue Limit State
Components and details shall be investigated for
fatigue as specified in Section 11.
5.6—GENERAL DIMENSIONS AND DETAILS
5.6.1—Minimum Thickness of Materials
C5.6.1
The minimum thickness of material for main
supporting members of steel truss-type supports shall
be 0.1793 in. For secondary members, such as bracing
and truss webs, the minimum thickness shall be
Main members are those that are strictly necessary
to ensure integrity of a structural system. Secondary
members are those that are provided for redundancy of
the system and stability of components and members.
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5-6.1
2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR STRUCTURAL
SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
0.125 in. The minimum thickness of material for all
members of pole-type supports and truss-type luminaire
Minimum thickness requirements may be based on
service considerations such as corrosion resistance as
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5-6.2
2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR STRUCTURAL SUPPORTS
FOR HIGHWAY SIGNS, LUMINAIRES AND TRAFFIC SIGNALS, FIRST EDITION
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SECTION 6: ALUMINUM DESIGN
TABLE OF CONTENTS
6.1—SCOPE ................................................................................................................................................................................6-1
6.2—DEFINITIONS ...................................................................................................................................................................6-1
6.3—NOTATION .......................................................................................................................................................................6-2
6.4—MATERIAL .......................................................................................................................................................................6-7
6.4.1—General .....................................................................................................................................................................6-7
6.4.2—Wrought Products ....................................................................................................................................................6-7
6.4.3—Cast Products ...........................................................................................................................................................6-9
6.4.4—Filler Metal for Welding .........................................................................................................................................6-9
6.4.5—Bolts, Washers, and Nuts ........................................................................................................................................6-9
6.5—DESIGN LIMIT STATES...............................................................................................................................................6-10
6.5.1—General ...................................................................................................................................................................6-10
6.5.2—Service Limit State ................................................................................................................................................6-10
6.5.3—Strength Limit State...............................................................................................................................................6-11
6.5.4—Extreme Limit State...............................................................................................................................................6-11
6.5.5—Fatigue Limit State ................................................................................................................................................6-11
6.6—MINIMUM THICKNESS ...............................................................................................................................................6-11
6.7—BUCKLING .....................................................................................................................................................................6-11
6.7.1—Buckling Constants................................................................................................................................................6-11
6.7.2—Element Dimensions .............................................................................................................................................6-13
6.7.3—Strength of Elements in Uniform Compression ..................................................................................................6-14
6.7.3.1—Flat Elements Supported on One Edge .....................................................................................................6-14
6.7.3.2—Flat Elements Supported on Both Edges ..................................................................................................6-15
6.7.3.3—Flat Elements Supported on One Edge and with a Stiffener on the Other Edge....................................6-15
6.7.3.4—Flat Elements Supported on Both Edges and with an Intermediate Stiffener ........................................6-16
6.7.3.5—Round Hollow Elements and Curved Elements Supported on Both Edges ...........................................6-18
6.7.3.6—Direct Strength Method..............................................................................................................................6-19
6.7.4—Strength of Elements in Flexural Compression ...................................................................................................6-19
6.7.4.1—Flat Elements Supported on Both Edges ..................................................................................................6-20
6.7.4.2—Flat Elements Supported on Tension Edge, Compression Edge Free ....................................................6-21
6.7.4.3—Flat Elements Supported on Both Edges and with a Longitudinal Stiffener ............................................6-21
6.7.4.4—Pipes and Round Tubes..............................................................................................................................6-22
6.7.4.5—Direct Strength Method..............................................................................................................................6-23
6.7.5—Elastic Buckling Stress of Elements.....................................................................................................................6-23
6.8—MEMBERS IN AXIAL TENSION ................................................................................................................................6-24
6.8.1—General ...................................................................................................................................................................6-24
6.8.2—Yielding ..................................................................................................................................................................6-24
6.8.3—Rupture ...................................................................................................................................................................6-25
6.8.4—Net Area .................................................................................................................................................................6-25
6.8.5—Effective Net Area .................................................................................................................................................6-25
6-i
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6-ii
2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR
STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
6.9—MEMBERS IN AXIAL COMPRESSION ....................................................................................................................6-26
6.9.1—General ...................................................................................................................................................................6-26
6.9.2—Member Buckling..................................................................................................................................................6-26
6.9.3—Local Buckling ......................................................................................................................................................6-28
6.9.4—Interaction between Member Buckling and Local Buckling..............................................................................6-28
6.10—MEMBERS IN FLEXURE ...........................................................................................................................................6-28
6.10.1—General .................................................................................................................................................................6-28
6.10.2—Yielding and Rupture ..........................................................................................................................................6-28
6.10.3—Local Buckling ....................................................................................................................................................6-29
6.10.3.1—Weighted Average Method......................................................................................................................6-29
6.10.3.2—Direct Strength Method............................................................................................................................6-30
6.10.3.3—Limiting Element Method........................................................................................................................6-30
6.10.4—Lateral-Torsional Buckling .................................................................................................................................6-30
6.10.4.1—Bending Coefficient Cb ............................................................................................................................6-31
6.10.4.2—Shapes Symmetric About the Bending Axis ..........................................................................................6-32
6.10.4.3—Singly Symmetric Open Shapes Unsymmetric About the Bending Axis ............................................6-33
6.10.4.4—Closed Shapes ...........................................................................................................................................6-33
6.10.4.5—Rectangular Bars ......................................................................................................................................6-33
6.10.4.6—Any Shape .................................................................................................................................................6-33
6.10.4.7—Interaction between Local Buckling and Lateral-Torsional Buckling..................................................6-34
6.11—MEMBERS IN SHEAR ................................................................................................................................................6-34
6.11.1—General .................................................................................................................................................................6-35
6.11.2—Members with Flat Webs Supported on Both Edges ........................................................................................6-35
6.11.3—Members with Flat Webs Supported on One Edge...........................................................................................6-37
6.11.4—Pipes and Round or Oval Tubes .........................................................................................................................6-37
6.11.5—Rods......................................................................................................................................................................6-38
6.12—MEMBERS IN TORSION............................................................................................................................................6-39
6.12.1—General .................................................................................................................................................................6-39
6.12.2—Pipes and Round or Oval Tubes .........................................................................................................................6-40
6.12.3—Rectangular Tubes ...............................................................................................................................................6-40
6.12.4—Rods......................................................................................................................................................................6-40
6.12.5—Open Shapes ........................................................................................................................................................6-41
6.13—COMBINED FORCES..................................................................................................................................................6-41
6.13.1—Flexure and Axial Force......................................................................................................................................6-41
6.13.2—Torsion, Flexure, Shear, and/or Axial Compression.........................................................................................6-42
6.14—WELDED CONNECTIONS ........................................................................................................................................6-42
6.14.1—General .................................................................................................................................................................6-42
6.14.2—Strength ................................................................................................................................................................6-42
6.14.3—Combination of Welds ........................................................................................................................................6-44
6.14.4—Post-Weld Heat Treatment .................................................................................................................................6-44
6.15—BOLTED CONNECTIONS..........................................................................................................................................6-44
6.15.1—Holes and Slots for Bolts ....................................................................................................................................6-44
6.15.2—Minimum Spacing of Bolts.................................................................................................................................6-44
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2022 INTERIM REVISIONS FOR THE LRFD SPECIFICATIONS FOR
STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
6-iii
6.15.3—Minimum Edge Distance of Bolts ......................................................................................................................6-45
6.15.4—Bolt Tension.........................................................................................................................................................6-45
6.15.5—Bolt Shear.............................................................................................................................................................6-45
6.15.6—Bolt Bearing .........................................................................................................................................................6-45
6.15.7—Slip-Critical Bolted Connections........................................................................................................................6-46
6.15.7.1—General ......................................................................................................................................................6-46
6.15.7.2—Material .....................................................................................................................................................6-46
6.15.7.3—Holes..........................................................................................................................................................6-46
6.15.7.4—Bolt Tension and Shear ............................................................................................................................6-46
6.15.7.5—Slip Resistance..........................................................................................................................................6-46
6.15.7.6—Washers .....................................................................................................................................................6-47
6.16—CONNECTED ELEMENTS ........................................................................................................................................6-47
6.16.1—Block Shear Rupture ...........................................................................................................................................6-47
6.16.2—Bearing Strength of Flat Surfaces ......................................................................................................................6-48
6.17—REFERENCES...............................................................................................................................................................6-48
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6-iv
2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR
STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
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SECTION 6:
ALUMINUM DESIGN
Editor’s Note: Since all of Section 6 was revised by the AASHTO Committee on Bridges and Structures at their
2021 Annual Meeting, the new text in this Section has not been underlined.
6.1—SCOPE
C6.1
This Section provides the design provisions for
structural supports for highway signs, luminaires, and
traffic signals described in Article 1.4 that are fabricated
using the aluminum products listed in Articles 6.4.2,
6.4.3, 6.4.4, and 6.4.5.
Design provisions in this Section use load and
resistance factor design (LRFD).
This Section is organized in a manner similar to
Section 5 (steel). The provisions are based on the
Specification for Aluminum Structures, which is Part I of
the 2020 Aluminum Design Manual published by the
Aluminum Association. The commentary to the
Specification for Aluminum Structures provides additional
explanation of these provisions.
6.2—DEFINITIONS
Available strength—The nominal strength multiplied by the resistance factor.
Beam—A structural member that has the primary function of resisting bending moments.
Column—A structural member that has the primary function of resisting a compressive axial force.
Element—A component of a shape’s cross section. Elements are connected to other elements only along their longitudinal edges.
Elements addressed by Section 6 include flat elements, described by their width b and thickness t, and curved elements,
described by their mid-thickness radius Rb and thickness t. An I-beam, for example, consists of five flat elements: a web element
and two elements in each flange.
Filler metal—Metal to be added in making a welded joint.
Fillet weld—Weld of generally triangular cross section made between intersecting surfaces of elements.
Flexural buckling—A buckling mode in which a compression member deflects laterally without twist or change in crosssectional shape.
Flexural-torsional buckling—A buckling mode in which a compression member bends and twists simultaneously without
change in cross-sectional shape.
Gauge—Transverse center-to-center spacing of fasteners.
Grip—Thickness of material through which a fastener passes.
Lateral-torsional buckling—The buckling mode of a flexural member involving deflection normal to the plane of bending that
occurs simultaneously with twist about the shear center of the cross-section.
Local buckling—The limit state of buckling of a compression element within a cross section.
Member—An individual, discrete component of a larger structure, such as a beam or column.Member buckling—Flexural,
torsional, or flexural–torsional buckling of the overall member.
6-1
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2022 INTERIM REVISIONS FOR THE LRFD SPECIFICATIONS FOR
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6-2
Net area—Gross area reduced to account for removed material.
Nominal strength—Strength of a structure or component (without the resistance factor applied) available to resist load effects, as
determined in accordance with this Section.
Pitch—Longitudinal center-to-center spacing of fasteners; center-to-center spacing of bolt threads along the axis of a bolt.
Post-buckling strength—The load or force that can be resisted by an element, member, or frame after initial elastic buckling has
occurred.
Required strength—Forces, stresses, and deformations acting on a structural component determined in accordance with Section
4.
Resistance factor—A factor, φ, that accounts for unavoidable deviations of the actual strength from the nominal strength and for
the manner and consequences of failure.
Slip-critical connection—A bolted connection designed to resist movement by friction on the faying surface of the connection
under the clamping forces of the bolts.
Stiffener—A structural element attached or integral to a member to distribute load, transfer shear, or prevent buckling. Stiffeners
may be longitudinal or transverse to the member’s longitudinal axis.
Torsional buckling—A buckling mode in which a compression member twists about its shear center axis.
Unbraced length—The length of a member between brace points or between a brace point and a cantilever’s free end, measured
between the longitudinal centroidal axes of the bracing members. For columns, brace points are points at which lateral translation
is restrained for flexural buckling or twisting is restrained for torsional buckling. For beams, brace points are points at which the
compression flange is restrained against lateral deflection or the cross section is restrained against twisting.
Weld-affected zone—Metal within 1 in. of the centerline of a groove weld or the root of a fillet weld that has not been post-weld
heat treated.
6.3—NOTATION
Ab
Ab
ABM
Ae
Aewz
Af
=
=
=
=
=
=
AFM
Ag
Agc
Agtw
Agto
Agv
Agvo
Agvw
Ai
An
Ant
Anv
As
=
=
=
=
=
=
=
=
=
=
=
=
=
nominal cross sectional area (unthreaded body area) of a bolt (in.2) (6.15.7.4)
bearing area (in.2) (6.16.2)
area of the base metal in the weld-affected zone (in.2) (6.4.2)
effective net area (in.2) (6.8.3) (6.8.5)
effective net area in the weld-affected zone (in.2) (6.8.3)
area of the member farther than 2c/3 from the neutral axis, where c is the distance from the neutral axis to the
extreme compression fiber (in.2) (6.10.4)
area of the filler metal (in.2) (6.4.2)
gross cross sectional area (in.2) (6.7.2) (6.8.2) (6.9.2) (6.9.4) (6.12.1)
gross cross sectional area in compression (in.2) (6.7.2)
gross weld-affected area in tension (in.2) (6.16.1)
gross area not weld-affected in tension (in.2) (6.16.1)
gross area in shear (in.2) (6.16.1)
gross area not weld-affected in shear (in.2) (6.16.1)
gross weld-affected area in shear (in.2) (6.16.1)
cross sectional area of element i (in.2) (6.9.3)
net area (in.2) (6.8.4) (6.8.5) (6.11.2) (6.11.3) (6.11.4)
net area in tension (in.2) (6.16.1)
net area in shear (in.2) (6.16.1)
area of an intermediate stiffener (in.2) (6.7.2)
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2022 INTERIM REVISIONS FOR THE LRFD SPECIFICATIONS FOR
STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
Av
Awe
Awz
Awzc
a1
a2
B
b
be
C
C
Cb
Cw
C1
C2
c
ccf
ccs
ccw
D
D
=
=
=
6-3
shear area (in.2) (6.11.2) (6.11.3) (6.11.4)
effective area of the weld (in.2) (6.14.2)
cross sectional area of the weld-affected zone (in.2) (6.4.2) (6.7.2) (6.8.2) (6.9.2) (6.10.4) (6.11.1) (6.11.2)
(6.11.3) (6.11.4) (6.12.1)
= cross sectional area of the weld-affected zone in compression (in.2) (6.4.2) (6.7.2)
= the lesser of the clear height of the web and the distance between shear stiffeners (in.) (6.11.2)
= the greater of the clear height of the web and the distance between shear stiffeners (in.) (6.11.2)
= inelastic buckling intercept, interpreted with the following subscripts (k/in.2) (6.7.1):
c – axial compression in members (6.7.1) (6.9.2)
p – uniform compression in flat elements (6.7.1) (6.10.3.2)
t – uniform compression in curved elements (6.7.1)
br – flexural compression in flat elements (6.7.1)
tb – flexural compression in curved elements (6.7.1)
s – shear in flat elements (6.7.1) (6.11.2) (6.12.2)
= element width (in.) (6.5.2) (6.7.2) (6.11.2) (6.11.3)
= element’s effective width (in.) (6.5.2)
= torsional shear constant (in.3) (6.12.3)
= inelastic buckling slope, interpreted with the following subscripts (k/in.2) (6.7.1):
c – axial compression in members (6.7.1) (6.9.2) (6.10.4)
p – uniform compression in flat elements (6.7.1) (6.10.3.2)
t – uniform compression in curved elements (6.7.1)
br – flexural compression in flat elements (6.7.1)
tb – flexural compression in curved elements (6.7.1)
s – shear in flat elements (6.7.1) (6.11.2) (6.12.2)
= bending coefficient accounting for moment variation along the length of a beam (6.10.4.1) (6.10.4.2)
(6.10.4.4) (6.10.4.5) (6.4.10.6) (6.4.10.7)
= warping constant (in.6) (6.9.2) (6.10.4.2) (6.10.4.6)
= lateral–torsional buckling factor for distance between transverse load application and shear center (6.10.4.6)
= lateral–torsional buckling factor for coefficient of monosymmetry (6.10.4.6)
= distance from a flexural compression element’s extreme compression fiber to the cross section’s neutral axis
(in.) (6.10.4)
= distance from the centerline of a uniform compression element to the cross section’s neutral axis (in.)
(6.10.3.1)
= distance from the extreme fiber of uniform compression element to the cross section’s neutral axis (in.)
(6.10.3.1)
= distance from a flexural compression element’s extreme compression fiber to the cross section’s neutral axis
(in.) (6.10.3.1)
= inelastic buckling intersection, interpreted with the following subscripts (6.7.1):
c – axial compression in members (6.7.1) (6.9.2)
p – uniform compression in flat elements (6.7.1) (6.10.3.2)
t – uniform compression in curved elements (6.7.1)
br – flexural compression in flat elements (6.7.1)
tb – flexural compression in curved elements (6.7.1)
s – shear in flat elements (6.7.1) (6.11.2) (6.12.2)
=
diameter of a rod (in.) (6.11.5) (6.12.4)
© 2022 by the American Association of State Highway and Transportation Officials.
All rights reserved. Duplication is a violation of applicable law.
2022 INTERIM REVISIONS FOR THE LRFD SPECIFICATIONS FOR
STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
6-4
D
D
Di
Do
d
de
df
=
=
=
=
=
=
=
E
=
Fb
Fbo
=
=
Fbw
=
Fc
Fci
Fco
=
=
=
Fcw
=
Fcy
Fcyw
Fe
Fex
Fey
Fez
Fn
=
=
=
=
=
=
=
FnBM
=
Fnw
Fs
=
=
Fso
=
Fsu
=
Fsuw
Fsw
=
=
Fsy
Fsyw
Ftu
Ftuw
Ftuwb
Ftuwf
Fty
=
=
=
=
=
=
=
diameter of a stud (in.) (6.14.2)
nominal diameter of a bolt (in.) (6.15.1) (6.15.4) (6.15.5) (6.15.6)
inside diameter of a pipe or tube (in.) (6.11.4)
outside diameter of a pipe or tube (in.) (6.11.4)
depth of a beam (in.) (6.10.4.2) (6.10.4.3) (6.10.4.5) (6.11.2)
distance from the center of the bolt to the edge of the part in the direction of force (in.) (6.15.6)
the distance between flange centroids; for tees, df is the distance between the flange centroid and the tip of
the stem (in.) (6.10.4.6)
modulus of elasticity (k/in.2) (6.4.1) (6.7.2) (6.9.2) (6.9.4) (6.10.3.2) (6.10.4) (6.10.4.6) (6.11.2) (6.11.3)
(6.11.4) (6.12.2)
stress corresponding to the flexural compressive strength (k/in.2) (6.7.2) (6.10.3.1) (6.13.2)
stress corresponding to the flexural compressive strength for an element if no part of the cross section were
weld-affected (k/in.2) (6.7.2)
stress corresponding to the flexural compressive strength for an element if the entire cross section were weldaffected (k/in.2) (6.7.2)
stress corresponding to the uniform compressive strength (k/in.2) (6.7.2) (6.9.2) (6.10.3.1) (6.13.2)
local buckling stress of element i (k/in.2) (6.9.3)
stress corresponding to the uniform compressive strength for an element if no part of the cross section were
weld-affected (k/in.2) (6.7.2)
stress corresponding to the uniform compressive strength for an element if the entire cross section were weldaffected (k/in.2) (6.7.2)
compressive yield strength (k/in.2) (6.4.1) (6.7.1) (6.7.2) (6.9.2) (6.10.2) (6.10.3.2)
compressive yield strength of the weld-affected zone (k/in.2) (6.4.1) (6.7.3) (6.7.4)
elastic buckling stress (k/in.2) (6.5.2) (6.7.2) (6.9.2) (6.9.4) (6.10.3.2) (6.10.4.6)
elastic buckling stress for buckling about the member’s x-axis (k/in.2) (6.9.2)
elastic buckling stress for buckling about the member’s y-axis (k/in.2) (6.9.2)
elastic buckling stress for buckling about the member’s z-axis (k/in.2) (6.9.2)
Fnt or Fnv determined in accordance with the Specification for Structural Steel Buildings (ANSI/AISC 360) for
a F3125 steel bolt (k/in.2) (6.15.7.4)
nominal stress of the base metal corresponding to its welded ultimate strength from Table 6.4.2-1 (k/in.2)
(6.14.2)
nominal stress of the weld metal corresponding to its ultimate strength from Table 6.4.4-1 (k/in.2) (6.14.2)
shear stress corresponding to the shear or torsional strength of an element (k/in.2) (6.11.1) (6.11.2) (6.11.3)
(6.11.4) (6.12.1) (6.12.2) (6.12.3) (6.13.2)
shear stress, Fs, corresponding to the shear or torsional strength for an element if no part of the cross section
were weld-affected (k/in.2) (6.11.2) (6.11.3) (6.11.4) (6.12.1)
shear ultimate strength (k/in.2) (6.4.1) (6.4.5) (6.11.2) (6.11.3) (6.11.4) (6.11.5) (6.12.1) (6.12.4) (6.15.5)
(6.16.1)
welded shear ultimate strength (k/in.2) (6.11.2) (6.11.3) (6.11.4) (6.11.5) (6.12.1) (6.12.4) (6.16.1)
shear stress, Fs, corresponding to the shear or torsional strength for an element if the entire cross section were
weld-affected (k/in.2) (6.11.2) (6.11.3) (6.11.4) (6.12.1)
shear yield strength (k/in.2) (6.4.1) (6.7.1) (6.11.2) (6.11.3) (6.11.4) (6.12.2) (6.12.4)
welded shear yield strength (k/in.2) (6.12.4)
tensile ultimate strength (k/in.2) (6.4.2) (6.4.3) (6.4.5) (6.8.3) (6.10.2) (6.15.4) (6.15.6) (6.16.1) (6.16.2)
tensile ultimate strength of the weld-affected zone (k/in.2) (6.4.2) (6.4.4) (6.8.3) (6.14.2) (6.16.1)
tensile ultimate strength of the weld-affected base metal given in Table 6.4.2-1 (k/in.2) (6.4.2)
tensile ultimate strength of the filler metal given in Table 6.4.4-1 (k/in.2) (6.4.2)
tensile yield strength (k/in.2) (6.4.1) (6.4.2) (6.4.3) (6.8.2) (6.10.2)
© 2022 by the American Association of State Highway and Transportation Officials.
All rights reserved. Duplication is a violation of applicable law.
2022 INTERIM REVISIONS FOR THE LRFD SPECIFICATIONS FOR
STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
Ftyw
Ftywb
Ftywf
fa
fb
fc
fs
G
Gf
g
g0
H
If
Io
=
=
=
=
=
=
=
=
=
=
=
=
=
=
Is
Iw
Ix
Iy
Iyc
Iyf
=
=
=
=
=
=
Iyt
J
kt
=
=
=
kx
ky
kz
k1
k2
L
Lb
LC
=
=
=
=
=
=
=
=
Ls
Lv
Lwe
Lx
Ly
Lz
MA
MB
MC
Mc
=
=
=
=
=
=
=
=
=
=
6-5
tensile yield strength of the weld-affected zone (k/in.2) (6.4.2) (6.4.4) (6.8.2)
tensile yield strength of the weld-affected base metal given in Table 6.4.2-1 (k/in.2) (6.4.2)
tensile yield strength of the filler metal given in Table 6.4.4-1 (k/in.2) (6.4.2)
maximum compressive stress in an element from service load combinations (k/in.2) (6.5.2)
compressive stress due to flexure (k/in.2) (6.13.2)
compressive stress due to axial compression (k/in.2) (6.13.2)
shear stress due to shear and torsion (k/in.2) (6.13.2)
shear modulus (k/in.2) (6.4.1) (6.9.2)
grip of a bolt (in.) (6.15.5)
transverse center-to-center spacing (gauge) between fastener gauge lines (in.) (6.8.4)
distance from the shear center to the point of application of the transverse load on a beam (in.) (6.10.4.6)
member buckling parameter (6.9.2)
moment of inertia of the uniform stress elements about the cross section’s neutral axis (in.4) (6.10.3.1)
moment of inertia of a section comprising the stiffener and one half of the width of the adjacent sub-elements
and the transition corners between them, taken about the centroidal axis of the section parallel to the stiffened
element (in.4) (6.7.2)
moment of inertia of the transverse stiffener (in.4) (6.11.2)
moment of inertia of the flexural compression elements about the cross section’s neutral axis (in.4) (6.10.3.1)
moment of inertia about the x-axis (in.4) (6.9.2) (6.10.4.6)
moment of inertia about the y-axis (in.4) (6.9.2) (6.10.4.1) (6.10.4.2) (6.10.4.3) (6.10.4.4) (6.10.4.6)
moment of inertia of the compression flange about the minor axis (in.4) (6.10.4.1) (6.10.4.3) (6.10.4.6)
moment of inertia of the flange on the negative side of the midheight (where the direction of the load is the
positive direction) about the minor axis of the shape (in.4) (6.10.4.1)
moment of inertia of the tension flange about the minor axis (in.4) (6.10.4.3)
torsion constant (in.6) (6.9.2) (6.10.4.2) (6.10.4.3) (6.10.4.4) (6.10.4.6) (6.12.2)
tension coefficient (6.4.2) (6.4.3) (6.8.3) (6.10.2) (6.11.2) (6.11.3) (6.11.4) (6.11.5) (6.12.1) (6.12.4) (6.14.4)
(6.16.1)
effective length factor for buckling about the member’s x-axis (6.9.2)
effective length factor for buckling about the member’s y-axis (6.9.2)
effective length factor for buckling about the member’s z-axis (6.9.2)
postbuckling constant (6.7.1) (6.7.2)
postbuckling constant (6.7.1) (6.7.2) (6.10.3.2)
member length (in.) (6.9.2) (6.10.4)
unbraced length (in.) (6.10.4.2) (6.10.4.4) (6.10.4.5) (6.10.4.6)
length of the connection in the direction of load, measured from the center of fasteners or the end of welds
(in.) (6.8.5)
length between transverse stiffeners, or overall length if no transverse stiffeners are present (in.) (6.12.2)
length of pipe or tube from maximum to zero shear force (in.) (6.11.4)
effective length of a weld (in.) (6.14.2)
length for buckling about the member’s x-axis (in.) (6.9.2)
length for buckling about the member’s y-axis (in.) (6.9.2)
length for buckling about the member’s z-axis (in.) (6.9.2)
absolute value of the moment at the quarter point of the unbraced segment (in.-k) (6.10.4.1)
absolute value of the moment at the midpoint of the unbraced segment (in.-k) (6.10.4.1)
absolute value of the moment at the three-quarter point of the unbraced segment (in.-k) (6.10.4.1)
available flexural strength (in.-k) (6.13.1)
© 2022 by the American Association of State Highway and Transportation Officials.
All rights reserved. Duplication is a violation of applicable law.
2022 INTERIM REVISIONS FOR THE LRFD SPECIFICATIONS FOR
STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
6-6
Me
=
Mmax
Mnlb
Mnmb
Mnmbo
=
=
=
=
Mnmbw =
Mnp
Mnu
Mr
n
Pc
Pnc
Pno
Pnt
Pnw
Pr
Rb
Rm
=
=
=
=
=
=
=
=
=
=
=
=
Rn
ro
rx
ry
rye
Sc
St
Swe
Sx
Sxc
=
=
=
=
=
=
=
=
=
=
s
s
Tn
t
U
V
Vn
xo
yo
x
=
=
=
=
=
=
=
=
=
=
=
=
=
=
y
Z
α
βx
elastic lateral-torsional buckling moment for a laterally unbraced span subjected to uniform bending (in.-k)
(6.10.4.6)
absolute value of the maximum moment in the unbraced segment (in.-k) (6.10.4.1)
nominal flexural strength for the limit state of local buckling (in.-k) (6.10.3) (6.10.3.1) (6.10.3.2) (6.10.3.3)
nominal flexural strength for the limit state of lateral-torsional buckling (in.-k) (6.10.4)
nominal flexural strength for the limit state of lateral-torsional buckling for members without welds (in.-k)
(6.10.4)
nominal flexural strength for the limit state of lateral-torsional buckling for members that are fully weldaffected (in.-k) (6.10.4)
nominal flexural strength for the limit state of yielding (in.-k) (6.10.2) (6.10.3.2) (6.10.4)
nominal flexural strength for the limit state of rupture (in.-k) (6.10.2)
required flexural strength determined in accordance with Section 4 (in.-k) (6.13.1)
number of threads per in. (/in.) (6.14.2) (6.15.4) (6.15.5)
available axial strength (k) (6.13.1)
nominal strength in axial compression (k) (6.9.2) (6.9.3) (6.9.4)
nominal strength in axial compression if no part of the member is weld-affected (k) (6.9.2)
nominal strength in axial tension (k) (6.8.2) (6.8.3)
nominal strength in axial compression if the member is entirely weld-affected (k) (6.9.2)
required axial strength determined in accordance with Section 4 (k) (6.13.1)
midthickness radius of a curved element (in.) (6.7.2) (6.11.4) (6.12.2)
1.0 except for unbraced lengths of singly-symmetric members subjected to double-curvature bending from
transverse loading (6.10.4.1)
nominal strength (k) (6.14.2) (6.15.4) (6.15.5) (6.15.6) (6.15.7.4) (6.16.1) (6.16.2)
polar radius of gyration about the shear center (in.) (6.9.2)
radii of gyration about the x-axis (in.) (6.9.2)
radii of gyration about the y-axis (in.) (6.9.2)
effective radius of gyration about the minor axis of a beam (in.) (6.10.4.2) (6.10.4.6)
section modulus on the compression side of the neutral axis (in.3) (6.10.2)
section modulus on the tension side of the neutral axis (in.3) (6.10.2)
effective throat of a fillet weld (in.) (6.12.4)
section modulus about the x-axis (in.3) (6.10.4.2) (6.10.4.3)
section modulus on the compression side of the member’s major axis (in.3) (6.10.3.2) (6.10.4) (6.10.4.4)
(6.10.4.6)
longitudinal center-to-center spacing (pitch) of any two consecutive holes (in.) (6.8.4)
transverse stiffener spacing (in.) (6.11.2)
nominal torsional strength (in.-k) (6.12.2) (6.12.3) (6.12.4) (6.12.5)
element thickness (in.) (6.7.2) (6.10.4.5) (6.11.2) (6.11.3) (6.11.4) (6.12.2)
lateral-torsional buckling distance (in.) (6.10.4.6)
shear force on the web at the transverse stiffener (k) (6.11.2)
nominal shear strength (k) (6.11.1) (6.11.2) (6.11.3) (6.11.4) (6.11.5)
x-coordinate of the shear center with respect to the centroid (in.) (6.9.2)
y-coordinate of the shear center with respect to the centroid (in.) (6.9.2) (6.10.4.6)
eccentricity of the connection in the x-axis direction (in.) (6.8.5)
eccentricity of the connection in the y-axis direction (in.) (6.8.5)
plastic modulus (in.3) (6.10.2)
coefficient of thermal expansion (/oF) (6.4.1)
coefficient of monosymmetry of the cross section (in.) (6.10.4.6)
© 2022 by the American Association of State Highway and Transportation Officials.
All rights reserved. Duplication is a violation of applicable law.
2022 INTERIM REVISIONS FOR THE LRFD SPECIFICATIONS FOR
STRUCTURAL SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
γ = density (lb/in.3) (6.4.1)
 = resistance factor (6.5.3) (6.5.4) (6.5.5)
λ = slenderness (6.7.2) (6.9.2) (6.9.4) (6.10.3.2) (6.10.4) (6.10.4.2) (6.10.4.4) (6.10.4.5) (6.10.4.6) (6.11.4) (6.12.2)
ν = Poisson’s ratio (6.4.1)
6.4—MATERIAL
C6.4
6.4.1—General
C6.4.1
The properties listed in Table 6.4.1-1 shall be used
to determine available and required strengths of
aluminum products.
The properties listed in Table 6.4.1-1 are average
values for aluminum alloys.
Although H-temper material is not included in this
Specification, properties for H-temper material are
included in Article 6.4.1 so that H-temper material
could be easily added in the future.
Table 6.4.1-1—Properties of Aluminum Alloys
Property
Symbol
ν
Value
Modulus of elasticity
E
10,100 ksi
Shear modulus of elasticity
G
3,800 ksi
Coefficient of thermal expansion
α
13  10-6/oF
Density
γ
0.10 lb/in3
Shear yield strength
Fsy
0.6 Fty
Shear ultimate strength
Fsu
0.6 Ftu
unwelded H-temper material
Fcy
0.9 Fty
all other material
Fcy
Fty
Fcyw
Ftyw
Poisson’s ratio
0.33
Compressive yield strength
Compressive yield strength of a weld-affected zone
6.4.2—Wrought Products
C6.4.2
This Specification applies to the wrought products
listed in Table 6.4.2-1. The nominal strengths used to
determine the available strength of wrought products shall
be as listed in Table 6.4.2-1.
The wrought alloys, tempers, and products listed
in Table 6.4.2-1 are those commonly used for
structural supports for highway signs, luminaires,
and traffic signals. The tensile yield and tensile
ultimate strengths are the minimum strengths
specified in the associated ASTM product
specification. The welded strengths match those in
the Specification for Aluminum Structures.
© 2022 by the American Association of State Highway and Transportation Officials.
All rights reserved. Duplication is a violation of applicable law.
6-7
2022 INTERIM REVISIONS FOR THE LRFD SPECIFICATIONS FOR
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6-8
Table 6.4.2-1. Nominal Strengths of Wrought Aluminum Products
Alloy
Temper
5052
6005
6005A
6005A
6061
6061
6061
6061
6061
6061
6061
6061
H32
T5
T5
T61
T6, T651
T6, T6510, T6511
T6, T651
T6
T6
T6
T6
T6
6063
6063
6063
6063
6063
6063
6063
6082
T5
T5
T52
T6
T6
T6
T832
T6, T6511
ASTM Specification,
Product
B209, sheet & plate
B221, extrusion
B221, extrusion
B221, extrusion
B209, sheet & plate
B221, extrusion
B211, bar, rod, & wire
B210, drawn tube
B241, pipe & tube
B429, pipe & tube
B247, forging
B308, standard structural
profile
B221, extrusion
B221, extrusion
B221, extrusion
B221, extrusion
B241, pipe & tube
B429, pipe & tube
B210, drawn tube
B221, extrusion
Thickness (in.)
0.017
–
–
–
0.010
All
0.125
0.025
All
All
–
0.062
–
0.501
–
–
–
–
0.050
0.200
2.000
1.000
0.999
1.000
4.000
8.000
0.500
4.000
0.500
1.000
1.000
1.000
1.000
1.000
0.259
6.000
Ftu
ksi
31
38
38
38
42
38
42
42
38
38
38
38
Fty
ksi
23
35
31
35
35
35
35
35
35
35
35
35
Ftuwb
ksi
25
24
24
24
24
24
24
24
24
24
24
24
Ftywb
ksi
9.5
15
15
15
15
15
15
15
15
15
15
15
1
1.25
1
1
1
1
1
1
1
1
1
1
22
21
22
30
30
30
40
45
16
15
16
25
25
25
35
38
17
17
17
17
17
17
17
28
8
8
8
8
8
8
8
16
1
1
1
1
1
1
1
1
The tensile ultimate strength, Ftuw, and tensile yield
strength, Ftyw, of the weld-affected zone used to determine
available strength is the weighted average of the strengths
of the weld-affected wrought material and the filler metal
as determined by Equations 6.4.2-1 and 6.4.2-2,
respectively.
= (Ftuwb ABM + Ftuwf AFM)/Awz
(6.4.2-1)
Ftuw
Ftyw
=
(Ftywb ABM + Ftywf AFM)/Awz
(6.4.2-2)
where:
Ftuwb = tensile ultimate strength of the weld-affected base
metal given in Table 6.4.2-1
Ftuwf
= tensile ultimate strength of the filler metal given in
Table 6.4.4-1
Ftywb = tensile yield strength of the weld-affected base metal
given in Table 6.4.2-1
Ftywf
= tensile yield strength of the filler metal given in Table
6.4.4-1
ABM
= area of the base metal in the weld-affected zone
AFM
= area of the filler metal
Awz
= area of the weld-affected zone, which extends 1 in.
from the centerline of a groove weld or the root of a
fillet weld
Awz
= ABM + AFM
(6.4.2-3)
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All rights reserved. Duplication is a violation of applicable law.
kt
2022 INTERIM REVISIONS FOR THE LRFD SPECIFICATIONS FOR
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6-9
6.4.3—Cast Products
C6.4.3
This Specification applies to cast products listed in
Table 6.4.3-1 that meet the following requirements:
a) Sand castings meet the requirements of ASTM
B26/B26M Aluminum-Alloy Sand Castings and permanent
mold castings meet the requirements of ASTM
B108/B108M Aluminum-Alloy Permanent Mold Castings
b) The casting’s dimensional tolerances meet the
requirements of Standards for Aluminum Sand and
Permanent Mold Castings.
c) The casting producer reports tensile yield strengths
of the castings.
The tensile ultimate strength, Ftu, tensile yield strength,
Fty, and tension coefficient, kt, of non-weld-affected
material used to determine available strength shall be as
listed in Table 6.4.3-1. Welded strengths of castings shall
be established by conducting AWS D1.2 groove weld
procedure qualification tests.
The cast alloys, tempers, and products listed in
Table 6.4.3-1 are those commonly used for structural
supports for highway signs, luminaires, and traffic
signals, typically at their bases. The tensile yield and
tensile ultimate strengths are the minimum strengths
specified in the associated ASTM product specification
for coupons cut from castings. Welded strengths of
castings are not stipulated in product specifications and
therefore this Section requires that they be established
by conducting an AWS D1.2 groove weld procedure
qualification test.
Table 6.4.3-1—Nominal Strengths of Cast Aluminum Products
Alloy
356.0
A356.0
356.0
A356.0
A356.0
Temper
T6
T6
T6
T61
T61
ASTM Specification, Product
B26
sand
B26
sand
B108
permanent mold
B108
permanent mold
B108
permanent mold
Ftu
ksi
22.5
25.5
24.7
28
33
Fty
ksi
15
18
16.5
26
26
Note
(1)
(1)
(1)
(1)
(2)
kt
1.0
1.0
1.0
1.0
1.0
Notes:
(1) These strengths apply at any location in the casting if the purchaser specifies that the strength of test specimens cut from any location in the casting
equal or exceed these strengths.
(2) These strengths apply in the locations specified by the purchaser if the purchaser specifies that strengths equal or exceed these strengths at these
locations. At other locations, the strengths in (1) apply.
6.4.4—Filler Metal for Welding
C6.4.4
This Specification applies to filler alloys that comply with
AWS A5.10/A5.10M and are listed in Table 6.4.4-1. Filler
metal nominal strengths used to determine available strength
shall be as listed in Table 6.4.4-1.
The filler metal alloys listed in Table 6.4.4-1 are
those commonly used for structural supports for
highway signs, luminaires, and traffic signals. The
strengths given in Table 6.4.4-1 match those given in
the Specification for Aluminum Structures. Filler
metal tensile ultimate strengths are used to determine
the strength of welded connections; filler metal
tensile ultimate and tensile yield strengths are used to
determine the strength of welded members.
Table 6.4.4-1—Nominal Strengths of Aluminum Filler
Metals
Filler
4043
5183
5356
5556
Tensile Ultimate
Strength Ftuwf (ksi)
24
40
35
42
Tensile Yield
Strength Ftywf (ksi)
11
18
14
19
6.4.5—Bolts, Washers, and Nuts
C6.4.5
This Specification applies to aluminum fasteners that
comply with ASTM F468, Nonferrous Bolts, Hex Cap Screws,
The strengths given in Table 6.4.5-1 match those
given in the Specification for Aluminum Structures.
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Socket Head Cap Screws, and Studs for General Use, and
aluminum nuts produced to ASTM F467, Nonferrous Nuts for
General Use.
Nuts for 1/4 in. bolts and smaller shall be 2024-T4; larger
nuts shall be 6061-T6 or 6262-T9.
Flat washers shall be Alclad 2024-T4. Spring lock
washers shall be 7075-T6.
Nominal strengths used to determine available strength
of aluminum bolts shall be as listed in Table 6.4.5-1.
Bolts, washers, and nuts of galvanized steel and
stainless steel are also used with aluminum structures.
Requirements for steel fasteners are given in Section
5.
Table 6.4.5-1—Nominal Strengths of Aluminum Bolts
Alloy and
Temper
Shear Ultimate
Strength
Fsu (ksi)
Tensile Ultimate
Strength
Ftu (ksi)
2024-T4
37
62
6061-T6
25
42
7075-T73
41
68
6.5—DESIGN LIMIT STATES
C6.5
6.5.1—General
C6.5.1
Structural components and connections shall be
proportioned to satisfy the requirements for service,
strength, extreme event, and fatigue limit states given in
Table 3.4-1. The available strength shall be the product of
the resistance factor and the nominal strength, and shall
equal or exceed the required strength.
The limit states given in Table 3.4-1 apply to
aluminum as to other materials.
6.5.2—Service Limit State
C6.5.2
Serviceability requirements are given in Section 10.
For elements with compressive stress, fa, greater than
their elastic buckling stress, Fe, effective widths shall be used
to determine the shape’s moment of inertia used to calculate
deflections.
The effective width, be, of such elements is:
For members that utilize post-buckling strength,
effective widths are used to determine the moment of
inertia used to calculate deflections.
If fa < Fe, be = b
(6.5.2-1)
If fa > Fe, be b Fe / fa
(6.5.2-2)
where:
be = element’s effective width
b = element’s width
Fe = element’s elastic local buckling stress from
Article 6.7.5
fa = maximum compressive stress in the element from
service load combinations
The effective width of elements subjected to flexure
shall be placed next to the compression flange.
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6.5.3—Strength Limit State
C6.5.3
Resistance factors, , for strength limit states shall be as
given in Table 6.5.3-1.
Resistance factors, , for strength limit states are
those historically used for aluminum structural
supports for highway signs, luminaires, and traffic
signals and are similar to those used for steel.
Table 6.5.3-1—Resistance Factors
Strength limit state

Axial tension—rupture of the net section
Axial tension—yield of the gross section
Axial compression
Flexure—rupture of the extreme tensile fiber
Flexure—all other strength limit states
Shear and torsion, buckling, or yielding
Shear and torsion, rupture
Welded connections
Bolts—shear or tensile rupture
Bolted connections—bearing
Slip-critical bolted connections—bolt tension
Slip-critical bolted connections—bolt shear
Block shear rupture
Bearing on flat surfaces
0.75
0.90
0.90
0.75
0.90
0.90
0.75
0.75
0.65
0.75
0.75
0.75
0.75
0.75
6.5.4—Extreme Limit State
C6.5.4
Resistance factors, , for extreme limit states shall be as
given in Table 6.5.3-1.
Resistance factors, , for extreme limit states
match those for strength limit states as for steel.
6.5.5—Fatigue Limit State
C6.5.5
Resistance factors, , for fatigue limit states shall be 1.0.
Fatigue requirements are given in Section 11.
Aluminum fatigue design rules are similar to
those for steel.
6.6—MINIMUM THICKNESS
C6.6
The minimum nominal thickness of main supporting
members of aluminum trusses shall be 0.150 in. The minimum
nominal thickness of secondary members shall be 0.125 in. The
minimum nominal thickness of pole-type supports and trusstype luminaire arms shall be 0.125 in.
Aluminum is resistant to corrosion from ambient
exposure without protective coatings. The minimum
thicknesses of aluminum parts are chosen to
minimize damage due to handling or unanticipated
loads rather than corrosion considerations.
6.7—BUCKLING
C6.7
6.7.1—Buckling Constants
C6.7.1
Buckling constants B, D, and C shall be determined from
Tables 6.7.1-1 and 6.7.1-2. Postbuckling constants k1 and k2
shall be determined from Table 6.7.1-3.
Buckling constants are based on the Specification
for Aluminum Structures Tables B.4.1, B.4.2, and
B.4.3. The buckling constants given in Table 6.7.1-1
are not needed for the wrought products given in
Table 6.4.2-1 but are provided for completeness.
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Table 6.7.1-1—Buckling Constants for Temper Designations Beginning with O, H, T1, T2, T3, or T4, and
Weld-Affected Zones of All Tempers
Type of Stress and
Member
Intercept
Member Buckling
  Fcy 

Bc  Fcy 1  
  1000 





Dc 
Bc  6 Bc 


20  E 
Uniform Compression
in Flat Elements
  Fcy 1 / 3 
 
B p  Fcy 1  
 

440

 
 
Dp 
B p  6B p 


20  E 
Uniform Compression
in Curved Elements
  Fcy 1 / 5 
 
Bt  Fcy  1  

6500   



B B 
Dt  t  t 
3.7  E 
Flexural Compression
in Flat Elements
  Fcy 

Bbr  1.3Fcy 1  

340  


Flexural Compression
in Curved Elements
  Fcy 1 / 5 
 
Btb  1.5 Fcy 1  
 


6500
 
 
Dtb 
Btb  Btb 


2.7  E 
Shear in Flat Elements
  Fsy 1 / 3 
 
B s  Fsy 1  
 


240
 
 
Ds 
Bs  6 Bs 


20  E 
Slope
1/ 2
1/ 3
Intersection
1/ 2
1/ 2
1/ 3




B  6B 
Dbr  br  br 
20  E 
Cc 
Cp 
2 Bc
3Dc
2Bp
3Dp
1/ 2
 
C t = 0.76 E 
 Fcy 
1/ 2
1/ 3
1/ 2
Cbr 
C tb 
2Bbr
3Dbr
B tb  Bt
D tb  D t
Cs 
2 Bs
3Ds
κ = 1.0 ksi
Table 6.7.1-2—Buckling Constants for Temper Designations Beginning with T5, T6, T7, T8, or T9
Type of Stress and
Member
Member Buckling
Intercept
  Fcy 

Bc  Fcy 1  

2250  


Slope
1/ 2




Intersection
1/ 2
B B 
Dc  c  c 
10  E 
C c  0.41
Uniform Compression
in Flat Elements
  Fcy 1 / 3 
 
B p  Fcy 1  
 


1500
 
 
Dp 
Uniform Compression
in Curved Elements
  Fcy 1 / 5 
 
Bt  Fcy 1  
 


50
,
000
 
 
B B 
Dt  t  t 
4.5  E 
Flexural Compression
in Flat Elements
  Fcy 

Bbr  1.3Fcy 1  

340  


Flexural Compression
in Curved Elements
1/
1/ 3
  F

cy

 Dtb  Btb  Btb 
Btb  1.5 Fcy 1  

50 ,000  
2.7  E 
 
Shear in Flat Elements
1/ 3
  Fsy 1 / 3 
 
B s  Fsy 1  
 


800
 
 
Bp  Bp 


10  E 
1/ 2
C p  0.41
1/ 3




B  6B 
Dbr  br  br 
20  E 
1/ 2
Ds 
Bs  Bs 
 
10  E 
Bc
Dc
Bp
Dp
1/ 2
 
C t = 0.70 E 
 Fcy 
1/ 2
Cbr 
C tb 
2Bbr
3Dbr
B tb  Bt
D tb  D t
C s  0.41
κ = 1.0 ksi
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Table 6.7.1-3—Postbuckling Constants
Type of Element
k1
k2
Flat Elements in Uniform Compression for Temper
Designations Beginning with O, H, T1, T2, T3, or T4,
and weld-affected zones of all tempers
0.50
2.04
Flat Elements in Uniform Compression for Temper
Designations Beginning with T5, T6, T7, T8, or T9
0.35
2.27
Flat Elements in Flexure
0.50
2.04
6.7.2—Element Dimensions
6.7.2
For flat elements:
a) supported on one edge, the element width, b, is
the distance from the element’s unsupported edge to the
toe of the fillet or bend at the element’s supported edge.
b) supported on both edges and flat elements
supported on one edge and with a stiffener on the other
edge, the element width, b, is the distance between the
toes of the fillets or bends at the element’s supported or
stiffened edges.
c) supported on both edges and with an intermediate
stiffener, the element width, b, is the largest distance
between the toe of the fillet or bend at the element’s
supported edge and the toe of the fillet or bend at the
intermediate stiffener.
For flat elements, if the inside corner radius exceeds
4 times the element thickness, the inside radius shall be
assumed equal to 4 times the thickness in calculating b.
For uniform compression on elements with linearly
varying thickness with  < 2.0:
a) For tapered thickness elements with the thick
edge supported and the thin edge free, the slenderness is
(1 – 0.12δ)b/tavg.
b) For tapered thickness elements with the thin edge
supported and the thick edge free, the slenderness is
b/tavg
c) For tapered thickness elements supported on both
edges, the slenderness is b/tavg.
Element dimensions used to determine buckling
strengths match those given in Sections B.5.1 through
B.5.3 of the Specification for Aluminum Structures.
where:
b
= element width
t max  t min
2
tavg =
(6.7.2-1)
= average thickness of the element
tmin = minimum thickness of the tapered thickness
element
tmax = maximum thickness of the tapered thickness
element

=
t max  t min
t min
(6.7.2-2)
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The radius of curved elements, Rb, shall be taken at
the mid-thickness of the element.
6.7.3—Strength of Elements in Uniform Compression
C6.7.3
The stress, Fc, corresponding to the uniform
compressive strength of elements is:
For unwelded elements:
(6.7.3-1)
Fc = Fco
The compressive strengths of elements given in this
Article address local buckling, and match those given in
Section B.5.4 of the Specification for Aluminum
Structures.
For welded elements:
Fc = Fco(1 – Awz /Ag) + Fcw Awz /Ag
(6.7.3-2)
where:
Fco = stress corresponding to the uniform compressive
strength calculated using Articles 6.7.3.1 through
6.7.3.5 for an element if no part of the cross
section were weld-affected. Use buckling
constants for unwelded metal and Fcy.
Fcw = stress corresponding to the uniform compressive
strength calculated using Articles 6.7.3.1 through
6.7.3.5 for an element if the entire cross section
were weld-affected. Use buckling constants for
weld-affected zones and Fcyw. For transversely
welded elements with slenderness < λ1, Fcw = Fs
Awz
Ag
= cross sectional area of the weld-affected zone
= gross cross sectional area of the element
6.7.3.1—Flat Elements Supported on One Edge
The stress, Fc, corresponding to the uniform
compressive strength of flat elements supported on one edge
is:
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Table 6.7.3.1-1—Uniform Compressive Stress for Flat Elements Supported on One Edge
Limit
State
Fc
Slenderness
b/t
Fcy
b/t < λ1
Bp – 5.0Dp b/t
λ1 < b/t < λ2
Yielding
Inelastic Buckling
Slenderness
Limits
λ1 =
B p − Fcy
5.0 D p
in columns whose buckling axis is not an axis of symmetry:
2
π E
Elastic Buckling
( 5.0b / t )
2
b/t > λ2
λ2 =
b/t > λ2
λ2 =
Cp
5.0
in all other columns and all beams:
k2 B p E
Post-Buckling
5.0b
t
k1 B p
5.0 D p
6.7.3.2—Flat Elements Supported on Both Edges
The stress, Fc, corresponding to the uniform
compressive strength of flat elements supported on both
edges is:
Table 6.7.3.2-1—Uniform Compressive Stress for Flat
Elements Supported on Both Edges
Limit
State
Fc
Slenderness
b/t
Yielding
Fcy
b/t < λ1
Inelastic
Buckling
Bp –1.6Dp b/t
λ1 < b/t < λ2
PostBuckling
k2 B p E
1.6b
t
b/t > λ2
Slenderness
Limits
λ1 =
λ2 =
B p − Fcy
1.6 D p
k1 B p
1.6 D p
6.7.3.3—Flat Elements Supported on One Edge
and with a Stiffener on the Other Edge
For flat elements
a) supported on one edge and with a stiffener on the
other edge,
b) with a stiffener of depth less than or equal to 0.8b, and
c) with a thickness no greater than the stiffener’s
thickness, the stress, Fc, corresponding to the uniform
compressive strength is
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c) with a thickness no greater than the stiffener’s
thickness, the stress, Fc, corresponding to the uniform
compressive strength is
Fc = FUT + (FST –FUT)ρST
(6.7.3.3-1)
where:
FUT is determined using Article 6.7.3.1 and neglecting
the stiffener
FST is determined using Article 6.7.3.2
=
ρST
a) ρST =
stiffener effectiveness ratio determined as
follows:
1.0
for b/t < λe/3
b) ρST =
for λe /3 < b/t < λe
c) ρST =
for λe < b/t < 2λe
rs
=
λe =
the stiffener’s radius of gyration about the
stiffened element’s mid-thickness
1.28
E
Fcy
Fc for the stiffened element determined using Article
6.7.3.3 shall not exceed Fc for the stiffener determined
using Article 6.7.3.1.
For flat elements
a) supported on one edge and with a stiffener on the
other edge, and
b) with a stiffener of depth greater than 0.8b or with a
thickness greater than the stiffener’s thickness,
the stress, Fc, corresponding to the uniform compressive
strength is Fc = FUT.
6.7.3.4—Flat Elements Supported on Both Edges
and with an Intermediate Stiffener
The stress, Fc, corresponding to the uniform
compressive strength of flat elements supported on both
edges and with an intermediate stiffener is:
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Table 6.7.3.4-1—Uniform Compressive Stress for Flat Elements
Supported on Both Edges with Intermediate Stiffener
Limit
State
Fc
Slenderness
λs
Yielding
Fcy
λs < λ1
Inelastic
Buckling
Bc – Dc λs
λ1 < λs < λ2
Elastic
Buckling
π2 E
Slenderness
Limits
λ1 =
λs > λ2
λs2
Bc − Fcy
Dc
λ2 = Cc
where:
λs =
As =
b
4.62  
t
1 + As
( bt )
1+ 1+
10.67 I o
bt
(6.7.3.4-1)
3
area of the stiffener only, not including any
part of the element stiffened
Io
=
moment of inertia of a section comprising the
stiffener and one half of the width of the
adjacent sub-elements and the transition
corners between them, taken about the
centroidal axis (denoted as o-o in Figure
6.7.3.4-1) of the section parallel to the stiffened
element.
b
=
distance between stiffener and supporting
element (see Figure 6.7.3.4-1)
t
=
thickness of the flat element supported on
both edges (see Figure 6.7.3.4-1)
Fc shall not exceed Fc determined using Article 6.7.3.2 for
the sub-elements of the stiffened element and shall not
exceed Fc of the stiffener determined using Article 6.7.3.1.
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t
As is the
area of the
shaded
portion
b /2
b /2
Io is the moment of
inertia of this portion
about the o-o axis
t
As is the
area of the
shaded
portion
b /2
b /2
Io is the moment of
inertia of this portion
about the o-o axis
o
Figure 6.7.3.4-1—Flat Elements with an Intermediate Stiffener
6.7.3.5—Round Hollow Elements and Curved
Elements Supported on Both Edges
The stress, Fc, corresponding to the uniform
compressive strength of round hollow elements and curved
elements supported on both edges is:
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Table 6.7.3.5-1—Uniform Compressive Stress for Non-Flat Elements Supported on Both Edges
Limit
State
Fc
Slenderness
λ
Yielding
Fcy
λ < λ1
Inelastic
Buckling
Bt − Dt λ
λ1 < λ< λ2
λ1 =
Bt − Fcy
Dt
π2 E
Elastic
Buckling
λ=
Slenderness
Limits
λ

16λ2 1 + 
35


2
λ2 = Ct
λ > λ2
Rb
t
For round hollow elements with transverse welds,
use of Article 6.7.3.5 is limited to elements with
Rb/t < 20.
6.7.3.6—Direct Strength Method
As an alternate to Articles 6.7.3.1 through 6.7.3.4, the
stress, Fc, corresponding to the uniform compressive
strength of flat elements without welds may be determined
as:
Table 6.7.3.6-1—Uniform Compressive Stress Using
Direct Strength Method
Limit
State
Fc
Slenderness
λeq
Yielding
Fcy
λeq < λ1
Inelastic
Buckling
Bp – Dp λeq
λ1 < λeq < λ2
Postbuckling
λeq =
k2 B p E
λ eq
π
λeq > λ2
Slenderness
Limits
λ1 =
B p − Fcy
λ2 =
Dp
k1B p
Dp
(6.7.3.6-1)
E
Fe
Fe = the elastic local buckling stress of the cross
section determined by analysis
6.7.4—Strength of Elements in Flexural Compression
C6.7.4
The stress, Fb, corresponding to the flexural
compressive strength of elements is:
For unwelded elements:
The compressive strengths of elements given in this
section address local buckling, and match those given in
Article B.5.5 of the Specification for Aluminum Structures.
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Fb =
(6.7.4-1)
Fbo
For welded elements:
Fb =
where:
Fbo =
Fbw =
Awzc =
Agc =
Fbo(1 – Awzc /Agc) + Fbw Awzc /Agc
(6.7.4-2)
stress corresponding to the flexural
compressive strength for an element if no
part of the cross-section were weld-affected.
Use buckling constants for unwelded metal
and Fcy.
stress corresponding to the flexural
compressive strength for an element if the
entire cross-section were weld-affected. Use
buckling constants for weld-affected zones
and Fcyw.
cross sectional area of the weld-affected zone
in compression
gross cross sectional area of the element in
compression
6.7.4.1—Flat Elements Supported on Both Edges
The stress, Fb, corresponding to the flexural
compressive strength of flat elements supported on both
edges and flat elements supported on the compression
edge with the tension edge free is:
Table 6.7.4.1-1—Flexural Compressive Stress for Flat Elements
Supported on Both Edges
Limit
State
Fb
Slenderness
b/t
Yielding
1.5Fcy
b/t < λ1
Inelastic
Buckling
Bbr – mDbr b/t
λ1 < b/t < λ2
k2 Bbr E
PostBuckling





mb 
t 
b/t > λ2
m
=
1.15 + co /(2cc)
for –1 < co /cc < 1
m
=
1.3/(1 – co /cc)
for co /cc < –1
m
=
0.65
for cc = – co
cc
=
distance from neutral axis to the element
extreme fiber with the greatest compressive
stress
co
=
distance from neutral axis to other extreme
fiber of the element
Slenderness
Limits
λ1 = Bbr − 1.5 Fcy
mDbr
λ2 = k1 Bbr
mDbr
Distances to compressive fibers are negative and
distances to tensile fibers are positive.
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6.7.4.2—Flat Elements Supported on Tension
Edge, Compression Edge Free
The stress, Fb, corresponding to the flexural
compressive strength of flat elements supported on the
tension edge with the compression edge free is:
Table 6.7.4.2-1—Flexural Compressive Stress for Flat Elements
Supported on Tension Edge with Compression Edge Free
Limit
State
Fb
Slenderness
b/t
Yielding
1.5Fcy
b/t < λ1
Inelastic
Buckling
Bbr – 0.29Dbr b/t
λ1 < b/t < λ2
PostBuckling
k2 Bbr E
(0.29b / t )
b/t > λ2
Slenderness
Limits
`λ1 =
λ2 =
Bbr − 1.5Fcy
0.29 Dbr
k1Bbr
0.29 Dbr
The moment of inertia of the longitudinal stiffener, IL,
about the web of the beam shall equal or exceed
IL =
2

0.02α s ftb 3  6 AL  s 
1 +
  + 0.4
E
bt  b 


(6.7.4.2-1)
where:
AL = cross-sectional area of the longitudinal
stiffener
d1 = distance from the neutral axis to the
compression flange
f
= compressive stress at the toe of the flange
b = clear height of the web
s = distance between transverse stiffeners
t
= web thickness
αs = 1 for a stiffener consisting of equal members
on both sides of the web
= 3.5 for a stiffener consisting of a member on
only one side of the web
For a stiffener consisting of equal members on both
sides of the web, the moment of inertia, IL, shall be the sum
of the moments of inertia about the centerline of the web. For
a stiffener consisting of a member on one side of the web
only, the moment of inertia, IL, shall be taken about the face
of the web in contact with the stiffener.
6.7.4.3—Flat Elements Supported on Both Edges
and with a Longitudinal Stiffener
The stress, Fb, corresponding to the flexural
compressive strength of flat elements supported on both
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edges and with a longitudinal stiffener located 0.4d1 from the
supported edge that is in compression is:
Table 6.7.4.3-1—Flexural Compressive Stress for Flat Elements Supported on
Both Edges and with a Longitudinal Stiffener
Limit
State
Fb
Slenderness
b/t
Yielding
1.5Fcy
b/t < λ1
Inelastic
Buckling
Bbr – 0.29Dbr b/t
λ1 < b/t < λ2
k2 Bbr E
b/t > λ2
PostBuckling
(0.29b / t )
Slenderness Limits
λ1 =
Bbr − 1.5 Fcy
λ2 =
0.29 Dbr
k1Bbr
0.29 Dbr
The moment of inertia of the longitudinal stiffener,
IL, about the web of the beam shall equal or exceed
IL =
2

0.02α s ftb 3  6 AL  s 
1 +
  + 0.4
E
bt  b 


where
AL =
d1
=
f
=
b
s
t
αs
=
=
=
=
=
(6.7.4.3-1)
cross-sectional area of the longitudinal
stiffener
distance from the neutral axis to the
compression flange
compressive stress at the toe of the
flange
clear height of the web
distance between transverse stiffeners
web thickness
1 for a stiffener consisting of equal
members on both sides of the web
3.5 for a stiffener consisting of a
member on only one side of the web
For a stiffener consisting of equal members on both
sides of the web, the moment of inertia, IL, shall be the
sum of the moments of inertia about the centerline of the
web. For a stiffener consisting of a member on one side
of the web only, the moment of inertia, IL, shall be taken
about the face of the web in contact with the stiffener.
6.7.4.4—Pipes and Round Tubes
The stress, Fb, corresponding to the flexural
compressive strength of pipes and round tubes is:
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Table 6.7.4.4-1—Flexural Compressive Stress for Pipes and Round Tubes
Limit
State
Upper Inelastic Buckling
Fb
Slenderness
λ
Slenderness
Limits
Btb − Dtb λ
λ < λ1
λ1 = Ctb
Lower Inelastic Buckling
Bt − Dt λ
λ1 < λ < λ2
2
π E
Elastic Buckling
λ
16λ 1 + 
 35 
2
2
λ > λ2
λ2 = Ct
Rb
t
λ=
6.7.4.5—Direct Strength Method
As an alternate to Articles 6.7.4.1 through 6.7.4.3 for
flat elements in flexure without welds, the stress, Fb,
corresponding to the flexural compressive strength may be
determined as:
Table 6.7.4.5-1—Flexural Compressive Stress Using Direct Strength Method
Limit
State
Fb
Slenderness λeq
Yielding
1.5Fcy
λeq < λ1
Inelastic
Buckling
Bbr – Dbrλeq
λ1 < λeq < λ2
Postbuckling
λeq =
Fe =
k 2 Bbr E
λ eq
π
λ1 =
Bbr − 1.5 Fcy
Dbr
λ2 = k1 Bbr /Dbr
λeq > λ2
E
Fe
Slenderness Limits
(6.7.4.5-1)
the elastic local buckling stress of the cross
section determined by analysis
6.7.5—Elastic Buckling Stress of Elements
C6.7.5
The elastic buckling stress of elements shall be
determined using Table 6.7.5-1.
Elastic buckling stresses are used to determine effective
widths of elements for calculating deflections.
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Table 6.7.5-1—Elastic Buckling Stress, Fe, of Elements
Element
Type
Element
Stress
Element
Support
Fe
flat
uniform
compression
supported on both
edges
flat
uniform
compression
supported on one
edge
flat
uniform
compression
supported on one
edge and with a
stiffener on the other
edge
flat
uniform
compression
supported on both
edges and with an
intermediate
stiffener
π2 E
 1.6b 


 t 


π2 E
 5.0b 


 t 


2
2
2
2
 5.0b 


 t 


 1.6b 


 t 


(1− ρST ) π E 2 + ρST π E 2
π2 E
λ2s
π2 E
curved
uniform
compression
supported on both
edges
flat
flexural
compression
supported on both
edges
flat
flexural
compression
supported on both
edges and with a
longitudinal
stiffener
6.8—MEMBERS IN AXIAL TENSION


 R 
b
 1 +
16 
 t 




Rb 
t 
35 
2


π2 E
 mb 
 
 t 
2
π2 E
 0.29b 


 t 
2
C6.8
Provisions for axial tension match those in Chapter
D of the Specification for Aluminum Structures.
6.8.1—General
The available tensile strength of members is the
lesser of the available strengths for the limit states of
tensile yielding of the gross section and tensile rupture
of the net section.
6.8.2—Yielding
The nominal tensile strength for yielding of the
gross section is:
For unwelded members and members with
transverse welds
Pnt = Fty Ag
(6.8.2-1)
For members with longitudinal welds
Pnt = Fty(Ag – Awz) + Ftyw Awz
(6.8.2-2)
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6.8.3—Rupture
The nominal tensile strength for rupture of the net
section is:
For unwelded members
Pnt = Ftu Ae/kt
(6.8.3-1)
For welded members
Pnt = Ftu(Ae – Aewz)/kt + Ftuw Aew
(6.8.3-2)
where:
Ae = effective net area
Aewz = effective net area in the weld-affected zone
6.8.4—Net Area
The net area, An, of a member is the sum of the
products of the thickness and the least net width of each
element computed as follows:
The width of holes shall be taken as the nominal
hole diameter for drilled or reamed holes and the
nominal hole diameter plus 1/32 in. for punched holes.
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 hole widths of all holes in the chain, and adding, for
each gauge space in the chain, the quantity s2/4g where
s = longitudinal center-to-center spacing (pitch) of
any two consecutive holes
g = transverse center-to-center spacing (gauge)
between fastener gauge lines
For angles, the gauge for holes in opposite legs shall
be the sum of the gauges from the back of the angles less
the thickness.
Weld metal in plug or slot welds shall not be
included in the net area.
6.8.5—Effective Net Area
The effective net area, Ae, for angles, channels, tees,
zees, rectangular tubes, and I-shaped sections shall be
determined as follows:
a) If tension is transmitted directly to each of the
cross-sectional elements of the member by fasteners or
welds, the effective net area, Ae, is the net area.
b) If tension is transmitted by fasteners or welds
through some but not all of the cross-sectional elements
of the member, the effective net area, Ae, is:

x

LC  
Ae =An  1 −

y 
 1 −

LC 
(6.8.5-1)
where:
An =
net area of the member at the connection
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LC =
x =
y
length of the connection in the direction of load,
measured from the center of fasteners or the end of
welds. If the length of the connection, LC, is zero,
the effective net area is the net area of the
connected elements.
eccentricity of the connection in the x-axis
direction
=
eccentricity of the connection in the y-axis
direction
The effective net area of the section need not be less
than the net area of the connected elements.
6.9—MEMBERS IN AXIAL COMPRESSION
C6.9
Provisions for axial compression match those in
Chapter E of the Specification for Aluminum Structures.
6.9.1—General
The available compressive strength of members is
the least of the available strengths for the limit states of
member buckling, local buckling, and the interaction
between member buckling and local buckling.
6.9.2—Member Buckling
The nominal member buckling strength, Pnc, is
Pnc = Fc Ag
(6.9.2-1)
where:
Table 6.9.2-1—Member Buckling Stress
Limit
State
Fc
Slenderness
Limits
Yielding
Fcy
Inelastic
Buckling
(Bc − Dc λ ) 0.85 + 0.15 Cc − λ 
Elastic
Buckling
0.85π 2 E
λ2
λ<



C c − λ1 
Bc − Fcy
Dc
Bc − Fcy
Dc
= λ1
< λ < Cc
λ > Cc
λ = greatest column slenderness determined as follows:
For flexural buckling, λ is the largest slenderness
ratio, kL/r, of the column.
For torsional or flexural-torsional buckling,
λ=π
E
Fe
(6.9.2-2)
where Fe is the elastic buckling stress determined by
analysis or as follows:
a) For doubly symmetric members:
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 π2 ECw
 1
+ GJ 
Fe = 
2
I +I
 (k z Lz )
 x y
(6.9.2-3)
b) For singly symmetric members where y is the
axis of symmetry:
4 Fey Fez H 
 Fey + Fez  




1
1
−
−
Fe = 

( Fey + Fez ) 2 
 2 H  

(6.9.2-4)
c) For unsymmetric members, Fe is the lowest root
of the cubic equation:
(Fe – Fex)(Fe – Fey)(Fe – Fez) – Fe2
(Fe – Fey)(xo /ro)2 – Fe2(Fe – Fex)(yo /ro)2 = 0
(6.9.2-5)
where:
ro2 = x0 2 + y0 2 +
H=1–
Fex =
Fey =
Fez =
Ix + I y
Ag
x0 2 + y0 2
(6.9.2-7)
r0 2
π2 E
 k x Lx 


 rx 
(6.9.2-8)
2
π2 E
 k y Ly 


 ry 


(6.9.2-9)
2
2


 GJ + π ECw 
2
(k z Lz ) 
Ag ro 
1
2
(6.9.2-6)
(6.9.2-10)
Ix, Iy = moments of inertia about the principal axes
xo, yo = coordinates of the shear center with respect to
the centroid
ro
= polar radius of gyration about the shear center
rx, ry = radii of gyration about the centroidal
principal axes
For members without welds, determine the nominal
member buckling strength, Pnc = Pno, using Bc, Dc, and
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Cc for unwelded material. For members that are fully
weld-affected, determine the nominal member buckling
strength, Pnc = Pnw, using Bc, Dc, and Cc for welded
material.
For members with transverse welds and:
a) supported at both ends with no transverse weld
farther than 0.05L from the member ends, Pnc = Pno
b) supported at both ends with a transverse weld
farther than 0.05L from the member ends or supported at
only one end with a transverse weld, Pnc = Pnw,
For members with longitudinal welds, the nominal
member buckling strength is:
Pnc = Pno(1 – Awz /Ag) + Pnw (Awz /Ag)
(6.9.2-11)
6.9.3—Local Buckling
The local buckling strength is
Pnc =
n


Fci Ai + Fcy  Ag −
Ai 


i =1
i =1


n
∑
∑
(6.9.3-1)
where:
Fci = local buckling stress of element i determined
using Article 6.7.3.
Ai
= area of element i
6.9.4—Interaction between Member Buckling and
Local Buckling
If the elastic local buckling stress, Fe, is less than
the member buckling stress, Fc, the nominal compressive
strength of the member shall not exceed
1/3
 0.85π2 E 
2/3
Pnc = 
 Fe Ag
2
λ


where:
λ = greatest column slenderness
(6.9.4-1)
Fe is the smallest elastic local buckling stress for all
elements of the cross section determined by Table
6.7.5-1.
6.10—MEMBERS IN FLEXURE
C6.10
Provisions for flexure match those in Chapter F of
the Specification for Aluminum Structures.
6.10.1—General
The available flexural strength of members is the
least of the available strengths for the limit states of
yielding, rupture, local buckling, and lateral-torsional
buckling.
6.10.2—Yielding and Rupture
For the limit state of yielding, the nominal flexural
strength, Mnp, of wrought products is the least of Z Fcy,
1.5St Fty, and 1.5Sc Fcy.
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For the limit state of yielding, the nominal flexural
strength, Mnp, of cast products is the lesser of St Fty and
Sc Fcy.
For the limit state of rupture, the nominal flexural
strength is
Mnu = Z Ftu/kt
(6.10.2-1)
where:
Z = plastic modulus
St = section modulus on the tension side of the neutral axis
Sc = section modulus on the compression side of the
neutral axis
6.10.3—Local Buckling
The nominal flexural strength for the limit state of
local buckling, Mnlb, shall be determined by Article
6.10.3.1, 6.10.3.2, or 6.10.3.3. Local buckling is not a
limit state for wire, rod, or bar.
6.10.3.1—Weighted Average Method
The nominal flexural strength for local buckling,
Mnlb, shall be determined as
Mnlb = Fc If /ccf + Fb Iw /ccw
where:
(6.10.3.1-1)
Fc = stress corresponding to the strength of an element in
uniform compression determined using Articles
6.7.3.1 through 6.7.3.6. The strength of stiffened
elements shall not exceed the strength of an
intermediate stiffener or an edge stiffener.
Fb = stress corresponding to the strength of an element in
flexural compression determined using Articles
6.7.4.1 through 6.7.4.5.
ccf = distance from the centerline of a uniform
compression element to the cross section’s neutral
axis
ccw = distance from a flexural compression element’s
extreme compression fiber to the cross section’s
neutral axis
If = moment of inertia of the uniform stress elements
about the cross section’s neutral axis. These
elements include the elements in uniform
compression and the elements in uniform tension
and their edge or intermediate stiffeners.
Iw = moment of inertia of the flexural compression
elements about the cross section’s neutral axis.
These elements include the elements in flexure and
their intermediate stiffeners.
If there are stiffeners located farther than the
compression flange from the cross section’s neutral axis,
the compressive flexural strength shall not exceed
Fcy If /ccs + Fb Iw /ccw where
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ccs = distance from the cross section’s neutral axis to the
extreme fiber of uniform compression element
6.10.3.2—Direct Strength Method
The nominal flexural strength for local buckling,
Mnlb, shall be determined as
Table 6.10.3.2-1—Nominal Flexural Strength for Local Buckling Using Direct Strength Method
Limit
State
Mnlb
λeq
Yielding
Mnp
λeq < λ1
Inelastic
Buckling

π 2 ES xc  (λ eq − λ 1 )
M np −  M np −

C p2  (C p − λ 1 )

λ1 < λeq < λ2
S xc k 2 B p E
PostBuckling
Slenderness
Limits
λ1 =
λeq > λ2
λ eq
B p − Fcy
Dp
λ2 = Cp
where:
λ eq = π
E
Fe
(6.10.3.2-1)
Fe = the elastic local buckling stress of the cross section
determined by analysis
6.10.3.3—Limiting Element Method
The nominal flexural strength for local buckling,
Mnlb, shall be determined by limiting the stress in any
element to the local buckling stress of that element,
determined in accordance with Articles 6.7.3.1 through
6.7.3.5 and Articles 6.7.4.1 through 6.7.4.4.
6.10.4—Lateral-Torsional Buckling
For the limit state of lateral-torsional buckling, the
nominal flexural strength, Mnmb, is:
Table 6.10.4-1—Nominal Flexural Strength for Lateral-Torsional Buckling
Limit
State
Mnmb
Inelastic
Buckling

λ  π 2 EλS xc
 +
M np 1 −
C c3
 Cc 
λ < Cc
Elastic
Buckling
π2ESxc/λ2
λ > Cc
Slenderness
Limits
for lateral-torsional buckling about an axis designated as
the x-axis.
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To determine the lateral-torsional buckling
slenderness, λ, use Articles 6.10.4.2 through 6.10.4.6. If
more than one Article applies, any applicable Article
shall be used.
For members without welds, determine the lateraltorsional buckling strength, Mnmb = Mnmbo, using Cc for
unwelded material. For members that are fully weldaffected, determine the lateral-torsional buckling
strength, Mnmb = Mnmbw, using Cc for welded material.
For members with transverse welds and:
a) supported at both ends with no transverse weld
farther than 0.05L from the member ends, Mnmb = Mnmbo
b) supported at both ends with a transverse weld
farther than 0.05L from the member ends, or supported
at only one end with a transverse weld, Mnmb = Mnmbw
For members with longitudinal welds, the lateraltorsional buckling strength, Mnmb, is
Mnmb = Mnmbo(1 – Awz/Af) +
(6.10.4-1)
Mnmbw (Awz /Af)
where:
Af = area of the member farther than 2c/3 from the
neutral axis, where c is the distance from the
neutral axis to the extreme compression fiber.
Awz = weld-affected area within Af
6.10.4.1—Bending Coefficient Cb
For members supported on both ends and subjected
to uniform bending moment, the bending coefficient, Cb,
is equal to 1. For other members, Cb shall be taken as 1
or determined as follows.
For singly and doubly symmetric shapes between
brace points
a) If Iyc /Iy < 0.1 or Iyc /Iy > 0.9, Cb = 1
b) If 0.1 < Iyc /Iy < 0.9,
Cb =
4 M max
M
2
max
+ 4 M A2 + 7 M B2 + 4 M C2
Rm < 3.0
(6.10.4.1-1)
where:
Mmax = absolute value of the maximum moment in the
unbraced segment
MA = absolute value of the moment at the quarter
point of the unbraced segment
MB = absolute value of the moment at the midpoint
of the unbraced segment
MC = absolute value of the moment at the threequarter point of the unbraced segment
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Rm
= 1.0 except for unbraced lengths of singlysymmetric members subjected to doublecurvature bending from transverse loading,
Rm
=
Iyf
= moment of inertia of the flange on the negative
side of the midheight (where the direction of
the load is the positive direction) about the
minor axis of the shape
Iy
= minor axis moment of inertia of the shape
 I yf 

0.5 + 2 
 Iy 


2
For doubly symmetric shape cantilevers unbraced at
the free end with loads applied at the centroid, for a
concentrated load applied at the free end Cb = 1.3 and for
uniform transverse load Cb = 2.1.
6.10.4.2—Shapes Symmetric About the Bending
Axis
The slenderness for shapes symmetric about the
bending axis is
λ=
Lb
(6.10.4.2-1)
rye Cb
where rye is:
a) Between brace points of beams subjected to end
moment only or to transverse loads applied at the beam’s
neutral axis, or at brace points:
rye =
Iy 
2
Cw + 0.038 JLb 


S 
(6.10.4.2-2)
x
b) Between brace points of beams subjected to
transverse loads applied on the top or bottom fiber
(where the load is free to move laterally with the beam if
the beam buckles):
rye =
2
Iy  d
d 2 C w 0.038 JLb 
± +

+
+
16 I y
Sx  4
Iy


(6.10.4.2-3)
d/4 is negative when the load acts toward the shear
center and positive when the load acts away from the
shear center.
where:
The y-axis is the principal axis in the plane of bending
Iy = moment of inertia about the y-axis
Sx = section modulus about the x-axis
d = depth of the beam
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6.10.4.3—Singly Symmetric Open Shapes
Unsymmetric About the Bending Axis
For singly symmetric open shapes unsymmetric
about the bending axis and with Iyc < Iyt, determine the
slenderness using Article 6.10.4.2 where rye is calculated
with Iy, Sx, and J determined as though both flanges were
the same as the compression flange with the overall
depth, d, remaining the same.
6.10.4.4—Closed Shapes
For closed shapes, the slenderness is
Lb S xc
λ = 2.3
(6.10.4.4-1)
Cb I y J
6.10.4.5—Rectangular Bars
For rectangular bars, the slenderness is
λ = 2.3 dLb
t
(6.10.4.5-1)
Cb
where:
d = dimension of the bar in the plane of flexure
t = dimension of the bar perpendicular to the plane of
flexure
6.10.4.6—Any Shape
For any shape, symmetric or unsymmetric about the
bending axis, the slenderness is:
ES xc
Cb M e
λ= π
(6.10.4.6-1)
where Me is the elastic lateral-torsional buckling moment
for a laterally unbraced span subjected to uniform
bending determined by analysis or as:

Me = π EI U + U + 0.038 JL
2
y
Lb
2
2
b
Iy

2
+
Cw 

Iy 

(6.10.4.6-2)
where:
The y-axis is the centroidal symmetry or principal
axis such that the tension flange has a positive y
coordinate and bending is about the x-axis. The origin of
the coordinate system is the intersection of the principal
axes.
U = C1g0 + C2βx/2
(6.10.4.6-3)
C1 and C2:
a) If no transverse loads are applied between the
ends of the unbraced segment, C1 = 0 and C2 = 1.
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b) If transverse loads are applied between the ends
of the unbraced segment, C1 and C2 shall be taken as 0.5
or determined by rational analysis.
g0 = distance from the shear center to the point of
application of the load; g0 is positive when the load
acts away from the shear center and negative when
the load acts towards the shear center. If there is no
transverse load (pure moment cases), g0 = 0.
βx=

1  3
y dA + yx 2 dA  − 2 y o

I x  A
A

∫
∫
(6.10.4.6-4)
For singly symmetric I shapes, as an alternative,
2
 2 I yc    I y  


− 1 1 −   
βx = 0.9d f
 Iy


   I x  
(6.10.4.6-5)
where:
Iyc = moment of inertia of the compression flange about
the y-axis
df = the distance between the flange centroids; for tees, df
is the distance between the flange centroid and the
tip of the stem.
yo = distance perpendicular to the bending axis from the
cross-section’s centroid to the shear center; positive
in the direction of the load
Alternately, for singly symmetric I shapes where the
smaller flange area is not less than 80 percent of the
larger flange area, βx shall be taken as –2yo.
6.10.4.7—Interaction between Local Buckling and
Lateral-Torsional Buckling
For open shapes:
a) whose flanges are flat elements in uniform
compression supported on one edge and
b) for which the flange’s elastic buckling stress, Fe,
is less than the lateral-torsional buckling stress of the
beam, Fb, determined in accordance with Article 6.10.4,
the lateral-torsional buckling strength shall not exceed
1/3




2


E
π
Mnmb = 

  L 2 
b

 
  rye Cb  


Fe2/3Sxc
6.11—MEMBERS IN SHEAR
(6.10.4.7-1)
C6.11
Provisions for shear match those in Chapter G of the
Specification for Aluminum Structures.
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6.11.1—General
The available shear strength of members is the least
of the available strengths for the limit states of buckling,
yielding, and rupture.
For the limit states of shear yielding and shear
buckling, the nominal shear strength, Vn, is
For unwelded members:
Vn = Fso Av
(6.11.1-1)
For welded members:
Vn = Fso(Av – Awz) + Fsw Awz
(6.11.1-2)
where:
Fso = shear stress, Fs, corresponding to the shear
strength for an element determined using
Article 6.11.2, 6.11.3, or 6.11.4 if no part of
the cross section were weld-affected.
Fsw = shear stress, Fs, corresponding to the shear
strength for an element determined using
Article 6.11.2, 6.11.3, or 6.11.4 if the entire
cross section were weld-affected.
Av = shear area as defined in Article 6.11.2, 6.11.3,
or 6.11.4
Awz = weld-affected portion of the shear area
6.11.2—Members with Flat Webs Supported on Both
Edges
The nominal shear strength, Vn , of flat webs
supported on both edges is
For the limit state of shear rupture
For unwelded members
Vn = Fsu An /kt
(6.11.2-1)
For welded members
Vn = Fsu (An – Awz)/kt + Fsuw Aw
where:
(6.11.2-2)
An = net area of the web
Awz = weld-affected area of the web
For the limit states of shear yielding and shear
buckling, Vn, is as defined in Article 6.11.1 with
Av = dt
(6.11.2-3)
and Fs determined from:
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Table 6.11.2-1—Shear Stress for Flat Webs Supported on Both Edges
Limit State
Fs
Yielding
Inelastic Buckling
Fsy
b/t < λ1
Bs – 1.25Ds b/t
λ1 < b/t < λ2
π2 E
Elastic Buckling
b/t
 1.25b 


 t



2
b/t > λ2
Slenderness Limits
λ1 =
Bs − Fsy
1.25Ds
λ2 = C s
1.25
B = clear height of the web for webs without transverse
stiffeners and
a1
for webs with transverse stiffeners
b=
a 
1 + 0.7 1 
 a2 
2
(6.11.2-4)
a1 = the lesser of the clear height of the web and the
distance between stiffeners
a2 = the greater of the clear height of the web and the
distance between stiffeners
t
= web thickness
d = full depth of the section
Transverse stiffeners shall have a moment of inertia
Is not less than the following:
s
0.55Vb 2  s 
(6.11.2-5)
≤ 0.4,
Is =
 
b
E
b
s
0.088Vb 2  b 
(6.11.2-6)
> 0.4,
Is =
 
b
E
s
where:
b = clear height of the web regardless of whether or not
a longitudinal stiffener is present
Is = moment of inertia of the transverse stiffener. For a
stiffener composed of members of equal size on
each side of the web, the moment of inertia of the
stiffener shall be computed about the centerline of
the web. For a stiffener composed of a member on
only one side of the web, the moment of inertia of
the stiffener shall be computed about the face of
the web in contact with the stiffener.
s = transverse stiffener spacing. For a stiffener
composed of a pair of members, one on each side
of the web, the stiffener spacing, s, is the clear
distance between the pairs of stiffeners. For a
stiffener composed of a member on only one side
of the web, the stiffener spacing, s, is the distance
between fastener lines or other connecting lines.
V = shear force on the web at the transverse stiffener
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Stiffeners shall extend from flange to flange but
need not be connected to either flange.
6.11.3—Members with Flat Webs Supported on One
Edge
The nominal shear strength, Vn, of flat webs
supported on one edge is
For the limit state of shear rupture
For unwelded members
Vn = Fsu An/kt
(6.11.3-1)
For welded members
Vn = Fsu(An – Awz)/kt + Fsuw Awz
(6.11.3-2)
where:
An
= net area of the web
Awz = weld-affected area of the web
For the limit states of shear yielding and shear
buckling, Vn, is as defined in Article 6.11.1 with
Av = bt
(6.11.3-3)
and Fs determined from:
Table 6.11.3-1—Shear Stress for Flat Webs Supported on One Edge
Limit
State
Fs
b/t
Yielding
Fsy
b/t < λ1
Inelastic
Buckling
Bs – 3.0Ds b/t
λ1 < b/t < λ2
Elastic
Buckling
π2 E
 3.0b 


 t 


2
Slenderness
Limits
λ1 =
Bs − Fsy
3.0 Ds
λ2 = C s
b/t > λ2
3.0
b = distance from the unsupported edge to the midthickness of the supporting element
t = web thickness
6.11.4—Pipes and Round or Oval Tubes
The nominal shear strength, Vn, of pipes and round
or oval tubes is
For the limit state of shear rupture
For unwelded members
Vn = Fsu An/(2kt)
(6.11.4-1)
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For welded members
Vn = Fsu(An – Awz)/(2kt ) + Fsuw Awz/2
(6.11.4-2)
where:
An = net area of the pipe or tube
Awz = weld-affected area of the pipe or tube
For the limit states of shear yielding and shear
buckling, Vn, is as defined in Article 6.11.1 with
Av = π(Do2 – Di2)/8
(6.11.4-3)
where:
Do
= outside diameter of the pipe or tube
Di = inside diameter of the pipe or tube
and Fs determined from:
Table 6.11.4-1—Shear Stress for Pipes and Round or Oval Tubes
Limit State
Fs
λ
Yielding
Fsy
λ < λ1
Inelastic
Buckling
1.3Bs – 1.63Ds λ
λ1 < λ < λ2
Elastic
Buckling
1.3π 2 E
(1.25λ )2
λ > λ2
λ = 2.9  Rb 


5/
 t 


8
L

R

1/

v 
b 
4
Slenderness
Limits
λ1 =
1.3Bs − Fsy
1.63Ds
λ2 =
Cs
1.25
(6.11.4-4)
Rb
= mid-thickness radius of a pipe or round tube or
maximum mid-thickness radius of an oval tube
t
= wall thickness
Lv
= length of pipe or tube from maximum to zero
shear force
6.11.5—Rods
The nominal shear strength, Vn, of rods is
For the limit state of shear rupture
For unwelded members
Vn = Fsu An /kt
(6.11.5-1)
For welded members
Vn = Fsu(An – Awz)/kt + Fsuw Awz
(6.11.5-2)
where:
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An = net area of the rod
Awz = weld-affected area of the rod
For the limit state of shear yielding, Vn, is as defined
in Article 6.11.1 with
(6.11.5-3)
Av = πD2/4
where:
D
= diameter of the rod
Fs = Fsy
6.12—MEMBERS IN TORSION
C6.12
Provisions for torsion match those in Section H.2 of
the Specification for Aluminum Structures.
6.12.1—General
The available torsional strength of members is the
least of the available strengths for the limit states of
rupture, yielding, and buckling.
For the limit state of torsional rupture, the shear
stress, Fs, corresponding to the torsional strength is
For unwelded members
Fs = Fsu/kt
(6.12.1-1)
For welded members
Fs = Fsu(1 – Awz /Ag)/kt + Fsuw Awz?Ag
(6.12.1-2)
For the limit states of shear yielding and shear
buckling, the shear stress, Fs, corresponding to the
torsional strength is
For unwelded members
Fs = Fso
(6.12.1-3)
For welded members
Fs = Fso(1 – Awz/Ag) + Fsw Awz/Ag
(6.12.1-4)
where:
Fso
= shear stress corresponding to the torsional
strength for an element determined using
Article 6.12 if no part of the cross section
were weld-affected.
Fsw =
shear stress corresponding to the torsional
strength for an element determined using
Article 6.12 if the entire cross section were
weld-affected.
Awz =
cross sectional area of the weld-affected zone
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Ag
= gross cross sectional area of the element.
6.12.2—Pipes and Round or Oval Tubes
The nominal torsional strength, Tn, for pipes and
round or oval tubes is
(6.12.2-1)
Tn = Fs J/Rb
For the limit state of torsional rupture, the shear
stress, Fs, corresponding to the torsional strength shall be
determined in accordance with Article 6.12.1.
For the limit state of torsional yielding and
torsional buckling, the shear stress, Fs, corresponding to
the shear strength is
Table 6.12.2-1—Torsional Stress for Pipes and Round or Oval Tubes
Slenderness
Limits
Limit State
Fs
λ
Yielding
Fsy
λ < λ1
Inelastic
Buckling
Bs – 1.25Ds λ
λ1 < λ < λ2
π2 E
Elastic
Buckling
(1.25λ )2
λ1 =
Bs − Fsy
1.25Ds
λ2 = C s
1.25
λ > λ2
Buckling constants Bs, Ds, and Cs are given in Table
6.7.1-1 or 6.7.1-2.
/8  L  / 4
s



 Rb 
λ = 2.9  Rtb 

5
1
(6.12.2-2)
Rb = mid-thickness radius of a pipe or round tube or the
maximum mid-thickness radius of an oval tube
T = wall thickness
Ls = length between transverse stiffeners, or overall length
if no transverse stiffeners are present
J = torsion constant of the pipe or tube
6.12.3—Rectangular Tubes
The nominal torsional strength, Tn, for rectangular
tubes is
Tn = Fs C
where C is the torsional shear constant.
(6.12.3-1)
For the limit state of torsional rupture, the shear
stress, Fs, corresponding to the torsional strength is
determined in accordance with Article 6.12.1.
For the limit state of torsional yielding and torsional
buckling, Fs, is determined in accordance with Article
6.11.2 for the side with the larger slenderness.
6.12.4—Rods
The nominal torsional strength, Tn, for rods for the
limit state of torsional yielding is
For unwelded members
Tn = 0.196Fsy D3
(6.12.4-1)
For welded members
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Tn = 0.196Fsyw D3
6-41
(6.12.4-2)
The nominal torsional strength, Tn, for rods for the
limit state of torsional rupture is
For unwelded members
Tn = 0.262Fsu D3/kt
(6.12.4-3)
For welded members
Tn = 0.262Fsuw D3
(6.12.4-4)
where:
D = diameter of the rod
6.12.5—Open Shapes
The nominal torsional strength, Tn, for open shapes
is the lesser of:
a) the limit states of yielding, local buckling, and
rupture due to normal stress determined in accordance
with Article 6.7.2, and
b) the limit states of yielding, local buckling, and
rupture due to shear stress determined in accordance
with Article 6.11.
C6.13
6.13—COMBINED FORCES
Provisions for combined forces match those in
Sections H.1 and H.3 of the Specification for Aluminum
Structures.
6.13.1—Flexure and Axial Force
For members subject to flexure and axial force,
Pr M rx M ry
+
+
< 1.0
Pc M cx M cy
(6.13.1-1)
where all terms are positive, and
x
= subscript for major principal axis bending
y
= subscript for minor principal axis bending
Pr = required axial strength determined in accordance
with Section 4
Pc = available axial strength determined in accordance
with Article 6.8 for axial tension and Article 6.9 for
axial compression
Mr = required flexural strength determined in accordance
with Section 4
Mc = available flexural strength determined in accordance
with Article 6.10
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6.13.2—Torsion, Flexure, Shear, and/or Axial
Compression
Stresses in flat elements subject to torsion, flexure,
shear, and/or axial compression shall satisfy the
following:
fc/(φFc) + [fb/(φFb)]2 + [fs/(φFs)]2 < 1.0
(6.13.2-1)
Stresses in curved elements subject to torsion,
flexure, shear, and/or axial compression shall satisfy the
following:
fc /(φFc) + fb /(φFb) + [fs /(φFs)]2 < 1.0
(6.13.2-2)
where:
fc = compressive stress due to axial compression
fb = compressive stress due to flexure
fs = shear stress due to shear and torsion
Fc = axial compressive stress corresponding to the
nominal axial compressive strength
Fb = flexural stress corresponding to the nominal flexural
strength
Fs =
shear stress corresponding to the nominal shear
strength
C6.14
C6.14
Provisions for welded connections match those in
Section J.2 of the Specification for Aluminum Structures.
6.14—WELDED CONNECTIONS
6.14.1—General
Welding shall comply with AWS D1.2 Structural
Welding Code—Aluminum.
6.14.2—Strength
The nominal strength, Rn, of groove, fillet, plug,
slot, and stud welded joints shall be the lesser of the base
material strength for the limit states of tensile rupture
and shear rupture and the weld metal strength for the
limit state of rupture as follows:
a) For the base metal
Rn = FnBM ABM
(6.14.2-1)
b) For the weld metal
Rn = Fnw Awe
(6.14.2-2)
where:
FnBM = nominal stress of the base metal corresponding to
its welded ultimate strength from Table 6.4.2-1
Fnw = nominal stress of the weld metal corresponding to
its ultimate strength from Table 6.4.4-1
ABM = cross-sectional area of the base metal
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Awe = effective area of the weld
FnBM, Fnw, ABM, and Awe are given in Table 6.14.2-1.
Table 6.14.2-1—Nominal Strength of Welded Joints
Base Metal
Load type and direction
relative to weld axis
Nominal Stress
FnBM
Weld Metal
Effective Area
ABM
Nominal Stress
Fnw
Effective Area
Awe
COMPLETE JOINT PENETRATION GROOVE WELDS
Tension or compression
normal to weld axis
Ftuwb
Tension or compression
parallel to weld axis
Ftuwf
Sw Lwe
tension or compression in parts parallel to a weld
need not be considered in designing welds joining the parts
0.6Ftuwb
Shear
SwLwe
SwLwe
0.6Ftuwf
Sw Lwe
PARTIAL JOINT PENETRATION GROOVE WELDS
Tension or compression
normal to weld axis
Ftuwb
Tension or compression
parallel to weld axis
SwLwe
FILLET WELDS
0.6Ftuwb
Shear
0.6Ftuwf
Tension or compression
parallel to weld axis
SwLwe
0.6Ftuwf
Sw Lwe
0.6(0.85Ftuwf)
(see note 1)
Swe Lwe
tension or compression in parts parallel to a weld
need not be considered in designing welds joining the parts
PLUG AND SLOT WELDS
Shear parallel to faying
surface
Sw Lwe
tension or compression in parts parallel to a weld
need not be considered in designing welds joining the parts
0.6Ftuwb
Shear
SwLwe
0.6Ftuwb
nominal area of the
hole or slot in the plane
of the faying surface
0.6Ftuwf
nominal area of the
hole or slot in the
plane of the faying
surface
STUD WELDS
Shear
0.6Ftuwb
π D2/4
0.6Ftuwf
(π/4)(D – 1.191/n)2
Tension
Ftuwb
π D2/4
Ftuwf
(π/4)(D – 1.191/n)2
Notes:
1. Alternately, the strength of fillet welds loaded transversely shall be taken as 1.36 times the strength given in Table 6.14.2-1.
2. Ftuwb for base metal is listed in Table 6.4.2-1.
3. Ftuwf for filler metal is listed in Table 6.4.4-1.
4. Lwe = effective length of a weld
5. Swe = effective throat of a fillet weld
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6.14.3—Combination of Welds
If two or more of the types of welds (groove, fillet,
plug, or slot) are combined in a single joint, the strength
of each shall be separately computed with respect to the
axis of the group in order to determine the strength of
the combination.
6.14.4—Post-Weld Heat Treatment
The nominal strength of the weld-affected zone of
post-weld-heat-treated base metal shall be taken as given
in Table 6.14.4-1. The tension coefficient, kt, of the
weld-affected zone after post-weld heat treatment for the
alloys listed in Table 6.14.4-1 shall be taken as the
tension coefficient, kt, of the non-weld-affected alloy.
Table 6.14.4-1—Nominal Strength of the Weld-Affected Zone of Post-Weld-Heat-Treated Base Metal
Base
Metal
Alloy
Temper Before
Welding
Maximum
Nominal
Thickness (in.)
Filler
Alloy
Post-Weld
Heat
Treatment
Nominal Post-Weld
Heat Treatment
Strength
6005A
T1
0.250
4043
T5
85% of unwelded T5
6061
T4
0.250
4043
T6
85% of unwelded T6
6063
T4
0.375
4043
T6
85% of unwelded T6
6.15—BOLTED CONNECTIONS
C6.15
Provisions for bolted connections match those in
Section J.3 of the Specification for Aluminum Structures.
6.15.1—Holes and Slots for Bolts
The nominal diameter of holes for bolts shall not be
more than 1/16 in. greater than the nominal diameter of
the bolt unless slip-critical connections are used.
The nominal width of slots for bolts shall not be
more than 1/16 in. greater than the nominal diameter of
the bolt. If the nominal length of the slot exceeds 2.5D
or the edge distance is less than 2D, where D is the
nominal bolt diameter, the edge distance perpendicular
to the slot length and slot length shall be sized to avoid
overstressing the material along the slot. Unless slipcritical connections are used, the length shall be
perpendicular to the direction of force.
6.15.2—Minimum Spacing of Bolts
The distance between bolt centers shall not be less
than 2.5 times the nominal diameter of the bolt.
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6.15.3—Minimum Edge Distance of Bolts
The distance from the center of a bolt to an edge of
a part shall not be less than 1.5 times the nominal
diameter of the bolt. See Article 6.15.5 for the effect of
edge distance on bearing strength.
6.15.4—Bolt Tension
The nominal tensile strength, Rn, of aluminum bolts
for the limit state of tensile rupture is:
Rn = (π(D − 1.191/n)2/4)Ftu
(6.15.4-1)
where :
Ftu = tensile ultimate strength of the bolt given in
Table 6.4.5-1
6.15.5—Bolt Shear
The nominal shear strength, Rn, of aluminum bolts
for the limit state of shear rupture is:
a) For bolts with threads in the shear plane,
Rn = (π(D − 1.191/n)2/4)Fsu
(6.15.5-1)
b) For bolts without threads in the shear plane,
Rn = (πD2/4)Fsu
(6.15.5-2)
where:
Fsu = shear ultimate strength of the bolt given in Table
6.4.5-1
If the grip (total thickness of parts being fastened) of
an aluminum bolt exceeds 4.5D, the bolt’s nominal shear
strength shall be reduced by dividing by ½ + Gf /(9D)
where Gf is the grip and D is the bolt’s nominal
diameter.
6.15.6—Bolt Bearing
The nominal bearing strength, Rn, of connected parts
for the limit state of bearing is:
a) For a bolt in a hole,
Rn = detFtu < 2DtFtu
(6.15.6-1)
b) For a bolt in a slot with the slot perpendicular to
the direction of force:
Rn = 1.33DtFtu
(6.15.6-2)
and the edge distance perpendicular to the slot length and
slot length shall be sized to avoid overstressing the
material between the slot and the edge of the part.
where:
de = distance from the center of the bolt to the edge
of the part in the direction of force.
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t = for plain holes, thickness of the connected part;
for countersunk holes, thickness of the
connected part less ½ the countersink depth
Ftu = tensile ultimate strength of the connected part
D = nominal diameter of the bolt
6.15.7—Slip-Critical Bolted Connections
6.15.7.1—General
Slip-critical connections between aluminum
members or between aluminum and steel members shall
comply with the Research Council on Structural
Connections (RCSC) Specification for Structural Joints
Using High Strength Bolts except as modified here. Slipcritical connections shall be designed for the limit states
of shear rupture in accordance with Article 6.15.7.4,
bearing strength in accordance with Article 6.15.6, and
slip in accordance with Article 6.15.7.5.
6.15.7.2—Material
Aluminum used in slip-critical connections shall
have a tensile yield strength of at least 15 ksi. Bolts shall
comply with ASTM F3125/F3125M Grades
A325/A325M, nuts shall comply with ASTM A563
Grade DH or ASTM A194 Grade 2H, and washers shall
comply with ASTM F436/F436M. Bolts, nuts, and
washers shall be zinc coated by the hot-dip or
mechanically deposited processes as specified in ASTM
F3125/F3125M.
6.15.7.3—Holes
Holes shall be standard holes, oversize holes, shortslotted holes, or long-slotted holes. The nominal
dimensions for each hole type shall not exceed those
shown in the RCSC specification.
6.15.7.4—Bolt Tension and Shear
The tensile or shear strength, Rn, shall be
determined for the limit state of rupture as follows:
Rn = Fn Ab
(6.15.7.4-1)
where:
Fn is Fnt or Fnv determined in accordance with the
Specification for Structural Steel Buildings (ANSI/AISC
360)
Ab = nominal cross sectional area (unthreaded body area)
of the bolt
6.15.7.5—Slip Resistance
Slip-critical connections shall be designed for the
limit state of slip in accordance with the Specification
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for Structural Steel Buildings with the following
exceptions:
a) For standard size and short-slotted holes
perpendicular to the direction of the load: φ = 1.00
b) For oversized and short-slotted holes parallel to
the direction of the load: φ = 0.85
c) For long-slotted holes: φ = 0.70
d) μ = mean slip coefficient = 0.50 for aluminum
surfaces abrasion blasted with coal slag to SSPC SP-5 to
an average substrate profile of 2.0 mils in contact with
similar aluminum surfaces or zinc-painted steel surfaces
with a maximum dry film thickness of 4 mils (Class B
surfaces). Determine slip coefficients for other surfaces
in accordance with RCSC specification Appendix A.
6.15.7.6—Washers
Washers shall be used under bolt heads and under
nuts. At a long-slotted hole in an outer ply, a galvanized
steel plate washer or bar at least 5/16 in. thick with
standard holes shall be used. The plate washer or bar
shall completely cover the slot but need not be hardened.
Where the outer face of the bolted parts has a slope
greater than 1:20 with respect to a plane normal to the
bolt axis, a beveled washer shall be used.
6.16—CONNECTED ELEMENTS
C6.16
Provisions for connected elements match those in
Section J.7 of the Specification for Aluminum Structures.
6.16.1—Block Shear Rupture
Block shear rupture strength, Rn, shall be
determined as follows:
a) For mechanically fastened connections on a
failure path with shear on some segments and tension on
the other segments:
Rn = [Fsu (Anv + Agv)/2 + Ftu Ant]/kt
(6.16.1-1)
where:
Agv = gross area in shear
Anv = net area in shear
Ant = net area in tension
b) For welded connections on a failure path with
shear on some segments and tension on the other
segments:
Rn = Fsuw Agvw + Ftuwb Agtw + (Fsu Agvo + Ftu Agto)/kt
(6.16.1-2)
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where:
Agvw = gross weld-affected area in shear
Agvo = gross area not weld-affected in shear
Agtw = gross weld-affected area in tension
Agto = gross area not weld-affected in tension
6.16.2—Bearing Strength of Flat Surfaces
The bearing strength, Rn, of flat surfaces in contact
shall be determined as follows:
(6.16.2-1)
Rn = 1.33 Ftu Ab
6.17—REFERENCES
Aluminum Association. 2006. Aluminum Standards and Data. Aluminum Association, Washington, DC.
Aluminum Association. 2010. Aluminum Design Manual 2010. Aluminum Association, Washington, DC.
ASTM. 2007. “Standard Specification for Anchor Bolts, Steel, 36, 55, and 105-ksi Yield Strength,” F1554-07a, Annual Book of
ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2009. “Standard Specification for Coatings of Zinc Mechanically Deposited on Iron and Steel,” B4-04 (2009), Annual
Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2009. “Standard Specification for Stainless Steel Nuts,” F594-09, Annual Book of ASTM Standards. American Society
for Testing Materials, West Conshohocken, PA.
ASTM. 2009. “Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware,” A153/A153M-09, Annual Book
of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2010. “Standard Specification for Aluminum-Alloy 6061-T6 Standard Structural Profiles,” B308/B308M-10, Annual
Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2010. “Standard Specification for Aluminum-Alloy Extruded Structural Pipe and Tube,” B429/B6M-10, Annual Book of
ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2010. “Standard Specification for Aluminum and Aluminum-Alloy Rivet and Cold-Heading Wire and Rods,” ASTM
B316/B316M-10, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2011. “Standard Practice for Preparation of Use and Care Booklets for Vacuum Cleaners,” F486-01(2011), Annual Book
of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2011. “Standard Specification for Hardened Steel Washers,” F436-11, Annual Book of ASTM Standards. American
Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Aluminum and Aluminum-Alloy Drawn Seamless Tubes,” B210-12, Annual Book of
ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Aluminum and Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire,” B21112, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Aluminum and Aluminum-Alloy Seamless Pipe and Seamless Extruded Tube,”
B241/B241M-12, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength,”
A325-12, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
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ASTM. 2013. “Standard Specification for Nonferrous Nuts for General Use,” F467-13 , Annual Book of ASTM Standards.
American Society for Testing Materials, West Conshohocken, PA.
ε2
ASTM. 2013. “Standard Specification for Stainless Steel Bolts, Hex Cap Screws, and Studs,” F593-13a, Annual Book of ASTM
Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Alloy-Steel and Stainless Steel Bolting for High Temperature or High Pressure
Service and Other Special Purpose Applications,” A193/A193M-14a, Annual Book of ASTM Standards. American Society for
Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Alloy-Steel and Stainless Steel Bolting for Low-Temperature Service,” A320/A320M14, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Aluminum-Alloy Investment Castings,” B618/B618M-14, Annual Book of ASTM
Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Aluminum-Alloy Permanent Mold Castings,” B108/B108M-14, Annual Book of
ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Aluminum-Alloy Sand Castings,” B26/B26M-14, Annual Book of ASTM Standards.
American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes,”
B221-14, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate,” B209-14, Annual Book of ASTM
Standards. American Society for Testing Materials, West Conshohocken, PA. |
ASTM. 2014. “Standard Specification for Carbon and Alloy Steel Nuts,” A563-07a(2014), Annual Book of ASTM Standards.
American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure or High Temperature
Service, or Both,” A194/A194M-14a, Annual Book of ASTM Standards. American Society for Testing Materials, West
Conshohocken, PA.
ASTM. 2014. “Standard Specification for High Magnesium Aluminum-Alloy Sheet and Plate for Marine Service and Similar
Environments,” B928/B928M-14a, Annual Book of ASTM Standards. American Society for Testing Materials, West
Conshohocken, PA.
ASTM. 2014. “Standard Specification for Structural Bolts, Alloy Steel, Heat Treated, 150 ksi Minimum Tensile Strength,”
A490-14a, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
AWS. 2008. Structural Welding Code—Aluminum, D1.2/D1.2M. American Welding Society, Miami, FL.
Crockett, H. 1942. “Predicting Stiffener and Stiffened Panel Stresses,” Journal of the Aeronautical Sciences, Vol. 9, November,
1942, p. 501. American Institute of Aeronautics and Astronautics, Reston, VA.
Galambos, T. 1987. Guide to Stability Design Criteria for Metal Structures, Fourth edition. Wiley Interscience, New York, NY.
Jombock, J. R., and J. W. Clark. “Bending Strength of Aluminum Formed Sheet Members,” Journal of the Structural Division,
ASCE, Vol. 94, No. ST2, February 1968. American Society of Civil Engineers, Reston, VA.
Kaufman, J. G. 2001, Fracture Resistance of Aluminum Alloys, ASM International, Materials Park, OH.
Kim, Y. 2003. Behavior and Design of Aluminum Members in Bending. PhD Dissertation, Cornell University, Ithaca, NY.
May, J., and C. Menzemer. “Strength of Bolted Aluminum Alloy Tension Members,” Journal of Structural Engineering, Vol.
131, No. 7, July 2005, pp. 1125–1134.
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Menzemer, C., L. Fei, and T. Srivatsan. “Design Criteria for Bolted Connection Elements in Aluminum Alloy 6061”, Journal of
Mechanical Design, Transactions of the ASME, Vol. 121, September 1999, pp. 348-358.
Menzemer, C., L. Fei, and T. Srivatsan. “Mechanical Response and Failure of Bolted Connection Elements in Aluminum Alloy
5083,” Journal of Materials Engineering and Performance, Volume 8, No. 2, April 1999, pp. 211-218.
Menzemer, C., Ortiz, R., Iasconne, R., and Srivatsan, T., “An Investigation of the Bearing Strength of Three Aluminum Alloys”,
Material Science and Engineering: A, Vol. 327, Issue 2, April 2002, pp. 203-212.
Sharp, M. L., “Strength of Beams or Columns with Buckled Elements,” Journal of the Structural Division, ASCE, Technical
Notes, May 1970, p. 1011. American Society of Civil Engineers, Reston, VA.
Sharp, M. L. 1993. Behavior and Design of Aluminum Structures. McGraw-Hill, New York, NY.
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SECTION 14: FABRICATION, MATERIALS, AND DETAILING
TABLE OF CONTENTS
14.1—SCOPE .............................................................................................................................................................................. 14-1
14.2—NOTATION...................................................................................................................................................................... 14-1
14.3—WORKING DRAWINGS ................................................................................................................................................ 14-1
14.3.1—Shop Drawings ....................................................................................................................................................... 14-1
14.3.2—Camber Diagram .................................................................................................................................................... 14-2
14.3.3—Marking and Shipping............................................................................................................................................ 14-2
14.3.4—Full-Size Tests ........................................................................................................................................................ 14-2
14.4—STEEL STRUCTURES ................................................................................................................................................... 14-2
14.4.1—Materials ................................................................................................................................................................. 14-2
14.4.1.1—Minimum Thickness of Material................................................................................................................. 14-2
14.4.1.2—Anchor Bolt Types ...................................................................................................................................... 14-3
14.4.2—Bolted Connections ................................................................................................................................................ 14-3
14.4.2.1—Bolts ............................................................................................................................................................. 14-3
14.4.2.2—Holes ............................................................................................................................................................ 14-3
14.4.3—Slip Type Field Splice ............................................................................................................................................ 14-3
14.4.4—Welded Connections .............................................................................................................................................. 14-3
14.4.4.1—Stiffened Tube-to-Transverse-Plate Connections ....................................................................................... 14-4
14.4.4.2—Backing Rings.............................................................................................................................................. 14-4
14.4.4.3—Mast-Arm-to-Pole Connections .................................................................................................................. 14-5
14.4.4.4—Circumferential Welded Splices ................................................................................................................. 14-6
14.4.4.5—Longitudinal Seam Welds ........................................................................................................................... 14-6
14.4.4.6—Tube-to-Transverse Plate Connection Welds ............................................................................................. 14-7
14.4.4.7—Hand-Hole Welds and Other Structural Welds.......................................................................................... 14-8
14.4.4.8—Weld Inspection ........................................................................................................................................... 14-8
14.4.5—Castings .................................................................................................................................................................. 14-9
14.4.5.1—Mild Steel Castings...................................................................................................................................... 14-9
14.4.5.2—Chromium Alloy-Steel Castings ................................................................................................................. 14-9
14.4.5.3—Iron Castings ................................................................................................................................................ 14-9
14.4.6—Fabrication Tolerances ......................................................................................................................................... 14-10
14.4.7—Protection.............................................................................................................................................................. 14-10
14.4.7.1—General ....................................................................................................................................................... 14-10
14.4.7.2—Painted Structures ...................................................................................................................................... 14-10
14.4.7.3—Galvanized Structures................................................................................................................................ 14-10
14.5—ALUMINUM STRUCTURES.......................................................................................................................................14-11
14.5.1—Materials ...............................................................................................................................................................14-11
14.5.2—Storage ...............................................................................................................................................................14-18.1
14.5.3—Cutting ...............................................................................................................................................................14-18.1
14.5.4—Holes ..................................................................................................................................................................14-18.1
14.5.5—Heating ..............................................................................................................................................................14-18.1
14-i
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14.5.6—Finishes .............................................................................................................................................................14-18.1
14.5.6.1—Where Protective Coating Is Required ..................................................................................................14-18.1
14.5.6.2—Surface Preparation ................................................................................................................................14-18.2
14.5.6.3—Abrasion Blasting...................................................................................................................................14-18.2
14.5.7—Contact with Dissimilar Materials.................................................................................................................... 14-18.2
14.5.7.1—Metals .....................................................................................................................................................14-18.2
14.5.7.2—Wood, Fiberboard, or Other Porous Materials ......................................................................................14-18.2
14.5.7.3—Concrete or Masonry..............................................................................................................................14-18.2
14.5.8—Fabrication Tolerances .................................................................................................................................... 14-18.3
14.5.9—Welding............................................................................................................................................................ 14-18.3
14.5.10—Bolt Installation ............................................................................................................................................. 14-18.3
14.5.8—Holes .................................................................................................................................................................... 14-16
14.5.8.1—General ...................................................................................................................................................... 14-16
14.5.8.2—Reamed or Drilled Holes .......................................................................................................................... 14-16
14.5.8.3—Accuracy of Hole Groups ......................................................................................................................... 14-16
14.5.8.3.1—Accuracy before Reaming ............................................................................................................... 14-16
14.5.8.3.2—Accuracy After Reaming ................................................................................................................. 14-17
14.5.8.4—Locating Holes .......................................................................................................................................... 14-17
14.5.9—Annealing and Stress Relieving .......................................................................................................................... 14-17
14.5.10—Castings .............................................................................................................................................................. 14-17
14.5.11—Protection ........................................................................................................................................................... 14-17
14.5.11.1—Galvanic Corrosion (Contact with Dissimilar Materials) ...................................................................... 14-17
14.5.11.2—Overall Painting ...................................................................................................................................... 14-19
14.5.11.3—Anodizing ................................................................................................................................................ 14-19
14.6—PRESTRESSED CONCRETE STRUCTURES ............................................................................................................ 14-19
14.6.1—General ................................................................................................................................................................. 14-19
14.6.2—Concrete Cover .................................................................................................................................................... 14-19
14.6.3—Fabrication Tolerances ........................................................................................................................................ 14-19
14.6.4—Inspection ............................................................................................................................................................. 14-20
14.6.5—Protective Systems ............................................................................................................................................... 14-20
14.6.5.1—Concrete Finish ......................................................................................................................................... 14-20
14.6.5.2—Surface Treatment ..................................................................................................................................... 14-21
14.7—COMPOSITE (FIBER-REINFORCED POLYMER) STRUCTURES ........................................................................ 14-21
14.7.1—Materials .............................................................................................................................................................. 14-21
14.7.1.1—Polymer Resins ......................................................................................................................................... 14-21
14.7.1.2—Glass Fiber Reinforcement ....................................................................................................................... 14-21
14.7.2—Connections ......................................................................................................................................................... 14-22
14.7.3—Fabrication Tolerances ........................................................................................................................................ 14-22
14.7.4—Manufacturing Methods ...................................................................................................................................... 14-22
14.7.5—Testing.................................................................................................................................................................. 14-23
14.7.6—Other Testing ....................................................................................................................................................... 14-23
14.7.7—Determination of Mechanical Properties of FRP ................................................................................................ 14-24
14.7.8—Minimum Protection for FRP Members ............................................................................................................. 14-24
14.8—WOOD STRUCTURES ................................................................................................................................................ 14-24
14.8.1—Materials .............................................................................................................................................................. 14-24
14.8.1.1—Wood Products .......................................................................................................................................... 14-24
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14-iii
14.8.2—Connections .......................................................................................................................................................... 14-25
14.8.3—Minimum Protection for Wood Products ............................................................................................................ 14-25
14.8.3.1—Preservative Treatment for Posts............................................................................................................... 14-25
14.8.3.2—Preservative Treatment for Poles .............................................................................................................. 14-25
14.9—REFERENCES ............................................................................................................................................................... 14-26
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14-11
extend a minimum of 4 in. into the concrete. Steel
anchorages located below grade and not encased in
concrete shall require further corrosion protection in
addition to galvanizing.
14.5—ALUMINUM STRUCTURES
C14.5
The Specification for Aluminum Structures Chapter
M addresses fabrication and erection issues in a similar
manner as in Section 14.5.
14.5.1—Materials
C14.5.1
This Article addresses the required material
properties for aluminum structural supports for highway
signs, luminaires, and traffic signals.
Aluminum wrought products shall comply with a
specification given in Table 6.4.2-1.
Aluminum castings shall comply with a specification
given in Table 6.4.3-1.
Aluminum filler metal for welding shall comply with
the specification given in Article 6.4.4.
Aluminum bolts and nuts shall comply with the
specifications given in Article 6.4.5. Stainless steel bolts
shall comply with ASTM F593 and stainless steel nuts
shall comply with ASTM F594.
14.5.1.1—General
Aluminum wrought products listed in Table 6.4.2-1
are those commonly used in aluminum structural supports
for highway signs, luminaires, and traffic signals. Other
aluminum products, alloys, and tempers are listed in the
Specification for Aluminum Structures Table A.4.3.
Quality control for aluminum castings typically
consists of visual inspection rather than radiographs.
ASTM B26 and B108 do not require radiographs, and
radiographs are not typically required for steel castings.
C.14.5.1.1
For principal materials used for structural members,
minimum mechanical properties for non-welded
aluminum alloys shall be as given in Table 6.4.1-1, and
for welded aluminum alloys in Table 6.4.2-1. Applicable
ASTM specifications are Designations B209, B210,
B211, B221, B241, B247, B308, and B429.
For aluminum alloys not found in Tables 6.4.1-1 and
6.4.2-2, reference should be made to the Aluminum
Design Manual (ADM), “Specifications for Aluminum
Structures” (Aluminum Association, 2000).
14.5.1.2—Storage of Materials
Material shall be stored out of contact with the
ground, free from dirt, grease, and foreign matter and out
of contact with dissimilar materials such as uncoated steel.
14.5.1.3—Minimum Thickness of Material
The minimum thickness of the material for primary
structural members shall be 0.125 in. Aluminum supports
for small roadside signs may be less than 0.125 in. in
thickness. Abrasion blasting shall not be used on
aluminum less than or equal to 0.125 in. thick.
C14.5.1.3
The minimum recommended thickness for welded
aluminum is 0.125 in.
14.5.1.4—Dimensional Tolerances
The diameter of round extruded aluminum tubing
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14-12
members or the dimension across the flat of square,
rectangular, octagonal, dodecagonal, and hexadecagonal
straight or tapered aluminum tubing members shall
comply with the applicable dimensional tolerances
specified in the Aluminum Standards and Data (ASD)
(Aluminum Association, 2009). For tapered round
aluminum members, the diameter tolerance variation shall
not vary more than two percent of the specified
dimension.
14.5.1.5—Plates
14.5.1.5.1—Direction of Rolling
Unless otherwise specified in the contract documents,
plates for main members and splice plates for flanges and
main tension members only shall be cut and fabricated so
that the primary direction of rolling is parallel to the
direction of the main tensile and/or compressive stresses.
14.5.1.5.2—Plate Edges
Plates more than 0.5 in. thick carrying calculated
stress shall not be sheared. All edges that have been cut by
the arc process shall be planed to remove edge cracks.
Oxygen cutting shall not be used. Re-entrant corners shall
be filleted to a radius of 0.75 in. or more.
14.5.1.6—Bent Plates
14.5.1.6.1—General
Bend lines in unwelded, load-carrying, rolled
aluminum plates shall be perpendicular to the direction of
rolling.
Before bending, the corners of the plates shall be
rounded to a radius of 0.0625 in. throughout the portion of
the plate over which the bending is to occur.
14.5.1.6.2—Cold Bending
C14.5.1.6.2
Cold bending shall not produce cracking. For 90degree bends, bend radii measured to the concave face of
the metal shall not be less than those listed in Table
14.5.1.6.2-1.
Recommended bend radii for 90-degree cold bends
for other alloys may be found in Table 7.6 of ASD.
Table 14.5.1.6.2-1—Minimum Bend Radii (in.) for 90-Degree Bends
Alloy
5083-H321
5086-H116
5456-H116
6061-T6
0.1875
0.28
0.28
0.38
0.55
Plate Thickness (in.)
0.25
0.375
Minimum Bend Radius, in.
0.35
0.79
0.47
0.98
0.59
1.18
0.83
1.77
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0.50
1.25
1.42
1.65
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14.5.1.7—Identification of Aluminum Alloys during
Fabrication
The Contractor shall issue cutting instructions and
mark individual pieces so as to be able to identify the
material used for each piece. Metal stamping marks, scribe
lines, and center punch marks shall not be used where they
will remain on fabricated material.
Material furnished from stock shall be identified by lot
and mill test reports.
Upon request by the Engineer, the Contractor shall
furnish an affidavit certifying that the identification of
pieces has been maintained in accordance with this
specification.
14-13
C14.5.1.7
ASD gives color codes for additional alloys and
other information on identification markings used by
aluminum producers.
During fabrication prior to assembly, each piece
shall clearly show its material specification. Writing the
material specification number on the piece or by using
the identification color codes shown in Table C14.5.1.7-1
shall be taken as compliance with this provision.
Aluminum alloys not listed in Table C14.5.1.7-1
shall be marked with colors listed in ASD.
Any piece which will be subject to fabrication that
might obscure its identification prior to assembly shall
have a substantial tag affixed showing the material
specification number.
Table C14.5.1.7-1—Identification Color Codes
5083
5086
6061
6060
Alloy
Color
Red and Gray
Red and Orange
Blue
Yellow and Green
14.5.2—Bolted Connections
14.5.2.1—Bolted Connections and Anchor Bolts
Design of bolted connections shall conform to the
Aluminum Design Manual (ADM) Chapters B and J
(Aluminum Association, 2010).
Fasteners shall not be considered to share load in
combinations with welds.
When the line of action of the resultant force does not
coincide with the center of gravity of the fastener or weld
group, the effect of the eccentricity shall be considered.
Design and installation of steel anchor bolts for
aluminum structures shall be in accordance with
Article 5.16.
14.5.2.2—Anchor Bolts
Anchor bolts for aluminum structures shall follow
guidelines in Article 14.4.1.2 for steel structures.
14.5.2.3—Bolt Material
Aluminum bolt material shall meet ASTM F486 and be
6061-T6 or 7075-T3. Nuts shall meet ASTM F467. Nuts for
C14.5.2.3
ASTM A325 hot-dip galvanized high-strength bolts
are normally used for structural connections in aluminum
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bolts larger than 1/4 inch shall be 6061-T6 or 6262-T9. Flat
washers shall be Alclad 2024-T4. Spring lock washers shall
be 7075-T6.
Carbon steel bolts, nuts, and washers shall be
galvanized by hot dip meeting ASTM A153 or by
mechanical means meeting ASTM B695. Galvanized
fasteners and nuts shall be lubricated in accordance with
ASTM A563. A490 bolts shall not be used.
Stainless steel bolts, nuts, and washers shall be 300
series. Bolts shall meet ASTM F593, A193, or A320. Nuts
shall meet ASTM F594 or A194.
14.5.2.4—Holes and Slots
The nominal diameter of a bolt hole shall not be more
than 0.0625 in. greater than the nominal diameter of the
fastener unless slip critical joints are used.
The width of slots for bolted connections shall not be
more than 0.0625 in. wider than the nominal diameter of the
bolt. If the nominal length of the slot is more than 2.5D
(D = nominal bolt diameter) or the edge distance is less than
2D, the edge distance perpendicular to the length of the slot
and slot length shall be sized to avoid overstressing the
material along the slot. Bearing load connections should be
made so that the action of the load is perpendicular to the
slot. Slip critical connections can be made with the load
action at any orientation to the slot.
structures.
ASTM A490 high-strength steel bolts are not used in
aluminum structures because they may become embrittled
by galvanizing. Galvanizing is typically required to
prevent galvanic corrosion of aluminum in contact with
steel.
C14.5.2.4
To avoid overstressing the material along the slot the
designer, as a minimum, should check bearing, rupture,
and beam action deformation on the edge side of the slot
when the force action is perpendicular to the slot.
14.5.2.5—Minimum Spacing and Edge Distance
of Bolts
The distance between bolt centers shall not be less than
2.5D (D = nominal bolt diameter).
The distance from the center of a bolt to the edge of a
part shall not be less than 1.5D.
See Article 6.9 for bearing design strength.
14.5.3—Welded Connections and Fit Up
14.5.3.1—Weld Inspection
All welds shall be visually inspected (VT). In addition
to visual inspection, full-penetration welds for all structures
that are designed according to the requirements of Section
11 shall be inspected by ultrasonic testing (UT) or dye
penetrant testing (PT), based on the thinnest mating
material:
Thickness < 0.25 in. PT
Thickness > 0.25 in. UT
As an alternative, the Owner may require that fullpenetration groove welds be inspected by destructive
methods acceptable to the Owner. The full length of all fullpenetration groove welds on all members of all structures
shall be inspected, except for welds to arms less than or
C14.5.3.1
There are no prequalified weld inspections in AWS
D1.2 (AWS, 2008). When UT, RT, or other weld
inspection is required by the contract documents, the
extent of testing, the procedure, and the acceptance criteria
shall be specified therein.
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14-15
equal to 6 in. in diameter over their entire length.
In addition to visual inspection, partial-penetration
groove welds and fillet welds for all structures that are
designed according to the requirements of Section 11 shall
be inspected by dye penetrant testing or by destructive
methods acceptable to the Owner. A required length of all
partial-penetration groove welds and fillet welds shall be
inspected on a random 25 percent of all structures, except
for welds to arms less than or equal to 6 in. in diameter over
their entire length. The structures to be inspected shall be
selected by the Owner, if requested. If there are fewer than
four structures, at least one structure shall be randomly
selected.
14.5.3.2—Welded Connections
Surfaces and edges to be welded shall be smooth,
uniform, clean, and free of defects which would adversely
affect the quality of the weld.
Brackets, clips, shipping devices, or other material not
required by the contract documents shall not be welded or
tacked to any member unless specified in the contract
documents and approved by the Engineer.
14.5.4—Fit of Stiffeners
C14.5.4
End bearing stiffeners and stiffeners intended as
supports for concentrated loads shall bear fully on the
component to which they transmit load or from which they
receive load. Stiffeners not intended to support concentrated
loads shall have a tight fit unless specified otherwise.
Full bearing may be obtained by milling, grinding, or
in the case of compression regions, welding.
14.5.5—Abutting Joints
Abutting ends of compression members of trusses and
posts or columns shall be milled or saw-cut to give a square
joint and uniform bearing. At other joints, the distance
between adjacent members shall not exceed 0.375 in.
14.5.6—Facing of Bearing Surfaces
The surface finish of bearing, base plates, and other
bearing surfaces that come in contact with each other or
concrete shall meet ANSI B46.1, Surface Roughness,
Waviness, and Lay, Part 1 (see Table 14.5.6-1).
Table 14.5.6-1—ANSI Surface Roughness Requirements
Bearing Surfaces
Milled ends of compression members, milled or ground
ends of stiffeners and fillers
Surface Finish
ANSI 12.5 µm (500 µin.) (RMS)
Bridge rollers and rockers fillers
ANSI 6.3 µm (250 µin.) (RMS)
Pins and pin-hole fillers
ANSI 3.2 µm (125 µin.) (RMS)
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14-16
ANSI 3.2 µm (125 µin.) (RMS)
Sliding bearings fillers
14.5.7—Straightening Material
C14.5.7
When permitted by the Engineer, straightening of
plates, angles, other shapes, and built-up members shall be
done by methods that will not produce fracture or other
damage to the metal. Distorted members shall be
straightened by mechanical means or by heat straightening.
Heat straightening of non-heat-treatable alloys and of heattreatable alloys after heat treatment shall be done only under
controlled procedures and with the approval of the
Engineer. Heat straightening shall conform to
ANSI/AWSD1.2 .
Aluminum may be heated for short periods of time to
temperatures up to 400 degrees without significant loss of
strength. Temperature and duration limits are given in
ANSI/AWS D1.2 Table 3.2 (AWS, 2008). Heating
aluminum alloys with magnesium contents greater than
three percent, which includes 5083, 5086, and 5456, to
temperatures between 150°F and 450°F will also result in
decreased resistance to exfoliation corrosion.
14.5.8—Holes
C14.5.8.1
14.5.8.1—General
Punching holes to the nominal diameter is not
preferred for aluminum parts subject to fatigue.
Holes shall be:


drilled to the nominal hole diameter, or

subdrilled to a diameter smaller than the
nominal hole diameter and then reamed to the
nominal hole diameter.
subpunched to a diameter smaller than the
nominal hole diameter and then reamed to the
nominal hole diameter, or
The difference between a subpunched hole diameter
and the nominal hole diameter shall be at least one-fourth
the thickness of the part and in no case less than 0.03125 in.
14.5.8.2—Reamed or Drilled Holes
Reamed or drilled holes shall be cylindrical,
perpendicular to the members. Burrs shall be removed. The
diameter of holes produced by drilling or reaming shall not
be more than 0.03125 in. greater than the nominal diameter
of the hole.
14.5.8.3—Accuracy of Hole Groups
14.5.8.3.1—Accuracy before Reaming
After assembling, but before any reaming, the holes in
any contiguous group shall allow a cylindrical pin that
is:

0.125 in. smaller in diameter than the nominal
diameter of the hole to enter at least 75 percent of
the holes perpendicular to the face of the member
without drifting

0.1875 in. smaller in diameter than the nominal
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14-17
diameter of the hole to enter every hole
perpendicular to the face of the member without
drifting
14.5.8.3.2—Accuracy After Reaming
After reaming or drilling, 85 percent of the holes in any
contiguous group shall show no offset greater than 0.03125
in. between parts.
14.5.8.4—Locating Holes
Holes shall be:
 subpunched or subdrilled in unassembled parts and
reamed when the parts are assembled,
 drilled to the nominal diameter using a template or
numerically controlled drilling, or
 drilled to the nominal diameter while the parts are
assembled.
Parts may be assembled in the shop or in the field for
the fabrication of holes.
14.5.9—Annealing and Stress Relieving
Holes shall be fabricated after all heat treatment has
been completed. Aluminum structural members shall not
receive heat treatment after welding.
14.5.10—Castings
Aluminum-alloy sand castings shall conform to ASTM
B/B26. Aluminum-alloy permanent mold castings shall
conform to ASTM B108.
14.5.11—Protection
C14.5.11
Structures of the aluminum alloys covered by these
Specifications are not ordinarily painted. Surfaces shall be
painted where the aluminum alloy parts are in contact with
or fastened to steel members or other dissimilar materials,
the structures are to be exposed to extremely corrosive
conditions, or the Owner has requested it be done for reason
of appearance.
Preparation, cleaning, and painting are covered in the
following Articles. Treatment and painting of the structure
in accordance with United States Military Specification
MIL-T-704 is also acceptable.
The reason that most aluminum structures are not
painted is that aluminum surfaces develop a thin, tough
oxide film that protects the surface against further
oxidation. If the surface is scraped so that the oxide film is
removed, a new film is formed immediately unless
oxygen is kept from the surface. The alloying ingredients
that give aluminum particular properties, such as extrahigh strength, affect resistance to corrosion. Painting is not
needed for the medium-strength alloys in general
structural use in atmospheric exposure.
14.5.11.1—Galvanic Corrosion (Contact with
Dissimilar Materials)
C14.5.11.1
Where the aluminum alloy parts are in contact with or
Galvanic corrosion can occur when another metal,
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fastened to steel members or other dissimilar materials, the
aluminum shall be kept from direct contact with the steel or
other material by painting as follows.
Steel surfaces to be placed in contact with aluminum
shall be painted with good-quality non-lead-containing
priming paint, such as zinc molybdate alkyd-type primer in
accordance with Federal Specification TT-P-645B. This is
to be followed by two coats of paint consisting of 2 lb of
aluminum paste pigment (ASTM D 962-88, Type 2, Class
B) per gallon of varnish meeting Federal Specification TTV-81, Type II, or equivalent. Where severe corrosion
conditions are expected, additional protection can be
obtained by applying a sealant capable of excluding
moisture during prolonged service to the faying surfaces in
addition to the zinc molybdate alkyd-type primer.
Aluminized, hot-dip galvanized, or electro-galvanized steel
placed in contact with aluminum need not be painted.
Stainless steel (300 series) placed in contact with aluminum
need not be painted except in high chloride-containing
environments.
Aluminum shall not be placed in direct contact with
porous materials that may absorb water and cause
corrosion. When such contacts cannot be avoided, an
insulating barrier between the aluminum and the porous
material shall be installed. Before installation, the aluminum
surfaces shall be given a heavy coat of alkali-resistant
bituminous primer or other coating having equivalent
protection to provide this insulating barrier. Aluminum in
contact with concrete or masonry shall be similarly
protected in cases where moisture is present and corrodents
will be trapped between the surfaces.
Aluminum surfaces to be embedded in concrete
ordinarily need not be painted, unless corrosive components
are added to the concrete or unless the assembly is
subjected for extended periods to extremely corrosive
conditions. In such cases, aluminum surfaces shall be
protected by one of the following methods:
(a) given one coat of suitable quality paint, such as
zinc molybdate primer conforming to Federal
Specification No. TT-P-645B or its equivalent;
(b) given a heavy coating of alkali-resistant
bituminous paint; or
(c) wrapped with a suitable plastic tape applied in
such a manner as to provide adequate protection at
the overlaps.
Aluminum shall not be embedded in concrete to which
corrosive components such as chlorides have added if the
aluminum will be electrically connected to steel.
Prepainted aluminum generally does not need
additional painting, even in contact with other materials
such as wood, concrete, or steel. Under extremely corrosive
conditions, additional protection shall be provided as
described in the preceding paragraphs.
such as steel, is coupled to aluminum in the presence of an
electrolyte. An aluminum part bolted to a steel structure
with moisture allowed in the faying surface or an
aluminum part in concrete and coupled to the steel
reinforcement are examples. The aluminum parts may act
as an anode and be sacrificed in time. The attack can be
prevented by isolating the two materials from each other.
Materials such as elastomeric spacers have also been
used to keep aluminum alloy parts from direct contact
with steel or other dissimilar materials.
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14.5.11.2—Overall Painting
Paintings or other coatings shall be in accordance with
the Owner’s requirements.
14.5.11.3—Anodizing
An anodized finish may be provided, if specified by the
Owner.
14-18.1
C14.5.11.2
Structures of the alloys covered by these
Specifications either are not ordinarily painted for surface
protection or are made of prepainted aluminum
components.
C14.5.11.3
Anodizing is an electro-chemical process that results
in a colored aluminum oxide layer on the pole surface.
The Owner should be aware that anodized finishes may
result in color variations between extrusions, coatings, and
weldments.
14.5.2—Storage
Aluminum shall not be stored in contact with the
ground or dissimilar materials.
14.5.3—Cutting
Cutting shall be by shearing, sawing, nibbling, routing,
arc cutting, laser, or abrasive water jet. Parts with a nominal
thickness greater than 0.5 in. shall not be sheared. Oxygen
cutting is prohibited.
14.5.4—Holes
The diameter of punched holes shall equal or exceed
the metal thickness. Castings shall not be punched.
14.5.5—Heating
Except for welding, post-weld heat treatment, and arc
or laser cutting, aluminum shall not be heated above 200oF.
C14.5.6
14.5.6—Finishes
Aluminum is sufficiently corrosion resistant that
protective coatings are not required in ambient conditions.
Coatings are typically used to prevent contact between
aluminum and dissimilar metals or porous materials such
as masonry, concrete, or wood.
14.5.6.1—Where Protective Coating Is Required
Aluminum shall be provided with a protective coating
when aluminum would otherwise be in contact with
dissimilar materials as described in Section 14.5.7.
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14-18.2
14.5.6.2—Surface Preparation
Surfaces to be coated shall be prepared immediately
before coating by:
a) Chemical cleaning (such as a solution of phosphoric
acid and organic solvents), or
b) Abrasion blasting, or
c) Unsealed anodizing, or
d) Chemical conversion coating, or
e) Using a procedure specified by the coating supplier.
14.5.6.3—Abrasion Blasting
Material shall not be abrasion blasted if the blasting
distorts, perforates, or reduces the thickness beyond
specified dimensional tolerances.
14.5.7—Contact with Dissimilar Materials
As an alternative to the requirements below, aluminum
shall be separated from the materials specified in this
Article by a nonporous isolator compatible with the
aluminum and the dissimilar material.
14.5.7.1—Metals
C14.5.7.1
Where 1) aluminum contacts other metals except 300
series stainless steel, zinc, or cadmium and 2) the faying
surfaces are exposed to moisture, the other metal shall be
painted or coated with zinc, cadmium, or aluminum.
Uncoated aluminum shall not be exposed to moisture or
runoff that has come in contact with other uncoated metals
except 300 series stainless steel, zinc, or cadmium.
Steel fasteners with a specified minimum tensile
ultimate strength greater than 120 ksi in the load-bearing
portion of the shank shall not be used in contact with
aluminum.
Contact with metals with a different electrical
potential than aluminum may cause galvanic corrosion.
Usually, low conductivity, a small difference in electrical
potential, or a low current density (as in the case of a small
steel fastener connecting much larger aluminum parts)
means that aluminum contact with 300 series stainless
steel and galvanized steel fasteners does not result in
significant galvanic corrosion.
Steel fasteners with a strength greater than 120 ksi in
contact with aluminum and moisture and subjected to
tensile stress may experience hydrogen-assisted stress
corrosion cracking. The use of such steel is therefore
prohibited.
14.5.7.2—Wood, Fiberboard, or Other
Porous Materials
Aluminum surfaces to be placed in permanent contact
with wood, fiberboard, or other porous material that absorbs
water shall be painted.
14.5.7.3—Concrete or Masonry
Aluminum shall not be embedded in concrete with
corrosive additives such as chlorides if the aluminum is
electrically connected to steel.
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14-18.3
14.5.8—Fabrication Tolerances
The outside diameter of tapered tubes shall not deviate
from the specified nominal diameter by more than two
percent.
14.5.9—Welding
C14.5.9 Welding
Welding shall comply with the AWS D1.2
Structural Welding Code—Aluminum.
AWS D1.2 addresses the qualification of aluminum
welding procedure specifications and welders, fabrication,
and inspection of aluminum weldments.
14.5.10—Bolt Installation
Unless the joint is a slip-critical connection, bolts need
only be installed snug tight, the tightness that exists when
all plies in a joint are in firm but not necessarily continuous
contact. Slip-critical connections shall be tightened and
inspected in accordance with the RCSC Specification for
Structural Joints Using ASTM A325 or A490 Bolts.
All joint surfaces, including surfaces to be under bolt
heads and nuts, shall be free of foreign material. Drifting
done during assembly shall not enlarge holes or distort the
metal.
Beveled washers shall be used where faying surfaces
have a slope of more than 1:20 with respect to a plane
normal to the bolt axis. A washer shall be provided under
the turned part.
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14-18.4
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14-25
as laminated veneer lumber may be used for structural
supports such as posts. Design of engineered wood
products, however, should be based on technical
information provided by the manufacturer and approved
by the Owner because the basic design values could vary
for products from different manufacturers.
14.8.2—Connections
C14.8.2
Mechanical connections and their installation shall
conform to the requirements of the NDS.
Connection hardware shall be hot-dip galvanized or
stainless steel.
Components at mechanical connections, including the
wood members, connecting elements, and fasteners,
should be proportioned so that the design strength equals
or exceeds the required strength for the loads acting on the
structure. The strength of the connected wood components
should be evaluated considering the net section,
eccentricity, shear, tension perpendicular to grain, and
other factors that may reduce component strength.
14.8.3—Minimum Protection for Wood Products
C14.8.3
Wood products shall be protected from biological
attack of wood-destroying organisms, such as decay, fungi,
insects, and marine borers. Minimum accepted preservative
treatments for wood posts and poles shall be in accordance
with Articles 14.8.3.1 and 14.8.3.2, respectively.
All Preservatives shall be registered with the U.S.
Environmental Protection Agency.
Preservative treatments are those that guard wood
against decay, insects, and marine borers. The three basic
types of pressure preservatives are:
• creosote and creosote solutions,
• oil-borne treatments (e.g., preservatives
dissolved in hydrocarbon solvents), and
• waterborne preservatives.
There are a number of variations on each of these
categories. The choice of the preservative treatment and
the required retention are specified by the standards from
the American Wood Protection Association (AWPA) or
by the evaluation reports issued by the International Code
Council Evaluation Service (ICC-ES).
The use and disposal of some wood preservatives
may be controlled or restricted by various local, state, or
governmental agencies.
14.8.3.1—Preservative Treatment for Posts
Posts shall be pressure treated in accordance with the
American Wood Protection Association (AWPA) U1-13,
Commodity Specification: B. Posts or AASHTO M 133.
14.8.3.2—Preservative Treatment for Poles
Round poles shall be pressure treated in accordance
with APWA U1-11, Commodity Specification: D. Poles or
AASHTO M 133.
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14-26
2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR STRUCTURAL
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14.9—REFERENCES
AASHTO. 2010. AASHTO LRFD Bridge Construction Specifications. American Association of State Highway and
Transportation Officials, Washington, DC.
AASHTO. 2012. Standard Specification for Preservatives and Pressure Treatment Processes for Timber, AASHTO M 133.
American Association of State Highway and Transportation Officials, Washington, DC.
AASHTO. 2014. LRFD Bridge Design Specifications, 7th Edition. American Association of State Highway and Transportation
Officials, Washington, DC.
ACI. 1995. Code Requirements for Nuclear Safety-Related Concrete Structures and Commentary, Appendix B, “Steel
Embedments,” ACI 349-06. American Concrete Institute, Farmington Hills, MI.
AGA. 2012. Design of Products to Be Hot-Dip Galvanized after Fabrication. American Galvanizer’s Association, Centennial,
CO.
Aluminum Association. 2010. Aluminum Design Manual, Specifications for Aluminum Structures. Aluminum Association,
Washington, DC.
Aluminum Association. 2013. Aluminum Standards and Data. Aluminum Association, Washington, DC.
Aluminum Association. 2020. Aluminum Design Manual, Aluminum Association, Arlington, VA.
ASME. 2009. Surface Texture, Surface Roughness, Waviness and Lay, ANSI/ASME B46.1-2009. American Society of
Mechanical Engineers, New York, NY.
ASTM. 1999. “Standard Specification for Ferritic Malleable Iron Castings,” ASTM A47/A47M-99, Annual Book of ASTM
Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2003. “Standard Specification for Gray Iron Castings,” A48/A48M-03, Annual Book of ASTM Standards. American
Society for Testing Materials, West Conshohocken, PA.
ASTM. 2006. “Standard Practice for Operating Light and Water Exposure Apparatus (Fluorescent UV Condensation Type) for
Exposure of Non-Metallic Materials,” G154-06, Annual Book of ASTM Standards. American Society for Testing Materials,
West Conshohocken, PA.
ASTM. 2008. “Standard Specification for Aluminum Powder and Paste Pigments for Paints,” D962-81(2008), Annual Book of
ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2009. “Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware,” A153/A153M-09, Annual
Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2009. “Standard Specification for Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring
Forgings,” B247-09, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2009. “Standard Specification for Coatings of Zinc Mechanically Deposited on Iron and Steel,” B695-04(2009),
Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2009. “Standard Specification for Reinforced Thermosetting Plastic Poles,” D4923-92 (Withdrawn 2010), Annual
Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2009. “Standard Specification for Stainless Steel Nuts,” F594-09, Annual Book of ASTM Standards. American Society
for Testing Materials, West Conshohocken, PA.
ASTM. 2010. “Standard Specification for Aluminum-Alloy 6061-T6 Standard Structural Profiles,” B308/B308M-10, Annual
Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2010. “Standard Specification for Aluminum-Alloy Extruded Structural Pipe and Tube,” B429/B429M-10, Annual
Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
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2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR STRUCTURAL
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14-27
ASTM. 2011. “Standard Practice for Preparation of Use and Care Booklets for Vacuum Cleaners,” F486-01(2011), Annual
Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless,”
A53/A53M-12, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength,”
A325-12, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Castings, Iron-Chromium, Iron-Chromium-Nickel, Corrosion Resistant, for General
Industrial Use,” ASTM A743/A743M-12, Annual Book of ASTM Standards. American Society for Testing Materials, West
Conshohocken, PA.
ASTM. 2012. “Standard Specification for Castings, Steel and Alloy, Common Requirements, for General Industrial Use,”
A781/A781M-12b, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Aluminum and Aluminum-Alloy Drawn Seamless Tubes,” B210-12, Annual Book of
ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Aluminum and Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire,”
B211-12, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Aluminum and Aluminum-Alloy Seamless Pipe and Seamless Extruded Tube,”
B241/B241M-12, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2012. “Standard Specification for Dimensional Tolerance of Thermosetting Glass-Reinforced Plastic Pultruded
Shapes,” D3917-12, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2013. “Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products,” A123/A123M-13,
Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2013. “Standard Specification for Ferritic Malleable Iron Castings,” ASTM A27/A27M-13, Annual Book of ASTM
Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2013. “Standard Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and
Shapes,” A500/A500M-13, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken,
PA.
ASTM. 2013. “Standard Specification for Nonferrous Nuts for General Use,” F467-13, Annual Book of ASTM Standards.
American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2013. “Standard Specification for Stainless Steel Bolts, Hex Cap Screws, and Studs,” F593-13a, Annual Book of ASTM
Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for General Requirements for Rolled Structural Steel Bars, Plates, Shapes, and Sheet
Piling,” ASTM A6/A6M-14, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken,
PA.
ASTM. 2014. “Standard Specification for Alloy-Steel and Stainless Steel Bolting for High Temperature or High Pressure
Service and Other Special Purpose Applications,” A193/A193M-14a, Annual Book of ASTM Standards. American Society for
Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure or High Temperature
Service, or Both,” A194/A194M-14a, Annual Book of ASTM Standards. American Society for Testing Materials, West
Conshohocken, PA.
ASTM. 2014. “Standard Specification for Carbon Steel Bolts, Studs, and Threaded Rod 60000 PSI Tensile Strength,” A307-14,
Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
© 2022 by the American Association of State Highway and Transportation Officials.
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14-28
2022 INTERIM REVISIONS TO THE LRFD SPECIFICATIONS FOR STRUCTURAL
SUPPORTS FOR HIGHWAY SIGNS, LUMINAIRES, AND TRAFFIC SIGNALS
ASTM. 2014. “Standard Specification for Alloy-Steel and Stainless Steel Bolting for Low-Temperature Service,”
A320/A320M-14, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Structural Bolts, Alloy Steel, Heat Treated, 150 ksi Minimum Tensile Strength,”
A490-14a, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Hot-Formed Welded and Seamless Carbon Steel Structural Tubing,” A501/
A501M-14, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Ductile Iron Castings,” ASTM A536-84(2014), Annual Book of ASTM Standards.
American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Carbon and Alloy Steel Nuts,” A563-07a(2014), Annual Book of ASTM Standards.
American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Steel Tubes, Low-Carbon or High-Strength Low-Alloy, Tapered for Structural
Use,” A595/A595M-14, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Aluminum-Alloy Sand Castings,” B26/B26M-14, Annual Book of ASTM Standards.
American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Aluminum-Alloy Permanent Mold Castings,” B108/B108M-14, Annual Book of
ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate,” B209-14, Annual Book of ASTM
Standards. American Society for Testing Materials, West Conshohocken, PA.
ASTM. 2014. “Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes,”
B221-14, Annual Book of ASTM Standards. American Society for Testing Materials, West Conshohocken, PA.
AWC. 2012. National Design Specifications (NDS) for Wood Construction with Supplement: Design Values for Wood
Construction,” American Wood Council, Leesburg, VA.
AWPA. 2011. “User Specification for Treated Wood,” AWPA U1-11. American Wood Protection Association (formerly the
American Wood Preservers’ Association), Birmingham, AL.
AWPA. 2013. Book of Standards 2013. American Wood Protection Association (formerly the American Wood Preservers’
Association), Birmingham, AL.
AWS. 2014. ANSI/AWS D1.2/D1.2M:2014 Structural Welding Code—Aluminum. American Welding Society, Miami, FL.
AWS. 2010. Structural Welding Code—Steel, ANSI/AWS D1.1-10. American Welding Society, Miami, FL.
AWS. 2008. Structural Welding Code—Aluminum, ANSI/AWS Dl.2/D1.2M:2008. American Welding Society, Miami, FL.
Jirsa, J. O., N. T. Cichy, M. R. Calzadilla, W. H. Smart, M. P. Pavluvcik, and J. E. Breen. 1984. Strength and Behavior of Bolt
Installations Anchored in Concrete Piers, Report No. FHWA/TX-85/51+305-1F. Texas State Department of Highways and
Public Transportation, Austin, TX.
RCSC. 2004. Specification for Structural Joints Using ASTM A325 or A490 Bolts. Research Council on Structural
Connections, Chicago, IL.
Roy, S., Y. C. Park, R. Sause, J. W. Fisher, and E.J. Kaufmann. 2011. Cost Effective Connection Details for Highway Sign,
Luminaire and Traffic Signal Structures. NCHRP Web Only Document 176 (Final Report for NCHRP Project 10-70).
Transportation Research Board, National Research Council, Washington, DC.
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15-9
otherwise damaged. Hammering that will damage or distort
the members is prohibited. Bearing surfaces, faying
surfaces, and other surfaces to be in permanent contact shall
be cleaned before the members are assembled. Splices and
field connections shall have one quarter of the holes filled
with bolts and one quarter filled with cylindrical erection
pins before installing and tensioning bolts in the unfilled
holes.
Any field welding shall be performed in accordance
with the requirements of AWS D1.1-10 (AWS, 2010).
15.8.4—Misfits
The correction of minor misfits involving small
amounts of reaming, cutting, grinding, and chipping shall
be included in the Contractor’s scope of work and shall be
at the Contractor’s expense. Any errors in the shop
fabrication or deformation resulting from handling and
transporting may be cause for rejection, however.
The Contractor shall be responsible for all misfits,
errors, and damage, and shall make the necessary
corrections and replacements.
15.8.5—Bolted Connections
Parts shall be assembled, well pinned, and firmly drawn
together before drilling, reaming, or bolting. All joint
surfaces, including surfaces to be under bolt heads or nuts,
shall be free of dirt or other foreign material. Assemblies
shall be taken apart, if necessary, for the removal of burrs
and shavings.
Drifting done during assembling shall be limited to that
which brings the parts into position and shall not enlarge
holes or distort the metal.
Bolts used as fit-up bolts may be reused for the final
installation. If other fit-up bolts are used, they shall be of
the same nominal diameter as the final bolts, and
cylindrical erection pins shall be 0.03 in. larger.
15.9—ALUMINUM STRUCTURES
15.9.1—General
15.9.1
This Article describes the erection of aluminum
structures and structural aluminum portions of other
structures in accordance with these Specifications and the
contract documents.
Details of design which are permitted to be selected by
the Contractor shall conform to the current LRFD
Specifications for Structural Supports for Highway Signs,
Luminaires, and Traffic Signals and subsequent interim
specifications, and Owner requirements.
Information on erection of aluminum structures is given
in the Specification for Aluminum Structures, Chapter M.
The same requirements for fabrication also apply for work
done in the field.
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The scope of this Article is the erection of aluminum
structures and members. Fabrication performed during
construction shall also comply with the requirements of
Article 14.5.
15.9.2—Inspection
Structural aluminum components shall be inspected by
the Contractor at the job site upon delivery and after
erection.
15.9.3—Bolted Connections
Parts shall be firmly drawn together before bolting. All
joint surfaces, including surfaces to be under bolt heads or
nuts, shall be free of dirt or other foreign material.
Assemblies shall be taken apart, if necessary, for the removal
of burrs and shavings.
Drifting done during assembling shall be limited to that
which brings the parts into position and shall not enlarge
holes or distort the metal.
Bolt installation shall be in accordance with Article 15.7.
Stainless steel bolts used in primary connections shall
have single or double nuts unless otherwise specified in the
contract documents. Lock washers may be included.
Beveled washers shall be used where faying surfaces have a
slope of more than 1:20 with respect to a plane normal to
the bolt axis. A washer shall be provided under the turned
part. Bolts shall be installed to the torque as specified by
the bolt manufacturer.
Bearing surfaces and other surfaces to be in permanent
contact shall be cleaned before the members are assembled.
Stainless steel splice bolts are sometimes used in
aluminum structures for corrosion resistance. Since these
are not high-strength bolts, lock washers may be used.
Bolts should be installed to torque at values provided by the
bolt supplier.
15.9.4—Field Assembly
The parts shall be accurately assembled as specified in
the contract documents or erection drawings, and any
match-marks shall be followed. The material shall be
carefully handled so that no parts will be bent, broken, or
otherwise damaged. Hammering that will injure or distort
the members is prohibited. Bearing surfaces, faying
surfaces, and other surfaces to be in permanent contact shall
be cleaned before the members are assembled. Splices and
field connections shall have one quarter of the holes filled
with bolts and one quarter filled with cylindrical erection
pins before installing and tensioning bolts in the unfilled
holes.
Bolts used as fit-up bolts may be reused for the final
installation. If other fit-up bolts are used, they shall be of the
same nominal diameter as the final bolts, and cylindrical
erection pins shall be 0.03 in. larger.
15.9.5—Misfits
The correction of minor misfits involving small
amounts of reaming, cutting, grinding, and chipping shall
be included in the Contractor’s scope of work and shall be
at the Contractor’s expense. Any errors in the shop
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fabrication or deformation resulting from handling and
transporting may be cause for rejection, however.
The Contractor shall be responsible for all misfits,
errors, and damage, and shall make the necessary
corrections and replacements.
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15-10.1
15-10.2
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APPENDIX C:
ALTERNATIVE METHODS FOR FATIGUE DESIGN
C.1—SCOPE
Section 11, Fatigue Design, provides a methodology for fatigue design of support structures using nominal stress-based
classifications of typical fatigue sensitive connection details as presented in Table 11.9.3.1-1. This appendix provides an
alternate local stress-based methodology for fatigue design, and an experimental procedure for establishing fatigue resistance of
connections in support structures. While the methods may be applied to connections that are tabulated in Table 11.9.3.1-1, it is
expected that the methods will be more useful for establishing the fatigue resistance of new connection details that are not listed
in Table 11.9.3.1-1. Accordingly, these connection details should be designed for infinite life.
The analytical and experimental protocols provided in the following articles were verified on connections evaluated under
NCHRP Web Only Document 176 (Roy et al., 2011) and are listed in Table C.11-1 of that report. Fatigue resistance of
connections as determined by the local stress-based methodology should be verified experimentally. If fatigue resistance is
determined by local stress-based methodology for connection details listed in Table 11.9.3.1-2, but with parameters outside the
specified range of applicability, experimental verification is not necessary provided the fatigue stress concentration factors
determined by the local stress-based methodology are less than those obtained for the limiting parameters of the specified range
of application. In such cases, the finite element model must be benchmarked against the respective connection detail listed in
Table C11.9.3.1-1 with respect to the tabulated fatigue stress concentration factors.
C.2—NOTATION
Fu
Fy
N
r
Smin
Sr
t
(∆f)l
(∆F)l
=
=
=
=
=
=
=
=
=
ultimate strength of material (ksi) (C.3.2.2)
yield strength of material (ksi) (C.3.2.2)
number of wind load induced stress cycles expected during the life time of the structure (C.3.1.2)
outer radius of round tube or half the outer flat-to-flat distance of multisided tube (in.) (C.3.1.1) (C4.1.1)
minimum stress in a stress-time history (ksi) (C.4)
stress range in a stress-time history (ksi) (C.4)
thickness of tube (in.) (C.3.1.1) (C4.1.1)
wind induced local stress at weld toe (ksi) (C.3) (C.3.1.2)
local fatigue resistance (ksi) (C.3) (C.3.2.2)
C.3—LOCAL STRESS-BASED DESIGN
As an alternative to the nominal stress-based design of Article 11.5.1, welded connections in support structures may be
designed using local stresses obtained from finite element (FE) analyses. The FE analyses may be carried out using any available
program that has been validated.
For local stress-based design, Equation 11.5-1 is rewritten as:
( ∆f )l ≤ ( ∆F )l
(C.3-1)
where:
(∆f)l = wind induced local stress at the weld toe as defined in Articles C.3.1.1 and C.3.2.1
(∆F)l = local fatigue resistance as determined in Articles C.3.1.2 and C.3.2.2.
It should be noted that the local stress-based method for finite life is only applicable to fatigue design of tubular
connections, including tube-to-transverse plate and tube-to-tube connections, where the geometric (out-of-plane distortion
induced) stress concentration affects the fatigue performance of the connection significantly. Further discussion of geometric
(out-of-plane distortion induced) stress concentration can be found in Article 11.9.3.1.
For other details that are primarily subjected to in-plane stresses, a nominal stress-based design methodology should be
sufficient with due consideration to the magnified nominal stress at a detail, if appropriate. As an example, see the discussion in
Article 11.9.3.1 for hand-hole details. Literature is available on stress concentration factors for various generic details and FE
analysis may be used to supplement the literature.
The local stress-based method for finite life evalution is calibrated against fatigue cracking at the weld toe. For infinite life
design, however, fatigue crack initiation and crack propagation should be inhibited. Because of this, the local stress-based
C-1
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C-2
method for finite life evaluation is not applicable to infinite life design. Separate methodologies should be used for finite life
evaluation and infinite life design as provided in Articles C.3.1 and C.3.2.
C.3.1—Assessment of Finite Life
The remaining fatigue life of existing structures may be assessed based on a finite life.
C.3.1.1—Determination of Local Stress
The local stress in welded connections that can experience fatigue cracking at the weld toe shall be determined from detailed
linear FE analyses of a three-dimensional (3-D) model of the connection. The nominal weld geometry shall be included in the
model. Because of the steep geometric stress gradient associated with the connection geometry, a 3-D FE model of the
connection should be used. In thin tubular structures, the weld acts like a tiny stiffener and influences the geometric stress
concentration. To achieve proper local stiffness and improved stress prediction, the nominal weld geometry should be modeled.
The FE model shall assume linear material properties.
The model shall be large enough such that the calculated results are not significantly affected by the assumptions made for
modeling the boundary conditions and the application of loads. If the model is too large to develop a mesh at the required
refinement, an analysis of a refined submodel driven by the analysis results of a less refined global model shall be performed.
Two dimensional (2-D) shell elements may be used for modeling other parts of the support structures away from the connections
to reduce computation costs.
Reduced integration 20-node solid isoparametric elements shall be used for modeling the connection. Twenty-node solid
hexahedron elements of isoparametric formulation are standard elements used for stress analysis. These elements, also known as
serendipity elements, assume an incomplete quadratic polynomial as displacement and geometric shape functions resulting in
linear strain and stress distributions. The element stiffness matrix is formed by assuming a reduced number of Gauss integration
points for better correlation of FE results with a true solution. In tubes, a mesh size of t × t shall be used for at least three rows of
elements in front of the weld toe, where t is the thickness of the tube. At least two elements shall be used in the thickness
direction. To avoid numerical instabilities and inaccuracy in solutions, the elements should be well shaped and proportioned. All
elements in the model shall be limited to a maximum aspect ratio of 1:4. The elements shall have corner angles between 30 and
150 degrees (Figure C.3.1.1-1).
Figure C.3.1.1-1—Typical FE Mesh for Determination of Local Stress for Finite Life Assessment
The maximum (tensile) principal stress on the tube surface at 0.1
 r  t  ahead of weld toe shall be used as the local stress
for fatigue design, where r and t are the outer radius and thickness of the tube respectively. For multisided cross sections, half of
the outer flat-to-flat distance shall be substituted for r.
When the weld toe is modeled with zero radius, the stress solution at the weld toe approaches infinity as the element size
decreases to zero. However, the effect of the connection geometry on the stress beyond the influence of the weld toe is of
interest. The scatter associated with weld toe micro-discontinuities is included by using experimentally obtained S-N curves. It is
well known from theory of thin tubes that the geometric stresses associated with secondary out-of-plane bending deformation at
tube boundaries—arising from the need to maintain compatibility at the connections—is a function of the tube geometric
parameter  r  t  . The coefficient to this parameter was determined empirically.
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