Prequalification of
Moment Connections
Presented by
Thomas M. Murray, Ph.D., P.E.
Department of Civil and Environmental Engineering
Virginia Tech, Blacksburg, Virginia
thmurray@vt.edu
28 October 2011
1
HIGH SEISMIC MOMENT
CONNECTIONS
• All High Seismic Moment Connections
must be Prequalified according to
ANSI/AISC 358.
• ANSI/AISC 358-10 Prequalified
Connections for Special and Intermediate
Steel Moment Frames for Seismic
Applications
2
Why is Prequalification Required?
Because of connection failures during
the Northridge, California Earthquake
on January 17, 1994.
3
ANSI/ASIC 358-10
4
Refers to
Relies on
5
AISC 341 Seismic – SMF Connections
Beam-to-column connections shall satisfy the
following Section 9.2a requirements:
•
An interstory drift angle of at least 0.04 radians.
•
The measured flexural resistance shall equal at
least 0.80 Mp of the connected beam at an 0.04
radians.
6
AISC 341 Seismic – SMF Connections
Requirements of Sect. 9.2a are to be satisfied
by one of the following methods:
1. Conduct qualifying cyclic tests in accordance with
Appendix S.
• Tests conducted specifically for a project
or
• Tests reported in the literature representative of
project conditions.
7
AISC 341 Seismic – SMF Connections
Project Specific Cyclic Test
Flush Moment End-Plate w/
Sixteen 1–½ in (75 mm)
A490 Bolts
8
AISC 341 Seismic – SMF Connections
2. Use connections prequalified for SMF in
accordance with Appendix P
•
•
Use connection prequalified by a review panel
that is approved by the Authority Having
Jurisdiction.
or
Use connections prequalified by the AISC
Connection Prequalification Review Panel
(CPRP) in Standard ANSI/AISC 358
9
Seismic App. S Qualifying Cyclic Tests
Permitted Test Subassemblages:
Actuator
M ount
Single Beam, Single Column
without a Concrete Slab
Lateral
Brace
Points
Actuator
Load Cell
Test Column
Test Beam
Reaction
Floor
Reaction
Floor
Reaction
Floor
10
Seismic App. S Qualifying Cyclic Tests
Two beams, single column w/ or w/o concrete slab
Actuator
Test Frame
Test Column
Lateral Support
Typ.
Composite
Slab
W14x257
Rigid Link
Pin Support
Rigid Link
W24x68
W24x68
Reaction
Frame
11
Seismic App. S Qualifying Cyclic Tests
Loading Protocol:
1
0.00375
6
2
0.005
6
3
0.0075
6
4
0.01
4
5
0.015
2
6
0.02
2
7
0.03
2
Continue with increments in q of 0.01, and
perform two cycles at each step
0.06
0.05
0.04
0.03
0.02
0.01
0
Angle
Number of
Loading
Cycles
Interstory Drift
Interstory
Drift A ngle, q
(rad)
Load Step
Number
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
6
6
6
4
2 2 2 2 2
Number of cycles
Notes: Quasi-static testing is permitted.
There is not a required number of tests.
12
Seismic App. S Qualifying Cyclic Tests
Quasi static test conducted at Virginia Tech
13
Seismic App. S Qualifying Cyclic Tests
Interior subassemblage test at UT-Austin
14
Seismic App. S Qualifying Cyclic Tests
Interior subassemblage test with concrete slab
15
Seismic App. S Qualifying Cyclic Tests
Beam Moment at Face of Column (in-kips)
40000
M 0.04 0.8 M p
30000
0.8 Mp
20000
10000
0
-10000
-20000
- 0.8 Mp
-30000
-40000
-0.08
M 0.04 0.8 M p
-0.06
-0.04
-0.02
0
0.02
Interstory Drift Angle (rad)
0.04
0.06
0.08
16
Seismic App. S Qualifying Cyclic Tests
Dynamic test conducted at UC San Diego
17
ANSI/AISC 358 Prequalified Connections
for Special and Intermediate Steel Moment
Frames for Seismic Applications
SOME SPECIFICS
18
Connections Prequalified
Including Supplement No. 1
• Reduced Beam Section Connection
• Bolted Unstiffened and Stiffened Extended EndPlate Moment Connections
• Welded Unreinforced Flange – Welded Web
• Bolted Flange Plate
• Kaiser Bolted Bracket
• ConXtech Moment Connection
The Double Tee Stub is currently being balloted.
19
Reduced Beam Section (RBS) Connection
20
End Plate Moment Connections
Unstiffened
4-Bolt: 4E
Stiffened
4-Bolt: 4ES
Stiffened
8-Bolt: 8ES
21
Bolted Flange Plate Connection
22
Welded Unreinforced Flange – Welded Web
Connection
23
Kaiser Bolted Bracket Connection
24
ConXTech Moment Connection
25
Double Tee Moment Connection
26
Prequalified Unique Requirements
•
•
•
•
Provisions apply only to the prequalified
connections.
Beam and Column cross-section limitations
based on specific test matrices
Rolled and Built-up Members permitted
Specific welding requirements for built-up
members
27
Prequalified Unique Requirements
•
•
•
Probable maximum moment at hinge
specified
Plastic hinge location specified for each
connection
Resistance Factors differ from AISC
Specification and Seismic Specification
28
Probable Maximum Moment at Hinge
Based upon connecting beam strength:
Mpr = Cpr Ry Fy Zx
where:
Mpr = probable maximum beam moment
Ry = 1.1 for Fy = 50 ksi
Zx = plastic section modulus of beam
29
Probable Maximum Moment at Hinge
 Fy  Fu 
  1.2
Cpr  

2
F
y


where:
Fy = yield strength
Fu = tensile strength
For A992 Fy = 50 ksi, CprRy = 1.1 x 1.15
= 1.27
Mpr = 1.27 Fy Zx or 27% increase
30
Connection Design Moment
Plastic
Hinge
Plastic
Hinge
L’ = distance between plastic hinges
Sh
Sh
L = distance between centerline of columns
Sh is specified for each prequalified connection.
31
Connection Design Moment
Plastic
Hinge
Vu Mpr
Sh
Mf = Mpr + Vu Sh
32
Connection Design Moment
The connection design moment is the moment
at the face of the column:
Mf = Mpr + Vu Sh
where:
Mpr = probable maximum beam moment
Vu = max. shear at the end of the beam
= 2Mpr/L’ + wuL’/2
Sh = distance from face of the column
to plastic hinge location
33
Resistance Factors
Different resistance factors in 358 Prequalified:
Specification and Ductile Limit States
d = 0.9
Seismic:
Non-Ductile Limit State n = 0.75
Prequalified:
Ductile Limit States
d = 1.0
Non-Ductile Limit States n = 0.9
34
Resistance Factors
REASON:
Specification and Seismic limit states represent max.
expected under strength, i.e. d = 0.9 and n = 0.75.
Whereas, Mpr = Cpr Ry Fy Zx = 1.27 Fy Zx, represents
the maximum expected over strength including some
strain hardening.
If both are used, very conservative designs result.
Therefore, the Prequalified resistance factors were
increased to d = 1.0 and n = 0.90, but only for limit
states included in the Prequalified Standard.
35
Specific Prequalified Connections
Reduced Beam
Section (RBS)
36
Reduced Beam Section (RBS)
RBS Concept:
•
Trim Beam Flanges
Near Connection
•
Reduce Moment at
Connection
•
Force Plastic Hinge
Away from Connection
37
Reduced Beam Section (RBS)
38
Connection was Prequalified at UT - Austin
39
Whitewashed Connection Prior to Testing
40
Whitewashed Connection Prior to Testing
41
Connection at q  0.02 radian.
42
Connection at q  0.02 radian.
43
Connection at q  0.03 radian.
44
Connection at q  0.04 radian.
45
Conformance Results
46
Reduced Beam Section (RBS)
Prequalification Requirements for RBS in SMF
• Beam depth:
Up to W36
• Beam weight:
Up to 300 lb/ft
• Column depth:
Up to W36 for wide-flange
Up to 24-inches for box columns
• Beam connected to column flange
(connections to column web not prequalified)
• RBS shape:
Circular
• RBS dimensions:
Per specified design procedure
47
Reduced Beam Section (RBS)
Prequalification Requirements for RBS in SMF
Beam flange welds: - CJP groove welds
- Treat welds as Demand Critical
- Remove bottom flange backing and
provide reinforcing fillet weld
- Leave top flange backing in-place; fillet
weld backing to column flange
- Remove weld tabs at top and bottom flanges
Beam web to column connection:
- Use fully welded web connection (CJP weld
between beam web and column flange)
See ANSI/AISC 358 for additional requirements (continuity plates,
beam lateral bracing, RBS cut finish, etc.)
48
Reduced Beam Section (RBS)
Reduced Section Geometry
0.5bf < a < 0.75bf
0.5d < b < 0.85d
0.1bf < c < 0.25bf
49
Reduced Beam Section (RBS)
Protected Zone
No Shear Studs.
No welded, bolted, screwed or shot-in attachments for
perimeter edge angles, exterior facades, partitions,
duct work, piping or other construction.
Decking arc-spot welds are permitted.
50
Lateral Brace Violates Protected Zone
51
Lateral Brace Violates Protected Zone
52
Specific Prequalified Connections
End-Plate Moment Connections
Unstiffened
4-Bolt: 4E
Stiffened
4-Bolt: 4ES
Stiffened
8-Bolt: 8ES
53
End-Plate Moment Connections
End-Plate Concept:
•
•
•
No Field Welding
•
•
Special welding requirements
Simple Erection
Connection is Stronger than
Beam
Concrete slab requirements
Connections were prequalified at Virginia Tech
54
End-Plate Moment Connections
55
AISC Design Guide 4
For High Seismic
and Wind
Applications
56
Design Methodology
• Basic Philosophy
–
–
–
–
Strong column
Strong connection (Thick Plate)
Weak connecting beam or girder
Reduced resistance factors
• Source of inelastic behavior
 Connecting beam or girder
57
Design Considerations
•
•
•
•
•
Required connection design moment
Connection strength
Welding procedure
Detailing
Column side limit states
58
Connection Design Moment
Mf = Mpr + Vu Sh
Sh = min.[d/2, 3bbf ] from face of column or
end of stiffener if one exits.
59
Connection Strength
• Design connection bolts to resist Mf
– Thick Plate so Prying forces are negligible
Mf < Mnp
Mnp
with  = 0.9
2(Pt)
2(Pt )
do
d1
Pt = tensile strength
of bolt
60
Connection Strength
• To avoid the formation of substantial bolt
prying forces the end-plate strength must
satisfy the following:
Mpl > 1.11 Mnp
Required end-plate thickness from yield-line
analysis is then:
t p  M pl /(Fyp Y)
with  = 1.0
where Y = yield-line parameter
61
Connection Strength
Example: 4E
Mnp
2(Pt )
2(Pt )
do
d1
Mn  Mnp  2(Pt )(do  d1 )
62
Connection Strength
bp
Example: 4E
Mpl = Fpy tp2 Y
where:
Fpy = end-plate material
yield stress
tp = end-plate thickness
g
pt
pf
pf
s
d
63
Connection Strength
bp
g
Example: 4E
Required end-plate thickness
pt
t p  M pl /(Fyp Y)
where
  1.0
pf
pf
s
d
 bp  1 1 
 2  bp  h 1 
Y  h  p t      pf  s      
 g  2  pf 2 
 2  pf s 
1
s  bpg
2
64
Connection Strength
bp
Example: 8Es
g
ts
pb
Design process is the same as
for the 4ES configuration.
pf
pf
pb
d
65
End-Plate Welding
Weld access hole not permitted because of
ruptures that occurred during testing.
Rupture
66
End-Plate Welding
Weld access hole not permitted because of
ruptures that occurred during testing.
Rupture
67
End-Plate Welding
Recommended welding procedure:
• No weld access holes
• Surface Preparation:
– All surfaces ground clean
– Flanges beveled 45º full depth
• Minimum root opening
45°
Typical Beam
45°
68
End-Plate Welding
Recommended welding procedure:
Welding Sequence:
1. Fillet welds on both sides of web
1
installed.
2. Fillet welds on inside of flanges
installed.
3. Flange groove weld root
backgouged and flange groove
welds installed.
Note: Welds over webs are not CJP.
Backgouge
3
2
Backgouge
3
69
Detailing Requirements
• Effective end-plate width in calculations
– Beam flange width + 1 in.
• Bolt gage < beam flange width
• Bolt spacing and pitch
– Provide adequate tightening clearances
• Finger shims
– Used to correct beam length variations
70
4ES and 8ES Stiffener Detailing
1"±
• Length of Stiffener
30°±
hst
1"±
Lst = hst / tan 30º
Lst
71
4ES and 8ES Stiffener Detailing
• End-plate stiffener thickness
– Stiffener should have same strength as the
beam web
ts = (Fyb / Fys) twb
• Stiffener Welds
– Full penetration groove welds are
recommended.
– Designed for one-half of the flange force
72
Other Limit States to Consider
• Column Side
–
–
–
–
–
–
Flange bending
Local web yielding
Web crippling
Compression buckling of web
Continuity plates
Panel zone
• See AISC Design Guides 4, 16, and 13
73
8-Bolt Stiffened Moment End-Plate, 8ES
74
8-Bolt Stiffened Moment End-Plate, 8ES
75
25000
25000
20000
20000
Moment at Column Centerline (in-kips)
Moment at Column Centerline (in-kips)
8-Bolt Stiffened Moment End-Plate, 8ES
15000
10000
5000
0
-5000
-10000
-15000
10000
5000
0
-5000
-10000
-15000
-20000
-20000
-25000
-0.08
15000
-0.06
-0.04
-0.02
0.00
0.02
0.04
Total Rotation (rad)
(a) Moment vs Total Rotation
0.06
0.08
-25000
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
Total Plastic Rotation (rad)
(b) Moment vs Plastic Rotation
Moment at Column Centerline Moment at Column Centerline
vs
vs
Total Rotation
Plastic Rotation
8ES-1.25-1.75-30
76
End-Plate Moment Connections
Prequalification Requirements:
• Beam depth:
Min. and max. in Table 6.1
• Beam weight:
No limit
• Column depth:
Up to W36
• Beam connected to column flange
(connections to column web not prequalified)
• Bolts:
A325 or A490
• Finger Shims:
Permitted
77
Connection Test with Concrete Slab
Actuator
Test Frame
Test Column
Lateral Support
Typ.
Composite
Slab
W14x257
Rigid Link
Pin Support
Rigid Link
W24x68
W24x68
Reaction
Frame
78
Test 1 with Concrete Slab
79
Test 1 with Concrete Slab
80
Test 1 with Concrete Slab
Premature Bolt Rupture
81
Test 2 with Concrete Slab
1'-11 1/4"
3'-4 1/2"
NO STUDS
HINGE ZONE
4'-8 1/4"
3'-0"
END OF
STIFFENER
1'-11 1/4"
3'-4 1/2"
NO STUDS
HINGE ZONE
END OF
STIFFENER
4'-8 1/4"
10'-0"
3'-0"
10'-0"
1/2" MIN. GAP
FORMED W/ NEOPRENE
FILLED W/ FOAM INSUL.
5" COMPOSITE SLAB
(3" COVER ON 2 COMPOSITE METAL DECK)
REINFORCED W/ 4x4-W2.9xW2.9 WWF
3/4"Ø X 4" SHEAR STUDS
@ 1'-0" MAX.
PAPPLIED
36)
82
Test 2 with Concrete Slab
83
250
250
200
200
150
150
Column Tip Load (kips)
Column Tip Load (kips)
Test 2 with Concrete Slab
100
50
0
-50
-100
100
50
0
-50
-100
-150
-150
-200
-200
-250
-0.05 -0.04 -0.03 -0.02 -0.01 0.00
0.01
0.02
0.03
Total Rotation (rad.)
Column Tip Load
vs .
Total Rotation
0.04
0.05
-250
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
Beam Rotation (rad.)
Column Tip Load
vs.
Beam Rotation
84
Requirement for All Prequalified Bolted
Connections
Compressible expansion joint material, at
least 1 in. thick, shall be installed to isolate
the column/connection from the concrete
slab.
85
Specific Prequalified Connections
Bolted Flange
Plate (BFP)
86
Bolted Flange Plate (BFP)
BFP Concept:
•
•
•
Shop Welded/Field Bolted
•
Hinge at end of flange
plates
A325 or A490 bolts
Top and bottom flange
plates must be identical
87
Bolted Flange Plate (BFP)
Prequalified at
U. of California
at San Diego
88
Bolted Flange Plate (BFP)
89
Bolted Flange Plate (BFP)
90
Bolted Flange Plate (BFP)
91
Bolted Flange Plate (BFP)
92
Bolted Flange Plate (BFP)
93
Bolted Flange Plate (BFP)
94
Bolted Flange Plate (BFP)
95
Bolted Flange Plate (BFP)
Fracture
Location
Close-up of Fracture
Location
96
Specific Prequalified Connections
Welded Unreinforced
Flange - Welded Web
(WUF–W)
97
Welded Unreinforced Flange- Welded Web
(WUF-W)
WUF-W Concept:
•
•
•
•
•
Full beam strength
Shop welded single plate
with bolts for erection
Field welded beam flange
to column flange
Field welded single plate to
beam web
Similar to pre-Northridge connection
98
Welded Unreinforced Flange- Welded Web
(WUF-W)
Erection Bolts
99
Specific Prequalified Connections
Proprietary
Kaiser Bolted
Bracket (KBB)
Flange Welded
Flange Bolted
100
Kaiser Bolted Bracket (KBB)
KBB Concept:
•
•
•
•
•
•
Cast steel bracket
Welded or bolted to
beam flanges
Bolted to column flange
Shop welded single plate web connection
Pretensioned 1-3/8 or 1-1/2 in. diameter A490
or A354 bracket bolts
Used for retrofiting
101
Kaiser Bolted Bracket (KBB)
102
Specific Prequalified Connections
Proprietary
ConXtech®
CONXLTM
Moment
Connection
103
ConXtech® CONXLTM Moment Connection
104
ConXtech® CONXLTM Moment Connection
Concept:
• Biaxial
• 16 in. square HSS or
built-up box concrete
filled columns
• Shop welded forged steel
fittings on beams and columns
• Field bolted with 1-1/2 in. A574 bolts
• All beams must be of same nominal depth
• Extremely fast erection
105
ConXtech® CONXLTM Moment Connection
106
ConXtech® CONXLTM Moment Connection
107
ConXtech® CONXLTM Moment Connection
108
Thank You!!
109