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1994 Northridge Earthquake
Widespread failure ofwelded flange - boltedweb moment connections
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Damage Observations:Steel MomentConnections
Backup Bar
Beam Flange
Column FlangeStiffener
Weld Access Hole
Pre-NorthridgeWelded Flange – Bolted Web Moment Connection
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StressConcentrations:
• Weld accesshole
• Shear in flange
• Inadequateflexuralparticipation ofweb connection
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Improved Weld AccessHole
See Figure 11-1 in the 2005AISC Seismic Provisions fordimensions and finishrequirements
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ANSI/ASIC 358-10
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Refers to
Relies on
ANSI/AISC 358 Prequalified Connectionsfor Special and Intermediate Steel Moment
Frames for Seismic Applications
SOME SPECIFICS
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• Reduced Beam Section Connection• Bolted Unstiffened and Stiffened Extended End-
Plate Moment Connections• Welded Unreinforced Flange – Welded Web
• Bolted Flange Plate• Kaiser Bolted Bracket
• ConXtech Moment Connection
The Double Tee Stub is currently being balloted.
Connections PrequalifiedIncluding Supplement No. 1
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Reduced Beam Section (RBS) Connection
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End Plate Moment Connections
Unstiffened Stiffened Stiffened4-Bolt: 4E 4-Bolt: 4ES 8-Bolt: 8ES
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Bolted Flange Plate Connection
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Welded Unreinforced Flange – Welded WebConnection
• Provisions apply only to the prequalifiedconnections.
• Beam and Column cross-section limitationsbased on specific test matrices
• Rolled and Built-up Members permitted• Specific welding requirements for built-up
members
Prequalified Unique Requirements
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Specific Prequalified Connections
Reduced BeamSection (RBS)
Reduced Beam Section (RBS)
RBS Concept:
• Trim Beam FlangesNear Connection
• Reduce Moment atConnection
• Force Plastic HingeAway from Connection
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Reduced Beam Section (RBS)
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Connection was Prequalified at UT - Austin
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Whitewashed Connection Prior to Testing
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Whitewashed Connection Prior to Testing
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Connection at 0.02 radian.
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Connection at 0.02 radian.
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Connection at 0.03 radian.
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Connection at 0.04 radian.
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Conformance Results
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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-flangeUp 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
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Beam flange welds: - CJP groove welds- Treat welds as Demand Critical- Remove bottom flange backing andprovide reinforcing fillet weld
- Leave top flange backing in-place; filletweld backing to column flange
- Remove weld tabs at top and bottom flanges
Beam web to column connection:- Use fully welded web connection (CJP weldbetween beam web and column flange)
See ANSI/AISC 358 for additional requirements (continuity plates,beam lateral bracing, RBS cut finish, etc.)
Reduced Beam Section (RBS)
Prequalification Requirements for RBS in SMF
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Reduced Section Geometry
fb0.75
61
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.
Reduced Beam Section (RBS)
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Lateral Brace Violates Protected Zone
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Lateral Brace Violates Protected Zone
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End-Plate Moment Connections
Unstiffened Stiffened Stiffened4-Bolt: 4E 4-Bolt: 4ES 8-Bolt: 8ES
Specific Prequalified Connections
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End-Plate Concept:
• No Field Welding• Simple Erection• Connection is Stronger than
Beam
• Special welding requirements• Concrete slab requirements
End-Plate Moment Connections
Connections were prequalified at Virginia Tech
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End-Plate Moment Connections
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For High Seismicand Wind
Applications
AISC Design Guide 4
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Weld access hole not permitted because ofruptures that occurred during testing.
Rupture
End-Plate Welding
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Weld access hole not permitted because ofruptures that occurred during testing.
Rupture
End-Plate Welding
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Recommended welding procedure:
• No weld access holes• Surface Preparation:
– All surfaces ground clean– Flanges beveled 45º full depth
• Minimum root opening
45°
45°
Typical Beam
End-Plate Welding
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Recommended welding procedure:Welding Sequence:1. Fillet welds on both sides of web
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
Backgouge
1
2
3
3
End-Plate Welding
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• 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
Detailing Requirements
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• Length of Stiffener
Lst = hst / tan 30º
30°±
1"±
Lst
1"±
hst
4ES and 8ES Stiffener Detailing
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8-Bolt Stiffened Moment End-Plate, 8ES
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8-Bolt Stiffened Moment End-Plate, 8ES
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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
End-Plate Moment Connections
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Rig
id L
ink
Lateral SupportTyp.
CompositeSlab
Pin Support
Rig
id L
ink
W24x68 W24x68
Test Column
ReactionFrame
ActuatorTest Frame
W14
x257
Connection Test with Concrete Slab
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Test 1 with Concrete Slab
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Test 1 with Concrete Slab
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Premature Bolt Rupture
Test 1 with Concrete Slab
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W27x84 (A992)NORTH
W27x84 (A992)SOUTH
W14x311 (A
36)
11'-0" 11'-0"
7'-0"
10'-0" 10'-0"
7'-0"
7'-2
"6'-11
"
PAPPLIED
LATERAL SUPPORT
W14X22FILLER BEAM
PIN SUPPORT
PIN
SU
PP
OR
T
PIN
SU
PP
OR
T
1 1/4" END PLATE (A36)W/ 1 1/8"Ø A325 BOLTS
5" COMPOSITE SLAB(3" COVER ON 2"COMPOSITE METAL DECK)
10'-0" 10'-0"
3'-0
"3'-0
"
1'-11 1/4"3'-4 1/2" 4'-8 1/4"
NO STUDSHINGE ZONE
EN
D O
FS
TIF
FE
NE
R
1'-11 1/4"4'-8 1/4" 3'-4 1/2"
NO STUDSHINGE ZONE
EN
D O
FS
TIF
FE
NE
R1/2" MIN. GAPFORMED W/ NEOPRENEFILLED 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.
DOUBLER PLATE(FAR SIDE)
Test 2 with Concrete Slab
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Test 2 with Concrete Slab
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-250
-200
-150
-100
-50
0
50
100
150
200
250
-0.05 -0.04 -0.03 -0.02 -0.01 0.00 0.01 0.02 0.03 0.04 0.05
Total Rotation (rad.)
Col
umn
Tip
Load
(kip
s)
-250
-200
-150
-100
-50
0
50
100
150
200
250
-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06
Beam Rotation (rad.)
Col
umn
Tip
Load
(kip
s)
Column Tip Load Column Tip Loadvs . vs.
Total Rotation Beam Rotation
Test 2 with Concrete Slab
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Requirement for All Prequalified BoltedConnections
Compressible expansion joint material, atleast 1 in. thick, shall be installed to isolatethe column/connection from the concrete
slab.
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Bolted FlangePlate (BFP)
Specific Prequalified Connections
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Bolted Flange Plate (BFP)
BFP Concept:
•Shop Welded/Field Bolted•A325 or A490 bolts
•Top and bottom flangeplates must be identical
•Hinge at end of flangeplates
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Prequalified atU. of California
at San Diego
Bolted Flange Plate (BFP)
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Bolted Flange Plate (BFP)
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Bolted Flange Plate (BFP)
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Bolted Flange Plate (BFP)
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Bolted Flange Plate (BFP)
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Bolted Flange Plate (BFP)
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Bolted Flange Plate (BFP)
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Bolted Flange Plate (BFP)
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FractureLocation Close-up of Fracture
Location
Bolted Flange Plate (BFP)
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Welded UnreinforcedFlange - Welded Web
(WUF–W)
Specific Prequalified Connections
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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
Welded Unreinforced Flange- Welded Web(WUF-W)
connection
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Welded Unreinforced Flange- Welded Web(WUF-W)
Erection Bolts
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[email protected]@kiau.ac.irLink d. Alireza rezaeian
با تشکر از توجه حضار گرامی
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