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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

42

Reduced Beam Section (RBS) Connection

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End Plate Moment Connections

Unstiffened Stiffened Stiffened4-Bolt: 4E 4-Bolt: 4ES 8-Bolt: 8ES

44

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

60

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

66

End-Plate Moment Connections

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For High Seismicand Wind

Applications

AISC Design Guide 4

68

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

70

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

78

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

98

Welded Unreinforced Flange- Welded Web(WUF-W)

Erection Bolts

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Farid_rezaeian@yahoo.comAlireza.rezaeian@kiau.ac.irLink d. Alireza rezaeian

با تشکر از توجه حضار گرامی

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