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7/28/2019 33.Thomas Murray-Conexiones Edificios de Acero 1

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Prequalification of

Moment Connections

Presented by

Thomas M. Murray, Ph.D., P.E.

Department of Civil and Environmental Engineering

Virginia Tech, Blacksburg, Virginia

[email protected]

28 October 2011


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HIGH SEISMIC MOMENT

CONNECTIONS

All High Seismic Moment Connectionsmust be Prequalified according to

ANSI/AISC 358. ANSI/AISC 358-10 PrequalifiedConnections for Special and I ntermediate

Steel Moment F rames for Seismic

Applications


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Why is Prequalification Required?

Because of connection failures during

the Northridge, California Earthquakeon January 17, 1994.


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ANSI/ASIC 358-10


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Refers to

Relies on


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Beam-to-column connections shall satisfy thefollowing Section 9.2a requirements:

An interstory drift angle of at least 0.04 radians.

The measured f lexural resistanceshall equal atleast 0.80 Mpof the connected beam at an 0.04radians.

AISC 341 SeismicSMF Connections


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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.



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Project Specific Cyclic Test

Flush Moment End-Plate w/

Sixteen 1 in (75 mm)

A490 Bolts



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2.Use connections prequalifiedfor SMF inaccordance 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



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Permitted Test Subassemblages:

SeismicApp. S Qualifying Cyclic Tests

TestColumn

FloorReaction Reaction

FloorFloorReaction

Brace

Load Cell

Test Beam

Points

Mount

Actuator

Actuator

Lateral

Single Beam, Single Column

without a Concrete Slab


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Two beams, single column w/ or w/o concrete slab

Rigid

Link

Lateral SupportTyp. CompositeSlab

Pin SupportRigi

dLink

W24x68 W24x68

Test Column

Reaction

Frame

ActuatorTest Frame

W

14x257



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Loading Protocol:

Load StepNumber

InterstoryDrift Angle, q

(rad)

Number ofLoadingCycles

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 qof 0.01, andperform two cycles at each step

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

Number of cycles

InterstoryDrift

Angle

6 6 6 4 2 2 2 2 2

Notes: Quasi-static testing is permitted.

There is not a required number of tests.



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Quasi static test conducted at Virginia Tech



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Interior subassemblage test at UT-Austin



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Interior subassemblage test with concrete slab



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0.8 Mp

- 0.8 Mp

M0.040.8 Mp

M0.040.8 Mp



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Dynamic test conducted at UC San Diego



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ANSI/AISC 358 Prequalif ied Connections

for Special and I ntermediate 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 Prequalified

Including Supplement No. 1


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Reduced Beam Section (RBS) Connection


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End Plate Moment Connections

Unstiffened Stiffened Stiffened

4-Bolt: 4E 4-Bolt: 4ES 8-Bolt: 8ES


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Bolted Flange Plate Connection


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Welded Unreinforced FlangeWelded Web

Connection


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Kaiser Bolted Bracket Connection


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ConXTech Moment Connection


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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-upmembers

PrequalifiedUnique Requirements


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Probable maximum moment at hingespecified

Plastic hinge location specified for eachconnection

Resistance Factors differ from AISCSpecificationand Seismic Specif ication

PrequalifiedUnique Requirements


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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

Probable Maximum Moment at Hinge

i i


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Probable Maximum Moment at Hinge

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

2.1F2

FFC

y

uy

pr


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Connection Design Moment

Sh is specified for each prequalified connection.

Plastic

Hinge

Plastic

Hinge

L = distance between plastic hinges

L = distance between centerline of columns

Sh

Sh

C i i


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Mf= Mpr + Vu Sh

Plastic

Hinge

Sh

Vu Mpr

C i D i M


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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/2Sh = distance from face of the column

to plastic hinge location

R i F


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Resistance Factors

Different resistance factors in 358 Prequalified:

Specif ication andDuctile Limit States d = 0.9Seismic: Non-Ductile Limit State n = 0.75Prequalified: Ductile Limit States d = 1.0

Non-Ductile Limit States n = 0.9

R i t F t


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Resistance Factors

REASON:

Specificationand Seismiclimit 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 somestrain hardening.

If both are used, very conservative designs result.

Therefore, the Prequalifiedresistance factors were

increased to d = 1.0 and n = 0.90, but only for limitstates included in the Prequali f ied Standard.


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Specific Prequalified Connections

Reduced Beam

Section (RBS)

R d d B S ti (RBS)


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Reduced Beam Section (RBS)

RBS Concept:

Trim Beam Flanges

Near Connection

Reduce Moment at

Connection

Force Plastic Hinge

Away from Connection

R d d B S ti (RBS)


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C ti P lifi d t UT A ti


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Connection was Prequalified at UT - Austin


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Whitewashed Connection Prior to Testing

C


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Whitewashed Connection Prior to Testing

C ti t 0 02 di


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Connection at q 0.02 radian.

C ti t 0 02 di


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C ti t 0 03 di


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C ti t 0 04 di


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C f R lt


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Conformance Results



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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



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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 weldbetween beam web and column flange)

See ANSI/AISC 358 for additional requirements (continuity plates,

beam lateral bracing, RBS cut finish, etc.)


Prequalification Requirements for RBS in SMF



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Reduced Section Geometry

0.5bf< a < 0.75bf0.5d < b < 0.85d

0.1bf< c < 0.25bf




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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.


Lateral Brace Violates Protected Zone


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End-Plate Moment Connections

Unstiffened Stiffened Stiffened

4-Bolt: 4E 4-Bolt: 4ES 8-Bolt: 8ES




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End-Plate Concept:

No Field Welding

Simple Erection

Connection is Stronger thanBeam

Special welding requirements

Concrete slab requirements


Connections were prequalified at Virginia Tech



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AISC Design Guide 4


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For High Seismic

and Wind

Applications

AISC Design Guide 4

Design Methodology


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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

Design Considerations


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Required connection design moment

Connection strength

Welding procedure

Detailing Column side limit states

Design Considerations



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Mf= Mpr + Vu ShSh = min.[d/2, 3bbf] from face of column or

end of stiffener if one exits.

Connection Strength


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Connection Strength

Design connection bolts to resist Mf Thick Plate so Prying forces are negligible

Mf< Mnp with = 0.92(Pt)

2(Pt )

d1do

Mnp

Pt = tensile strength

of bolt

Connection Strength


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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:

where Y = yield-line parameter

Connection Strength

Y)F/(Mt ypplp with = 1.0

Connection Strength


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)d)(d2(PMM 1otnpn

Connection Strength

Example: 4E2(Pt )

2(Pt )

d1d

o

Mnp

Connection Strength


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Mpl = Fpy tp2 Y

where:

Fpy = end-plate material

yield stress

tp = end-plate thickness

g

bp

s

p

d

pf

t pf

Connection Strength

Example: 4E

Connection Strength


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Required end-plate thickness

where 1.0Y)F/(Mt ypplp

2

1

p

h

2

b

g

2sp

s

1

p

1

2

bphY

f

p

f

f

p

t

gb2

1s p

gbp

sp

d

p fpf

Connection Strength

Example: 4E

Connection Strength


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Design process is the same as

for the 4ES configuration.

g

pf

pb

pb

pf

d

bp

ts

Connection Strength

Example: 8Es

End-Plate Welding


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Weld access hole not permitted because of

ruptures that occurred during testing.

Rupture

g

End-Plate Welding


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Weld access hole not permitted because of

ruptures that occurred during testing.

Rupture

g

End-Plate Welding


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Recommended welding procedure:

No weld access holes

Surface Preparation:

All surfaces ground clean Flanges beveled 45 full depth

Minimum root opening

45

45

Typical Beam

g

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 flangesinstalled.

3. Flange groove weld root

backgouged and flange groove

welds installed.

Note: Welds over webs are not CJP.

Backgouge

Backgouge

1

2

3

3

g

Detailing Requirements


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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

e g equ e e s

4ES and 8ES Stiffener Detailing


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Length of Stiffener

Lst

= hst

/ tan 30

30

1"

Lst

1"

hst

g

4ES and 8ES Stiffener Detailing


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g

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

Other Limit States to Consider


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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

8-Bolt Stiffened Moment End-Plate, 8ES


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Total Plastic Rotation (rad)- 0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08

MomentatColumnCenterline(in-kip

s)

-25000

-20000

-15000

-10000

-5000

0

5000

10000

15000

20000

25000

Total Rotation (rad)- 0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08

MomentatColumnCenterline(in-kip

s)

-25000

-20000

-15000

-10000

-5000

0

5000

10000

15000

20000

25000

Moment at Column Centerline Moment at Column Centerlinevs vs

Total Rotation Plastic Rotation

8ES-1.25-1.75-30



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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

Connection Test with Concrete Slab


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R

igidLink

Lateral Support

Typ.Composite

Slab

Pin SupportRigidLink

W24x68 W24x68

Test Column

Reaction

Frame

ActuatorTest Frame

W14x257

Test 1 with Concrete Slab


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Premature Bolt Rupture



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10'-0" 10'-0"

3'-0"

3'-0"

1'-11 1/4"

3'-4 1/2" 4'-8 1/4"

NO STUDS

HINGE ZONE

END

OF

STIFFENER

1'-11 1/4"

4'-8 1/4" 3'-4 1/2"

NO STUDS

HINGE ZONE

END

OF

STIFFENER

1/2" MIN. GAPFORMED 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" X 4" SHEAR STUDS@ 1'-0" MAX.



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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.)

ColumnTipLoad(kips

-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.)

ColumnTipLoad(kips

Column Tip Load Column Tip Load

vs . vs.Total Rotation Beam Rotation

Requirement for All Prequalified Bolted

C ti


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Connections

Compressible expansion joint material, at

least 1 in. thick, shall be installed to isolate

the column/connection from the concrete

slab.

S ifi P lifi d C ti


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Bolted Flange

Plate (BFP)


Bolted Flange Plate (BFP)


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BFP Concept:

Shop Welded/Field Bolted

A325 or A490 bolts

Top and bottom flange

plates must be identical

Hinge at end of flange

plates



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Prequalified at

U. of California

at San Diego



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FractureLocation Close-up of Fracture

Location



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Welded Unreinforced

Flange - Welded Web(WUFW)


Welded Unreinforced Flange- Welded Web


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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

(WUF-W)

connection

Welded Unreinforced Flange- Welded Web


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(WUF-W)

Erection Bolts



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Proprietary

Kaiser BoltedBracket (KBB)

Flange Welded Flange Bolted


Kaiser Bolted Bracket (KBB)


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KBB Concept:

Cast steel bracket

Welded or bolted tobeam 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

Kaiser Bolted Bracket (KBB)


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Proprietary

ConXtechCONXLTM

Moment

Connection


ConXtech CONXLTM Moment Connection


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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



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Thank You!!

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