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Large-Scale Testing of Steel Reinforced Concrete (SRC) Coupling Beams

Christopher J. Motter, UC Los Angeles John W. Wallace, UC Los Angeles

Ron Klemencic, John Hooper, Dave Fields Magnusson, Klemencic Associates

Los Angeles Tall Building Structural Design Council May 2013, Los Angeles, CA

Charles Pankow Foundation

ACI Pankow Foundation Student Fellowship

Presentation Outline

n Background n Motivation n Specimen Design n Testing Program n Test Results n Backbone Modeling n Conclusions &

Recommendations

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Background Coupling Beams n RC coupling beams

n Diagonally-reinforced n Concrete-encased structural steel

n Primary functions n Added strength & stiffness n energy dissipation

n Primary issues n Detailing issues (ductility) n Modeling (e.g., backbone relation)

3 Diagonally-Reinforced Concrete-Encased Steel

T C

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Embedment Model

Marcakis & Mitchell (1980)* :

Mattock & Gaafar (1982)* :

'0.85 ( )

1 3.6( )

c eff en

e

f b l cV

el c

=

+

0.66' 1

10.58 0.224.5 ( )

0.88 ( ) / ( )n c e e

tV f b l cb a c l c

= + +

b

beff

t

*Modified to include interface spalling per Harries et al (2000)

c = 0.003n.a.

2'

0 0

2 c cc cf f

=

'0.85c cf f=1x

x

Vn

aLe

strain

c

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AISC 2010 Seismic Provisions n Flexural capacity using strain

compatibility or plastic analysis

n Shear capacity using

n Initial stiffness using 0.35Ig

n Embedment length consistent with Mattock and Gaafar (1982)

n Transfer bars and bearing plates required

n Vertical boundary steel: Asfy > Vn,beam

1.1 1.56comp y steel RCV R V V= +

bearingplates

auxiliary transfer bars

Asfy > Vbeam

Vbeam

Test Sub-Assembly

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Vb

V

Vb

Split at Coupling Beam Inflection Point (Center)

M M

Mid-level: intermediate level detailing (ordinary boundary element)

Upper-level: No boundary transverse reinforcement when boundary < 400/fy)

V

P P

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Motivation n Large-scale SRC beam n Realistic boundary conditions (load paths)

n Wall strain gradient across connection

Flat M

C T

Vbeam

n.a.

Flat M

C T

Vbeam

n.a.

Embedment into reaction block: No strain gradient Load path satisfied

Embedment into wall boundary: Strain gradient at embedment Imposes demands on wall

Motivation Impact of Load Paths

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Increases Local Tension

Reduces Local Compression

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Testing Program Overview

n Two test specimens n Each specimen

n One wall n Two coupling beams,

one on each side n Coupling beam tests

n Individually with wall loads applied

n Second specimen designed after testing completed on first specimen

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Summary of Test Variables

n Beam 1: Long embedment (conservative design)

n Beam 2: Shorter embedment n Beam 3: Shorter aspect ratio n Beam 4: No boundary

confinement, bound < 400/fy

beam=L/h Le bound. bound. trans. Beam 1 (3.33-32-6C) 3.33 32 0.024 (14#6) #2@4" Beam 2 (3.33-24-7C) 3.33 24 0.033 (14#7) #2@4" Beam 3 (2.40-26-5C) 2.40 26 0.017 (14#5) #2@4" Beam 4 (3.33-24-3NC) 3.33 24 0.006 (14#3) none

Vbeam

L/2

bound

h

bound. trans.

Le

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Coupling Beam

n Flexure-controlled n ~1/2-scale W24x250

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12

W12x96, flanges

trimmed to 5.5 width

#2 @ 3 (two U-bars)

Longitudinal bars not

embedded into shear

wall

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Shear Wall Boundary

Ordinary boundary element No boundary Confinement 12

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Embedment Detailing

n Pre-drilled holes in web of steel section

n Threaded rods and side plates to maintain boundary confinement

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Test Set-Up

14

8'

200 kip act.

STRONG FLOOR

2'-6"

4'-9"

1'-6"

8'7'-3"

2'-9"

1'-6"

Le

2'

400 kip actuator

400 kip actuator

15'

5'-6"

5'

STEEL LOADING BEAM

1'

24'

8'-8.5"

22'

CONCRETETOP BEAM

SHEAR WALL

EMBEDDEDSTEEL

SECTION

FOO

TING

300 kip actuator

Le

STEEL (AXIAL) LOADING BEAM

LOADING JACK

2'typ.

typ.

EMBEDDEDSTEEL

SECTION

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Vbeam 15

Vwall

0.4*Vwall

0.4*Vwall

Wall Loading n Proportional loading: Vu and Mu n Wall moment demands at connection

n Beam 1: Exceeded cracking moment (low moment, long Le) n Beam 2: Approached yield moment (high moment, short Le)

n Wall moment demands at connection n Beam 3 and Beam 4: Similar to Beam 2

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(+), Up (-), Down Beam 1 0.5 0.5 Beam 2 1.25 1.25 Beam 3 1.0 0.5 Beam 4 1.0 0.5

k = Vwall / Vbeam =

Vbeam

0.4*Vwall

Vwall = k*Vbeam

0.4*Vwall

380-kips (Beam 3 & Beam 4 only)

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Testing Protocol n Reversed cyclic loading n 3 cycles at each level up to 4%, then 2 cycles n Load-controlled to (+/-) *Vyield, then

displacement- controlled

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Observed Damage (Beams 1 & 2)

n Concentrated at beam-wall interface Beam 1 (3.33-32-6C) after 3% rotation

Beam 1 (3.33-32-6C) after 6% rotation

Beam 2 (3.33-24-7C) after 3% rotation

Beam 2 (3.33-24-7C) after 6% rotation

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Beam 1: 3.33-32-6C (end of test)

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Beam 2: 3.33-24-7C (end of test)

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Observed Damage (Beams 3 & 4)

n Included embedment damage

Beam 3 (2.40-26-5C) after 3% rotation

Beam 3 (2.40-26-5C) after 6% rotation

Beam 4 (3.33-24-3NC) after 3% rotation

Beam 4 (3.33-24-3NC) after 6% rotation

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2.40-26-5C (end of test)

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3.33-24-3NC (end of test)

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Observed Damage

Photo showing significant gapping between flange and concrete (3.33-24-7C)

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Modeling Recommendation

n Harris et al (2000) recommend taking the effective fixity point at Le/3 inside the beam-wall interface for modeling purposes

Vbeam

L/2 Le Le/3

gapping 25

Load-Displacement

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Load-Displacement

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Load-Displacement

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Load-Displacement

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Test Results

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Test Results

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Test Results

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Backbone

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Backbone

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Recommendation(1) - Capacity

n Flexural capacity, Mn, determined using plastic section analysis with the design steel stress, Fy, and a Whitney stress block

n Probable flexural capacity for computing embedment length, Mn,pr, considers expected steel stress Ry*Fy

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1 Cc1Cc2Cc3

Cs,fCs,w

Tw

Tf

x

Fy

Fy f'cSTRESSES FORCES

Recommendation(2) - Backbone n For peak shear:

n Interface fixity, use clear span, L

n Use initial stiffness 0.2EcIg

n For reliable shear: n Effective fixity, use Leff = L

+ Le/3 n Use initial stiffness

0.35EcIg Vbeam

beam(rad.)0.08

V@Mn using L

V@Mn using Leff

0.35EcIg

0.2EcIg

Peak StrengthReliable Strength

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Recommendation(3) - Embedment

n Embedment length per Marcakis and Mitchell (1980), Mattock and Gaafar (1982), or AISC 2010 Seismic Provisions n Use design fc

n Transfer bars and bearing plates n Not needed if sufficient quantity of wall

boundary vertical reinforcement, i.e. Beam 1, Beam 2

n May improve embedment performance if insufficient embedment length or wall boundary vertical reinforcement, i.e. Beam 3, Beam 4

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Shear Wall Testing

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Objectives

n Typical wall tests: n Thin walls, i.e. 6 n Special boundary elements, s=4

n This specimen: n Thick wall

n 12 test specimen, 24 thick full-scale n Intermediate confinement, i.e. ordinary

boundary element n s=4 test specimen, s=8 full scale

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Shear Wall Testing

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Shear Wall Testing

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Thank you

n Questions?

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