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