collapse of lightly confined reinforced concrete frames during earthquakes · 2012-08-02 ·...
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Collapse of Lightly Confined Reinforced Concrete Frames during Earthquakes
Jack Moehle
Pacific Earthquake Engineering Research Center
University of California, Berkeley
NATO SfP Project 977231:Seismic Assessment and Rehabilitation of Existing Buildings
International Closing Workshop Istanbul Turkey 30 May-1 June 2005
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Collapse of Buildings in Past Earthquakes
Column failures Joint failures
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Shear-critical columns
Drift at shear failure
Axial Load Failure
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Shake Table Tests
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4’-10”
6’
Transverse torsional beam
5’ wide beam designed to model bending stiffness of typical spandrel beam(masses not shown for clarity)
Force transducers to measure reactions at base of columns
Shear-Critical Column
Designed to support gravity loads after failure of center column A B
9”
9”
W2.9 wire @ 6” o.c.
#4 corner bars
#5 center bars
Section A
10”
#3 spiral @ 2”
#4
Section B
Shake Table Tests
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Top of Column - Total Displ.
Relative Displacements
Specimen #2 – Moderate Axial Load
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Axial Load Capacity versus Shear Damage
Tasai, 2000
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Shear-Friction Model for Axial Failure
P
s
Aswfy
Aswfy
N Vsf
θθθθ
Elwood, 2002
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Implementation in OpenSees
Lateral response
Axial response
P
∆∆∆∆horz
Axial limit curve
Shear limit curve
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Analytical modelapplication
sw
Axial Load
analysis
test
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Case study frame
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Calculated static nonlinear response(pushover curve)
0
20
40
60
80
100
120
0 1 2 3 4 5 6 7 8 9
Drift (%)
Base S
hea
r F
orc
e (
KN
)
Long. steel
yielding
Shear failure
initiation
Residual shear
strengths
Spalling
Non-Ductile
Outer Col.
Ductile
Outer Col.Non-Ductile
Inner Col.
Ductile
Inner Col.
First Floor Columns
Axial failure
initiationProjected behavior
X
Collapse
FEMA 356
Collapse Prevention
Limit
xx
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Calculated dynamic response
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1994 Northridge earthquake recording stations
PGV = 80 to 110 cm/s
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Response spectra of selected motions
0.0
0.5
1.0
1.5
2.0
2.5
0.0 1.0 2.0 3.0
Period (sec)
Sp
ec
tra
l A
cc
ele
rati
on
(g
)
Mean spectrum
Sylmar - Converter Sta East
Sylmar - Olive View Med FF
Sylmar - Converter Sta
Jensen Filter Plant
Newhall - W Pico CanyonRd.
Newhall - Fire Sta
Rinaldi Receiving Sta
Initial period of case-study building
(PGV = 80 to 110 cm/s)
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Calculated response to Northridge ground motions
-10
-8
-6
-4
-2
0
2
4
6
8
10
0 1 2 3 4 5 6 7Time (sec)
1s
r F
loo
r D
rift
(%
)
RRS228
JEN292
SCS142
NWH360
SCE011
SYL360
WPI046
SCS142neg
X
Initiation of axial load loss at +7% drift
Initiation of shear failure at +/-2% drift
Long. bar yielding at +/-0.8% drift
X
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Collapse of Concrete Buildings in Past Earthquakes
OperationalHeavy
Collapse
Mexico City, 1985
Erzincan, 1992
0
20
40
60
80
100
Percentage
Kobe, 1995
Luzon, 1990
Otani, 1999Building Damage Rating
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California hospital retrofit program
San Jose Mercury News, 10 Feb 2005
“Hospital retrofit delays sought - …The price tag for all this retrofitting has been estimated between $21 billion and $41 billion. Of about 430 California hospitals, 366 did not meet standards set for either 2008 or 2030…. The price tag for hospitals through[out] the state is pretty large, and it’s probably going to force some hospitals to close.”