seismic repairing of a seismically damaged bridge column
TRANSCRIPT
Seismic Repairing of a Seismically Damaged Bridge Column with Low-Grade GFRP Material
Mosharef Hossain, MASc,
Structural Engineer-in-Training, Stantec, Victoria, BC
M. Shahria Alam, PhD, PEng
The University of British Columbia, Okanagan
BACKGROUND
Interstates 5 and 14San Fernando earthquake, 1971
Cypress viaductLoma Prieta Earthquake, 1989
Fukae Viaduct Kobe Earthquake, 1995
Shizunai BridgeUrakawa-oki Earthquake, 1982
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Lack of lateral reinforcement
BRIDGE COLUMN RETROFITTING TECHNIQUES
Confinement Techniques
Active
External
Pre-stressing
SMA Spirals
Passive
Concrete Jacketing
Steel Jacketing
ECC Jacketing
Ferro Cement
Jacketing
FRP Composite Jacketing
✓ Flexural and shear Stiffness
o Only for circular column
✓ Strength, stiffnessand ductility
o Costlyo temperature
sensitiveo Only for circular
column
✓ Flexural and shear Strength
✓ Low cost✓ Underwater worko Biaxial stress state
causes reduced compressive strength
✓ Low cost✓ Readily available ✓ Good aesthetico Corrosiono Heavy weighto Difficulty in
cutting and welding
✓ Ductile✓ High energy
dissipation✓ Strain hardeningo High costo Limited design
guidelines
✓ Low cost✓ Easy application✓ Both circular and
rectangular column
o Low durabilityo Poor aesthetics
✓ High strength✓ Lightweight and
easy application✓ Flexural and
shear enhancement
o Costly
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AVAILABLE RETROFITTING TECHNIQUES
Additional longitudinal
reinforcement
Additional ties
Original Column
Concrete Jacket
Steel Jacket
Concrete Infill
Original Column
External Pre-stressing
FRP Jacketing
Concrete Jacketing
Steel Jacketing
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EFFECT OF GFRP CONFINEMENT ON THE
COMPRESSIVE STRENGTH OF CONCRETE
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Type of FRP Tensile Strength (MPa)
Elastic Modulus(GPa)
Strain at Break(%)
CFRP 1720-3690 120-580 0.5-1.9
GFRP 480-1600 35-51 1.2-3.1
AFRP 1720-2540 41-125 1.9-4.4
BFRP 1035-1650 45-59 1.6-3.0
FRP COMPOSITES
• Carbon Fiber Reinforced Polymer (CFRP)• Glass Fiber Reinforced Polymer (GFRP)• Aramid Fiber Reinforced Polymer (AFRP)• Basalt Fiber Reinforced Polymer (BFRP)
Fig: Bi-directional Woven Roving Glass Fibers
+ Polyester Resin (epoxy)
+ Methyl Ethyl Ketone Peroxide (catalyst)
Cheaper
Tensile Strength, Corrosion resistant
Available and reliably serve the purpose
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FRP CONFINEMENT MECHANISM
Overlap
tfrp
2R
fc
fc
fl
fl
2R
ffrpnfrptfrp ffrpnfrptfrp
Plain Concrete
FRP layer
fl fl
fc
fc
2R h
fc
fc
fl
fl
2R
ffrpnfrptfrp ffrpnfrptfrp
Plain Concrete
FRP layer
fl fl
fc
fc
h2R
FRP wrapped cylinder
Overlapping on final layer
Free body diagram of FRP confined concrete
Tri-axial stress stage of concrete
Resulting strength(Mander et al. 1988)
150 mm
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EXPERIMENTAL INVESTIGATION ON MATERIALS
Coupon test for tensile strength Coupon test for bond strength
75
10
0
60
75
75
2
5
25
Cri
tical
Secti
on
75
Lb+
25
60
75
25
2
5
75
Ov
erl
ap
Regio
n,
*all dimensions are in mm
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PROPERTIES OF GFRP
Table - Properties of GFRP obtained from tests
Properties Value
Tensile strength (MPa) 275-290
Young’s modulus of elasticity (GPa) 13.5-18
Fracture strain (%) 2.2-2.9
Strength of epoxy (MPa) 50
Optimum overlap length (mm) 150
Stress-strain relationship of GFRP Bond between GFRP layers
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0
50
100
150
200
250
300
0 0.01 0.02 0.03
Ten
sile
Str
eng
th
(MP
a)
Strain (mm/mm)
1 Layer (0.85 mm)
2 Layers (1.55 mm)
3 Layers (2.12 mm)210
220
230
240
250
260
0 50 100 150 200 250
Bo
nd
Stt
ren
gth
(MP
a)
Overlap Length (mm)
APPLICATION OF GFRP ON TEST SPECIMENS
Priming Epoxy on glass fiber
First layer Pressing with grooved roller
Last layer
Control cylinders GFRP confined cylinders
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Specimen
Type 22
22 MPa
Old Infrastructure
Type 32
32 MPa
Recent Construction
EFFECT OF GFRP CONFINEMENT
Stress-strain curves for Type 22 and Type 32 cylinders
0
10
20
30
40
50
60
-0.06 -0.04 -0.02 0 0.02 0.04 0.06
Com
pre
ssiv
e S
tren
gth
(M
Pa)
Transverse Strain (mm/mm Axial Strain (mm/mm)
3 Layers2 Layers1 LayerType 22 Control
* Average of 3 specimens
0
10
20
30
40
50
60
70
80
-0.025 -0.015 -0.005 0.005 0.015 0.025
Co
mp
ress
ive S
tren
gth
(M
Pa
)
Transverse Strain (mm/mm) Axial Strain (mm/mm)
3 Layers2 Layers1 LayerType 32 Control
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47.9%
88.9%
142%
21.9%
59.4%
125%
0
10
20
30
40
50
60
70
80
Control 1 Layer 2 Layers 3 Layers
Co
mp
ress
ive
Str
en
gth
* (M
Pa)
Type 22 Type 32
FAILURE MODE
Control Specimen 1 layer of GFRP confinement
2 layers of GFRP confinement
3 layers of GFRP confinement
Gra
du
al r
up
ture
Gra
du
al r
up
ture
Sud
de
n r
up
ture
Dis
tort
ion
un
de
r co
mp
ress
ion
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SUMMARY
• GFRP confinement can significantly improve compressive strength and strain capacity of low strength concrete.
• Multi-layer of GFRP (thick) show better mechanical properties than a single layer.
• Number of layer = Compression carrying capacity + sudden blast type failure X
• Two layer of GFRP is considered to be the optimum confinement as it improves the compressive strength by 101% and shows gradual failure of fibers.
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CYCLIC PERFORMANCE OF RC CIRCULAR BRIDGE PIERS
REPAIRED AND RETROFITTED WITH GFRP
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DESIGN AND GEOMETRY OF BRIDGE PIER
900 mm
N8
N7
N6
N5
N4
N3
N2
N1
Beam element
Frame element
Zero length
Spring element
Axial load
Lateral load
Deck
Girder
Pier
Footing
Bearing
pad
4.6 m
5.2 m
300 mm
18-10M
6 mm dia hoops
50 mm dia
Plastic Pipe
Loading Direction
20 mm Clear Cover
Prototype
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17
30
mm
410 mm
15M liftinghook
41
0 m
m
Lateralload point
800 mm
680
mm
6 mm hoops @ 75 mm c/c
20 mm clear cover
18-10M longitudinal rebar
15M rebar
152
5 m
m
10M @50 mm c/c
10M @50 mm c/c
40 mm clear cover
20 mm clear cover
10M vertical stirrup
300 mm dia
50 mm duct for post-tensioning
75 mm duct for base anchorage
5 horizontal rod@100 mm c/c
Strain gauges
Test specimen Cross-sectional detailing
Table : Geometric comparison of prototype and test specimens
Description of properties Prototype Test Specimens
Diameter (mm) 900 300
Effective height (m) 5.2 1.73
Clear cover (mm) 60 20
Longitudinal reinforcement ratio (%) 2.52 2.55
Volumetric ratio of lateral reinforcement (%) 0.173 0.178
Tie spacing (mm) 15M @ 300 6mm @ 75
Axial Load, P/f’cAg (%) 10 10
Yield Strength of Longitudinal reinforcement (MPa) 450 450
Yield Strength of transverse reinforcement (MPa) 400 400
Compressive strength of concrete (MPa) 35 35
Thickness of GFRP layer (mm) 1.55
DESIGN AND GEOMETRY OF BRIDGE PIER
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0
50
100
150
200
250
300
0 0.005 0.01 0.015 0.02 0.025
Ten
sile
Str
ength
(MP
a)
Strain (mm/mm)
MATERIAL PROPERTIES
Repair Concrete GFRP
Ready-mix Concrete Steel
ft = 285 MPa
E = 16.5 Gpa
t = 1.55 mm
0
10
20
30
40
0 0.0005 0.001 0.0015 0.002 0.0025
Com
pre
ssiv
e S
tres
s
(MP
a)
Strain (mm/mm)
f’c = 35 MPa
E = 23 GPa
0
200
400
600
800
0 0.05 0.1 0.15 0.2 0.25
Ten
sile
Str
ength
(MP
a)
Strain (mm/mm)
fy = 450 MPa
E = 190 GPa
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0
10
20
30
40
0 7 14 21 28 35
Com
pre
ssiv
e S
tren
gth
(MP
a)
Time (days)
f’c = 36 MPa
TEST SETUP
Setup for bridge pier test under lateral cyclic load
Post tension rebar
Load cell
Strong floor
Data acquisition system
Controller
LVDTs
Hydraulicactuator
Strain gauges
Steel plate
Specimen
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TEST SETUP
Applied loading protocol on test specimen(Chai et al. 1991, Ghannoum et al. 2012, Teng et al. 2013)
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5.1 mm/min 15.3 mm/min
Pseudo-static loading Rate:(Ghannoum et al. 2012)
Before Yielding: 5.1 mm/min
After Yielding: 15.3 mm/min
TEST SETUP
GFRP retrofitted pier under lateral cyclic test
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REPAIRING AND RETROFITTING METHOD
Damaged Pier Vertical Support andAxial Load Removal
Formwork for pouring repair concrete
Repaired pier Repaired pier with GFRP confinement
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CYCLIC RESPONSE
Deficient Pier Repaired Pier
MaximumForce(kN)
MaximumDrift(%)
Deficient 62.3 4
Repaired >78 25% >6.9 73%
Retrofitted >79 27% >6.9 73%
Retrofitted Pier Skeleton Curve
-80
-60
-40
-20
0
20
40
60
80
-8 -6 -4 -2 0 2 4 6 8
Fo
rce
(KN
)
Drift (%)
-80
-60
-40
-20
0
20
40
60
80
-8 -6 -4 -2 0 2 4 6 8
Forc
e (K
N)
Drift (%)
-80
-60
-40
-20
0
20
40
60
80
-8 -6 -4 -2 0 2 4 6 8
Forc
e (K
N)
Drift (%)
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-80
-60
-40
-20
0
20
40
60
80
-125-100 -75 -50 -25 0 25 50 75 100 125
Forc
e (K
N)
Displacement (mm)
Deficient
Repaired
Retrofitted
STRAIN RESPONSE
Steel (deficient) Steel (repaired) Steel (retrofitted) GFRP (repaired)
Concrete (deficient) Concrete (repaired) Concrete (retrofitted) GFRP (retrofitted)
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-80
-60
-40
-20
0
20
40
60
80
-0.01 0 0.01 0.02
Lo
ad o
n C
olu
mn (
KN
)
Strain (mm/mm)
PushPull
Pull
Push
-80
-60
-40
-20
0
20
40
60
80
-0.002 0 0.002 0.004 0.006
Lo
ad o
n c
olu
mn (
KN
)
Strain (mm/mm)
Pull
Push
-80
-60
-40
-20
0
20
40
60
80
-0.01 0 0.01 0.02
Lo
ad o
n C
olu
mn (
KN
)
Strain (mm/mm)
PushPull
Pull
Push
-80
-60
-40
-20
0
20
40
60
80
-0.002 -0.001 0 0.001 0.002
Lo
ad o
n C
olu
mn (
KN
)
Strain (mm/mm)
Pull
Push
-80
-60
-40
-20
0
20
40
60
80
0 0.005 0.01
Lo
ad o
n C
olu
mn (
KN
)
Strain (mm/mm)
Pull
Push
-80
-60
-40
-20
0
20
40
60
80
-0.01 0 0.01 0.02
Lo
ad o
n c
olu
mn (
KN
)
Strain (mm/mm)
PushPull
Pull
Push
-80
-60
-40
-20
0
20
40
60
80
-0.005 0 0.005 0.01 0.015
Lo
ad o
n c
olu
mn (
KN
)
Strain (mm/mm)
Pull
Push
-80
-60
-40
-20
0
20
40
60
80
0 0.005 0.01
Lo
ad o
n c
olu
mn (
KN
)
Strain (mm/mm)
Pull
Push
MOMENT-CURVATURE RESPONSE
Measurement of curvature (φ)(Ibrahim et al. 2016)
M
d
l
Dt Dc
N.A.
d
ec
et j
𝑁𝐴 =𝑑 ∗ 𝜀𝑐𝜀𝑡 + 𝜀𝑐
𝜑 =𝜀𝑐𝑁𝐴
=𝜀𝑡
𝑑 − 𝑁𝐴=
𝜀𝑡| + |𝜀𝑐𝑑
𝑀 = 𝐹 ∗ 𝐿𝑒
Moment-curvature relationshipobtained from test
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0
20
40
60
80
100
120
140
0 0.0001 0.0002 0.0003
Mom
ent
(KN
-m)
Curvature (1/mm)
Deficient
Repaired
Retrofitted
DUCTILITY ANALYSIS
Table: Ductility of Piers obtained from test results
Specimen
type
Yielding Ultimate Displacement
ductility
Curvature
ductilityForce
(kN)
Displacement
(mm)
Moment
(kN-m)
Curvature
(1/mm)
Force
(kN)
Displacement
(mm)
Moment
(kN-m)
Curvature
(1/mm)
Deficient 38.9 19.6 64.38 3.52x10-5 62.3 69.3 103.11 9.64x10-5 3.54 2.74
Repaired 43.13 25.2 71.38 5.25x10-5 77.9 120 127.6 2.9x10-4 >4.76 >5.52
Retrofitted 39.1 19.2 64.71 3.44x10-5 79 120 130.75 2.66x10-4 >6.25 >7.73
Yield / Ultimate
Strain
Strain Response
• Force• Moment
Cyclic Response
• Displacement
Moment-Curvature Response
• Curvature
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ENERGY DISSIPATION AND RESIDUAL DRIFT
Cumulative energy dissipation Residual Drift
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0
10
20
30
40
50
60
70
80
0 1 2 3 4 5 6 7 8
Dis
sip
ate
d E
ner
gy (
KN
-m)
Drift (%)
Deficient
Repaired
Retrofitted
0
1
2
3
4
0 1 2 3 4 5 6 7 8
Res
idu
al
Dri
ft (
%)
Drift (%)
Deficient
Repaired
Retrofitted
FAILURE MODE
Diagonal
shear crack
Buckling of
reinforcement
Horizontal
cracks
Spalling
concrete
Fractured hoops in
plastic hinge regionDistorted
GFRP
Distorted
GFRP
Deficient Pier Repaired Pier Retrofitted Pier
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SUMMARY
• For the seismically damaged RC circular piers, repairing and retrofitting technique using passive confinement demonstrated the purpose of restoring strength and ductility of piers.
• The deficient pier once confined with GFRP jacketing showed increased lateral capacity (27%) and ductility (73%).
• From the experimental results it was found that, initial stiffness doesn’t change for passive confinement techniques like GFRP jacketing.
• Except some horizontal distortions, GFRP repaired and retrofitted pier didn’t show any significant damage up to the applied drift in the test.
• Damaged column repaired and strengthened with GFRP can perform similar to a retrofitted column under constant axial load and cyclic lateral load.
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Acknowledgements