Seismic Repairing of a Seismically Damaged Bridge Column ...

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

Applied Laboratory for Advanced Materials & Structures

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


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


EFFECT OF GFRP CONFINEMENT ON THE

COMPRESSIVE STRENGTH OF CONCRETE


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


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


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


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


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


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


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


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.


CYCLIC PERFORMANCE OF RC CIRCULAR BRIDGE PIERS

REPAIRED AND RETROFITTED WITH GFRP


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


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


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


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


TEST SETUP

Applied loading protocol on test specimen(Chai et al. 1991, Ghannoum et al. 2012, Teng et al. 2013)


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


REPAIRING AND RETROFITTING METHOD

Damaged Pier Vertical Support andAxial Load Removal

Formwork for pouring repair concrete

Repaired pier Repaired pier with GFRP confinement


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 (%)


-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)


-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


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


ENERGY DISSIPATION AND RESIDUAL DRIFT

Cumulative energy dissipation Residual Drift


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


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.


Acknowledgements

Seismic Repairing of a Seismically Damaged Bridge Column ...

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Transcript of Seismic Repairing of a Seismically Damaged Bridge Column ...