1
FRP Retrofitting FRP Retrofitting -- 11
Seismic Evaluation and Retrofit of BeamSeismic Evaluation and Retrofit of Beam--Column Joints of MidColumn Joints of Mid--American BridgesAmerican Bridges
Part 1: Fiber Reinforced Polymer Retrofit Part 1: Fiber Reinforced Polymer Retrofit
Pedro F. Silva, Ph.D., P.E.Pedro F. Silva, Ph.D., P.E.GendaGenda Chen, Ph.D., P.E.Chen, Ph.D., P.E.
University of MissouriUniversity of Missouri--Rolla (UMR)Rolla (UMR)[email protected]@umr.edu
Geotechnical and Bridge Seismic Design WorkshopGeotechnical and Bridge Seismic Design WorkshopNew Madrid Seismic Zone ExperienceNew Madrid Seismic Zone Experience
October 28October 28--29, 2004, Cape Girardeau, Missouri29, 2004, Cape Girardeau, Missouri
FRP Retrofitting FRP Retrofitting -- 22
Participants Participants
Pedro F. Silva, Ph.D., P.E.Pedro F. Silva, Ph.D., P.E.GendaGenda Chen, Ph.D., P.E.Chen, Ph.D., P.E.
Nick Nick ErecksonEreckson, M.S. Graduate Student , M.S. Graduate Student
2
FRP Retrofitting FRP Retrofitting -- 33
Research Objectives
♦ Plastic hinges to form at the ends of the columns
♦ Beams protected against any significant flexural or shear inelastic actions
♦ Beam/column joints retrofitted in order to minimize inelastic rotations in the beam/column joint regions
Develop a Comprehensive Research Program to Establish the Seismic Retrofit of a Beam/Column
Joint According to Modern Seismic Design Principles Using CFRP Systems
FRP Retrofitting FRP Retrofitting -- 44
Plastic Hinges Can Form Either in the Beams or Joints under Moderate Seismic Events
Current Design Deficiencies
♦ Excessive - Column flexural reinforcement
♦ Inadequate - Column shear reinforcement
♦ Inadequate - Beam shear reinforcement
♦ Inadequate - Beam flexural reinforcement
♦ Inadequate - Joint shear reinforcement
3
FRP Retrofitting FRP Retrofitting -- 55
Evaluation of Bridge Structures
A-1) Ductile Flexural Response
A-2) Brittle Shear Response
A-3) Confinement of Plastic Hinge
A-4) Buckling of Longitudinal
Reinforcement
A) Column
B-1) Ductile Flexural Response
B-2) Brittle Shear Response
B) Bent Cap
C-1) Brittle Crushing of Diagonal Compression
Strut
C-2) Brittle Joint Shear Failure with
Reinforcement Pullout
C) Bent/Cap Joint
Performance Levels for a Typical Bent Cap/Column-bent Connection
FRP Retrofitting FRP Retrofitting -- 66
Evaluation of Bridge Structures
35Steel Continuous871968A-2428
44Steel Continuous751976A-3478
34Steel Continuous113.751971A-2430
45Steel Continuous901968A-2429
35Steel Continuous931968A-2427
26Steel Continuous651968A-2336
28Steel Continuous701968A-2334
26Steel Continuous721968A-2333
26Steel Continuous651968A-2332
35Steel Continuous1121970A-2024
35Steel Continuous951969A-1938
24Steel Continuous521969A-1931
25Steel Continuous681966A-1466
(#)(#)(type)(feet)(Year)(#)
No. of Columns/Bent
No. of BentsGirder TypeMain Span
LengthYear BuiltBridge #
4
FRP Retrofitting FRP Retrofitting -- 77
Evaluation of Bridge Structures
FAILFAILFAILA-2428
MARGINALFAILFAILA-3478
PASSFAILPASSA-2430
PASSFAILPASSA-2429
PASSPASSFAILA-2427
MARGINALFAILPASSA-2336
MARGINALMARGINALPASSA-2334
MARGINALMARGINALPASSA-2333
MARGINALFAILPASSA-2332
FAILMARGINALPASSA-2024
PASSMARGINALPASSA-1938
PASSMARGINALPASSA-1931
PASSPASSFAILA-1466
(PASS/ FAIL)(PASS/ FAIL)(PASS/ FAIL)(#)
Column ShearJoint Shear FailureFlexural Failure
Column Bent Cap Bridge #
FRP Retrofitting FRP Retrofitting -- 88
♦ Unit 1 – Incremental retrofit at different performance levels
♦ Unit 2 – Complete retrofit before testing
Test Matrix
Design of Two Test Units for Evaluation of Retrofit of Beam/Column Systems Using
Carbon-FPP Composites
5
FRP Retrofitting FRP Retrofitting -- 99
Prototype Structure
FRP Retrofitting FRP Retrofitting --1010
Top & Bot.Bars BentAt Ends
Center of Bent Cap
Bolts
5 - D25 (#8) -Top Reinf
610
D13 (#4) Hoops @ 120 o/c (0.40%)
D16 (#5) Stirrups@ 184 o/c
10 – D25 (#8) Bottom Reinf.
14 - D29 (#9)( ρl ≅ 3.5%)
50 Cover
610
880
1710
No Stirrups
152
1 - D16 (#5)(Each Side)
Longitudinal Section
6
FRP Retrofitting FRP Retrofitting --1111
740
0.61
D13 (#4) Hoops @ 120 o/c (0.40%)
880
14 - D29 (#9)( ρl ≅ 3.5%)
Beam & Column X-Sections
5 - D25 (#8) Top Reinf.D16 (#5) Stirrups
@ 184 o/c
10 – D25 #8) Bottom Reinf.Arranged in 2 Layers
1 - D16 (#5)(Each Side)
FRP Retrofitting FRP Retrofitting --1212
7
FRP Retrofitting FRP Retrofitting --1313
FRP Retrofitting FRP Retrofitting --1414
Demand Evaluation( )
( )
⎪⎪⎪
⎩
⎪⎪⎪
⎨
⎧+
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛
−=
⎪⎪
⎩
⎪⎪
⎨
⎧
−⋅
+⎟⎠⎞⎜
⎝⎛ −
−⋅
=
2P
2hH
HL
M
V
4DLP
2hH
DLLH
2M
M
b
OC
crB
1
b
oC
crB
Hc
h
C
b
A
C
Support Blocks
Column
Critical Section
Critical Section
h
DE F
G
D
lsls
L
H
L1P/2 P/2
Hc
h
C
b
Critical Section
h
G
D
lsls
L
L1
P
V
B
8
FRP Retrofitting FRP Retrofitting --1515
Material Properties
54194993Column
46094216BeamSpecimen
#2
36973525Column
53425026BeamSpecimen
#1
(psi)(psi)
Strength atTime of Testing
28 DayStrength
789
808
605
874
Yield Strength(ksi)
Bar#
Concrete Steel Rebar
FRP Retrofitting FRP Retrofitting --1616
0.00 1.00 2.00 3.00 4.00
Displacement Ductility
0.00
0.50
1.00
1.50
M /
M'y
Column Shear Capacity Evaluation
Unit ACI 318-02 UCSD
9
FRP Retrofitting FRP Retrofitting --1717
0.00 1.00 2.00 3.00 4.00
Curvature Ductility
0.00
0.50
1.00
1.50
2.00
M /
M'y
Beam Shear Capacity Evaluation
Negative Moment
Unit ACI 318-02 UCSD Demand
FRP Retrofitting FRP Retrofitting --1818
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
Curvature Ductility
0.00
0.50
1.00
1.50
2.00
2.50
3.00
M /
M'y
Positive Moment
Beam Shear Capacity Evaluation
Unit ACI 318-02 UCSD Demand
10
FRP Retrofitting FRP Retrofitting --1919
0.00 1.00 2.00 3.00 4.00
Displacement Ductility
0.00
0.10
0.20
0.30
0.40
0.50
'C
Tf
ρ
Joint Principle Stresses Evaluation
Principal Tensile Stresses
0.29
0.42
Unit Joint Shear Failure Joint Shear Cracking
FRP Retrofitting FRP Retrofitting --2020
1 Column shear failure at µ∆ < 3 or onset of column cover concrete spalling
2 Onset joint shear failure at µ∆ > 2
Predicted Seismic ResponseUn-strengthened System
11
FRP Retrofitting FRP Retrofitting --2121
Column RetrofitSplicedCircular
14 - D29 (#9)( ρl ≅ 3.5%)
0.616 Plies
50mm Clear Gap
9 PliesN
o PliesIn LoadStud
3 Plies6 Plies
50mm Clear Gap
9 PliesN
o PliesIn LoadStud
3 Plies
( )CC
'
ujuj
Cuj fD
fε0.004ε0.10t −
=
Confinement (9 Plies)
Shear (2 Plies)
Retrofit Design Target µ∆=12.0
( )cotθDfπ0.5
VVVφV
tuj
PSCS
o
j
++−=
FRP Retrofitting FRP Retrofitting --2222
0.00 4.00 8.00 12.00
Displacement Ductility
0.00
0.50
1.00
1.50
2.00
2.50
3.00
M /
M'y
Column Retrofit Evaluation
Unit Original Unit Retrofit ACI 318-02 UCSD
12
FRP Retrofitting FRP Retrofitting --2323
Carbon Fiber Reinforced Polymer (CFRP)
0.0065 in/plyNominal Thickness
24 in.Fabric Width
33,000 ksiTensile Modulus
1.67%Ultimate Rupture Strain
550 ksiUltimate Tensile Strength
Specimen # 1 and 2
Material Properties
FRP Retrofitting FRP Retrofitting --2424
Column
Retrofit
13
FRP Retrofitting FRP Retrofitting --2525
Joint Retrofit( ) ( )2
V2
HCFRP FFF +=
⎟⎟⎠
⎞⎜⎜⎝
⎛ −=
b
UCH 0.5h
0.5c0.7DTF
⎟⎠⎞
⎜⎝⎛ −
=0.5D
0.5cDTF UBV
ujj
CFRPjj fw
12
Ftn =
Joint Retrofit (3 Plies)
TCCC
FH
FV
TBL
CBL TBR
CBR
hB
Pull
FRP Retrofitting FRP Retrofitting --2626
JointRetrofit
14
FRP Retrofitting FRP Retrofitting --2727
Unit 2 – Retrofit Specimen
GFRP Anchors Layout CFRP Sheets Layout
FRP Retrofitting FRP Retrofitting --2828
Experimental Results
0 5 10 15 20 25 30Number of Cycles (#)
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
14
Disp
lace
men
tDuc
tility
( mD)
Loading LevelsLocations where dynamic testing was performedLocations where retrofit was added to the structure
(Specimen #1 Only)
V=1
9.43
k
V=38
.85
k
V=58
.28
k
Single Cyclesto First Yield
(LoadControl)
3 Cycles at EachDisplacement Level
Above Yield(Displacement Control)
m1.0
Dy=0.78"
m1.5
D=1.17"
m2.0
D=1.56"
m3.0
D=2.34"
m4.0
D=3.12"
m5.0
D=3.90"
m6.0
D=4.68"
m8.0
D=6.24"
m12.0
D=9.36"
0 5 10 15 20 25 30Number of Cycles (#)
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
14
Disp
lace
men
tDuc
tility
( mD)
0 5 10 15 20 25 30Number of Cycles (#)
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
14
Disp
lace
men
tDuc
tility
( mD)
Loading LevelsLocations where dynamic testing was performedLocations where retrofit was added to the structure
(Specimen #1 Only)
V=1
9.43
k
V=38
.85
k
V=58
.28
k
Si
Loading LevelsLocations where dynamic testing was performedLocations where retrofit was added to the structure
(Specimen #1 Only)
V=1
9.43
k
V=38
.85
k
V=58
.28
k
Single Cyclesto First Yield
(LoadControl)
3 Cycles at EachDisplacement Level
Above Yield(Displacement Control)
m1.0
Dy=0.78"
m1.5
D=1.17"
m2.0
D=1.56"
m3.0
D=2.34"
m4.0
D=3.12"
m5.0
D=3.90"
m6.0
D=4.68"
m8.0
D=6.24"
m12.0ngle Cyclesto First Yield
(LoadControl)
3 Cycles at EachDisplacement Level
Above Yield(Displacement Control)
m1.0
Dy=0.78"
m1.5
D=1.17"
m2.0
D=1.56"
m3.0
D=2.34"
m4.0
D=3.12"
m5.0
D=3.90"
m6.0
D=4.68"
m8.0
D=6.24"
m12.0
D=9.36"
15
FRP Retrofitting FRP Retrofitting --2929
-600
-400
-200
0
200
400
600
Late
ral l
oad
(kN
)
-102 -51 0 51 102Lateral Displacement (mm)
-12 -8 -4 0 4 8 12Displacement Ductility
Unit 2: Experimental Results
Life Safety MCE Reliable: µ∆= 6FU = 400kN
Occupational MCE Reliable: µ∆= 2FU=530kN
Cycles at Peak ∆max
FRP Retrofitting FRP Retrofitting --3030
Unit 2: Experimental Results
16
FRP Retrofitting FRP Retrofitting --3131
♦ Column shear capacity was enhanced by applying CFRP sheets in the hoop direction
♦ Strengthening of the joint region wasadequate in preventing joint shear failure
♦ Some level of strength degradation wasobserved in the joint region
♦ Main failure mode was characterized by fracture of the column long. reinforcement
Unit 2 - Conclusions
FRP Retrofitting FRP Retrofitting --3232
0.00 1.00 2.00 3.00Structural Natural
Period TN (sec)
0.00
1.00
2.00
3.00
Spec
tral
Acc
eler
atio
n (%
g) Distance From Fault Zone
1.6 km16 km160 km
6500.9116010001.3916.021302.991.60
VE(kN)
SA%g
Distance From NMSZ(km)
h
C
b
A
CColumn
BDE F
G
D
L
H
h
C
b
G
D
L
W
V
h
C
b
A
CColumn
BDE F
G
D
L
H
h
C
b
G
D
L
W
V
Elastic Shear Forces
0.31sec.T10.2mm∆
320kNF710kNW
N
Y
Y
==
==
Natural Period
17
FRP Retrofitting FRP Retrofitting --3333
New Madrid Seismic Zone
FRP Retrofitting FRP Retrofitting --3434
Life Safety MCE Reliable: µ∆= 6FU = 400kN
Occupational MCE Reliable: µ∆= 2FU=530kN sT25.1
T)1(1R −µ+= ∆
5354851.33Operational4002402.66Life Safety
160
5357521.32Operational4003782.61Life Safety
16
53516231.31Operational400 8322.55Life Safety
1.6
System Capacity
(kips)
Demand(kips)RPerformance
ObjectiveDistance From
NMSZ (km)
Seismic Demand
Response Modification Factor
18
FRP Retrofitting FRP Retrofitting --3535
♦ Column shear capacity was enhanced by applying CFRP sheets in the hoop direction
Adequate for any Seismic Level Hazard
♦ Strengthening of the joint region wasadequate in preventing joint shear failure
Life Safety: 16km from the NMSZ faultOperational: 160km from the NMSZ fault
Seismic Evaluation Conclusions