1. CIVI 6061-Strengthening of bridges using FRP
11/15/2014
CIVI 6061-Strengthening of bridges using FRP
Case Study 1 :
War Memorial Bridge in Macon County, Alabama
Main causes of deterioration of bridges
-Increase of traffic load
-Environmental Effect
Low quality materials
- Limited maintenance program
-Built in 1945
-Nature of damage : Flexural Cracking
-Strengthening area :Positive moment regions
-Strengthening technique : Externally bonding FRP strips.
-Design code : ACI
-Back ground and Design procedure :
Section 1 :
Laboratory test :
-Eight RC beams half scale each reinforced with epoxy-bonded FRP was built and exposed to load cycles during the curing of epoxy .
- One beam was unstrengthened and used as a control specimen . .

2. CIVI 6061-Strengthening of bridges using FRP
11/15/2014
CIVI 6061-Strengthening of bridges using FRP
Testing procedure :
1-Loading the member to induce flexural cracking.
2. Applying pre-repair service load cycles to the member.
3. Preparing the concrete surface of the member where the FRP would be applied.
4. Applying epoxy and bonding FRP to the member
5. Allowing epoxy to cure for 48 hours while undergoing load cycles (if applicable).
6. Stopping load cycles and attaching strain gauges to FRP surfaces.
7. Applying post-repair service load cycles to the member.
8. Loading member to failure.
Instrumentation :
Steel bar strain gauges
The gauges were placed at locations where a flexural crack was expected
Seven locations were instrumented steel bars
FRP Instrumentation
14 gauges were used for frps
-Strengthening plates system :
Flexural plates : FRP thickness = in. (1.4 mm)
Epoxy thickness = in. [1.6 mm])
Application of FRP to Beam

3. CIVI 6061-Strengthening of bridges using FRP
11/15/2014
CIVI 6061-Strengthening of bridges using FRP
DISCUSSION OF RESULTS :
Failure mode of test specimens:
localized debonding at a flexural crack
Total debonding of FRP
The unstrengthened capacity (584 kip-ft [792 kN-m]).
ACI 440.2R-02 :
Unsafe limiting strains to prevent FRP debonding for the FRP
Failure mode :
There are four potential flexural failure modes for externally bonded strengthening
1-Concrete crushing before yielding of the steel
2-Steel yielding followed by concrete crushing
3-steel yielding followed by FRP rupture
4-Debonding of FRP at the concrete-FRP interface
Further research needs to be performed on the limiting FRP strain to prevent debonding failure . .
Flexural crack after debonding

4. CIVI 6061-Strengthening of bridges using FRP
11/15/2014
CIVI 6061-Strengthening of bridges using FRP
CONCLUSIONS:
-There was an increase in flexural strength of 19 – 28 percent
-The effects of load cycles during epoxy cure time were found to be minimal.
- For all strengthened members, failure was caused by localized debonding at a flexural crack under one of the load points
-The ductility of the strengthened members was reduced to approximately 10% of that of the unstrengthened specimen.
=effective strain level in FRP

5. CIVI 6061-Strengthening of bridges using FRP
11/15/2014
CIVI 6061-Strengthening of bridges using FRP
Field strengthening
-Instrumentation :
14 strain gauges were installed on the steel reinforcement at each critical location.
Strain gauges were bonded to the positive moment reinforcing bars as well as the FRP surfaces .
Load test : Four trucks(AASHTO M-18 Truck) were used for both Before and after strengthening .
Steel Strain Comparison for Span 9 Girder 3
The structure was load tested on several occasions:
-prior to strengthening: Load test 1 (Existing Load Test )
-Right after installation of the CFRP :Repair 1
-Six months after strengthening :Repair 2
Summary of result :
There was a decrease in steel bar stresses ranged from 4 to 12% for

6. CIVI 6061-Strengthening of bridges using FRP
11/15/2014
CIVI 6061-Strengthening of bridges using FRP
Case Study 2 :
Strengthening of Church Street Bridge
-Built in 1954 in New York
-Nature of damage : flexural and shear cracking at the cap beams
-Strengthening technique : Bonded-FRP laminates
-Strengthening plates system :
Flexural plates : 13-mm thick, 254mm wide, and m long
Shear plates : 7-mm thick, 1.1-m wide, and 1.7-m long
-Instrumentation :
A total number of 26 strain gauges were installed
-Load test : Four trucks(AASHTO M-18 Truck) were used for both
Before and after strengthening .

7. CIVI 6061-Strengthening of bridges using FRP
11/15/2014
CIVI 6061-Strengthening of bridges using FRP
Data Collection :
-Before installation collected data
-Flexural strains in the steel reinforcement bars
and concrete in both positive and negative moment
-Concrete strains
-After installation load test:
in addition to the strains measured in the before
installation test, flexural strains in
the FRP plates in both positive and negative moment
regions were measured .
Data analysis :
-Reduced live load stresses in the steel reinforcement bars
in the negative and positive moment regions by
about 10 ( 24.5 to 27 for 325 KN.m)and 6 percent, respectively.
-Analysis of shear strain data showed that concrete shear strain at
the critical section near the center pier was reduced by 10 percent.

8. CIVI 6061-Strengthening of bridges using FRP
11/15/2014
CIVI 6061-Strengthening of bridges using FRP
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