EFFECT EVALUATION OF REPAIRING METHOD USING CFRP SHEET FOR STEEL GIRDER END
Nagaoka University of Technology

1. INTRODUCTION
In recent years, a new method to repair corroded steel
girders ends using CFRP (Carbon Fiber ReinforcedPolymer) sheets has been proposed. This new method has
been already included on the Nippon Expressway Company
Standards Manual.
Even though many laboratory tests have been performed,
and the increase on ultimate strength and a decreased onstress level in members where CFRP sheets were bonded
have been already verified, there are restrictions in thelaboratory test that impedes the examination of certain
corrosion cases. Additionally, since this is a new method,
there are only a few cases where CFRP was used to repair
steel bridges, and the data about its performance on real
bridges is still scarce. Therefore, one of the objectives of thisstudy is the evaluation of the CFRP repair method
performance on a corroded steel girder end by verifying thestrain reduction on this section.
In addition, the correction coefficient (Cn) used during thedesign procedure is examined. This correction coefficientconsiders the delay in stress transfer between the steel plate
and CFRP sheet due to the insertion of a high-elongation
putty layer.

2. BRIDGE OF STUDY
During the inspection of a steel bridge in service severe
corrosion damages were found in the vicinity of two
supports. After several evaluations, it was decided to repair
the bridge by using CFRP sheets.
The above mentioned bridge is a steel bridge with 4
I-shaped girders and a RC deck. It is a 72.0 m long-bridge,
and it possesses two spans of 36.0 m. It was completed andopened to traffic in 1973 (See Figure 1).

Structural Analysis Laboratory

Galicia Garcia David

Academic Supervisor

Miyashita Takeshi

3. ON-SITE MEASUREMENTS & STRUCTURALIDENTIFICATION
Before and after applying the CFRP repair method,full-scale static and dynamic tests were conducted in thebridge. The main purpose of these tests is to grasp thebehavior of the damaged and repaired bridge, and based onthese results, to evaluate the strengthening effect by CFRP
repair method. In these tests, the corresponding relative
strain variation from the measured strain response before
and after bonding CFRP sheets was determined (See Figure
2 & 3). It should be noticed that in some sections, the strain
gauges were attached above the CFRP sheets (lower sectionof the after repair case).
In addition, vibration measurements for structural
identification were also conducted.

4. FINITE ELEMENT MODELA three-dimensional linear elastic Finite Element Model ofthe bridge of study was created. The geometry and material
properties of the original model were modeled based on thedesign drawings (See Figure 4 & Table 1). In addition, amodel which considers corrosion damages, and other modelwhich considers the CFRP repair were also created. CFRPelements were modeled using laminate plate elements (stackof individual sheets oriented at certain angle from theprincipal material directions).
The model is updated based on the dynamic response of thebridge measured on-site. The spring coefficient stiffness is
modified until finding a good correlation between the natural
frequency measured on-site and the one obtained from theFinite Element Model.

Figure 1. Bridge of Study.

Figure 2. Strain Gauge Location at G2.

Figure 3. Loading Position (Static Loading Test).

Figure 4. Finite Element Model.

Member

Element Type

Table 1. Finite Element Model Properties.
Material
Elastic Modulus (MPa)Main Girders
Box Beam
Stiffeners
BracesSlabPavement
CFRP Sheets

Plate
Plate
Plate
Beam
Solid
Solid
Laminate Plate

Steel
Steel
Steel
Steel
Concrete
Asphalt
CFRP

200,000
200,000
200,000
200,000
31,000200
640,000

Poisson's Ratio

Density (kg/m3)

0.30
0.30
0.30
0.30
0.15
0.40
0.31

7,860
7,860
7,860
7,860
2,400
2,250
2,100

Figure 5. Upper Section Before Repair.

Figure 6. Upper Section After Repair.

Figure 7. Lower Section Before Repair.

Figure 8. Lower Section After Repair.

Figure 9. Strain Distribution after Repair for different Cn (Lower Section).

5. RESULTS
The obtained results can be summarized as:A) Strain Distribution (Upper Section): Because thesection was out from the CFRP bonding area, no big
difference in the strain level before and after repair isobserved neither in the on-site measurements nor FE
analysis results (See Figure 5 & 6).
B) Strain Distribution (Lower Section): Since the strain
gauges were attached above the CFRP sheets (after repair), it
was necessary to consider a Cn. Firstly, the steel strain
reduction was calculated considering the Cn used during thedesign procedure, this is 0.74. However, comparing thisstrain distribution with the one obtained from FE analysis, it
was found that slightly bigger strains were obtained from theon-site measurements. A different value of Cn (=0.44)
considering the development length (distance from corrosion
area to the edge of the outermost CFRP sheet) and shift
amount (distance between the ends of each carbon fibersheet) of all the analyzed sections was calculated. The strain
distribution for this value of Cn presented a good matchingwith the FE analysis, founding errors below 10% for cases
where the load is near to the support A2, location of thestrain gauges (See Figures 7, 8 & 9).

6. CONCLUSIONS
The repair effect on each of the analyzed sections can besummarized as follows:
1. For the upper section, it is thought that no repair effectfor this section was obtained (no CFRP sheets werebonded here).
2. For the lower section, it was found that the strain level
was reduced in a range from 55~80%, with an averaged
value of 69%, when Cn=0.44 was used. The strain
reduction was 75% when a Cn =0.74 was considered.
About the correction coefficient, the obtained conclusions
can be summarized as:
1. It was confirmed that the Cn is strongly influenced by
the development length and shift amount.
2. Since there is no big difference between the strain
reduction levels obtained for each coefficient (0.44 &0.74), it seems like its determination for each section
can be omitted and the value described in the design
manual can be adopted without significant variation in
the results.