Seismic Retrofit of Steel Truss Bridge using CFRP Sheet（鋼トラス橋の CFRP シートによる耐震補強）
Department of Civil and Environmental Engineering
Steel Structure Laboratory
Academic Supervisor: TAKESHI Miyashita
Vazquez Pelaez Mario Adriel
1. Introduction
In road bridges, there are members with an H-Shaped cross-section designed to work with tension forces. Whenan earthquake occurs, it is determined that local buckling will occur on those members due to compression forces.
These members require reinforcement, but conventional methods like using steel plates and HTB have thefollowing inconveniences:
The increase in dead load affects the regular stress state of the structure and increases the reinforcement
range needed.

Drilling tends to increase the thickness of the plate.

It is difficult to reinforce long members since it is needed to apply along the surface.

Concerns on corrosion, deterioration, and maintenance.

A viable method for reinforcing these members is to use Carbon Fiber
Reinforcement Polymer Sheets since it has material properties such as
high elasticity, high strength, lightweight, and has less corrosion thansteel materials. This material is also easy to apply since it is bonded tothe member to repair/reinforce by an adhesive resin, so there is no needfor special machinery or skills to apply it, there is no heat effectgenerated by welding on steel materials, and there is no damage
generated by drilling. The inconveniences of conventional methods areFigure
1.1
CarbonFiber
Reinforcement Polymer Sheets

solved.
2. Objectives

Make load-bearing capacity tests on members with an H-shaped cross-section reinforced with CFRP sheets to:Prove if CFRP sheet can be used as reinforcement material under a compressive load.

Get data on the effect of Carbon Fiber Reinforcement Polymer Sheets when used as reinforcement material.

Make the basis of the model of an H-Shaped cross-section member for future model analysis.

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3. Experiment Outline
A total of 13 specimens are going to be evaluated on a load-bearing capacity test considering the member’s plate
thickness of flanges and web, presence or absence of reinforcement, the direction of the fibers of CFRP sheets,
and the number of CFRP sheets on flanges and web. The specimens are divided into 4 cases:
Specimen without reinforcement (b, a, c, d). to serve as comparators for the next experiments, as a way tosee how the others improve.

Specimens reinforced with CFRP sheets with fibers on vertical direction (a-1, c-1, d-1).

Specimens reinforced with CFRP sheets with fibers in vertical and horizontal direction (a-2, c-2, d-2).

Specimens reinforced with CFRP sheets with fibers in vertical and horizontal direction, but horizontal
ones reduced to the half (a-3, c-3, d-3).

The experiment cases are summarized in table 3.1. In the table the reduced plate thickness is marked with red forflanges and blue for the web. In the part where reinforcement method is explained, the number of stacks refers tothe sheets to be laminated on one flange and one side of the web.

Table 3.1 Specimen Parameters2For obtaining the plate thickness of the specimens, the standard load-bearing capacity curve of stiffening plate wasused and from it, it is considered that when R>0.7, it is contemplated that the member will buckle, and when R≤0.7
it will not.

Fig. 3.1 Standard load-bearing capacity curve of stiffening plate
The different thickness of the specimens was gotten using the following formula:This equation was used in order to decide the plate thickness of both web and flanges of each experimental cases.
The thickness was decided pretending to control where the local buckling will occur and having that in mind know
where it is needed to reinforce with CFRP sheets.
For obtaining the number of CFRP sheets, First, a formula to get the Required reinforcement thickness for both
web and flanges based on the width-thickness ratio formula mentioned before is utilized.

3The number of sheets was determined using the following formula:

4. Specimen Reinforcement and Preparation
Before applying the CFRP sheets, the surface of the specimen is sanded with grit sandpaper and a primer is appliedin the surface prepare the surface for the next things to be applied. Then, a High Elongation Elasticity Putty isapplied , which purpose is to avoid CFRP sheets from peeling after buckling load and also to reduce stresstransmitted to CFRP sheets. After it, an Epoxy made of Polyurea and Resin is applied as an adhesive to CFRP
sheets and prevents peeling. Then CFRP sheets are applied one above the other with a layer of epoxy between
them.

Figure 4.1 Specimen preparation process4In all specimen, displacement transducers and strain gauges were applied to measure vertical displacement, outof-plane displacement, and strain during the experiments and analyze data afterwards. The location of strain
displacement transducers and strain gauges is presented in the following figures:

Figure 4.2 Displacement transducers location

Figure 4.3 Strain Gauges location

55. Specimen Results
The results of the specimen with no reinforcement regarding the vertical displacement are shown in Figure 5.1.
Results regarding the Maximum load are shown in table 5.1. With the results of specimen with no reinforcement,
it is seen that there are two things to improve with reinforcement. It is necessary to improve the stiffness loss after
web buckling and also to improve the brittle behavior presented after max load is reached.

Figure 5.1 and Table 5.1 Results of specimen with no reinforcement
With the results regarding the out-of-plane displacement of specimen with no reinforcement shown in figures 5.2
and 5.3 of specimen c and d, two fracture processes are obtained. First, local buckling on the web occurs andoverall stiffness decreases. After this, two scenarios are possible. In the first one, like in specimen c, flange
buckling occurs and out-of-plane displacement increases, which causes a decrease in yield strength after maximum
load is reached, so a brittle behavior is obtained. In the second scenario, flange yields normally, like in specimend, and a ductile behavior is obtained afterwards.

Figure 5.2 and 5.3 Out of plane displacement of specimen c and d respectively

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The following figures show the results of series a, c, and d containing all the cases regarding the verticaldisplacement:

Figure 5.4, 5.5, 5.6 Vertical displacement of series a, c and d respectively
Table 5.2 Experiment Results
Buckling LoadMax
Specimen
Load
Web
Flange
a
1171
1062
1029
a-1
1295
1006
1236
a-2
1395
1304
1295
a-3
1490
1227
1346
b
1577
1497
1553
c
1032
815
991
c-1
1224
961
1125
c-2
1472
1201
c-3
1443
1202
1176
d1413
1188
d-1
1546
1293
1398
d-2
1581
1342
d-3
1615
133114407

What was found from the previous results is:
CFRP sheets in vertical direction used as a reinforcement method do help to increase the buckling load andload-bearing capacity of the H-shaped cross-section member. However, overall stiffness loss after web
buckling is not improved.

Adding sheets in the horizontal direction helps to increase buckling load even more compared to case 1. It also
helps increase overall load-bearing capacity.



By reinforcing with Vertical and horizontal CFRP sheets, the overall rigidity loss due to local buckling of theweb is improved.

Reinforcing the flanges with CFRP sheets in vertical and horizontal directions helps to slow the decline inyield strength after the maximum load is reached, getting a ductile behavior.

The buckling load of the flange increases by halving the horizontal sheet. Also, there is little change in thebuckling load of the web.

6. FEM analysis of Specimen with no reinforcement
A FEM analysis of the specimen with no reinforcement (specimen b, a, c and d) is done to make the fundaments
and basis for future designs related to this member and CFRP sheets reinforcements. The parameters of the models
are shown in the following tables:

Table 6.1, 6.2, 6.3 Model parameters

8FEM models of the specimen with no reinforcement were done applying the effect of initial deflection according
to Japan's Road Bridge Specifications. With this effect, the results of maximum load and buckling load of most ofthe models were in agreement with the experimental results. However, the behavior of stiffness and toughness
were very different, as shown as an example in figure 6.1, showing model a and specimen a vertical displacement.
The reason of this, is because in all real specimens, welding was done to assemble them. One of the effects ofwelding is to produce residual stresses in the assembled members. Residual stress sometimes causes a reductionin the performance of a member. Since the models of the analysis do not have the effect of welding implemented,
it could be one of the reasons that there is a difference between analysis and real results. Adding the effect ofresidual stress could make the results closer to the real ones.

Table 6.4, 6.5 and Figure 6.1 Comparison of results of the models and specimens
7. Conclusions and Future Research

Using CFRP sheets as a reinforcement material do helps to increase the load-bearing capacity ofcompression forces. By using, CFRP sheets in the vertical and horizontal direction, the method is more
effective than by using just CFRP sheets in the vertical direction. This is because horizontal CFRP sheets
help to decrease the Out-of-Plane displacement when buckling occurs, helping to get a ductile behavior.
By halving CFRP sheets in the horizontal direction, there is not so much change on the web, but it
improves buckling load in the flanges. Reducing the CFRP sheets in horizontal direction proves to give
good results, so more experiments reducing CFRP sheets will be done in the future to get more data
regarding this matter.

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Future Research:
Make experiments reducing the number of CFRP sheets in the vertical and horizontal direction to see how it
affects buckling load and load-bearing capacity.

Make experiments using CFRP sheets as reinforcement, but this time using longer members than the ones usedin this case of study to see how CFRP sheets reinforcement affects them.

Improve FEM models by adding the effect of residual stress to improve the results from the analysis so they
could be more similar to the ones obtained from the experiments.

Find a way to model CFRP sheets and make models of members reinforced with CFRP sheets to compare theanalysis results with the results obtained from the experiments.

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