Research on CFRP sheet reinforcement of shear steel girders
せん断鋼桁の CFRP シート補強に関する研究
環境社会基盤工学課程 4 年 鋼構造研究室
1. Research BackgroundOn the year Heisei 29 the Road Bridge Specification
was revised. As part of this revision, thetraditionally used Allowable Stress Methos waschanged for the Limit State Design Method, which
is based in statistical data for design parameters.
However, there currently does not exist a concrete
procedure for delimiting the states and carryingout investigations for every type of structure andstructure member.
Limit States are limits within the structuralmember’s capacity to bear loads and deform.
Traditionally, we try to keep structures within thefirst limit, or in other words, its elastic limit, but thelimit state design method allows structures to go
beyond this elastic limit and accept a certain
degree of plastic deformation.
Figure 1 Limit States Grap h for Members

20328586 Maldonado Gutierrez Carlos Eligio❖ Collect base data for setting the limit states forreinforcement and repair- Verify the repair effectiveness of CFRP
through the testing of CFRP reinforcedmembers．
-Organize the data (events) for the states ofeach member section．

3. Experiment Outline
For this study 3 specimens were used: anunreinforced one, one reinforced with CFRP sheets,
and one reinforced with CFRP sheets and steel
plates. These specimens are labeled S-1, S-2, and S3 respectively.
❖ Web（1 Panel）-

740×6，1110mm，α=1.5，SM490Y-

0.2% Proof Stress （Material Testing）-

σy=402MPa→（E=200GPa）εy=2010μ❖ Flanges （ Upper & Lower ） ， VerticalStiffeners- 236×16，95×16，SM490Y-

0.2% Proof Stress（ Material Testing ）-σy=377MPa→（E=200GPa）εy=1885μ❖ CFRP（Medium Elasticity Type）-

2. Research Objectives
The objectives for this research are as follows. With
regards to shear steel girders:❖ Carry out an examination for setting the limit
states of newly constructed members- Organize the data (events) for the states ofeach member section through structuralexperiments.

Yield Strain: εu＝8891μ

A total of 421 sensors were installed in thespecimens for collecting data from the tests,
including: uniaxial strain gages, triaxial strain gages,
and deflectometers.
The Von Mises yield criterion (equation 1) was used
for calculating the equivalent strain on the webfrom the triaxial strain gages.
1𝜀 = √ {(𝜀1 − 𝜀2 )2 + 𝜀12 + 𝜀22 }2(1)Here, 𝜀1 : Maximum Strain, 𝜀2 : Minimum Strain

Figure 5 S-3 Event Organization

4. Data Analysis
Figure 2 Displacement of all 3 specimens

There was a 12% and 26.3% increase in the loadbearing performance of the specimens over theunreinforced specimen for the S-2 and S-3specimens respectively. The maximum load for theS-2 specimen represents the moment its CFRP
reinforcement tears, causing a drastic reduction inits load-bearing capabilities. This behavior iscontrolled in the S-3 specimen with the addition of
the steel plates.
Figure 3 S-1 Event Organization

The yielding pattern of the member’s sections
changed as reinforcement was added. The central
sections of the web were the quickest to yield,
adding CFRP reinforcement did not improved yieldloads, but greatly limited post-buckling
deformation. This also improved the rigidity of thespecimens. Due to the reduced web deformation,
bending strain was reduced on the flanges,
changing their yielding behavior. The vertical
stiffeners were virtually undamaged.
The displacement at the time of the maximum load
for each specimen became larger as the load
carrying capabilities of the girder improved.
However, the residual displacement after eachloading cycle became smaller.

-Figure 4 S-2Event Organization-5. Conclusions
The event organization for each specimen wascompiled, and visual and numericalrepresentations of the results were presented.
Base data for the elaboration of the limit
states was collected.

Findings-The usage of CFRP as a reinforcement method
allows for the improvement of the loadbearing capacity and the buckling load for an
I-shaped girder.

-CFRP does not provide an improvement of thegeneral displacement of the girder undersimilar loading patterns, however, the out-ofplace deformation of the web after buckling isvastly reduced.