Behavior of FRP-strengthened RC elements subjected to pure shear

The shear behavior of fiber reinforced polymer strengthened reinforced concrete (FRP-strengthened RC) has been the focus of extensive research studies. However, the mechanism of this complex phenomenon has not been fully clarified. Recent analytical models which were developed for predicting the shear capacity of FRP strengthened RC girders were based on test results of simply supported beam specimens with various shear span-to-depth (a/d) ratios. In such tests no region of the specimen is subjected to uniform stress conditions, Therefore, the results of such tests cannot predict the true pure shear behavior due to non-uniformity of stresses, the presence of flexural and other non-shear related effects such as a/d ratio that cannot be filtered out. Therefore, proper design of shear strengthening using FRP requires testing of elements that are subjected to pure shear case primary before adding other governing effects. This allows a careful investigation and full understanding of the behavior at the element level. In order to accomplish this task, panel testing of representative RC specimens strengthened with FRP sheets were needed. This paper reports the testing of 10 FRP strengthened RC panels subjected to pure shear stress field. The tests were carried out to evaluate the effects of three variables: FRP stiffness, FRP wrapping scheme, and transverse steel reinforcement ratio. The test results showed that these three variables greatly affected the shear behavior due to various types of failure modes associated with FRP strengthening. In addition, it was observed that the magnitude of increased shear capacity associated with the application of FRP sheets depends not only upon the stiffness of FRP, but also on the stiffness of internal shear reinforcement. With the increase of internal steel shear reinforcement, the effectiveness of shear gain due to externally bonded FRP decreases.