Softening-Coefficient for FRP Shear-Strengthened Reinforced Concrete Elements

The use of Fiber-Reinforced Polymer (FRP) materials in civil engineering as an economical alternative to traditional methods for strengthening of deficient reinforced concrete elements dates back to the early 1970s. The complex behavior and failure modes of FRP composite structures were studied through extensive experimental and analytical investigations. While research related to the flexural behavior of FRP-strengthened elements has reached a mature phase, studies related to FRP shear strengthening is still in a less advanced stage. Several analytical models to predict the gain in shear capacity due to FRP strengthening were recently proposed. However, most of these models resulted in large discrepancies and produced large errors when compared to experimental results. In all of these models, the constitutive behavior of concrete and FRP was described independently. The true behavior, however, should account for the high level of interaction between the two materials. In this research, new constitutive relations for FRP-strengthened reinforced concrete elements subjected to pure shear are developed. These relations provide a better understanding of the shear behavior of the composite structure. In order to generate these relations, large-scale tests of a series of FRP-strengthened reinforced concrete panel elements subjected to pure shear are conducted. The University of Houston is equipped with a unique universal panel testing machine that was used for this purpose. The results of this research are expected to greatly enhance the understanding of the complex shear phenomenon of FRP-strengthened elements, which will ultimately improve the accuracy of available design guidelines.