Constitutive relationships and smart aggregate-based damage evaluation of FRP retrofitted concrete membrane elements

The use of Fiber-Reinforced Polymer (FRP) materials in civil engineering as an economical alternative to traditional methods for strengthening of deficient reinforced and prestressed concrete elements dates back to the early 1970s. 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. In fact, many of these studies to date have even resulted in controversial conclusions. 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. This is due in part to the high level of complexity associated with the shear behavior, but more importantly to the lack of accurate constitutive models for FRP shear-strengthened elements. 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.;Constitutive relations for FRP-strengthened reinforced concrete elements should provide a better understanding of the shear behavior of the composite structure. An element-based approach is adopted in which constitutive relations of panel elements making up a composite structure are developed, and then integrated using the finite element method to predict the overall behavior of the entire structure. In order to generate these relations, large-scale tests of eight FRP-strengthened reinforced concrete panels subjected to sequential loading were conducted. The University of Houston is equipped with a unique universal panel testing machine that was used for this purpose.;These constitutive relations were integrated into a finite element model using fiber beam-column formulations. A comparison between the results from the numerical method and available code guidelines was then performed. This study is set to result in breakthrough understanding of the complex shear phenomenon of FRP-strengthened elements, which will ultimately improve the accuracy of available design guidelines.;In addition, structural health monitoring is considered to be an important issue for the maintenance of large-scale civil infrastructure. In this study, an innovative piezoceramic-based approach, utilized as a transducer, is developed for the structural health monitoring of FRP strengthened reinforced concrete columns. To investigate the seismic behavior of reinforced concrete bridge columns, structural health monitoring tests were performed on several specimens under combined reversed cyclic loading at the University of Houston, Missouri University of Science and Technology, and the University of Nevada, Reno. These experimental results show that the proposed smart aggregate-based approach successfully evaluated the health status of the concrete columns for all types of failure modes.