Flexural performance and bond characteristics of FRP strengthening techniques for concrete structures

Strengthening of reinforced concrete structures using FRPs has emerged as a potential solution to the problems associated with civil infrastructure. Many researchers have reported significant increases in strength and stiffness of FRP retrofitted concrete structures. Nevertheless, possible brittle failures of the retrofitted system could limit the use of the full efficiency of the FRP system. These brittle failures include premature debonding of the FRP, which could occur at load levels significantly less than the strength of the FRP material used in the retrofitted system. Therefore, there is a need for an improved understanding of various failure mechanisms of FRP strengthened concrete structures as a basis for a reliable retrofit design. Innovative structural detailing is also needed to utilize the FRP system more effectively.; The work reported in this thesis deals with the development of a comprehensive approach towards understanding the flexural behaviour of FRP strengthened concrete structures. This study presents a comparison among various FRP strengthening techniques and develops fundamental criteria governing the choice of a specific technique. The applicability of cracked section analysis as well as non-linear finite element simulations for the analysis of concrete structures strengthened with FRP reinforcement is enumerated. Design guidelines regarding the use of FRP in retrofitting applications are provided. Mathematical models are proposed to quantify the bond characteristics and load transfer mechanisms of various FRP strengthening schemes using bars and strips for near surface mounted configurations as well as externally bonded sheets and strips.; A two-phase experimental program was conducted at the University of Manitoba to examine the structural performance of concrete structures strengthened with various FRP systems. The experimental program was designed to ensure full utilization of the strengthening schemes and to avoid possible premature failure of the retrofitted system. Three half-scale models of a typical concrete bridge slab were constructed and tested in the first phase of the investigation. The performance of near surface mounted FRP bars and strips as well as externally bonded FRP sheets and strips was evaluated. The three specimens were used to perform a total of nine tests in this phase. A cost analysis for each of the FRP strengthening techniques considered in this investigation was performed. Complementary to the experimental program, numerical simulations were performed using finite element analysis to predict the behaviour of concrete members strengthened with near surface mounted FRP reinforcement. Based on test results, the investigation was extended to a second stage to provide fundamental data for the bond characteristics of efficient FRP techniques. A total of 24 concrete T-beams were tested to characterize the load transfer mechanisms between FRP and concrete. Three different strengthening techniques were investigated. For each technique, different bond lengths were considered. Based on the experimental results, development lengths for various FRP strengthening techniques are proposed.; The thesis also presents three analytical models, proposed to predict the behaviour of concrete structures strengthened with near surface mounted FRP bars, near surface mounted FRP strips and externally bonded FRP sheets. (Abstract shortened by UMI.)...