Static and fatigue performance of reinforced concrete beams retrofitted with external CFRP composites

Fiber reinforced polymer (FRP) composites have recently appeared as a new material and technology to retrofit reinforced concrete structures in civil engineering because of their high strength-to-weight ratio, resistance to corrosion and ease of handling during the application. When FRP composites are used to strengthen or repair existing structures, they are usually externally bonded to the critical or the deficient parts of the structures. In this dissertation, the bond properties between a commercially available carbon fiber reinforced polymer (CFRP) system and concrete were first studied. Then the performances of reinforced concrete beams retrofitted with this CFRP system subjected to both static and fatigue loads were investigated.; A series of CFRP-concrete bond joints with different bond lengths were tested to study the force transfer, bond development length, failure mechanism and bond strength between FRP and concrete. Based on the experimental observations, an analytical model was developed and design recommendations were proposed.; The second part of the work was the static study of failure characteristics of reinforced concrete beams externally bonded with the CFRP system. Medium-sized concrete beams with several CFRP strengthening and repair schemes were tested. Numerical simulation and analysis of the crack patterns by the finite element method were conducted to further understand the failure process. The experimental and numerical results, in addition to the mode and manner of failure, were used to refine a previously established analytical model. The final comparisons were made between the analytical results and experimental results.; The final part of the work pertained to the fatigue study of similar beams to the static test. Several maximum load levels were employed in order to apply higher stress levels to the steel reinforcement. The crack development, the stress changes in the steel reinforcement, FRP and concrete, and the failure modes were observed and analyzed. Regression analyses of the S-N data from both this study and the available studies in the literature were conducted and compared with the existing fatigue design rules for reinforced concrete beams. Finally, the two-parameter Weibull distribution was employed to incorporate failure probability into the S-N relationships of reinforced concrete beams retrofitted with external FRP composites.