| External bonding of fiber reinforced plastic (FRP) strips to reinforced concrete (RC) beams has been widely accepted as an efficient and effective method for strengthening and upgrading members. With more and more attention being paid to the strengthening area for RC structures using FRP strips, there was been an exponential growth of research. The objective of the present thesis is to study the enhancement of the mechanical performance of strengthened virgin/precracked RC beams through optimization of design variables (e.g. taper ended FRP strips) based on experimental investigation, accompanied with confirmation by numerical analysis and fracture toughness measurement. This thesis also develops reliable theoretical models for proper evaluation of strengthened beam capacity, identifies the tendency of occurrence of various failure modes and establishes practical guidelines for optimized design criteria and material selection.; To prove the experimental results, the finite element method was used to analyze the interlaminar principal, shear and normal stress distributions along the FRP strip-concrete interface, with a special focus on stress concentration at the end of FRP strips. The numerical study indicates that all stress concentrations at the FRP strip ends are reduced with the tapered ends, which in turn leads to a larger load carrying capacity. In addition, the effects of other taper parameters are studied. A simple guideline is proposed for optimal design of tapered FRP strips for given RC beam properties and dimensions. The solutions are formulated based on the determination of critical transition conditions of FRP strips that can give rise to the maximum strengthening performance. The effect of taper configuration of FRP strips on interlaminar fracture behavior is studied through the asymmetric double cantilever beam (ADCB) test. It is found that the taper configuration can significantly affect the load-displacement behavior as well as the crack growth resistance curves. In the sample with tapered FRP strips, there were apparently separate stages of crack propagation corresponding to different FRP strip thicknesses. (Abstract shortened by UMI.)... |
