Flexural Strengthening with Carbon Fiber-Reinforced Polymer Composites of Preloaded Full-Scale Girders

This paper presents results of an experimental investigation on the effectiveness of flexural strengthening with epoxy-bonded, carbon fiber reinforced polymer (CFRP) laminates. The laminates were applied to 20 ft long reinforced concrete (RC) T-girders preloaded to different levels of stress. The main objective of the study was to evaluate the performance of precracked girders under service load, where the service load is defined as a percentage of the yield strength for the section. The girders were loaded at a predefined stress level, locked into place, and then retrofitted with CFRP fabric. Eight T-girders were tested in all. A control girder with no wrap and a reference girder with two layers of CFRP wrap were tested up to failure in one run for comparison purposes. In the other girders, the level of preload and the wrapping technique used were varied. The girders were preloaded up to 65, 85, and 117% of control yield moment and locked and strengthened with two layers of CFRP wraps before resuming the loading up to failure. The results demonstrate the feasibility of rehabilitating and strengthening damaged RC structures with CFRP wrap while the structures are under service load. The level of preload prior to the installation of CFRP does not affect the overall behavior of the wrapped specimens. Preloaded partially wrapped members, however, exhibit less ductility and strength than the corresponding preloaded fully wrapped specimens. They also exhibit an undesirable mode of bond failure by delamination of the bottom concrete cover along the level of the longitudinal steel reinforcement. Therefore, the use of partial wrapping should be used only when full wrapping is not feasible. Preloaded fully wrapped members perform similarly to the reference wrapped member, which was not subjected to preload. Retrofitting the predamaged specimens with a full wrap of externally applied CFRP sheets substantially increases the yield and ultimate moments (7 and 11% per CFRP layer, respectively), reduces the deflection at a given applied moment, and significantly decreases the ultimate deflection.