Flexural strengthening with carbon fiber-reinforced polymer composites of preloaded full-scale girders

This paper presents results of an experimental investigation on the effecti veness of flexural strengthening with epoxy-bonded, carbon fiber reinforced polymer (CFRP) laminates. The laminates were applied to 20 ft long reinfor ced concrete (RC) T-girders preloaded to different levels of stress. The ma in objective of the study was to evaluate the performance of precracked gir ders 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 predefi ned 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 re ference girder with two layers of CFRP wrap were tested up to failure in on e run for comparison purposes. In the other girders, the level of preload a nd the wrapping technique used were varied. The girders were preloaded up t o 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 servic e load. The level of preload prior to the installation of CFRP does not aff ect the overall behavior of the wrapped specimens. Preloaded partially wrap ped members, however exhibit less ductility and strength than the correspon ding preloaded fully wrapped specimens. They also exhibit an undesirable mo de of bond failure by delamination of the bottom concrete cover along the l evel 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 wh ich was not subjected to preload. Retrofitting the predamaged specimens wit h a full wrap of externally applied CFRP sheets substantially, increases th e yield and ultimate moments (7 and 11% per CFRP layer respectively), reduc es the deflection at a given applied moment, and significantly decreases th e ultimate deflection.