Evaluation of the efficacy of CFRP strengthening composites on unbonded prestressed concrete beams with pre-cracks

Abstract

Research efforts on the pre-cracked unbonded prestressed concrete (UPC) beams strengthened with externally bonded fibre-reinforced polymer (FRP) systems are still very limited. Thus, this study intends to experimentally investigate the efficacy of FRP strengthening composites on UPC beams with pre-cracks. The experimental program comprised four large-scale UPC beams with a T-section strengthened with longitudinal carbon FRP (CFRP) sheets and CFRP U-wrap anchors. The experimental results showed that only after cracks reopened the CFRP strengthening system became effective. The CFRP composites carried tensile stress, controlled cracks and thus reduced the stiffness degradation of the precracked beams. As a result, in both the serviceability stage and ultimate stage, the CFRP-strengthened beams had better performances as compared to the unstrengthened counterpart concerning the deflection, crack width and load-carrying capacity of the beam. In addition, the premature debonding of the longitudinal CFRP sheets was effectively averted by the use of U-wrap anchors, which increased the contribution of the longitudinal CFRP sheets.

Keywords: Pre-cracks; strengthening; CFRP composites; unbonded prestressing tendons.