Flexural behaviour of RC beams strengthened with combinations of two CFRP systems and P-SWRs

Externally bonded (EB) carbon fibre-reinforced polymer (CFRP) sheets, near-surface-mounted (NSM) CFRP bars and prestressed steel wire ropes (P-SWRs) are widely used for strengthening reinforced-concrete (RC) beams. Existing research has shown that it can be inefficient or infeasible to provide sufficient load-carrying capacity using one strengthening method because of the CFRP strain limitation at debonding or the upper bound on the amount of strengthening materials due to limited space for strengthening. Moreover, some already strengthened RC beams need to be further strengthened under heavier loading conditions. Therefore, using a combined strengthening scheme for one beam should be considered in both these situations. In this study, five concrete beams were strengthened and tested to explore the effects of different combined schemes on beam flexural behaviour. The results demonstrate that P-SWRs are of crucial importance in improving the cracking behaviour and ductility of beams originally strengthened with EB-CFRP sheets or NSM-CFRP bars. The strengthening scheme of NSM-CFRP bars and P-SWRs is found to be better than that of EB-CFRP sheets and P-SWRs. A recommendation for the appropriate selection of strengthening schemes is given based on the test results.