Sagging and hogging strengthening of continuous unbonded posttensioned HSC beams by NSM and EBR

Continuous unbonded posttensioned concrete beams might require strengthening to cope with higher demands. Strengthening with carbon-fiber-reinforced plastics (CFRP) is a viable option; however, because of the limited number of studies in this area and lack of experimental data, the guidelines covered only bonded prestressed concrete members, in particular when these are made from high-strength concrete (HSC). This paper reports on the results of an experimental investigation on the flexural behavior of continuous unbonded posttensioned HSC beams strengthened using CFRP. In this application, the CFRP is either externally bonded reinforcement (EBR) or internally near-surface mounted (NSM) in both hogging and sagging regions. The results show that both service and ultimate states of continuous unbonded posttensioned concrete beams were considerably improved by CFRP strengthening, and also that the efficiency of the NSM method is greater than that of the EBR method, especially in crack propagation and ultimate load.