Postfatigue Monotonic Behavior of RC Beams Strengthened with Prestressed NSM CFRP Strips: Ductility Evaluation

Abstract

The flexural behavior of fatigued reinforced concrete (RC) beams strengthened using prestressed near surface mounted (NSM) carbon fiber–reinforced polymer (CFRP) strips was investigated. Five RC beams were tested; one beam served as a control unstrengthened beam, while the other beams were prestressed to strain values corresponding to 0, 21, 40, and 60% of the CFRP ultimate tensile strain. The beams were subjected to fatigue load conditions for 3 million cycles. Thereafter, the postfatigue monotonic flexural behavior of the beams was compared with identical unfatigued beams. Test results showed that the fatigue loading had a minor effect on the bond performance at the concrete-epoxy interface of the RC beams. In general, fatigue loading did not affect significantly the postfatigue monotonic performance of the tested beams in terms of yield and ultimate loads and deflections, as compared with identical unfatigued beams tested in static conditions. The ductility of the tested beams was also evaluated and compared with similar unfatigued beams using several ductility models found in the literature. No fatigue effect on ductility (NFED) prestress strain was introduced and proposed as a mean to define the prestress strain at which the fatigue loading has no effect on the ductility of the RC strengthened beams. The NFED prestress strain for the particular specimens that were considered in this research ranges from 62 to 82% of the CFRP ultimate tensile strain, which indicates that the ductility of the fatigued beams is higher than that of the unfatigued beams for most of the practical prestress values.