Deflection calculation of FRP-strengthened reinforced concrete flexural members

Externally bonded fibre-reinforced polymer (FRP) composite plates can enhance the flexural strength, as well as stiffness to a limited degree, of reinforced concrete (RC) flexural members. Understanding the behaviour of these strengthened members at the serviceability and ultimate load ranges of response is of particular importance to engineers. The description of such behaviour is best described via plotting of the complete moment-curvature, as well as load-deflection responses from initial load to member failure. Based on the assumption of a tri-linear momentcurvature relationship, closed-form analytical solutions are presented in this paper for calculating the complete load-deflection response of FRP flexurally-strengthened one-way RC slabs and beams, which are simply-supported (three- and four-point bending), as well as cantilevered (free-end point load). The analytical predictions compare well with test results and the basis of a new "quad-linear" moment-curvature relationship is proposed that may better capture a so-called "pseudo-ductile" response occasionally observed in experiments. The influence of anchorage of the FRP strengthening for the prevention or delaying of debonding and a procedure for its inclusion in the analytical model is also discussed. Finally, the results of parametric studies are presented.