Calculation of deflection of FRP-strengthened RC slabs using a tri-linear moment-curvature relationship

Numerous experimental studies have confirmed the ability of externally bonded fibrereinforced polymer (FRP) composite plates to enhance the flexural strength, as well as stiffness to a limited degree, of reinforced concrete (RC) members. Of particular importance to engineers in the design of these strengthened members is describing their behaviour under serviceability and ultimate load ranges of response. Such behaviour is best described via their moment-curvature as well as their load-deflection responses. Based on the assumption of a tri-linear moment-curvature relationship, which has also been assumed by other researchers for FRP-strengthened RC beams [e.g. 1], closedform analytical solutions are presented herein enabling calculation of the complete loaddeflection response of FRP flexurally-strengthened RC slabs which are simplysupported (three- and four-point bending) as well as cantilevered (free-end point load). The analytical predictions compare well with tests and the basis of a new "quad-linear" moment-curvature relationship is finally proposed which may better capture a so-called "pseudo-ductile" response occasionally observed in experiments.