Effect of bond on flexure of concrete beams prestressed with FRP tendons

The objective of this study is to reveal the effect of bond between composite tendons and concrete on the short-term behavior of fiber reinforced polymer (FRP) prestressed concrete beams. Based on a nonlinear model that has been calibrated by experimental data, numerical tests are performed on both simply supported and continuous beams prestressed with bonded and unbonded FRP tendons. Various levels of prestressing reinforcement ratio (ρp) are used. The analysis shows that the bond condition of FRP tendons has a remarkable influence on the flexural response of FRP prestressed concrete beams, including failure mode, crack pattern, deformation, increase in tendon stress and neutral axis movement. Moment redistribution by unbonded FRP tendons is obviously higher than that by bonded ones at a low ρp level, but the redistribution discrepancy appears to be insignificant at a high ρp level. ACI 318-11 can satisfactorily reflect the bond effect on moment redistribution in FRP prestressed concrete continuous beams but CSA A23.3-04 cannot.