Softened Truss Model for FRP Strengthened RC Members Under Torsion Including Tension Stiffening Effect

Abstract

This paper presents an analytical model for prediction of torsional behavior of reinforced concrete beams strengthened with fiber reinforced plastics (FRP). Improved model proposed in this study is based on softened truss model (STM) which was developed to predict the response of reinforced concrete (RC) members under torsional loading. Tensile strength of concrete being very low, its contribution to torsional capacity of a RC member was neglected in the original STM. However, previous studies have suggested that neglecting tension stiffening may lead to considerable discrepancies in STM predictions. Therefore, in the present study the original STM has been modified to include the effect of tension stiffening for improved predictions of FRP strengthened RC beams. The developed model has been validated with experimental data obtained from literature. The proposed model shows the contribution of externally bonded FRP to the torsional capacity of RC members in addition to enhancing the ductility and is well supported by the experimental results. RC beams with two different FRP configurations, i.e. continuously wrapped and strip wise wrapped, were considered in this study. The analytical prediction of the overall torque-twist behavior compare favorably with the test data. The developed model can also be used for future parametric studies on FRP retrofitted RC beams under torsion.