FRP-PC members: Evaluation of torsional capacity

Concrete design codes contain detailed provisions for determining the torsional resistance of conventional reinforced/prestressed concrete members, but similar provisions are lacking for Fibre Reinforced Polymer (FRP) Reinforced Concrete (RC) members. In general, there is paucity of research on torsional behaviour and resistance of FRP Prestressed Concrete (FRP-PC) structures. Since the torsional design provisions of the Canadian Standard CSA A23.3 for conventional Prestressed Concrete (PC) are quite rational, it may be possible to adapt them for application to FRP-PC members. To be able to do so, at least two critical design parameters need to be determined: the appropriate strength and inclination of the diagonal struts that form the inclined members of the space truss model for torsion. The Canadian Standard CSA A23.3 provides explicit expressions for the determination of these quantities as function of the longitudinal strain at mid-height of the member. In the draft of the revised edition of the Canadian Standard CSA S806, which deals with the design and retrofit of FRP reinforced/strengthened structures, the CSA A23.3 method is adapted for application to FRP-PC structures. In this study the adapted method results are compared with available experimental data from FRP prestressed concrete beams subjected to torsion. For comparison, Zhou's approach, which is based on the traditional 45° space truss model, is also used to evaluate the torsional capacity of the same test beams. Based on the results, suggestions are made for design of FRP-PC members against torsion.