Mechanistic model for prediction of the residual tensile strength of FRP wires

In-service cables made of fiber-reinforced polymer (FRP) wires experience repeated loading during their service life, which gradually degrades their load-carrying capacity. This paper proposes a mechanistic model to predict the residual tensile strength of the FRP wire, based on the state of damage inside the FRP wire as a function of the loading cycle. The mechanistic residual strength model developed here is an extension of the progressive fatigue damage model (PFDM) proposed recently by the authors. The main failure mode in the FRP wire in the PFDM is fiber breaks, allowing for the state of damage in the FRP wire to be determined for a specified maximum fatigue stress level and number of cycles. These results are then used as the input to calculate the residual strength of the FRP wire. Results indicate that the model can predict the residual strength of FRP wires well compared with the experimental data that has appeared in the literature. The proposed model is shown to provide a better understanding of the influence of the fatigue loading conditions on the residual tensile behavior of FRP wires, specifically, the effect on the residual stress-strain response, the kinetics of fiber element breaks, and the critical damage cluster. Moreover, the proposed model allows validation of the adequacy of safety factors typically adopted by designers to consider the degradation in strength of FRP cables, which is critical for the successful design and realizing the full potential of FRP cables.