Reliability-Based Calibration of Strength-Reduction Factors for Flexural Design of FRP-RC Beams Under Various Load Combinations

The aim of this paper is to conduct reliability analysis of flexural strength design provisions of FRP-reinforced concrete (FRP-RC) beams in accordance with CSA S806. In particular, different load combinations, including dead, live, wind and snow, are investigated. Through this, the various sources of uncertainty related to the material strength and geometrical properties are taken into account when examining the reliability of the flexural strength provisions of CSA. The uncertainty inherent in the flexural strength model is assessed using a large experimental database of 303 FRP-RC beams assembled from the literature. The first-order reliability method (FORM) is employed for reliability analysis. The results indicated that the reliability index, β, of the current code is not consistent for different failure modes, yielding overly conservative values for the FRP rupture mode (β = 4.895) compared to the concrete crushing mode of failure (β = 3.726). Based on the reliability-based calibration of the existing design equations, modifications to the current provisions are proposed to achieve a variety of target reliability indexes of 3.5, 3.8, and 4 for the failure modes of concrete crushing and FRP rupture, separately, and for a common range of load ratios in the different load combinations. The results presented enable designers to choose proper strength-reduction factors to reach the desired level of safety for each failure mode in the flexural design of FRP-RC beams.