Reliability analysis of shear strength provisions for FRP-reinforced concrete beams

This paper is aimed at conducting a reliability based assessment on shear strength provisions of the existing design codes for fiber-reinforced polymer reinforced concrete (FRP-RC) beams. Herein, shear design equations of the latest versions of ACI 440.1R and CSA S806, which are two of the most widely used codes for FRP-RC beams, are studied. The shear strength formula of ACI 440.1R is different from that of CSA S806 in that how they incorporate various parameters. It is, therefore, of interest to evaluate the reliability levels offered by these design equations. In doing so, the uncertainty in mechanical and geometrical variables, the error inherent in shear resistance models, and the probabilistic characteristics of various types of loads including dead, live, snow, wind, and earthquake under different load combinations are considered. The shear model errors have been assessed using a large database of shear-failed test results, which was assembled from literature and contained 288 FRP-RC beams without stirrup and 109 beams with FRP stirrups. It was revealed that the safety level for shear capacity of beams without stirrup is different from that for beams with stirrup in ACI, and to a lesser extent, in CSA. Moreover, the reliability indexes of shear strength of FRP-RC beams in ACI differ from those in CSA. In order to meet the target reliability index, the modified shear design formulae and the corresponding safety factors are proposed. Besides, the shear compression capacity, which proves to play a key role in the reliability index of shear strength of beams with FRP stirrups, is revised for different reliability levels.