Shear modeling of FRP-reinforced FRC beams via enhanced modified compression field theory

Replacing steel rebars with fiber-reinforced polymer (FRP) bars in concrete beams is one of the effective solutions to durability issues caused by corrosion. However, due to the relatively low elastic modulus of FRP bars, structural members often exhibit insufficient axial stiffness, resulting in wider cracks and more significant deflection during service. Incorporating fibers into FRP-reinforced concrete beams is a robust method to enhance the axial stiffness of the members, though the addition of fibers complicates the shear transfer mechanism in the beams. Based on the fiber pull-out failure mechanism, this study systematically analyzes the stirrup strain characteristics of FRP-reinforced fiber concrete beams under ultimate conditions by introducing axial stiffness correction coefficients and shear span-to-depth ratio parameters into the modified compression field theory, aiming to quantitatively evaluate the shear capacity and provide a basis for engineering design. An experimental database containing 411 beam specimens was established to investigate the influence law of shear span-to-depth ratio and validate the reliability of the proposed model. The results demonstrate that the calculated values of the model show good agreement with experimental results, with the average (AVG.) and coefficient of variation (COV.) being 1.04 and 50.31%, respectively.