Shear behavior of high-strength concrete beams reinforced with carbon fiber-reinforced polymer bars

Abstract

This study experimentally investigates the shear performance of high-strength concrete (HSC) beams reinforced with carbon fiber-reinforced polymer (CFRP) bars. Thirteen HSC beams were tested under four-point monotonic loading until failure, focusing on parameters such as the shear span-to-depth (a/d) ratio, longitudinal reinforcement ratio, transverse reinforcement ratio, and the type of longitudinal reinforcement (CFRP, steel, and hybrid CFRP-steel). The study analyzed failure modes, shear cracking patterns, cracking load, ultimate shear capacity, and load-deflection responses. Results indicated that shear failures in CFRP-reinforced HSC beams can occur suddenly due to the brittle nature of both FRP and HSC. Adding longitudinal steel bars alongside CFRP bars significantly enhanced the ultimate shear capacity while balancing both ductility and durability. The ultimate shear capacity was primarily influenced by the longitudinal reinforcement ratio and the a/d ratio. Specifically, the ultimate shear capacity decreased by approximately 72 % as the a/d ratio increased from 1.0 to 3.0. Furthermore, the maximum midspan deflection increased by 135 %, rising from 4.0 mm to 9.4 mm with the same change in the a/d ratio. Conversely, increasing the longitudinal reinforcement ratio from 0.6 % to 1.7 % led to a 43 % increase in ultimate shear strength due to enhanced dowel action mechanism and improved crack control, which contributed to a higher shear resistance in the concrete beam. Both CFRP and steel-reinforced beams exhibited similar shear capacity, indicating comparable shear transfer mechanisms. Additionally, a proposed shear model based on regression analysis of 139 FRP-reinforced HSC beams demonstrated better predictive accuracy than existing design codes.