Shear Resisting Mechanisms of ECC FRP Strengthened RC Beams

Abstract

This paper presents the results of a study that investigates the mechanisms of shear resistance in reinforced concrete (RC) beams that are shear-strengthened with engineered cementitious composites (ECCs) and fiber-reinforced polymer (FRP). The ECC FRP utilizes ECC as the bonding agent between the FRP and concrete and the FRP as the high-strength reinforcement. The test program was divided into three groups: (1) 15 dog-bone shaped ECC FRP coupons; (2) 27 ECC FRP push-off blocks; and (3) two ECC FRP shear-strengthened RC beams 125 mm wide, 300 mm high, and 2,640 mm long. Groups 1 and 2 aimed at investigating the uniaxial tension and push-off behavior, respectively, by simulating the crack separation and sliding mechanisms. These mechanisms are fundamental to understanding the shear resistance of the ECC FRP and are characterized by the applicable tensile stress–strain and shear stress–sliding laws. The embedded FRP mesh in the ECC FRP composites significantly enhances the crack sliding that is required for shear strength development, with a minimal impact on the tensile and shear strengths. In addition, the precrack width reduced the shear strength of the ECC FRP. Group 3 aimed to investigate the shear behavior of the ECC FRP beams. The crack width and sliding were monitored during loading, which provides insights into the shear contributions from the concrete, steel stirrups, and ECC FRP. The results reveal a major shift in the shear capacity contribution from the concrete to the ECC FRP in the strengthened beams, which led to a substantial shear improvement. The contributions of the ECC FRP to shear resistance by crack separation and sliding were comparable throughout the loading process. The FRP meshes in the ECC FRP composites effectively limited deformation, maintained structural integrity, and redistributed the shear capacity from the ECC FRP to concrete.