Behavior and evaluation of the lap splice for steel-FRP composite bars embedded in concrete beams

Abstract

Lap splice is a convenient method for connecting discrete non-weldable bars into a reinforcing unit via adequate splice lengths. When placed into concrete beams, it also serves as a bond test protocol that simulates the non-uniform stress states in structural components. Steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a novel rebar composed of an inner steel bar and an outer FRP layer. With a higher initial elastic modulus than FRP bars and a stable positive post-yield hardening stage, SFCBs are likely to exhibit lap splice performance distinct from both FRP bars and steel bars. Four-point bending tests were conducted exploratorily on concrete beams with lap-spliced SFCBs. The variables include the embedment length in lap splices (10d_b, 15d_b, 20d_b), the presence or absence of stirrups in the splice zone, and the rebar arrangement (distributed or bundled reinforcement). The lap splice specimens failed in pre-yield, near-yield, and post-yield states, and specimens with sufficient embedment length demonstrated post-yield stiffness. With increasing embedment length from 10 d_b to 15 d_b and 20 d_b, the average bond strength decreased by 14 % and 26 %. Stirrups within the splice zone effectively prevented brittle failure, while they did not significantly affect load-carrying capacity when embedment lengths were relatively short. When the cross-section for distributed reinforcement is congested, the two-bar bundled lap splice specimens exhibit a 15 % higher average bond strength. A simplified bond stress distribution model matches the experimental observations and demonstrates potential for predicting the achievable tensile stress of lap-spliced SFCBs in concrete members.