Cyclic Behavior of Wall-Slab Joints with Lap Splices of Cold-Straightened Rebars and Mechanical Splices

In the construction of reinforced concrete structures, bent reinforcing bars (rebars) are manually straightened to connect wall-slab joints in tall buildings, retaining wall-slab joints, and temporary openings, among other uses. Plastic deformation is unavoidable in the cold bending and straightening of rebars, and the work-hardening effect, the aging-hardening effect, and the Bauschinger effect weaken the rebars. Mechanical splices offer an alternative to the bending and straightening of rebars. In this study, tensile tests were conducted on cold-bent and straightened rebars to identify the resulting changes in yield strength, modulus of elasticity, tensile strength, and ductility. Cyclic loading tests were subsequently conducted on wall-slab joints to compare the structural performance of joints with mechanical splices with that of joints constructed with cold-straightened rebars. The test results indicate that the joints with mechanical splices exhibited typical flexural behavior and were equivalent in capacity to monolithic joints. In contrast, the joints with cold-straightened rebars developed a greater amount of bond cracks in the surface and spalling of the side cover concrete of the slab; these joints consequently displayed less strength and deformation capacity and lost stiffness more rapidly than did the joints with straight rebars. This phenomenon was apparent for joints with larger diameters and for higher-grade rebars. Therefore, joints with cold-straightened rebars should be used with caution in design and construction.