Experimental Evaluation of Precast Concrete Diaphragm Critical Shear Joint under Seismic Demands

Abstract

Recent seismic design approaches for precast concrete diaphragms recognize the need to preclude in-plane shear failure. However, the reliable shear capacity of the precast concrete diaphragm, involving a complicated shear force transfer mechanism in the failure critical section within the joints between the precast floor units, has not been fully established. In particular, the effect of the actual set of seismic forces that could act on this joint, including combinations of in-plane shear, in-plane moment, and axial thrust, compressive and tensile, as well as different joint opening demands, to our best knowledge, has not been examined, particularly in the nonlinear (postpeak) regime. In this work, the shear critical joint in a precast concrete floor diaphragm is experimentally evaluated under anticipated seismic demands using the hybrid (adaptive) testing technique. The test specimen consists of two half-scale untopped precast floor units connected by typical diaphragm reinforcement. The test specimen is placed in a loading fixture capable of simultaneously providing shear, axial force, and moment to the joint. The test simulates the maximum considered earthquake seismic response of a long floor span structure configuration. During this response, the test specimen undergoes high shear loading in the presence of nonuniform and nonproportional joint opening, in-plane moment, and cyclic axial thrust. The shear strength, stiffness, cyclic shear deformation capacity, and postpeak response of the joint are examined. Design recommendations are provided.