Performance of exterior RC beam-column joints using different concretes and reinforcement detailing under cyclic loads

Abstract

Seismic activities demand special design and detailing of Reinforced Concrete (RC) structures, possessing adequate lateral strength, ductility and energy absorption capacity. The shear strength, ductility and energy absorption capacity need to be established for the type of concrete and detailing of lateral reinforcement for ensuring safety of RC joint region. In order to achieve adequate shear strength and ductility, beam-column joints in MRFs need to be designed with High Strength Concrete (HSC) and good reinforcement detailing. The premature joint failure can be prevented when HSC is used in the joint region and hence ensures sufficient load carrying capacity and energy dissipation. This study attempts to accomplish and investigate the performance of five geometrically identical exterior RC beam-column joints with different forms of detailing of reinforcement and also with steel fiber reinforced concrete in the joint region under reverse cyclic loading. The beam-column joints designed for gravity loads and routine live loads made up of low strength concrete are vulnerable to diagonal shear cracking under seismic loading. Adequate anchorage length of beam bars with closely spaced horizontal hoop reinforcement and use of fiber reinforced high strength concrete in the joint region plays predominant role in enhancing the shear strength and performance. Adequate anchorage length of beam bars and good detailing of reinforcement improve the joint shear strength and reduce the joint stiffness degradation. The joint shear strength, ductility, energy absorption and hysteresis pinching response have been improved under reversed cyclic loading with steel fiber reinforced HSC in the joint region. The deflection of beam and the corresponding load at the ultimate stage increase with good detailing in the joint region. The addition of small quantity of steel fibers in HSC could alter the failure of joint from brittle to ductile under reversed cyclic loads.