Seismic Behavior of R.C. Beam-Column Joints Designed for Gravity Only

Abstract

The inherent seismic vulnerability of reinforced concrete beam-column connections designed for gravity load only is herein investigated. Experimental tests on six 2/3 scaled beam-column subassemblies, with structural deficiencies typical of Italian construction practice between the 50’s and 70’s, were performed under simulated seismic loads. Interior, exterior tee and knee joints, characterized by the use of smooth bars, inadequate detailing of the reinforcement (i.e. total lack of transverse reinforcement in the joint region), deficiencies in the anchorage (hook-ended bars) and the absence of any capacity design principles, were subjected to quasistatic cyclic loading at increasing levels of interstorey drift. The experimental results underlined the significant vulnerability of the joint panel zone region and the critical role of the slippage phenomena due to the use of smooth bars and of inadequate anchorage. A particular “concrete wedge” brittle failure mechanism, due to the interaction of shear cracking and stress concentration at the hook anchorage location, was observed in the exterior specimens. The inaccuracy of traditional shear degradation models for exterior joints in predicting similar damage mechanisms is discussed and possible modifications are suggested.