Seismic Response of Strengthened RC Beam Column Joints with Haunch Effects

Abstract

From the study of a large number of buildings, it has been recognized that beam column joint is one of the critical elements of a building system. This element should be designed and detailed properly, especially when the frame is subjected to earthquake loading. Beam column joints are brittle in nature. The breakdown of beam column joint during earthquake is controlled by bond and shear failure mechanism. The main reinforcement of columns just above the joint region, discontinuous bottom beam reinforcement and little or no joint transverse reinforcement are the most critical details of beam column joints in buildings. Therefore, current international code of practices gives more importance to provision of adequate anchorage to longitudinal bars and confinement of core concrete so as to resist shear. Modern codes propose for reduction of seismic forces through provision of special ductility requirements. Details for achieving ductility in reinforced concrete structures are given in IS 13920-1993. In the present study, a two-bay five-storey reinforced cement concrete moment resisting frame for a general building has been analyzed and designed by using STAAD Pro as per IS 1893–2002 code procedures and detailed as per IS 13920-1993 recommendations. An exterior beam column joint has been modelled to 1/5th scale of the prototype and the specimen has been subjected to cyclic loading to study its behaviour during earthquake loading. The experimental programme consists of two interior beam-column joint specimens, one is RC haunch and other one is strengthened RC haunch. The specimens are designated as RC and RCH respectively. In this study key structural issues such as load carrying capacity, load deflection behavior, stiffness degradation, energy dissipation capacity, ductility factor and cracking pattern have also been examined.