Concrete jacketing of deficient exterior beam column joints with one way spiral ties

Abstract

Post-earthquake examination of the structures designed for gravity loads showed that one of the weakest links in the lateral load-resisting system is the beam-column joints, especially exterior ones because of a sudden geometric discontinuity andalso they are not confined by beams from all the sides. Seismic retrofitting of reinforced concrete structures is aimed at strengthening its structures, in general, and components, in particular, to achieve more and consistent strength ductility and energy dissipation. Experimental investigation is carried out on non ductile beam column joint sub assemblage specimens keeping a scale ratio of 3. The two group of specimensdesignated as control specimens and retrofitted specimens. The specimens were prepared using M 25 grade concrete with average 8 mm sized coarse aggregate and manufacturedsand. The seismic loading simulation was arranged through reverse cyclic loading using hydraulic jacks. The control specimens clearly showed poor performance under cyclic loading. The behaviour was characterized by the diagonal cracks at joint region leading to plastic hinge formation. The upgraded specimens using concrete jacket were exhibited well performance than the deficient joint sub assemblage. The performance improvement of upgraded specimens was characterized by 26.20 % higher displacement ductility, 40 % higher ultimate load carrying capacity and 127.10 % higher energy dissipation capacity than control specimens. The ultimate failure in case of retrofitted specimens occurred on beam at jacket interface, which contributes to most acceptable failure modes i.e., strong column weak beam. The proposed technique of providing one wayspiral ties was useful in reducing the reinforcement congestion in thin wall concretejacketing around joint. The experimental results revealed that the concrete jacketingaround the beam column joint sub assemblage is effective in inducing the seismic requirements in the external beam column joints.