SEISMIC EVALUATION OF RC BEAM COLUMN JOINT STRENGTH WITH FRP UNDER CYCLIC LOADTHENED

Abstract

Devastating earthquakes in the past few years have shown that seismically deficient concrete frames are particularly vulnerable to seismic action and are a major cause of loss of lives. This structural type constitutes a large share of the building stock, both in developed and developing countries, and hence represents a substantial exposure. Direct observation of damaged structures has shown that damage occurs usually at the beam-column joints, with failure in bending or shear, depending on geometry and reinforcement distribution and type. While substantial literature exist for the design of concrete frame joints to withstand this type of failure, after the earthquake many structures were classified as slightly damaged and, being uneconomic to replace them, at least in the short term, suitable means of repairs of the beam column joint area are being studied. The study reports the results of cyclic tests carried out on cruciform beam-column joint specimens, with two different configurations of steel reinforcement detailing and strengthening by externally bonded FRP wrapping. One specimen was designed to comply with gravity load design codes and the other with detailing according to IS: 13920-1993. GFRP wrapping is used for retrofitting of damaged joints with epoxy resin. Analytical modelling of the same is done with the help of the software package and its behavior with the actual one is compared. Main emphasis remains on comparison of the strength and ductility of the undamaged and retrofitted specimen. Also the behavior of confined specimen is compared with the unconfined one. Effect of GFRP wrapping confinement is discussed as a viable option for restoring the strength of beam column joint upto a significant level.