Experimental investigation on behavior of reinforced concrete (RC)interior beam column joints retrofitted with fiber reinforced polymers(FRP)

Abstract

Beam Column joints experience large shear forces during seismic events and may undergo brittle failure which is not preferred. Eminent scholars suggested different technologies and methods to strengthen the beam column joints. FRPs, which have high strength to weight ratio, are also suggested as retrofitting materials for strengthening RC structural members. From literature review, it is found that FRPs are very effective in strengthening the shear, flexural and axial capacities of beams and columns. They are being effectively used for retrofitting exterior and corner joints due to ease of accessibility and placement. This experimental study is under taken to study the behavior of RC interior beam-column joints which lack in shear reinforcement and strengthened by FRPs and additional tie bars. The samples are constructed with transverse beams and slab. Total eight models have been prepared of which three joints have been strengthened by Carbon FRP (CFRP) Fabrics, two joints have been strengthened by CFRP Plates and one model has been strengthened by adding tie bar into the joint. The samples have been subjected to incremental cyclic loading provided by hydraulic jacks under constant axial or gravity load and their load-deformation behaviors have been measured by dial gauges and video extensometer. The behaviors of the strengthened joints are compared with the control models. The joints without shear reinforcement undergo brittle failure under cyclic loading. But their ductility increases with increased concrete strength. The joints strengthened by the CFRPs show better load bearing capacity with enhanced ductile behavior. Location of the plastic hinges shifts from column to beam in case of the joints strengthened by CFRP plates and fabrics. The joint strengthened by additional tie bar and micro-concrete undergo large rotational deformation before they fail. Joints strengthened by CFRP fabrics exhibit better ductility and strength than those of the joints retrofitted by CFRP plates and tie bars. Joints strengthened by CFRP Plate exhibited high rotational stiffness and are effective in resisting the diagonal crack travelling to transverse beams.