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Non-Invasive Hybrid Retrofit for Seismic Damage Mitigation of Gravity Load Designed Exterior Beam–Column Sub-Assemblage

ABSTRACT The gravity load designed (GLD) reinforced concrete (RC) framed structures have undergone severe damage during earthquake excitation due to their inherent weaknesses. This underlines the need for development of an effective retrofit strategy for seismic damage mitigation of the beam–column sub-assemblages which are the most critical components of existing GLD RC structures. In the present study, an innovative steel bracket and haunch hybrid retrofit system is developed for strengthening of earthquake damaged GLD structures. Also, experimental investigations are carried out on three types of GLD beam–column specimens, namely, (a) control undamaged specimen, (b) control specimen upgraded with single haunch and (c) damaged specimen repaired and retrofitted with the innovative steel bracket and haunch hybrid system, under reverse cyclic loading to evaluate the comparative seismic performance of hybrid retrofit system. An improvement in load carrying capacity of 1.82 and 1.61 times that of control specimen is observed in the repaired and retrofitted specimen in positive and negative cycles, respectively. Moreover, the specimen retrofitted with hybrid retrofit system sustained larger drifts compared with the control specimen and showcased improvement in the total cumulative energy to the tune of 4.48 times that of the control specimen. This demonstrates that the steel bracket and haunch hybrid retrofit system is an excellent candidate for seismic strengthening of earthquake damaged GLD beam–column sub-assemblages. Further, the hybrid retrofit system is found to be superior to single haunch retrofit strategy.