INFILL WALLS AS A SPINE TO ENHANCE THE SEISMIC PERFORMANCE OF NON-DUCTILE REINFORCED CONCRETE FRAMES

This paper reports the results of an investigation on the efficacy of using rocking spines of strengthened infill walls as a retrofit measure for non-ductile reinforced concrete (RC) frames with unreinforced masonry (URM) infill walls. The study examines the effects of spines of strengthened URM infill walls on the behavior of the RC frame, with particular emphasis on whether spines could reduce the tendency to form a soft story mechanism. For this purpose, a nine story frame with five bays is selected to represent complex multi-story behavior, where the collapse of stiff infill walls may lead to the formation of a soft story mechanism. The effect of the proposed retrofit is investigated through nonlinear static and dynamic analyses. Fragility relationships are obtained for the frames using pseudo-acceleration corresponding to the first mode as the intensity measure and maximum interstory drift ratio as the response variable. For the analyses, a progressive collapse algorithm, previously developed and implemented into the object-oriented open system for earthquake engineering simulation (OpenSees) is utilized and the interaction between the inplane strength of the infill wall and its out-of-plane strength is taken into consideration. Analyses show that infill retrofit with rocking spines provides significant improvement in the seismic performance of non-ductile RC frames.