Modeling of URM Infills and Their Effect on Seismic Behavior of RC Frame Buildings

Abstract

Un-reinforced Masonry (URM) infilled Reinforced Concrete (RC) frames are the most common structural system for multi-storey buildings in India and many other parts of the world. The infills are known to change the behavior and failure pattern of the infilled frames under lateral loading significantly, due to infill-frame interaction. The behavior is further affected by the construction sequence of infilled frames, as the infills are usually added after completion of the frame, and it results in a gap between the infill and soffit of the beam above. This paper presents a macro model for URM infilled frames to simulate the gap and can be implemented on available software. Using the developed model, an analytical study on effect of infills and their construction sequence, on the seismic performance of RC frame buildings designed as per relevant Indian Standards is presented. The infills are modeled as diagonal struts, with stiffness as defined in ASCE 41 and strength in various modes of failure is considered. Nonlinear ‘Gap’ elements are used to simulate the gap between the infill and the beam and a sequential analysis is performed to take into account the construction sequence of infill panels relative to frames.