ESTIMATION OF CAPACITY CURVE PARAMETERS FOR INDIAN RC BUILDINGS WITH URM INFILLS Putul Haldar, Yogendra Singh & D. K. Paul Department of Earthquake Engineering, IIT Roorkee, India SUMMARY: Failure of Un-Reinforced Masonry infilled Reinforced Concrete frame buildings during Bhuj earthquake highlighted the need for vulnerability assessment of existing stock of such buildings in India. In order to get reliable estimation of capacity curve parameters, governed by local materials and construction practices, infilled RC frame buildings surveyed during a pilot survey in the National Capital Region, are classified depending on the number of storeys, roof/floor system, design force level, and detailing of reinforcement. Thereafter, parametric study is carried out considering all possible failure modes of infill panels and surrounding frame members. Infill panels are represented by concentric diagonal struts with stiffness as defined in ASCE-41 (2007 ) and strength obtained from the weakest failure mode. Non-linear static analysis is performed to obtain the capacity spectrum parameters. These parameters have been implemented in the spreadsheet-based seismic risk assessment tool 'SeisVARA'. Keywords: URM infills, RC frame, Non-linear analysis, Capacity curve parameters, Model Building Types 1. INTRODUCTION Un-Reinforced Masonry (URM) infilled Reinforced Concrete (RC) frame is the most popular structural system for modern multistory buildings in India, like many other countries of the world. The wide spread failure of such buildings and consequent extensive physical and social losses, particularly during the 2001 Bhuj earthquake, the first large earthquake in an urban area of India, highlighted the need for vulnerability assessment of the existing stock of such buildings in India. In order to develop effective policies for mitigation against future earthquakes, reliable estimation of capacity curve parameters is required. Estimation of capacity curve parameters for RC frame structure with URM infills in India is a challenging task. Most of these buildings are not designed for earthquake load at all. Sometimes earthquake forces are considered in analysis but construction and detailing do not comply with specifications of the standards. Further, Inadequate guidelines for design of such buildings have resulted in a huge stock of seismically deficient buildings throughout India. With the view to develop analytical capacity curve parameters for reliable estimation of vulnerability functions for URM infilled RC frame buildings in India, a parametric study has been carried out for representative URM infilled Model Building Types (MBTs) selected from the database of a pilot survey in the National Capital Region of India (DEQ 2009 ), considering all parameters affecting seismic response of the structure. All possible failure modes of infill panels and surrounding frame members also have been considered for this purpose. 2. SELECTION OF REPRESENTATIVE BUILDINGS FOR PARAMETRIC STUDY For reliable estimation of capacity curve parameters, the ideal way is to carry out nonlinear analysis of each and every building of the URM infilled RC building class and generate the statistical data to