Seismic Vulnerability Assessment of Masonry Infilled RC Frame Structures in Pakistan

Abstract

The influence of masonry infills on seismic response of reinforced concrete frame structures is one of the major fields of investigation for civil engineers in last few decades. Literature from proceedings of years of researches reveals that the effects of masonry infills are far from negligence; both for their beneficial effects (higher resistance to lateral loads, higher stiffness, improved energy dissipation capacity) and for their adverse ones (increase in seismic demand, possible mechanism of shear failure in frame members). Contrary to that, due to large number of parameters involved in modeling of infill panels, diversities in construction practices in different parts of world and influence of workmanship, no convergence has been reached on the adoption of unique model in the analysis by the experts. This study is aimed at the development of a frame work for the seismic vulnerability assessment of masonry infilled reinforced concrete frame structures taking Pakistan as a case study. In this research various techniques available in literature for analytical modeling of infill panels are studied, out of which three strut model is employed. As this research is focused on Pakistani buildings, therefore, testing is conducted to evaluate the compressive strength of typical Pakistani brick masonry required for material modeling of the equivalent struts. A two dimensional single bay, two storey frame has been modeled in Finite element software with three equivalent struts in each direction. After the modeling, non-linear static cyclic analysis is carried out and the hysteresis loop obtained is compared with the other experimentally obtained hysteresis loops investigated by the other researchers. Based on the capacity curve obtained from hysteresis loop, vulnerability curve for masonry infilled RC frame structure is derived using the procedure proposed by Kyriakides (2007) and is compared with that of bare frame derived by Qayyum (2012) and GESI expert opinion based curve.