Determining fragility of urban low-to-mid rise masonry infilled building

In seismic analysis of building, infill wall is usually modelled as non-structural elements and, hence, are not taken into account in analytical models. In general, engineers and scientists model these widely used structural system of masonry infilled reinforced concrete frame by considering the infill wall as load applied to the open confining frame. The presence of masonry infills, however, may significantly alter both the stiffness and the strength of the overall structural frame system. This present study aims to evaluate seismic performance of this type of building by developing fragility functions of the structure. Masonry wall was modelled as diagonal strut within the concrete frame. The masonry constituents and its composite properties were determined for the model. Then, the structure was subjected to incremental static lateral loading while adaptive pushover analysis was utilized to predict the response of the structure. As the damage states were defined from the spectral capacity curves, the fragility functions were developed for the structure. Effect of masonry wall included in the analysis was then compared to the results of open frame. The result of the eigen value analysis shows, the period for modelling a structure with an infill wall is smaller compared to modelling a structure without infill wall (open frame). This shows that the existence of infill wall elements in modelling increases the value of structural stiffness so that it reduces the period of the structure. Whereas, the results of the fragility curve in both structural modelling show that at some level of damage, the probability of damage for modelling structures with infill walls is smaller when compared to open frame. Realistic and rational results is presented in this work which show that modelling masonry wall with compression strut is beneficial.