Effect of Uncertainties in Development of Fragility Curves for URBM Building

Abstract

Seismic fragility analysis of Un-reinforced Brick Masonry (URBM) Buildings is useful for determining the possible extent of damage in the event of an earthquake. It is known that there are uncertainties with respect to both the mechanical properties of masonry and the characteristics of earthquake ground motion. This paper presents sensitivity studies: by considering Weibull distribution as candidate distribution for compressive strengths of brick and mortar and varying the Coefficient of Variation (COV); and by using 12 different earthquakes time histories available in the strong motion atlas of India separately. For this purpose a one room, single storey URBM building has been considered and the fragility curves have been obtained by integrating Improved storey shear modelling, Monte Carlo simulation and Incremental dynamic analysis. From the study, it has been observed that while using the Weibull distribution as candidate distribution for mechanical properties of masonry, fragility curves of URBM buildings are not significantly affected by the COV whereas they are sensitive to the choice of earthquake ground motion. Fragility curves obtained using different earthquake time histories show three bands. For the suite of earthquake time histories considered in this study, the observed fragilities are generally increasing with the epicentral distance. In other words observed fragilities corresponding to the far-field earthquake time histories are generally higher than those corresponding to the near-field earthquake time histories. Thus, for vulnerability analysis, selection of suite of earthquake time histories judiciously is more important than modelling the statistical variations in mechanical properties of masonry.