Seismic risk assessment of masonry-infilled RC building portfolios: impact of variability in the infill properties

In the last years, many research efforts have been focusing on the development of fragility and risk models of different building classes and structural typologies for large-scale seismic risk applications. Although the role of masonry infills is well recognised, less attention has been paid to the quantification of the variability surrounding their mechanical properties and how this might affect the collapse fragility curves and loss estimates. This study investigates and quantifies, in a thorough manner, the impact of the variability in the characteristics of masonry infill on the expected annual losses (EALs) of existing infilled reinforced concrete frames of different configurations. To do so, a fully integrated portfolio, representative of buildings designed according to the Italian codes in force between 1970 and 1980, is used as case-study. Infill-related variability is accounted for by means of a macro-level distinction of five common infill types, defined in terms of stiffness and shear strength. Moreover, building-to-building variability is also included through different geometrical configurations. Multiple-stripe analyses are carried out and fragility curves are developed for buildings with different heights, in-plan layouts and structural typologies. Finally, EALs are computed and analysed in a statistical fashion in order to quantify, in a simplified manner, the uncertainty induced by the variability of the masonry infill properties, as a function of the number of storeys and masonry infill typology.