Fragility models for existing masonry infilled RC frames in the Emilia area

Fragility models are important tools for seismic risk assessment and seismic damage scenarios estimation. Some models are already available in the literature, however, in the case of infilled RC frames, further investigations are necessary, given the high uncertainty about their behaviour. In fact, damage observations following seismic events, suggest that the presence of masonry infills can strongly influence the response of reinforced concrete (RC) frames and affect their collapse mechanisms. The main goal of this work is to contribute to the seismic vulnerability assessment of the existing building stock in the Emilia-Romagna region in northern Italy, developing fragility models for infilled RC frame buildings. On the basis of an analysis of both census data on the existing building stock and on damage survey forms after the 2012 Earthquake, a set of representative structures was defined and modelled with finite elements, adopting a concentrated plasticity approach. Different modelling approaches of the infill walls were considered, using single and multi-strut models, in order to simulate shear failure in columns. Non-linear static (push-over) analyses were then carried out on these models to obtain their capacity curves. Displacement demands were computed using simplified procedures (IN2 method). The definition of damage levels in the models was based on the achievement of local deformation capacity limits of structural and non-structural elements, according to the classification provided by the EMS-98 Macro-seismic scale. Fragility curves were finally obtained by considering uncertainties in material properties, by means of the Response Surface method, as well as ground-motion record-to-record variability.