Fragility models for RC frames with masonry infills and analysis of the efficiency of different IMs

The Italian territory is historically known as a seismic zone, but insufficient attention to seismic design in the past years has led to a high vulnerability of the existing building stock. Fragility models have become important tools for assessing the seismic vulnerability of existing buildings. This work aims to contribute to the assessment of fragility models for reinforced concrete (RC) frames with masonry infills. Based on an analysis of census data on existing buildings and on AeDES forms following the 2012 earthquake in Emilia, a representative 4-storey RC building was defined and modelled with finite elements. A concentrated plasticity approach has been adopted and infill panels have been schematized through an equivalent strut model. Structural capacity has been determined conducting a series of pushover analysis, considering the uncertainties in the mechanical characteristics by means of a Latin Hypercube Sampling. Displacement demand has been evaluated through a multi-stripe non-linear dynamic analysis on the equivalent single degree of freedom systems, by using a set of recorded accelerograms. Fragility curves have been evaluated by means of a regression model on the exceedance of each damage state, defined according to the EMS-98 scale. Particular attention was given to comparing the efficiency of various ground motion Intensity Measures (IMs) in correlating with displacement demand and in describing damage evolution in the building.