AN APPROACH FOR LARGE-SCALE SEISMIC VULNERABILITY ASSESSMENT OF URM BUILDINGS IN AGGREGATE

In Italy and in many other European countries the historical centres are generally composed by UnReinforced Masonry buildings (URM), which are, in most of the cases, arranged in an aggregate configuration, as the result of a discontinuous and unplanned development. As a consequence the single units composing the aggregate, generally built in different eras and characterized by different construction techniques, materials and structural details, interact with the adjacent ones under seismic actions. The mutual interaction could influence the seismic behavior of the building itself especially toward the occurrence of the out-of-plane mechanisms, which represent a common response in historical masonry buildings as evidenced by many earthquakes including the recent events occurred in Central Italy. Consequently, the assessment of the seismic vulnerability of buildings arranged in aggregate configuration, cannot refer to single independent units, but it requires to take into account the possible interactions among the adjacent structural units. Such interaction plays a paramount role for the derivation of reliable fragility curves of historical centres at the regional scale. Based on the above considerations, the main aim of this paper is to propose a multistep approach to evaluate, in analytical terms, the fragility curves for the most probable out-of-plane mechanisms of the perimeter façades of buildings in historical centres by considering the mutual interaction between structural units. To this purpose, the contribution of friction actions, which develop at the connections between the façade wall prone to the failure and the walls of adjacent buildings, is accounted for in the analysis of the out-of-plane mechanisms. The proposed approach is then applied to derive the fragility curves of the building typologies characterizing the historical centre of Sora, a medium size town of Central Italy analysed within the research project CARTIS and herein assumed as case study.