The problem of large scale evaluation of masonry building seismic risk in defining intervention priorities

The severe seismic events which struck Italy in the latest years have confirmed the notable vulnerability of masonry buildings to seismic actions, definitely showing the importance of a territorial control. The existing methods for large scale vulnerability assessment are here discussed and their limits in identifying the priorities in interventions are focused. The recent Italian law [1] proposes a basic level of seismic risk evaluation also for cultural heritage (LV1). The purpose of this method is to find some simplified parameters to quantify the seismic risk for each building. Starting from this method, a new procedure is proposed with the specific aim of defining a territorial priority list to program the interventions. In this paper, the results of a simplified seismic analysis of 30 masonry buildings with artistic-historical value are presented. The SIVARS program, which applies the LV1 level, has been applied together with simple models based on equilibrium approach considering the out-of-plane collapse mechanisms. The proposed method thus starts from a critical analysis of the real crack pattern of each building, which conversely is not taken into account by SIVARS method. In this way, the kinematic analysis is able to describe the local collapse mechanisms, which the results of the analysis has generally pointed out as the most dangerous for historical masonry buildings, while the SIVARS approach supplies a safety index connected only to the in-plane mechanisms. The results obtained with this combined procedure are able to focus the most dangerous mechanisms in the analysed building population, giving an intervention priority list by mechanisms rather than by buildings. This allows to optimize the budget in order to raise the minimum safety factor of the whole buildings population, not focusing on the single buildings.