Proposal for an expeditious seismic vulnerability evaluation of the Italian medieval defensive walls

Medieval defensive walls are a distinctive feature of Italian cultural heritage. These structures testify the origins of historical centres and, in some cases, the consequences of the events occurred over time. The typical configuration of medieval defensive walls, generally characterized by high slenderness ratios, out-of-plumb, the absence of deep and adequate foundations, made these elements particularly vulnerable toward seismic actions. This study focused on the assessment of the seismic safety of Italian medieval defensive walls toward out-of-plane failure mechanisms induced by seismic actions. To this end, a simple approach based on the use of generalized dimensionless capacity curves is presented. These curves, derived by the Authors from a calibration process involving a set of selected real cases, allows for a rapid preliminary seismic assessment of masonry walls particularly useful for getting an initial idea of the condition of the walls with respect to seismic actions also considering the presence of pre-existing out-of-plumb configurations. The proposed approach has been applied in the paper to the real case study of medieval walls of Cittadella, a town in northern Italy, considering the pre-existing out-of-plumb configuration. The obtained results have shown the vulnerability of these walls in case of occurrence of masonry disaggregation and, consequently, the importance of performing specific surveys finalized to investigate this phenomenon. The application of the proposed approach has clearly shown its feasibility and usefulness for the seismic evaluation. Moreover, the comparison with the corresponding results obtained by using the actual capacity curves, rather than the generalized ones, has underlined its good level of reliability.