Fragility curves for out-of-plane failure mechanisms of masonry wall typologies in the archaeological sites: A focus on T-shaped elements in Pompeii

The assessment of the safety conditions of the archaeological heritage under horizontal actions induced by different hazards is crucial to preserve its cultural value. Out-of-plane (OOP) failure mechanisms in archaeological remains can be easily activated, even for low-intensity seismic actions, due to the lack or poor quality of the connections between the masonry elements that compose the remains. The analytical approaches usually adopted to investigate the OOP response of masonry buildings can be used with some modifications to account for some specific features of the archaeological remains, as irregular shapes, lacking floors, overlapping of different construction materials and techniques, ageing of materials over very long time. In this framework, the paper presents the application of a limit analysis-based approach to some typological classes of masonry elements representative of the most frequent ones in archaeological sites, with a specific focus on the typologies in the Pompeii Archaeological Park. A classification of archaeological walls is initially proposed based on a few morphological and typological criteria; it aims at uniquely defining different typologies and their vulnerability to several OOP mechanisms. Then, one of the most recurring typologies in the Pompeii Archaeological Park (i.e., T-shaped wall system) is deeply analysed; limit analysis is carried out to investigate the influence of geometrical and mechanical parameters on its vulnerability to the simple rocking-sliding mechanism, also by varying the level of mutual connections between orthogonal walls. A large database of T-shaped wall systems with three increasing levels of connection is generated (a sample of 1320 elements generated for each connection type) and examined to build fragility curves in terms of OOP seismic capacity. Finally, fragility curves for some subsets of T-shaped wall systems, based on some geometrical parameters, are presented in order to provide homogeneous OOP vulnerability classes. This study represents the kick-off step in defining a new methodological approach to assess the seismic vulnerability of archaeological remains to OOP mechanisms, eventually extendable to any archaeological context.