Comparative seismic vulnerability analysis on ten masonry towers in the coastal Po Valley in Italy

Ten existing masonry towers, located in the coastal Po Valley (Italy), are analysed in the presence of seismic excitations. They show some affinities which justify a comparative analysis: they are located in the same region and made of masonries having similar mechanical properties, and the majority of them are almost coeval. On the other hand, they exhibit different geometries (e.g. slenderness, thickness of the perimeter walls, height, percentage of perforations, etc.) which may be responsible for their different structural response to the same seismic excitations. Therefore, the aim of the work is to study the effect of the geometry on the seismic behaviour of such towers by assuming as mechanical properties for masonry the ones provided by the technical literature for existing towers in the coastal Po Valley. Full non-linear dynamic analyses are performed by means of a specific Rigid Body and Spring Model (RBSM). This is based on a relatively refined 20 discretization obtained by assembling rigid quadrilateral elements interconnected by non-linear axial and shear springs, exhibiting softening and realistic energy dissipation under cyclic loads. The geometry of the towers is deduced from both existing available documentation (cross-section, front and planar views) and in situ surveys. On the basis of such geometrical data an equivalent 2D mesh is built, where different thicknesses are assigned to adjoining elements, wherever necessary, in order to properly take into account the actual behaviour of the structure within a 20 approach. Four artificial design consistent horizontal accelerograms are applied to the 2D models and the response in terms of collapse mechanisms and force-displacement histories are analysed in detail. Although this study is only a first attempt to analyse the relationship between some typological features of the chosen towers and the structural response they exhibit in the presence of seismic excitations, the results obtained and the comparative analysis that follows are enough to show clearly the strong dependence of the towers' structural behaviour on their geometric characteristics (slenderness, base shear area, presence of belfry, big perforations, presence/absence of internal vaults, etc.). (C) 2012 Elsevier Ltd. All rights reserved.