Torsional response of unreinforced masonry buildings

Ordinary masonry buildings, made of stone or brick, constitute a large part of the existing building stock. These constructions, often conceived exclusively for vertical actions and without established construction rules, are characterised by very thick walls that are sometimes weakly connected to each other and have weak horizontal diaphragms. Because of the relevant non-linearity in their structural response, collapse analysis should be performed adopting a nonlinear dynamic approach. Anyway, the intrinsic difficulty of this method, combined with the uncertainty of the modelling, often suggests preferring the simpler nonlinear static procedure ("pushover" analysis). The results obtained with this approach are generally characterised by small errors in the case of regular buildings, whereas, for irregular buildings, serious inaccuracies might be introduced, due to the occurrence of a significant torsional response. This circumstance can even invalidate the results obtained using the usual methods implemented by commercial software. For this reason, this paper proposes an approach for the analysis of irregular masonry buildings characterised by an important torsional response, discussing the effects that this response has on failure, especially in the evaluation of out-of-plane thrusts caused by torsional stress.