Effect of uncertainties on seismic fragility for out-of-plane collapse of unreinforced masonry walls

A new approach for the evaluation of fragility curves of UnReinforced Masonry (URM) walls is proposed. Uncertainties on geometrical and mechanical properties, as well as on magnitude and position of the applied loads, are considered using fuzzy set theory. Fuzzy set theory has been broadly applied to civil engineering problems, particularly to reinforced concrete structures, though its application to masonry, to the authors’ knowledge, is investigated here for the first time to evaluate the seismic response of masonry walls in the presence on vague and imprecise information. The proposed procedure allows computing fragility curves based on available typological databases, integrated with experimental tests and survey data. One of the main advantages of this procedure is that it can account for the variability of structural typologies on a territorial scale. The effectiveness of the method is shown through numerical examples concerning walls made of fired clay bricks and lime mortar, which are typical construction materials in the Po River Plain, in Northern Italy. Linear kinematic and nonlinear time-history analyses are used to calculate the seismic response. The computed fuzzy-like fragility curves include both aleatory and epistemic uncertainties. An extensive sensitivity analysis based on suitable sets of representative input parameters is carried out to validate the proposed procedure.