Model uncertainties in seismic analysis of existing masonry buildings: the Equivalent-Frame Model within the Structural Element Models approach

This work deals of model uncertainties within the Structural Element Models (SEM) approach for the seismic vulnerability of unreinforced masonry (URM) buildings. The equivalent-frame is the most largely worldwide diffused model, in order to allow an efficient safety assessment of URM buildings in seismic areas. This paper addresses the effect of different options for the Equivalent-Frame Model (EFM) on the results of nonlinear analysis, also in comparison with different structural element approaches. The work is developed within a probabilistic framework, varying the material properties. A preliminary application of experimental design to simple cases allows appreciating the differences of several modelling strategies in terms of maximum intensity of seismic action. Successively, the response surfaces for a selected case study demonstrate the influence of different material characteristics on the lateral strength of the structure. Finally fragility curves are used as a comparison tool among different models of the case study. Results highlight that different modelling hypotheses can significantly affect the failure probability estimate.