Open issues on non-linear modelling for seismic assessment of existing masonry buildings

The difficulties on the assessment of the seismic capacity of existing masonry buildings through non-linear FEM analyses have been examined in this paper, in the framework of the equivalent frame modeling. A significant problem lies in identifying an adequate equivalent frame idealization of the walls, i.e., capable of providing an acceptable response of the numerical model. Indeed, the geometrical complexity characterizing real masonry buildings, often due to irregular distribution of the wall openings, leads to choices and expedients which are impossible to codify and may only be defined on a case-by-case basis. Consequently, an adequate engineering judgment, which must obviously be considered when the results are being interpreted, is required. Linear and non-linear analysis were adopted on equivalent frame schemes of existing walls highlighting the problems of identifying geometric patterns, as well as defining the mechanical model of the spandrels or the influence of connection degree between orthogonal walls on the seismic behavior. In this paper some possible solutions to the problems are proposed, also with reference to specific study cases.