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 frame pattern for each wall, 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 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 behaviour.

In this paper some possible solutions to the problems are proposed also with reference to specific study cases.