Seismic evaluation of URM buildings with flexible diaphragms. Proposal of a simplified 'ENT' method

The structural behaviour of an existing masonry building, when subjected to seismic action, is affected by the inplane mechanical properties of the floors and roofs. The goal of the present paper is to investigate the influence of the diaphragms properties (and therefore the influence of the different refurbishment techniques) on the global seismic behaviour of simple e regular masonry buildings. For this purpose a simplified elastic no-tension (ENT) method for modelling masonry structures have been proposed and adopted in order to perform push-over non linear analysis in function of different parameters of the building. According to the ENT method, at every step all the elements which are outside a Ranking failure surface are eliminated, and the analysis is repeated with an updated geometry of the model: a "globally nonlinear" behaviour is therefore determined through a series of linear analyses. The results of the push-over analyses show a lesser influence on the on the maximum level of the load and on the maximum displacement of the floor stiffness in case of URM buildings endowed with regularity and symmetry of the geometry.