Out-of-plane dynamic behaviour of unreinforced masonry walls in buildings with flexible diaphragms

This paper investigates the influence of the flexibility of diaphragms and roofs on the out-of-plane behaviour of the external walls of unreinforced masonry buildings subjected to seismic excitation. Kinematic non linear analyses of assemblages of rigid blocks have been performed at a first time to derive the force-displacement curve of the single wall in out-of plane bending. The flexible diaphragm at the top of the wall has been modelled as a translational spring with a suitable flexibility. The out-of-plane behaviour in presence of flexible diaphragms has been studied also by means of dynamic analyses with a simplified two degrees of freedom model (2-DOF). The equations of motion of the 2-DOF systems have been derived to describe in a simplified way the dynamic behaviour of the wall, removing the hypothesis of equal and in phase bottom and top displacement. An algorithm for the numerical integration of the equations is being developed.