Time-history analysis of unreinforced masonry walls in out-of-plane bending: Influence of diaphragm flexibility

The purpose of this paper is to study the dynamic out-of-plane response of the external walls of unreinforced masonry buildings with flexible diaphragms. In particular, the influence of diaphragms flexibility on the displacement capacity and demand of walls has been investigated. A two-degree-of-freedom model (2DOF) has been developed to perform the dynamic analyses. The wall has been modelled as an assemblage of two rigid bodies connected by an intermediate hinge and restrained at the top by a spring: the damping has been modelled through the introduction of the coefficient of restitution. The equations of motion of the 2DOF system have been derived and integrated in the time domain. Time-history analyses of a set of walls with Gaussian impulses and recorded ground motions have been performed in order to compare the response of the simply supported wall with that of the wall with an elastic spring at the top.