Effect of Diaphragm Flexibility on the Dynamic Behaviour of Unreinforced Masonry Walls in Out-of-Plane Bending

This paper investigates the dynamic behaviour of the external walls of unreinforced masonry historic buildings with flexible diaphragms subjected to out-of-plane bending. The influence of diaphragms flexibility on the displacement capacity and demand of walls in out-of-plane bending has been studied by means of dynamic analyses with a simplified two-degrees-of-freedom model (2DOF). 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. Dynamic analyses of a set of walls with Gaussian impulse and recorded accelerogram inputs have been performed in order to compare the response of the simply supported wall with the one of the wall with an elastic spring at the top.