Effect of ground-motion sequences on a unreinforced masonry wall restrained by an elasto-plastic tie-rod

This work investigates the effect of international ground-motion sequences on the out-of-plane response of an ordinary-building façade. The following assumptions are made on the wall boundary conditions: the wall is resting on a foundation, it is adjacent to transverse walls and restrained by elasto-plastic tie rods with finite elongation capacity. Four walls are considered of different aspect ratio and size; two types of masonry are assumed, and the tie is designed following a force-based procedure according to the Commentary to the Italian Building Code. The walls are modelled as rigid blocks of finite thickness and free to rotate on one side only. The rocking response of the walls, excited in the out-of-plane direction under 56 sequences of records, is evaluated. The effect of sequences is estimated by the comparison of the response experienced during the sequence and under a single record, strongest in terms of either peak ground acceleration or velocity. Finally, in order to reduce the vulnerability originated by a seismic sequence, a proposal of a reduced behaviour factor to be adopted in the design of tie rods is formulated.