Seismic demand on a unreinforced masonry wall restrained by elasto-plastic tie-rods under earthquake sequences

Existing masonry buildings show significant vulnerability to seismic sequences. This topic has so far received limited attention, concentrated on simplified simulations of the global response, governed by in-plane wall behaviour, or on a very detailed representation of monumental buildings. This paper looks at the out-of-plane response of an ordinary-building wall restrained by an elastoplastic tie-rod under Italian seismic sequence conditions. A recently proposed model is extended to account for a flexible interface defined by its compressive strength and stiffness. Response to 30 series of four events belonging to six seismic sequences shows limited damage accumulation in most cases, with most hysteretic energy dissipated in a single plastic cycle. In these cases, we find a strong correlation between the maximum rotation and intensity measures such as peak ground acceleration, peak ground velocity and acceleration spectrum intensity. This suggests that current hazard studies are adequate and that design can be based on the features of the maximum event expected. However, exceptions are noticed for the 2016 Central Italy Earthquakes, in which the considered sequence is made of multiple mainshocks inducing significant damage accumulation, but can still be resolved by a practitioner resorting to equivalent static procedures by reducing the commonly assumed behaviour factor.