On the seismic behavior of out-of-plane loaded masonry walls

The paper provides a contribution to the study of seismic behaviour of unreinforced masonry structures by means of both experimental and modelling approaches. To this purpose, a shake-table laboratory campaign on a tuff masonry U-shaped assemblage is presented. The specimen is made of a facade wall, which is adjacent but not interlocked with two transverse walls; such condition is common in actual historical buildings due non-synchronic construction and/or later addition. Scaled natural accelerograms are adopted, which induce on the facade an out-of-plane motion of increasing intensity, from the starting of rocking up to overturning. The tests confirm the existence of a significant dynamic reserve of stability, which allows the facade to be set into motion without necessarily collapsing. Furthermore, the main factors affecting the dynamic behaviour of the wall are highlighted, such as the presence of imperfections and tilted foundation, the dependency on the input and on the energy dissipations. Two modelling approaches are presented, based on the Discrete Element Method and on a Single-Degree-of-Freedom analytic model, respectively. The two approaches prove capable of reproducing the tests, in terms of both entire time history and maximum rotation, even if model parameters are roughly assumed. Eventually, experimental and numerical data, generated through the established models, are used to check force and displacement-based seismic code assessment procedures.