Shake table testing of U-shape masonry structures: Out-of-plane response to varying ground motion signals

Historical structures consisting of unreinforced masonry (URM) are highly vulnerable to seismic forces, with out-of-plane failure mechanism being a primary concern. This vulnerability has often resulted in the collapses of the masonry structures during seismic events. Masonry walls tend to rock and overturn in the out-of-plane direction due to the dynamic loading, leading to either one-way or two-way bending. These mechanisms mainly depend on the boundary conditions and the degree of connectivity between the structural elements. Previously the one-way and, in particular, the two-way bending mechanisms of masonry structures have been explored to some extent. However, research is still needed to develop reliable analytical and numerical models for predicting the mechanism under seismic action. This paper presents an extensive experimental campaign carried out on the shake table at the University of Minho (PT) to assess the sensitivity of the out-of-plane behavior of U-shapes structures to varying ground motions. Two signals were chosen from the database to enable a comprehensive analysis of how different types of seismic events influence the structural response. To replicate the behavior of historical URM structures, the specimens were constructed using dry-stack granite blocks in U-shaped configuration, consisting of a façade and two orthogonal walls. Dry joints allow the walls to be rebuilt after each test, ensuring the repeatability at large displacements. The response of the structure was assessed under varying geometries and at different intensities of the applied ground motion inputs. The outcomes of the experimental campaign are expected to contribute to the development of better predictive models for seismic risk assessment and conservation strategies for historical URM structures.