Influence of the Boundary Conditions on the Seismic Response of Existing Masonry Infills From In‐Plane and Dynamic Out‐of‐Plane Tests

Despite increasing attention to the seismic performance of masonry infills, their out‐of‐plane dynamic behaviour remains insufficiently explored, particularly under pre‐existing in‐plane damage. This study presents a comprehensive experimental campaign designed to investigate the seismic behaviour of an existing weak masonry infill typology, characterising its in‐plane cyclic response, the out‐of‐plane dynamic response, and the in‐plane and out‐of‐plane interaction under varying boundary conditions. Full‐scale infill specimens were constructed within steel‐reinforced concrete composite frames and tested in two batches. The first batch comprised five specimens; four were built in full adherence to the surrounding frame and tested both in‐plane and out‐of‐plane, and one was only attached at the top and bottom boundaries with vertical gaps at columns and tested only out‐of‐plane. The second batch included similar specimens, introducing a thin gap at the top boundary simulating a deteriorated connection. In‐plane pseudo‐static cyclic tests and out‐of‐plane dynamic shaking table tests were performed, individually and sequentially (in‐plane followed by out‐of‐plane). The in‐plane response and the effect of previous in‐plane damage on the out‐of‐plane dynamic behaviour were explored for specimens fully connected to the frame in both batches (with and without the thin gap at the top). The out‐of‐plane response was characterised for infills with four different boundary conditions: fully connected and one‐way spanning specimens connected well or poorly at the top. The results are presented in terms of in‐plane and out‐of‐plane damage propagation and failure mechanisms, force‐displacement relationships, out‐of‐plane acceleration and displacements, and in‐plane/out‐of‐plane interaction, highlighting the influence of varying boundary conditions.