Experimental and empirical study of in-plane seismic performance of unreinforced masonry walls with large and multiple openings

Modern unreinforced masonry constructions with large and multiple openings are particularly vulnerable to earthquake-induced damage due to their poor seismic performance. This study investigates the in-plane seismic behavior of large-scale unreinforced masonry wall specimens constructed with fired clay bricks, representing two typical configurations: one with a single large opening and another with two identical openings. The specimens were subjected to vertical stress equivalent to two-story masonry buildings and cycles of lateral in-plane displacements till the verge of collapse. The findings of this research study revealed significant cracking in the exterior spandrel joints of both specimens, leading to its early instability and loss of structural integrity due to out-of-plane movement, rather than any in-plane failure mechanisms developing within the piers. The specimen with multiple openings exhibited lower lateral strength, reduced energy dissipation, and greater deformation capacity compared to the single-opening specimen, primarily due tothe pronounced flexural response of individual piers. Lateral strength and drift capacities at various performance levels were also estimated using ASCE and Eurocode. These codes accurately predicted lateral strength, while overestimating the ultimate drifts and performance levels due to differences in failure mechanisms and boundary conditions introduced by the spandrels. Furthermore, an empirical relation was proposed based on incorporating the effect of these factors along with the aspect ratio of the piers and axial compression ratio, to effectively estimate the displacement capacity of piers in actual masonry walls or buildings. The proposed relation demonstrated a stronger correlation with experimental results compared to estimation from ASCE and Eurocode.