Assessment of ASCE 41 Height-to-Thickness Ratio Limits for URM Walls

Unreinforced masonry (URM) walls with sufficient anchorage to the diaphragms will crack above mid-height when subjected to out-of-plane ground motions. This study investigates the sensitivity of the out-of-plane response to varying height-to-thickness (h/t) ratios for URM walls connected to rigid diaphragms. ASCE 41, Seismic Rehabilitation Standard, provides guidelines for permissible h/t ratios for out-of-plane URM walls. To assess these limits, a rigid-body numerical model, calibrated to full-scale shake table tests, was used. The focus of the analysis was to identify the minimum h/t ratio that would cause collapse of the wall when subjected to seismic shaking. The analysis was performed for 80 input motions and accounted for variability in the crack location. The results of the study suggest that the probability of collapse is dependent on the site class and that walls with limited overburden and satisfying the h/t limits in ASCE 41 have a very low probability of collapse.