Effect of in-plane damage on out-of-plane strength of unreinforced masonry walls

The out-of-plane capacity of unreinforced masonry (URM) walls is crucial for their overall stability and safety, especially after being damaged by in-plane forces. A nonlinear finite element model was developed to investigate the behavior of load bearing URM walls having different slenderness ratio and aspect ratio under combined in-plane and out-of-plane loading. The walls were subjected to sequence of cyclic in-plane drifts and monotonically increasing out-of-plane pressure and reduction in out-of-plane capacity due to in-plane damage was estimated. The reduction was larger for walls having slenderness ratio and aspect ratio greater than 20 and 2.0, respectively. Under severe in-plane damage, the out-of-plane capacity of cracked URM wall reduced to nearly one-third of its undamaged capacity. Fragility curves were generated to predict the probability of out-of-plane failure of URM walls with prior in-plane damage. These curves can be used to evaluate the vulnerability of URM walls in out-of-plane direction for expected in-plane damage corresponding to a specified performance level.