Effect of boundary conditions and other factors on URM wall out-of-plane behaviour: design demands, predicted capacity, and in situ proof test results

Unreinforced masonry (URM) building construction is prominent in the form of loadbearing, partition, and infill walls. Significant out-of-plane (OOP) failures of URM walls often occur during moderate and severe earthquake shaking and such walls are often identified in structural engineering assessments as being amongst the most vulnerable elements to OOP demands, especially earthquakes. For undamaged, in situ wall conditions where material properties are known and boundary conditions reflect idealised conditions assumed in analytical predictive models, these predictive models are easily applied, although the accuracy of the model outputs may still not be well understood. Furthermore, when in situ conditions do not reflect idealised conditions assumed in analytical predictive models, engineers are often uncertain as to which analytical models and inputs are most appropriately applied. Hence, experimental and analytical campaigns were undertaken to provide specific examples for structural engineering practitioners assessing the OOP seismic behaviour of URM walls. A total of nineteen experimental proof tests were performed in situ in six different buildings. The considered wall configurations represented a variety of geometries, boundary conditions, pre-test damage states, and material properties. It was observed that twoway OOP flexure as compared to one-way vertical OOP flexure, can substantially improve the OOP load-carrying capacity of tested infill walls, and that the boundary restraints and presumed "arching’ action in walls bounded by the building frame can greatly increase the OOP capacity of URM walls. The effects of simulated in-plane damage on the OOP capacity of a URM infill wall was also investigated, and the damage was found to reduce out-ofplane strength by up to 40%. The experimental results were compared to predictive results for eighteen of the tests. The average ratio and associated coefficient of variation (CV) of predicted strengths to measured strengths were determined to be 0.84 (CV 0.56) and 0.93 (CV 0.25) for the “unbounded” and “bounded” wall conditions, respectively.