Numerical evaluation of masonry infill walls behaviour under out-of-plane loads

Observation of damage in seismic events has highlighted that collapse of infill walls in the out-of-plane direction may occur even for moderate intensity of ground motion. Different analytical models have been proposed in the last decades for the assessment of the out-of-plane response of infills and their applicability under different conditions has been checked also with experimental tests. In this paper, a numerical solution is adopted by using a smeared crack approach, in which the masonry panel is modelled as a a non-linear continuum and contact surfaces are located only at the interface between masonry and frame elements; horizontal out-of-plane loads are applied monotonically as body forces. Height/thickness ratio, height/length ratio, masonry compressive strength and stiffness of frame elements are varied to investigate their influence on the out-of-plane resistance. Results confirm previous experimental evidence, such as the inverse proportionality of the strength with respect to the span length, the strength reduction with varying height/length ratio slightly affected by masonry compressive strength and thickness. Comparisons of the results with analytical models show that, in general, the latter give a conservative estimate of the strength, but the degree of approximation of the considered equations is strongly affected by the height/thickness of the infill, and, to a much lesser extent, by the infill height/length ratio, whereas it is not influenced by the masonry compressive strength. It is found that each equation is suitable in a different range of height/thickness ratios.