Failure of masonry infill walls under out-of-plane loads

The failure of infills, which may develop both in-plane and/or out-of-plane, causes casualty risk and heavy socio-economic consequences. In addition, the total or partial collapse of an infill may lead to unfavourable conditions affecting the overall structural response, such as the formation of an open storey. The collapse of infill walls, especially in the out-of-plane direction, may occur even for moderate intensity of the ground motion. For these reasons, the interest in the out-of-plane behaviour of masonry walls has been growing in the last years. Previous studies have shown that the height/thickness ratio, the height/length ratio and the boundary conditions are key parameters affecting the out-of-plane behaviour of infills. Moreover, the presence of an opening in the infill may also influence the out-of-plane response. In this regard, the few studies available in the literature up to now present contradictory results. In this paper, the out-of-plane resistance of infill walls is investigated by means of non-linear monotonic (push-over) finite element analyses, where masonry is modelled with a smeared-crack approach and contact interfaces are used to model the interaction between the masonry panel and the surrounding frame. The influence of different factors on the out-of-plane resistance is investigated, namely the height/thickness and height/length ratios of the infill, the masonry compressive strength and presence of a central opening.