Failure of wall–slab joint in unreinforced masonry building

Investigations on buildings severely damaged due to earthquakes or explosions have indicated that unreinforced masonry buildings with simply supported precast concrete floor slabs exhibit deficiencies in resistance to progressive collapse, compared to unreinforced masonry buildings with continuous cast in situ concrete floor slabs. The collapse mechanisms observed in the two types of unreinforced masonry buildings are closely related to wall–slab joint failure. The purpose of this study is to investigate the failure behavior of wall–slab joints and the effect on the collapse of the two types of unreinforced masonry buildings. Six wall–slab joint specimens and eight grooved wall specimens, induced by partial failure of wall–slab joints, were tested under monotonic vertical and horizontal loading. Numerical models were then developed, verified, and used to perform a parametric study. It was found that the wall–slab joints failed in various modes, that is, slab failure, wall failure, and slab pullout failure. The grooved wall could fail in bending or in compression. Analyses indicated that the collapse of unreinforced masonry buildings with simply supported precast concrete floor slabs develops in both vertical and horizontal directions. However, the collapse of unreinforced masonry buildings with continuous cast in situ concrete floor slabs is prone to develop only in the vertical direction, resulting in improved progressive collapse resistance.