No More Drop Panels in the Design for Punching Shear in Flat Plates

Punching shear failure at column-slab connection occurs in a brittle manner, which involves the formation of a truncated cone or a truncated pyramid. A set-up of swimmer bars system takes the shape of truncated steel pyramids to counteract the potential truncated pyramids of cracks. Each counteract truncated steel pyramid is formed by swimmer bars will generate four inclined planes intercepting approximately perpendicularly the four inclined planes of the failure truncated pyramid. A reference to a testing program of four square slabs with a concentric column will be used; these were constructed with overall dimensions of 2000 mm by 2000 mm, 150 mm thickness and 140 by 140 mm column in the middle. The results obtained from testing has proved that the efficiency of using swimmer bars system in slab-column connections has increased their punching shear capacity to more than 250% and has decreased their deflection by increasing the stiffness of the slab in the vicinity of the concentrated loads, moreover, the nature of the punching shear failure becomes ductile instead of brittle and obviates sudden failure. The need for drop panels to resist the punching shearing forces becomes unnecessary. The ultimate strength of punching shear is limited by the compression shear failure, which was never measured for the case of punching shear. The gain in ductility can reach levels matching those in flexural behavior.