Enhancement of punching shear strength of flat slabs using shear-band reinforcement

Abstract

Flat-slab system is widely used nowadays. Major and critical problem of this system is its sudden brittle failure is called punching shear failure. To overcome the punching failure problem, there are many ways to increase the punching shear strength of concrete slabs, increasing slab thickness in the area adjacent to the column, increasing column thickness which is against the architectural desire, and finally providing slab with shear reinforcement. Shear reinforcement is more advanced from both the structural and economical point of view.

An experimental program includes seven full scale square flat slab interior column specimens tested under gravity loads. All slabs have same dimensions of 1700 mm × 1700 mm with thickness 160 mm and reinforcement ratio of 1.2%. Column was square of 200 mm length and 250 mm height. Elongated steel strips of 25 mm width and 1.5 mm thickness undulated into the slab in different ways to investigate punching shear resistance.

The program is divided into five groups. First group investigates the effect of installing the shear-band reinforcement (hanged up on top mesh, knit the top and bottom mesh together). The second group investigates the effect of inclination of shear reinforcement (shear band with vertical leg, with bended leg 45°). The third group investigates the effect of concentrating the shear reinforcement by increasing the quantity around the column. The fourth group investigates effect of radial distribution of shear-band system around the column. Finally, the fifth group investigates the effect of box distribution of shear-band system around the column.