Study on minimum shear reinforcement of flat slabs

Resumo

In a preliminary study that aims to define the minimum shear reinforcement of flat slabs that, leading to a shear failure that crosses that reinforcement, can avoid a sudden failure, nine slabs with 1800 mm x 1800 mm x 130 mm dimensions were tested. Their main variables were the number of layers of shear reinforcement of the stud type, the cross-section area of that reinforcement in each layer and the diameter of the studs. In the attempt of defining the minimum punching reinforcement of the slabs, the parameter k, equal to the total force in the transverse reinforcement inside the truncated cone bounded by the shear crack divided by the punching strength of similar slab without shear reinforcement, was used. The values of k of the slabs varied between 0.27 and 1.03 and the punching failure surface crossed the shear reinforcement when k was smaller than around 0.70. The value of k equal to 0.6 was defined as close to the minimum for slabs with effective depth of 90 mm and flexure reinforcement ratio of 1.38%. In comparison with the slab with no shear reinforcement, slabs having k of that order had punching strength and rotation increase of about 10% and 30%, respectively.