Shear Capacity of Slabs with Voiding Elements

Abstract

In the current version of EN 1992-1-1, the shear and punching capacity of beams and slabs without shear reinforcement is governed by the smallest width of the cross section in the tensile area. The semi-empirical formula in this code is appropriate for rather deep beam elements without contribution of the flanges and transfer stiffeners to the shear capacity. However, it can be presumed that for rather stocky beams or slabs with small void formers these components contribute and improve the shear capacity of the global element. To evidence the increased capacity of such slabs in comparison with the single beam theory, a limited test program was set up by Airdeck Building Concepts and Hasselt University (Belgium). Four-point bending tests were carried out on elements with a width of 600 mm, span of 2400 mm and thicknesses of 220 and 340 mm with or without void formers. Because these systems are mostly composed by a precast plank with a thickness from about 60 to 70 mm (with fixed void formers) and a topping cast on site, special attention was taken to the interface to avoid an early failure at the shear interface. Different approximations are investigated for deducing the resistance of the slab with voiding elements by application of a reduction factor on the resistance of a solid slab. It appears from this preliminary set of tests that a volumetric reduction ratio provides the best though safe estimate for this slabs.