Shear strength of prestressed 160 mm deep hollow core slabs

Abstract

Prestressed hollow core (HC) slabs have been used all over the world due to their technical and economic advantages for diverse applications. Therefore, knowledge of the structural behaviour of this precast element is required for successful floor design, especially in relation to its actual shear failure mode. For this purpose, many analytical and empirical equations have been proposed to predict the shear strength of HC slabs; however, the depth of the slab influences its failure mode. Shear tests on HC slabs with 160 mm depth were carried out to describe the failure mode of these slabs. The failure loads were compared with the equations available in the literature, to identify which of the equations better represent the shear strength obtained from the shear tests. Two series of tests were carried out for slab elements with the same transversal section, but with different numbers of strands. Some HC slabs had cores filled with concrete in order to analyse the influence of the concrete filling on the shear strength of these slabs. In this case, an expansive additive was used to compensate the shrinkage of the concrete cast in the cores. Additionally, some slabs were tested under pure flexure in order to determine the effective prestress losses at the strands. Additional tests were carried out to estimate the actual transmission length of prestress to the concrete. The results show that the equations based on the flexural shear failure mode suggested by Brazilian Standard NBR 14861 and by European standard EN 1168 predicted the shear strength of the 160 mm deep HC slabs with good accuracy. Furthermore, equations based on the tension shear failure mode with an adequate reduction in flexural stiffness can be used to predict the shear strength of these slabs. The filled cores did not contribute to an increase of the shear strength of the slabs, which is overestimated by the equations reported by some standards. Good prediction accuracy of the shear strength of these slabs can be achieved by equations based on the tension shear failure mode with an adequate reduction in flexural stiffness.