Enhancing the shear strength of hollow-core slabs by using polypropylene fibres

Experimental and numerical research studies demonstrated that the addition of fibres in correct proportions, enhances the shear behaviour of Reinforced Concrete (RC) elements, allowing to totally or partially replace the conventional web reinforcement. However, despite of this increase of knowledge about Fibre Reinforced Concrete (FRC), there is still a gap in the applicability of fibres as a shear reinforcement in certain prestressed structural elements where the use of conventional transverse reinforcement is difficult due to their manufacturing process, e.g. extruded elements in dry concrete. In this context, the present paper evaluates the possibility of enhancing the shear strength of Hollow-Core Slabs (HCS) by using Polypropylene Fibre Reinforced Concrete (PFRC). HCS can be critical in shear at their end zones, since these zones are disturbed regions (already stressed in tension by splitting forces) in which the beneficial effects of the prestressing actions on the shear strength are not active yet. Five full-scale HCS (42 cm high, 120 cm wide and 600 cm long) were tested under shear loading (1 in RC and 4 in PFRC). Two tests were performed on each slab varying the shear-span-to-effective depth ratio (a/d = 2.8 according to EN1168 and a/d = 3.5). Results show that macro-synthetic fibres are able to improve the shear strength of hollow-core slabs of about 25%; furthermore tests according to EN1168 are more affected by arch actions as compared to a/d = 3.5. Finally, the comparison between experimental results and predictions of four international codes (Eurocode 2, ACI 318-14, Model Code 2010 and EN1168), highlighted the need of improving the actual shear formulations.