Influence of polypropylene fibre reinforcement and width-to-effective depth ratio in wide-shallow beams

Many experiments available in the literature show that fibres, when provided in sufficient amount to guarantee an adequate toughness to Fibre Reinforced Concrete (FRC), are significantly effective as shear reinforcement. However, most of the experiments relate to elements reinforced by steel fibres and very few present research on structures produced with other kinds of fibres, i.e. polypropylene (PP) fibres, which can present a series of advantages (durability and corrosion avoidance above all). Today PP fibres might be able to impart significant toughness and ductility to concrete. This paper reports the results of a recent experimental programme on reinforced concrete (without any shear reinforcement, PC) and Polypropylene Fibre Reinforced Concrete (PFRC) Wide-Shallow Beams (WSBs) subjected to shear, focusing on the role of the width-to-effective depth ratio (b/d) and on the beneficial influence of newly developed PP fibres. Fourteen WSBs with different widths and depths, fibre content and, also, minimum amount of classical shear reinforcement, were tested. Results show that PC WSBs having width-to-effective depth ratio from 2 to 3 reach a higher ultimate shear stress (compared to the corresponding not-wide PC beams), generally disregarded by most of standards. Moreover, the ability of PP fibres in promoting a substantially more stable shear behaviour was experimentally observed, as well as the possibility of using PP fibres as minimum shear reinforcement.