A beam and arch action model for computing the shear strength of prestressed and reinforced HSFRC beams

Details of an experimental investigation of fully/partially prestressed high strength fibre reinforced concrete (HSFRC) beams using concrete of 65 MPa with varying levels of fibres are presented in this paper. The behaviour of prestressed beams, which were designed to be shear-dominant in the absence of fibres, has been discussed and the influence of fiber content and fiber location on the shear behaviour of the beams has been examined. The parameters varied in the experimental program were the levels of prestressing force, fibre volume fractions (0, 0.5, 1.0 and 1.5%), fiber location (full depth and full length, and full depth and over shear span only), the presence or absence of stirrups in the shear span, and shear span to depth ratio. An analytical model based on flexure-shear interaction to find the shear strength due to beam and arch mechanisms separately has been proposed. This model takes into account the fiber effects, effect of prestressing, deformed bars, shear span-to-depth ratio, aggregate size, and strength of concrete both in tension and compression. The results show good comparison with test results and with those reported in the literature. Different equations proposed in the literature to compute the shear capacity of reinforced and prestressed concrete beams have also been used to evaluate the shear capacity of the beams tested in this study. From the experimental program, it has been observed that the beams with or without fibres over the entire section (no stirrups) failed in pure diagonal shear. However, beams having fibres only in the shear span (with or without stirrups in the shear span), were found to develop their full flexural capacity, i.e., the dominant crack leading to failure developed in the pure moment zone. It has been found that the stirrups in the shear span can be replaced by an amount of fibers giving equivalent structural performance