Diagonal shear in thin-webbed reinforced concrete beams: fibre and stirrup roles at shear collapse

Abstract

The combination of steel or polymeric fibers with stirrups in reinforced concrete (RC) shear-sensitive elements has been recognized as an efficient means of resisting sheal; but so far few models have attempted to describe fibre-stirrup interaction. A recently proposed limit-analysis model for the description of the ultimate behaviour of thin-webbed RC and prestressed concrete (PC) beams subjected to shear is extended here to the study of the role of fibres. A stabilized shear-crack pattern is assumed, with the stirrups at or beyond the yielding threshold, and the end sections of the concrete struts at the onset of failure in shear compression. The shear cracks, either limited to the web (PC beams) or extended to the lower flange (RC beams), are modelled with non-uniform opening and slip distributions, with mode l prevailing at the crack tip and mixed mode along the cracks. The fibres are introduced as fully kinked, randomly oriented, randomly embedded, linear connectors across the shear cracks, and their contribution to shear resistance is analysed in three different types of fibres (crimped and hooked-end or smooth steel fibres, and polyacrylonitrilic (PAN) fibres), different fibre contents, normal and high-strength concretes. In combination with stirrups, the role of crimped fibres and PAN fibres is found to be quite substantial. A comparison with other limit analysis models and 22 fibre-reinforced concrete tested beams is also presented.