The shear failure of reinforced concrete beams has been widely investigated over many years. Despite this, there is no consensus on the relative importance of the underlying mechanisms of shear resistance. The main objective of this thesis is to develop improved design guidelines for shear enhancement in beams with multiple concentrated loads applied on their upper side within a distance of 2d from the edge of supports (where d is the beam effective depth). The research involves a combination of laboratory testing, nonlinear finite element analysis and analytical work.
Many tests have been carried out on beams with single point loads within 2d of supports but only a handful on beams with multiple point loads within 2d of supports. This is a significant omission since such loading commonly arises in practice. The author carried out a series of tests on beams loaded with up to two point loads within 2d of supports. The tests were designed to investigate the influences on shear strength of loading arrangement, cover and bearing plate dimensions. The latter two were varied to investigate the underlying realism of key assumptions implicit in the Strut and Tie Modelling (STM) technique. Detailed measurements were made of the kinematics of the critical shear crack. These measurements were used to assess the relative contributions of aggregate interlock, dowel action and the flexural compressive zone to shear resistance.
Novel STMs are proposed for modelling shear enhancement in simply supported and continuous beams. NLFEA is used to assist in the development of the STM. The STM are validated with test data and are shown to give reasonable strength predictions that are of comparable accuracy to the author's NLFEA. STM gives particularly good predictions of shear resistance if the strut strengths are calculated in accordance with the recommendations of the modified compression field theory rather than the recommendations of Eurocode 2, which can result in strength being overestimated. However, the STM are shown to overestimate the influences of bearing plate dimensions and cover on shear resistance.