Shear enhancement near supports in RC beams

Abstract

Shear strength is enhanced within the short shear span of reinforced concrete beams that are loaded on their upper side within a distance of around 2–2·5d of supports (where d is the beam effective depth). Eurocode 2 and fib Model Code 2010 (MC2010) account for this by reducing the design shear force, unlike the previous UK code BS 8110, which increases the shear resistance provided by concrete. Eurocode 2 and MC2010 also allow shear enhancement to be modelled using strut-and-tie models. Very few test data are available to assess the comparative merits of these approaches for the design of beams with multiple point loads within 2d of supports. Consequently, 12 beams were tested to investigate the influence of loading arrangement on shear resistance. Comparisons are made between the strengths of the tested beams and the predictions of BS 8110, Eurocode 2, MC2010, strut-and-tie modelling and non-linear finite-element analysis. Significantly, the BS 8110 approach of enhancing shear resistance is found to give better strength predictions than the load reduction methods of Eurocode 2 and MC2010. Accuracy of the non-linear finite-element analysis and strut-and-tie model is broadly comparable, but the former requires calibration, unlike the latter.