Shear enhancement in RC beams with stirrups simultaneously loaded within 2d and at 3d from supports

Abstract

Shear enhancement occurs in reinforced concrete (RC) beams when loads are applied within around 2d of supports where d is the beam effective depth. This paper examines shear enhancement in RC beams, with stirrups, which are loaded both within 2d of supports and at 3d from supports where shear enhancement is minimal. Simultaneously loading beams both inside and outside 2d of supports commonly occurs in practice but has not previously been systematically studied. A total of eight beams were tested in two groups of four having different reinforcement arrangements. The tests suggest that the shear resistance depends on the angle of the failure plane which is related to the loading arrangement. A strut and tie model (STM) is developed for analysing beams simultaneously loaded within and outside 2d of supports. The accuracy of the STM predictions is shown to be improved by relating strut strength to the strain in the flexural reinforcement. The proposed STM and nonlinear finite element analysis (NLFEA) with 3D solid elements are used to investigate parametrically the influence of loading arrangement on shear resistance. The strength predictions of the STM are shown to compare well with those of NLFEA. Comparisons are also made with shear strengths calculated using fib Model Code 2010 (MC2010) and the draft new generation of Eurocode 2 (prEN1992-1:21). The differing philosophies of these two methods are discussed.