Shear enhancement in RC beams loaded on the tension face

Abstract

Shear strength of reinforced concrete beams significantly enhances when loads are applied closer to the support due to the arching action. This enhancement is widely investigated and has been included in the design codes. However, scarce resources are available in the literature regarding this enhancement for the case of multiple point loads applied within the enhancement zone; in addition, the available literature focuses on loads applied to the flexural compression face. Situations where multiple point loads are applied on the tension face are found in practice in structures like balanced-cantilever crosshead girders of bridges and transfer girders near the supports. Nevertheless, research considering this configuration has not been found in the available literature. The aim of this research is to study the effect of the loading arrangements on the shear strength enhancement of deep beams loaded on the compression or tension face with multiple point loads. This research was motivated by differences in the principal compressive stress trajectories obtained with nonlinear finite element analysis for the two different configurations. The author conducted an experimental program to investigate the influence of loading face, the effect of varying the ratio between loads applied within the enhancement zone and the influence on shear enhancement of partly loading the beam outside the enhancement zone. Detailed measurements of the crack kinematics and global deformation were obtained during the tests using the digital images correlation system. These measurements were used to provide descriptive models of the deformed beams and to evaluate the shear transfer actions of the tested beams. Strength of the tested beams was estimated using design codes (BS8110, EC2 2004 and MC2010) and non-linear finite element analysis. A novel practical strut-and-tie model was developed for the case of multiple point load applied to the tension face of the beams. This model correctly predicted the failure plane, fairly represented the stress field, and it is suitable for multiple loads applied entirely inside or partly outside the shear enhancement zone.Open Acces