A Study on the Distribution of Shear Forces Between Resisting Mechanisms in a RC Element Without Stirrups

This paper explores how the shear force distributes itself among the three main shear resistance mechanisms: shear resistance of the uncracked compressed chord, aggregate interlock, and dowel effect. Today's dominating shear models, the critical crack theory (Muttoni et al. [1]) and the compression field theory (Collins et al. [2]) maintain that the main shear -resisting mechanism is aggregate interlock, while more recent studies (Mari et al. [3]), maintain that the main resistance mechanism is the shear resistance on the uncracked compression chord. In this paper FEM modelling is used to study a test carried out at the Universidad Politecnica de Madrid (UPM) to try to assign the shear force to the different shear mechanisms for different loading steps and elucidate what finally causes the failure of the structure. The results show that as load is increased the relative part of the shear force taken by the uncracked compressed chord increases until, finally, shear failure is reached when the principal tensile stress in the area located close to the load but towards the support reaches the tensile resistance of concrete, generating a crack that precipitates the failure of the beam. It should be pointed out that the study included in this paper is only preliminary and should be extended to other cases exploring different sizes, reinforcement ratios, etc.