Strength capacity of RC beams without shear reinforcement: Numerical analysis and comparisons with code provisions

The investigation of the behavior of reinforced concrete (RC) elements without shear reinforcement is a current focal point, driven by the incomplete consolidation of predictive formulas for shear strength in RC elements. Currently, the literature provides, indeed, a limited number of experimental and numerical studies on this subject. This paper seeks to advance the comprehension of the behavior and collapse mechanisms of RC beams not provided of shear reinforcement, as commonly employed in RC slabs of bridges. The paper commences with a critical review of several predictive formulas for the shear strength of RC elements lacking transverse reinforcement, as stipulated by various international codes. The objective is to identify the principal parameters involved in the formulations and discuss their roles also by means of sensitivity analysis. Following this, the results of nonlinear numerical analyses, based on a three-dimensional finite element (FE) model, are presented. The FE model was initially calibrated using experimental results from a benchmark beam lacking shear reinforcement, retrieved from the literature, which exhibited a brittle shear failure. Subsequently, several specimens were prepared for the numerical investigation, assuming multiple combinations of geometrical and mechanical parameters. For specimens experiencing shear failure, the strength was compared with that provided by code formulas, as well as using the strut-and-tie approach for the cases characterized by a reduced shear span-to-depth ratio. In general, these analytical tools significantly underestimated the numerical strength, underscoring the necessity for further insights based on experimental tests. The numerical outcomes have been, indeed, prodromal to design an experimental campaign.