Experimental evidences of flexural to shear to crushing failure mode transition in reinforced concrete beams without stirrups

The results of a series of experimental bending tests carried out on reinforced concrete members without transverse reinforcement are reported and illustrated as a contribution to the study of the flexural to shear to crushing failure mode transition. A total of 45 beams were tested to investigate the effects of a wide range of longitudinal reinforcement amounts – 0.25% to 3.39% –, beam depths – 5 to 80 cm – and beam slendernesses – 3 to 24. The analysis of the experimental data encompasses the identification of the overall mechanical response, the assessment of the ultimate load and the detection of the critical crack that leads to the final collapse of the beam. The results are interpreted with reference to a global failure mode transition scheme, which allows to analyze all the failure modes within the same framework. As a result, an effective and synthetic prediction of the failure mode transition is achieved on the basis of dimensionless numbers, namely NP, NC and λl, defined in the framework of linear elastic fracture mechanics. Besides, strengths and weaknesses of the provisions of some codes of practice are highlighted on the basis of the experimental results. In this context, some drawbacks are reported for what concerns the inclusion of the size effect in the models provided to assess the shear capacity of reinforced concrete beams.