Shear failures in reinforced concrete members without transverse reinforcement: An analysis of the critical shear crack development on the basis of test results

Shear in concrete members without transverse reinforcement can be carried by various potential sheartransfer actions, whose activation depends much on the actual cracking pattern and kinematics at failure. Failures can occur in a progressive manner (at the end of a stable propagation of a critical shear crack) or in a sudden manner (by an unstable progression or development of a new crack). In addition, the development and shape of the failure crack may also be very different from case to case. These differences influence which shear-transfer actions may be governing for a given member and loading situation. Despite the large number of specimens tested in shear, almost no information on the actual crack development during the process of failure is yet available. This paper presents the results of an experimental programme consisting of thirteen beams. The tests were designed to investigate different structural systems and loading conditions commonly found in practice (cantilevers with concentrated and distributed loading, single span beams with distributed loading and continuous beams). The cracking patterns and their associated kinematics were tracked in detail by using photogrammetric techniques at high frequencies during testing and particularly during the process of failure, providing data on the actual crack development leading to shear failure. The observations show that very different cracking patterns may be found and that they might be also developed in different manners. The results are interpreted with reference to the measured crack kinematics and related to the various potential shear-transfer actions, with the aim of providing a useful material towards the development of rational approaches for shear design.