Systematic study on the shear behavior of reinforced concrete members with regard to the transition of members without and with shear reinforcement

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Shear behavior is a complex and important problem in structural concrete and has been an object of research for more than 100 years. Despite elaborate investigations, a range of open questions still remains. This situation is generally not adequate, especially regarding the assessment of existing structures, as bridge superstructures often have deficits in the calculated shear capacity due to insufficient shear reinforcement, but do not exhibit any signs of damage. The goal of this research project is to characterize the effect of the boundary and loading conditions on shear behavior of RC members without and with small shear reinforcement ratios. To meet this goal, shear crack geometry and growth, development of deformations and flow of internal forces will be systematically investigated on RC beams with different boundary conditions, load types and shear reinforcement ratios. The project fills a gap in basic knowledge of the internal behavior at the transition from shear transfer in members without shear reinforcement to members with sufficient shear reinforcement to establish full truss action. The proposed experimental program comprises 70 tests on beams with different static systems and systematically varied shear reinforcement ratios by gradually increasing the bar diameter of the stirrups while maintaining the stirrup spacing. The resulting flow of forces will be characterized by advanced measu¬ring techniques. At the transition from a member without to one with shear reinforcement, the governing shear transfer mechanisms, i.e. direct strut action as well as contribution provided by compression zone, crack processing zone, aggregate interlock, dowel action and shear reinforcement, vary considerably, as demonstrated by the many different shear models. However, the quantification of the different shear transfer mechanisms in the course of the transition is still under consideration. Since these aspects have not been sufficiently studied yet, systematic investigations of the governing effects on the flow of forces and shear resistance are necessary. Based on an experimental and theoretical work program, physically based models to describe the shear behavior of RC members will be developed and extended. These shear models will provide background for design concepts that are physically consistent and, thus, generally valid for members with different boundary conditions. Sharing a similar attitude and having complementary approaches to shear modeling, the collaboration between the applicant and co-applicant will be very effective in gaining more insight into this challenging issue, which is of great academic and practical interest.