Direct Evaluation of Shear Carrying Mechanisms in Reinforced Concrete Deep Beams

Reinforced concrete deep beams, such as hammerhead piers, corbels and transfer girders, are common elements found in a variety of structures. These members are characterized by relatively small shear span-to-depth ratios and are often shear critical. The Two-Parameter Kinematic Theory (2PKT) has been shown to successfully predict the complete response of these members, including the shear strength and post-peak response. This modelling approach proposes that the shear carried in deep beams is the summation of the shear transfer by the critical loading zone, by aggregate interlock, by the transverse reinforcement and by dowel action.
This paper uses experimental data from five recently conducted large-scale deep beam tests to directly quantify the shear transfer mechanisms of deep beams. Digital Image Correlation (DIC) equipment was used to measure the displacements and strains in the uncracked critical loading zone. A refined grid of infrared position tracking targets is used to measure the global deformations. Together these measurements are used to back-calculate the stresses in the critical loading zone, the aggregate interlock along the critical crack, the stress in the transverse reinforcement and the dowel action of the longitudinal reinforcement. The summation of the shear transfer along the critical shear crack is then determined and compared with the experimentally applied load. The paper discusses the detailed constitutive models used to translate local strains to stresses in the critical loading zone and along the shear crack. A comparison of the different models is conducted. The results indicate that reasonable estimates of the applied load are obtainable using several of the constitutive models studied. The paper also discusses the significance of each shear transfer mechanism in deep beams.