Behavior and shear design provisions of reinforced concrete D-region beams

This paper studied the behavior and shear design provisions of D-regions in reinforced concrete (RC) normal-size beams. In D-regions, the load is transferred to the support mainly through arch action mechanism associated with nonlinear strain distribution, while in B-regions, the strain is linear. Shear design for B-regions follows the conventional sectional method (CSM), while the strut and tie modeling (STM) approach has been introduced for D-region recently. Depending on the shear span to depth ratio, normal-size beams may contain both B-regions and D-regions, thus, creating a unique class of beams. The impact of the shift in the shear design provisions from CSM to STM has not received enough attention. The study involved testing eight reinforced concrete beams with and without stirrups having various flexural reinforcement ratios loaded under a shear span to depth ratio less than two, to create D-regions. The beams were simulated numerically via nonlinear finite element (NLFE) for verifications. Comparisons of results were made among those obtained from the experimental program, STM, CSM, and NLFE. The study provided some insight into the behavior of these regions and compared the prediction capability of the numerical methods. Finally, the study pointed to potential shortcomings that may arise when this class of beams is designed on the basis of STM.