Numerical Evaluation of Shear Strength Degradation Mechanism Dependent on the Size Increase of RC Deep Beams with Height up to 1.5 Meter by Using 3D Rigid-Body-Spring-Method

The purpose of this paper is to clarify the mechanism of shear strength reduction for reinforced concrete deep beams with varying stirrup ratios, due to the beam size increase. Three Dimensional Rigid-Body-Spring-Method was the applied numerical tool. By using the simulation results of reinforced concrete deep beams with the effective depth smaller than 1500 mm, the size dependence of each shear resistance component such as arch, beam and truss actions were investigated, along with the size dependence of localized information such as crack pattern, diagonal crack width and compressive stress. It was revealed that the size effect on shear strength results from the size dependence of the arch action, and the change of stirrup ratio does not show any inhibiting effects on it. The crucial reason for the size effect on the arch action is the size dependence of concrete compressive resultant on beam cross sections, and the critical diagonal crack width, which increases with beam size, is a key factor for the deterioration of concrete compressive strength and the capacity of compressive stress in struts. Moreover, it was found that the critical diagonal crack width not only affects the normalized shear strength, but also has influence on the post-peak behavior of deep beam.