Title: Shear Strength of Reinforced Concrete Simple and Continuous Deep Beams
Author(s): Hui Chen, Wei-Jian Yi, Zhongguo John Ma, and Hyeon-Jong Hwang
Publication: Structural Journal
Appears on pages(s): 31-40
Keywords: continuous deep beam; database; shear strength; simple deep beam; strut-and-tie model
This study focuses on the shear strength of reinforced concrete (RC) simple and continuous deep beams. The experimental phenomena and nonlinear finite element analyses showed that the crack pattern and stress state of a continuous deep beam differed from those of a simple deep beam, indicating the diagonal strut in the continuous deep beam had a higher degree of deterioration and, therefore, had a lower effective compressive strength. Regardless of the discrepancy between simple and continuous deep beams, however, the strut-and-tie model (STM) in ACI 318-14 prescribes the same strut effective coefficient only based on simple deep beam test results. Thus, it is necessary to validate the applicability and safety of the existing STM for continuous deep beams. In this study, the STM specified in ACI 318-14 was systematically evaluated using a reliable and extensive test database for shear strength of simple and continuous deep beams. The results showed that the safety margin of the shear strength of continuous deep beams was much lower than that of simple deep beams when web reinforcement passing through diagonal struts failed to resist the transverse tension force. Based on the selected test results and nonlinear finite element and theoretical analysis results, it was concluded that the ACI STM with a strut effective coefficient of 0.51 overestimated the effect of concrete compressive strength on the shear strength of continuous deep beams. Therefore, a modification of the strut effective coefficient was proposed and verified.