Title: Strut-and-Tie Model without Discontinuity for Reinforced Concrete Deep Beams
Author(s): Jung-Yoon Lee and You Min Kang
Publication: Structural Journal
Appears on pages(s): 123-134
Keywords: deep beams; nodal zone; shear span-depth ratio; shear strength; simplified STM; strut-and-tie model (STM)
The current design codes (including ACI 318-19, EC2-04, CSA-14, and fib model code) recommend the strut-and-tie model (STM) for the design of deep reinforced concrete (RC) members with higher accuracy in predicting the shear strength compared to existing semi-empirical shear design equations. Though the STM in these codes are more rational and effective than the previous semi-empirical formulations, their application is still difficult. Several inconsistencies and contradictions exist in the current STMs—such as a complex design process, the unclear mecha-nism for model selection, inconsistent boundary points between B regions and D regions, and an impractically larger prediction for the required amount of shear reinforcement—which question the reliability of STM and create mistrust among designers. In this study, a model was proposed to design RC deep beams by simpli-fying the current STM of the ACI 318-19 code. The proposed model reduces the calculation efforts required for the design process and eliminates the complexities and contradictions in the current STM, especially the differences in STM and beam theory predictions at the boundary between the B region and D region. The proposed model presents practical solutions for the contradictions in the design process of the existing STM and effectively reduces the calculation efforts needed by introducing a check for bearing and potential nodal failure. The simplified model was verified against an extensive experimental database consisting of 595 RC deep beams collected from the literature. Comparison of the results shows that the proposed STM predicted the strength of deep beams with similar accuracy to that of the detailed STM but with remark-ably less calculation effort compared to the detailed STM.