Strut-and-Tie Modeling of Reinforced Concrete Deep Beams

Strut-and-tie models (STMs) are often used for the design of shear critical deep members because they can rationalize the shear transfer within discontinuous or disturbed regions in reinforced concrete structural elements. Most current codes of practice adopt the strut-and-tie method but provide very little guidance on how to select appropriate strut-and-tie layout and dimensions. Furthermore, the effectiveness factors used to account for the biaxial state of stresses in struts of deep beams are not reliable. This paper reviews the application of STMs for the design of RC deep beams and evaluates current formulations of the effectiveness factor. Experimental and numerical studies are used to assess how the effectiveness factor is influenced by different parameters, including concrete compressive strength, shear span:depth ratio, and shear reinforcement ratio, and to arrive at a more reliable strain-based effectiveness factor. Various effectiveness factors are examined against an extensive database of experimental results on RC deep beams with and without shear reinforcement. The results show that the proposed effectiveness factor yields the most-reliable and most-accurate predictions and can lead to more-economical and safer design guidelines.