Optimum Strut-and-Tie Models for Reinforced Concrete Beams

In this study, the authors suggested three optimum strut-and-tie models (STMs), which consider all reinforced concrete (RC) beams’ failure behavior characteristics. The recommended models are valid for the RC beams with a shear span ratio (a/d) of less than 4.5. For each model, the authors also proposed a force distribution ratio, described by the portion of force carried by a truss mechanism, to assist structural designers in conducting the appropriate design using the current design codes’ STM methods. In determining the force distribution ratios, the authors incorporated the influences of the main design variables, such as the a/d ratio, flexural rebar ratio, and concrete strength. The authors verified the appropriateness of the suggested STMs and force distribution ratios by using them for the strength verification of 758 RC beams tested to failure. The proposed STMs and force distribution ratios predicted the RC beams’ failure strength quite well. The average test-to-predicted strength ratios (and coefficient of variations) by the present study and conventional STM models of design codes were 1.07 (21.3%) and 1.75 – 1.82 (27.6 – 45.7%), respectively.