Advanced unified failure model on uniformly reinforced concrete box section members

Based on the traditional Nielsen model, a unified failure model on the uniformly reinforced concrete box section members under combined forces was introduced by Luo and Liu. One of their contributions is adjustment of the shear carrying capacity of concrete at the member failure surface. In the unified failure model, the comparison with the experimental results verified this adjustment. Nevertheless, it should be pointed out that the adjustment factor of shear carrying capacity at member failure surface for the reinforced concrete members in the unified failure model is a fixed adjustment constant for all experiment data, which is basically determined by curve fitting. However, the adjustment factor should vary with the normal stress at the member failure surface. In this paper, an advanced theoretical model is introduced, in which the adjustment factor of shear carrying capacity at failure surface is a variable related to the normal stress at failure surface. Furthermore, the advanced unified failure model on the uniformly reinforced concrete box section member can still be expressed in a simple form. Finally, the comparison with several groups of test data has verified that this advanced model is more accurate and feasible to be used in design.