A novel confined concrete constitutive model for steel-reinforced concrete (SRC) columns with cross-shaped steel (CSS) sections is proposed. The model is based on the similar characteristics of descending branches in the stress–strain curves of confined and unconfined concrete (UCC), considering confinement degradation caused by buckling of the steel section or longitudinal reinforcement. The confined region of SRC columns with CSS sections was divided into four parts: highly steel-confined concrete (HSCC), partially steel-confined concrete (PSCC), stirrup-confined concrete (StCC) and UCC. Relevant effective confinement coefficient expressions were also derived. Simulations of existing tests showed that (a) the load–strain curves obtained using the modified stress–strain constitutive model agreed well with the experimental results, with the error in the descending branch less than 5%; (b) the HSCC region for SRC columns with CSS sections in the finite-element model was in good agreement with that in the proposed region division; (c) the simulation of confined concrete region boundaries for SRC columns with CSS sections were determined using plumb lines for improving the calculation efficiency.

中文翻译：

---

十字形钢筋混凝土柱的约束机制

提出了一种新型的十字型钢（CSS）截面钢筋混凝土（SRC）柱约束混凝土本构模型。该模型基于约束混凝土和无约束混凝土（UCC）应力-应变曲线中下降分支的相似特征，考虑了型钢或纵向钢筋屈曲引起的约束退化。 CSS截面SRC柱的约束区域分为四部分：高钢筋约束混凝土（HSCC）、部分钢筋约束混凝土（PSCC）、箍筋约束混凝土（StCC）和UCC。还推导了相关的有效约束系数表达式。现有试验的模拟结果表明：( a )采用修正的应力-应变本构模型得到的载荷-应变曲线与试验结果吻合较好，下降分支误差小于5%； ( b ) 有限元模型中带有 CSS 截面的 SRC 柱的 HSCC 区域与建议的区域划分非常一致； ( c )采用铅垂线确定具有CSS截面的SRC柱的约束混凝土区域边界的模拟，以提高计算效率。