矩形钢管对核心混凝土的约束效应有其特殊性，准确预测受弯构件截面塑性发展能力可有效保证构件的承载安全。为提高矩形钢管混凝土受弯构件截面强度的计算精度，在套箍系数的基础上进一步考虑高宽比和含钢率的影响，建立塑性发展系数多因素模型和抗弯强度改进模型。首先，基于钢管混凝土统一理论，研究矩形钢管混凝土受弯构件塑性发展系数的变化规律，并与当前规范计算公式进行对比；然后，结合规范和工程需求构造2 160个矩形钢管混凝土受弯数值模拟构件，利用改进的本构关系和构件失效判据开展纤维模型法精细分析，研究宽厚比、高宽比、含钢率、强度比对塑性发展系数的影响，确定高宽比和含钢率为塑性发展系数的主要影响因素，通过回归分析拟合与高宽比和含钢率相关的函数表达式，由此建立矩形钢管混凝土塑性发展系数多因素模型和抗弯强度改进模型；最后，利用搜集到的128组试验数据，将抗弯强度改进模型与国内外主要设计规范进行对比验证。结果表明，建立的塑性发展系数多因素模型克服了现行规范中计算模型精确性不足的缺陷，能够更加准确地反映矩形钢管混凝土受弯构件的塑性发展能力；建立的矩形钢管混凝土受弯构件抗弯强度改进模型求解的极限承载力与试验值比值的均值为0.971，均方根误差为0.118，吻合良好，具有更高的计算精度。

The constraint effect of rectangular steel pipe on core concrete has special characteristics, and the accurate prediction of the plastic development capacity of bending members can effectively ensure the load-bearing safety. In order to improve the calculation accuracy of the sectional strength of rectangular CFST members under pure bending, this study established a multi-factor model of plastic development coefficient and an improved bending strength model based on the confinement coefficient and further considering the influence of height-width ratio and steel ratio. First of all, based on the unified theory of CFST members, the change law of plastic development coefficient of rectangular concrete-filled steel tube was studied and compared with the current standard calculation formula. Then, combined with the specification and engineering needs, 2 160 numerical simulation components of rectangular CFST members under pure bending were constructed and the refined analysis of the fiber model method was conducted using the improved constitutive relationship and component failure criterion. The influence of width-thickness ratio, height-width ratio, steel ratio and strength ratio on plasticity development coefficient was investigated to determine that the height-width ratio and steel ratio are the main factors influencing the plasticity development coefficient, and the function expressions related to the height-width ratio and steel ratio were fitted through regression analysis. Thus the multi-factor model of plasticity development coefficient and strength calculation of rectangular CFST members under pure bending were established. Finally, the bending strength improvement model was verified against the main design specifications at home and abroad by using the 128 sets of experimental data collected. The results show that the established multi-factor model of plasticity development coefficient overcomes the defects of the current specification that the calculation model is not accurate enough, and it can more accurately reflect the plasticity development capacity of rectangular CFST members under pure bending. The established improvement model of the bending strength of rectangular CFST members under pure bending solved for the ratio of the ultimate load carrying capacity to the experimental value has a mean value of 0.971 and a root-mean-square error of 0.118, indicating a good match and a higher calculation accuracy.