火灾下约束钢柱受力性能实用分析方法(Ⅱ)-轴力和弯矩共同作用下的约束钢柱

Practical analysis method for restrained steel columns in fire (Ⅱ)——restrained columns under combined axial force and bending moment

对火灾升温条件下压弯约束钢柱的轴力和截面弯矩发展规律进行了研究,给出了确定其屈曲温度和破坏温度的简化方法。约束钢柱屈曲前,随着温度升高钢柱轴力线性增加,截面弯矩基本保持不变;约束钢柱屈曲后,钢柱轴力减小,截面弯矩突然增大,钢柱处于轴力和弯矩共同作用下。确定屈曲温度时,采用无约束压弯钢柱屈曲温度的计算公式,钢柱轴力考虑轴向约束的影响;确定破坏温度时,破坏准则采用截面屈服条件表示的轴力-弯矩相关关系,轴力取初始轴力。利用有限元方法对本文公式进行了验证,对通常情况下的约束钢柱(荷载比小于0.7,约束刚度比小于0.1),本文方法与有限元方法计算结果吻合较好。

Through studying the evolution of axial force and bending moment in restrained steel columns under combined axial force and bending moment at elevated temperatures in fire, a simplified method for calculating the buckling temperature and failure temperature is developed. Before buckling of the restrained column, the axial force in the column increases linearly and the bending moment changes little. After buckling, the bending moment suddenly increases, and the axial force begins to decrease. Design equations for unrestrained columns under combined axial force and bending moment in fire are adopted to calculate the buckling temperature. Effects of axial restraint are included when calculating the axial force. The yield axial strength-plastic bending moment failure temperature. The proposed design methods are interaction curve of column section is adopted for calculating the verified by using a calibrated finite element model. For restrained columns with realistic parameters （load ratio less than 0.7, restraint stiffness ratio less than 0.1 ）, the buckling temperature and failure temperature predicted by the proposed method agree well with those of the finite element method.