约束钢筋混凝土十字形柱的高温轴力分析

利用结构抗火分析软件SAFIR，研究了高温下约束十字形柱的轴力变化过程，考察了众多参数对该过程的影响规律，初步建立了其实用计算方法。研究结果表明：①荷载比、轴向约束刚度比、转动约束刚度比、荷载偏心率、截面尺寸对该变化过程影响较大，而柱长度、材料强度、混凝土保护层厚度、配筋率则对该过程影响较小。②随着轴向约束刚度比增加，轴压柱和偏压柱的轴力变化系数峰值均逐渐增大，且后者的增大效应相比前者更为显著。③有无转动约束存在对轴压柱和偏压柱的轴力变化系数峰值影响有限，非零转动约束刚度比盼大小对轴力变化系数随升温时间的变化过程影响很小。④随着荷载比增加，轴力变化系数峰值迅速减小，这一趋势对于偏压柱更为显著；随着荷载偏心率增加，轴力变化系数迅速增大。由于火灾中相邻构件之间相互约束作用的客观存在，正确把握高温下约束构件的内力变化过程对科学解释其真实火灾行为是必要的。

Analysis on Axial Force of Restrained Cross-Shaped Reinforced Concrete Columns under High Temperature

The variation process of the axial force of restrained cross-shaped columns under high-tempera ture is studied using the computer program SAFIR. The influence law of some parameters on the axial force in restrained cross-shaped columns in fire is examined and a practical calculation method for axial force of restrained cross-shaped columns during fire is proposed in this paper. Simulation results show that： （a） the influence of axial load ratio, axial restraint stiffness ratio, rotational restraint stiffness ratio, load eccentricity ratio, and sectional dimensions on axial force of restrained cross-shaped columns is significant, while the effect of column height, thickness of concrete cover, reinforcement ratio, and strengths of materials is marginal; （b） with the increase of the axial restraint stiffness ratio, the maximum value of the ratio of additional axial force under high temperature to axial force under room temperature （i. e. , axial force variation coefficient in this paper） increases for both concentric and eccentric loading columns, and this trend is more significant for the eccentric loading columns; （c） the maximum value of the axial force variation coefficient of columns without rotational restraint is close to that of columns with rotational restraint, while the effect of non-zero rotational restraint ratio on the axial force variation coefficient is negligible ; and （d） with the increase of the axial load ratio, the maximum value of the axial force variation coefficient reduces quickly, this trend is more significant for the eccentric loading columns; and with the increase of the load eccentricity ratio, the axial force variation coefficient improves greatly. Since the restrained actions occur in adjacent elements of practical structures in fire, it is important to make clear the variation of the internal forces in restrained structures under high temperature.