考虑端部轴向约束的火灾下钢管混凝土柱力学性能有限元研究

FEA on mechanical behavior of axially restrained concrete-filled steel tubular columns subjected to fire

实际结构中受相邻构件的约束,火灾下构件内力与变形发生变化,将影响其耐火极限,但目前关于钢管混凝土柱抗火性能的研究大多针对单根柱,未考虑相邻构件产生的端部约束效应。为此,基于ABAQUS软件,建立了考虑端部轴向约束的圆钢管混凝土柱有限元模型,分析了轴向约束作用对其轴力、变形以及耐火极限的影响。研究结果表明,轴向约束作用显著影响柱的轴力,表现为膨胀阶段柱内力增加,压缩阶段内力减小,进而使得变形减小,耐火极限提高。此外,分析了截面尺寸、荷载比、长细比以及偏心率对考虑端部轴向约束作用的钢管混凝土柱耐火极限的影响。结果表明,对于轴向约束刚度比0.02的圆钢管混凝土柱,当长细比在30以内时,轴向约束作用对耐火极限的提高幅度在10%~40%之间,可考虑约束作用对耐火极限的提高。与无端部约束柱类似,随着截面尺寸的增加、荷载比和长细比的减小,考虑端部约束的构件耐火极限也逐渐增大;而与无约束柱不同的是,偏心率对有端部约束的钢管混凝土柱的耐火极限影响较大。

The internal force and the deformation of the column exposed to fire in structure change due to the restraint provided by adjacent members,which may affect the fire resistance. However,most of previous studies focused on the fire performance of individual concrete-filled steel tubular( CFST) column, without considering the structural interactions between the column and its adjacent members. A finite element model of axially restrained circular CFST column was developed with ABAQUS to analyze the influence of axial restraint on the axial force,axial displacement and fire resistance. It is found that axial restraint has significant influence on the axial force,which intensifies the axial force during the expansion period and relieves the axial force during the contraction period. The axial displacement decreases correspondingly,which enhances the fire resistance. The influences of parameters on the fire resistance of axially restrained columns were studied,including cross-sectional dimension,load ratio,slenderness ratio and load eccentricity ratio. The results show that the fire resistance can be increased by 10% to 40% for columns with the axial restraint stiffness ratio of 0. 02 and slenderness ratio less than 30,and the beneficial effect on the fire resistance can be considered. The higher fire resistance can be attained with larger cross-sectional dimension,smaller load ratio and smaller slenderness ratio for both axially restrained and unrestrained columns. Different from members without axial restraint,the load eccentricity ratio has noticeable influence on the fire resistance of restrained columns.