局部火灾下正放四角锥网架中杆件约束效应分析

Analysis of the Restraint Action among Chords for Square Pyramid Spacial Truss Exposed to Localized Fires

基于改进的正放四角锥网架结构在非均匀温度场中的数值分析模型,建立了147例数值分析模型。借助ANSYS软件的热力耦合数值分析功能,得到了网架结构高温力学特征量数据库,从杆件纵向变形与杆件应力历程的角度,研究了局部火灾下杆件间的约束效应分布规律,同时研究了温度场非均匀性、荷载比、网格尺寸对杆件约束效应的影响规律,研究表明,在局部火灾下,网架结构斜对称轴上中间位置处腹杆受到的轴向约束最强,表现为压应力增加;垂直于斜对称轴方向的杆件表现为拉应力增加;杆件轴向约束程度随温度场非均匀性的增强及网格尺寸的减小而增大;在结构高荷载比情况下,温度场非均匀性和网格尺寸对杆件轴向约束的影响尤为显著。

Square pyramid spaeial truss models exposed to non-uniform fire temperature fields were improved on the basis of existing research. 147 improved models have been built in this pa- per. With the help of finite element software ANSYS, we calcutated the thermo-mechanical cou- pling effects. We have simulated the square pyramid spaeial trusses mechanical characteristic da- tabase at high temperature. We describe the bars constraint action under local fire by studying the relation of change of members＇ length and members＇ stress process. This paper summarizes the effects of non-uniform fire temperature fields, loading ratio and mesh size on the bars con- straint action. The results show that webs at oblique axis of symmetry and nearby are restricted much more than others. For webs at parallel oblique axis of symmetry, added temperature stress is produced. For webs at vertical oblique axis of symmetry, added temperature tensile stress is produced. More non-uniform fire temperature fields and less mesh size produce greater restraint action, but it is nothing to do with load ratio. And under high load ratio, non-uniform fire tem- perature fields and mesh size have more effect on restraint action.