不同应力—温度路径下平面钢框架火灾反应的非线性分析

Nonlinear Analysis of Plane Steel Frames under Different Stress-Temperature Paths in Fire

采用考虑温度—应力路径影响的高温下钢材的应力—应变关系,对火灾中钢框架结构的反应进行了非线性分析,旨在尝试提出一种更加符合实际情况的钢结构抗火反应分析新方法。根据已有的试验结果,对高温材性试验数据进行了回归分析,得到了Q235钢在升温恒载、升温加载、升温降载3种基本应力—温度路径下单向拉压时的本构关系式,进而得到不同应力—温度路径下热非弹性应力—应变增量关系式。利用虚功原理,推导出不同应力—温度路径下平面钢框架有限元分析的单元热非弹性刚度方程的显式。同时,对增量迭代法进行了修正,提出升温恒载路径、升温加载路径及升温降载路径3种路径之间切换的判断准则,为结构抗火全过程分析提供了理论基础。

In this paper, the nonlinear analysis of steel frame in fire is carried out by adopting a new constitutive relationship which takes account of the temperature-stress path. The aim of this study is to put forward a new and more reasonable method for analyzing plane steel frames in fire. According to the experimental data, the constitutive relation of steel Q235 is obtained through regression analysis under three kinds of stress-strain paths, that is, heating and constant-load, heating and loading, heating and unloading. Then the incremental expressions of stress-strain relations for different stress-temperature paths are obtained. Based on the principle of virtual work, the non-elastic thermal elemental stiffness equations of plane steel frames for finite element analysis under different stress-temperature paths are derived. Moreover, the incremental iteration method is modified and a criterion is proposed for selection of one of the three kinds of stress-strain-paths. This study will provide a theoretical basis for the whole process analysis of steel frame in fire.