不同火灾工况下钢梁-钢管混凝土柱平面框架受火全过程分析

采用多尺度建模方法建立了考虑钢材高温蠕变的三层三跨钢梁-钢管混凝土柱平面框架火灾全过程热-力耦合数值模型，研究不同火灾工况下平面框架经历常温加载、恒载升温、降温和火灾后等不同受火阶段的力学性能。在与已有试验对比验证的基础上，分析了框架经历升温和降温后受火钢梁跨中挠度和受火柱顶轴向变形与升降温时间关系，计算了火灾后框架底层柱底水平荷载P-框架顶层水平位移Δ关系曲线。研究结果表明：钢材的高温蠕变是钢材在热力耦合作用下应变的一部分，计算过程中需要考虑其影响；钢梁在升温过程中由于高温膨胀对框架柱产生外推作用，而进入降温阶段后钢梁产生明显的收缩变形；框架底层三跨同时受火时钢梁跨中挠曲变形最大，受火初期柱顶轴向压缩变形小于膨胀变形；受火后框架水平承载力和初始刚度均随受火区域的增大呈下降趋势。

Analysis of planar frame with steel beam-concrete-filled steel tubular columns after exposure to complete fireprocess under different fire cases

A finite element (FE) model was developed to predict the mechanical behavior of a three-story-three-bay planar frame with concrete-filled steel tubular (CFST) columns after exposure to complete fire process under different fire cases based on multi-scale FE method, considering the steel high-temperature creep and loading at ambient, heating, cooling and post-fire conditions. The FE model was verified by others’ experimental results. The deflection of beam and axial deformation of columns were calculated under heating and cooling conditions, respectively. The lateral load P versus lateral displacement Δ relationship of planar frame was simulated after exposure to fire. The results show that the steel high-temperature creep is a part of steel thermal strains and should be considered in the FE model. The frame columns are pushed toward outside due to the thermal expansion of steel beams in heating stage and shrinkage deformation during cooling phase. The beam mid-span sectional deflection is the maximum when fire regions located at three-span in first floor frame and the axial compression deformation of columns is less than the inflation deformation in early heating stage. The bearing capacity and initial stiffness of planar frame are reduced with the fire regions increased.