钢框架梁抗火承载力的有限元分析

为深入了解火灾下钢框架梁的破坏模式和各种因素对其抗火承栽力的影响，采用有限元法对工字形钢框架梁在不同荷载、不同约束下的极限承载力进行了理论计算，同时时平面框架进行了热一结构耦合计算．结果表明：钢框架中工字钢梁在火灾下的破坏模式为下翼缘侧移失稳，初始几何缺陷时刚接工字钢梁和简支工字钢梁的极限温度影响很小；受火梁由于梁的变形产生悬链力，会抵消一部分温度应力，且刚接梁在粱端部产生的局部屈曲进一步削弱了温度应力的影响；荷载较大时刚接梁的极限温度和耐火时间比简支梁高，且荷载时刚接梁的极限温度和耐火时间影响较小，对简支梁影响较大；粱柱节点是钢框架抗火的薄弱环节，火灾发生后非受火构件的内力也会发生较大的变化．

Finite Element Analysis of the Fire-Resistance Capacity of Steel Frame Girders

In order to thoroughly understand the ultimate state and the effect of various factors on load capacity of the steel frame girder in fire, the finite element analysis of the ultimate load capacity of the I-section steel frame girder in fire subjected to different loads and restrictions, and thermal-structure coupling analysis of plane steel frame are performed. The results show that lower flange lateral twisting is the failure mode of the steel frame girder in fire. The effect of initial geometric imperfections on the limit temperature of both rigidly connected and simply supported I-section girder is limited. The catenary force due to the increment of the girder's deflection and the local buckling of the rigidly connected girder can counteract the thermal stress. Under higher loads, the limit temperature and fire-resisting time of the rigidly connected girder are higher than that of the simply supported girder. The influence of the load on the limit temperature and fire-resisting time of the rigidly connected girder is less than that on the simply supported girders. The joint is the weakest area of steel frame for fire-resistant. Change of internal forces of the unfired components is obvious after fire occuring.