火灾全过程下双腹板顶底角钢节点破坏机理研究

Failure mechanism of top and seat with web angle connections under and after fire

火灾下钢结构梁柱节点破坏是导致结构连续性倒塌的主要原因之一,研究梁柱节点在高温下和高温后的破坏机理对评估钢结构抗火性能具有重要意义。为此,对双腹板顶底角钢节点在常温、升温、升温-降温、火灾后的力学性能进行缩尺模型试验研究,并建立缩尺和足尺节点有限元模型,研究温度场景、荷载、缩尺比例对节点抗火性能的影响。研究表明:火灾全过程下双腹板顶底角钢节点的破坏模式、临界温度、残余承载力与温度场景、持载、角钢与螺栓相对强度有关,升温阶段和火灾后缩尺节点的破坏模式分别为下角钢螺栓孔受拉破坏和下角钢螺栓剪切破坏,而足尺节点模型的破坏模式为下角钢螺栓受拉破坏,主要原因是温度场景和缩尺比例的耦合作用下,角钢与螺栓的相对强度发生变化,导致破坏模式的变化;火灾下持荷对火灾后节点残余承载力有较大影响(误差可达60%),不考虑荷载影响结果偏不安全。有必要在火灾后结构抗火性能评估中考虑持载的影响,不同比例结构模型的抗火性能对应关系还需要进一步研究。

Failure of beam-to-column connections under fire is one of the main reasons for fire-induced progressive collapse of steel structures.It is important to explore the failure mechanism of steel connections under and after fire for predicting structural fire performance of steel structures.To this end,scaled experiments are conducted on the top and seat with web angle connections at ambient temperature,heating stage,heating-cooling stage and post-fire stage,respectively.Finite element models of scaled and full-scale connections are established to investigate the effect of temperature conditions,loads and scaled ratios on the performance of connections in fire.The results show that the failure mode,critical temperature and post-fire capacity of such connections depend on the temperature condition,loading condition,relative strength between angles and bolts.The failure mode of scaled connections in the heating and post-fire stage is tension fracture of bolt holes and shear failure of bolts in the bottom angle,respectively.This is different from the failure mode of full-scale connections in a manner of tension fracture of bolts in the bottom angle.This is mainly due to the different relative strength between angles and bolts under a combined effect of temperature and scale conditions.Loading on the connection during the heating and cooling stages has a great influence on the post-fire capacity of connections(with a difference of 60%),and excluding the effect of loading will lead to unsafe results.It is necessary to consider the effect of loading when evaluating the post-fire performance of structures,and further work is needed to study the relation of structural fire performance between structures with different scales.