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Progressive collapse analysis of 3D steel frames with concrete slabs exposed to localized fire

机译：带有局部火灾的混凝土板的3D钢框架的逐步倒塌分析

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This paper numerically investigates progressive collapse resistance of three-dimensional steel frames with reinforced concrete slabs exposed to localized fire using LS-DYNA. An explicit dynamic analysis is carried out and the real fire time is scaled down to save the computational cost. The prototype of the model is based on the eight-storey building in Cardington tests. The scenario of heating individual columns on the ground floor is first studied followed by a sever case of simultaneously heating four columns in one compartment. The collapse modes and load redistribution scheme of the frame subjected to different load ratios and fire locations are investigated. The modelling parameters such as mesh size, initial imperfection, timescale are first studied by validating against the fire test data. It is found that the mesh size has little influence on the responses of members at elevated temperature. The initial imperfection has significant effect on the load-bearing capacity of columns. The quasi-static behaviour of structures under a fire duration of hours can be simulated in a dynamic analysis by being scaled to seconds without causing oscillation of responses. The numerical results of the 3D frame show that the frame does not collapse in the case of single column heated for a fire design load (load ratio of 0.25 for columns). By increasing the load ratio to 0.5 as for the ambient design, progressive collapse occurs. For a fire of four columns heated, the frame collapses for the corner bay fire and long edge bay fire but withstands for the internal and short edge bay fires. The collapse modes are dominated by the uneven load redistribution in the two horizontal directions and the fire location, which cannot be simulated by a 2D model. The loads previously sustained by the buckled heated column are transferred more along the short span than the long span. The critical temperature of a column in a frame is significantly lower than that given in EC3, due to the fact that the translational and rotational restraint increase its load ratio and reduce its effective length, respectively. The critical temperature for the global collapse of the frame is about 50-100 degrees C higher than that of individual heated columns. (C) 2016 Elsevier Ltd. All rights reserved.
机译：本文使用LS-DYNA数值研究了钢筋混凝土板承受局部火灾的三维钢框架的渐进抗倒塌性能。进行了显式的动态分析，并按比例缩小了实际起火时间，以节省计算成本。该模型的原型基于Cardington测试中的八层建筑。首先研究了加热一楼的单个色谱柱的方案，然后研究了在一个隔室中同时加热四个色谱柱的严重情况。研究了框架在不同载荷比和火灾位置下的塌陷模式和载荷再分配方案。首先通过对着火测试数据进行验证来研究诸如网格尺寸，初始缺陷，时间尺度等建模参数。发现网孔尺寸对构件在高温下的响应几乎没有影响。初始缺陷对色谱柱的承载能力有重大影响。在数小时的火灾持续时间内，结构的准静态行为可以在动态分析中进行仿真，方法是将其缩放到几秒钟而不会引起响应振荡。 3D框架的数值结果表明，在承受火设计荷载（对于圆柱的荷载比率为0.25）的情况下，在加热单列的情况下，框架不会塌陷。对于环境设计，通过将载荷比增加到0.5，会发生逐渐塌陷。对于四列加热的火，框架在拐角托架着火和长边托架着火时会折叠，但可承受内部和短边托架着火。塌陷模式主要由两个水平方向上的不均匀载荷重新分布和火灾位置决定，而二维模型无法模拟这种情况。先前由弯曲的加热柱承受的载荷沿短跨度传递的比长跨度传递的更多。由于平移约束和旋转约束分别增加了其负载比并减小了其有效长度，因此框架中列的临界温度明显低于EC3中的临界温度。框架整体塌陷的临界温度比单个加热柱的临界温度高约50-100摄氏度。 （C）2016 Elsevier Ltd.保留所有权利。

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