平面三角形桁架和Warren平行弦桁架结构火灾下倒塌预警方法

Early-warning method for fire-induced collapse of planar triangle and Warren trusses

为研究火灾下平面三角形和Warren平行弦钢桁架结构的倒塌预警方法,建立有限元模型研究两类桁架在火灾下的倒塌机理与倒塌模式;在此基础上,研究了两类平面钢桁架在各倒塌模式下关键物理量变化规律,并基于桁架关键节点的位移、位移速率以及桁架受火杆件的温度等多参数,提出了火致倒塌分级预警方法。为了科学预测桁架的倒塌剩余时间,采用预警时间比与倒塌剩余时间比两个参数,通过蒙特卡洛采样法得到了具有可靠度意义、可在实际工程中直接使用的时间比数值。并将提出的火灾倒塌预警方法和时间比数值通过真实火灾倒塌试验和数值算例进行验证。结果表明:平面三角形桁架和Warren平行弦桁架呈现转铰型、滑移型、屈曲后转铰型、屈曲后滑移型以及再平衡等多种倒塌模式;当预警时间比的可靠度为70%~80%时,可以较为准确地预测Warren平行弦和平面三角形桁架的实际倒塌剩余时间。

To investigate the early-warning methods for fire-induced collapse of planar steel triangle and Warren trusses,the collapse mechanism and collapse modes of these two types of planar steel trusses under fire were investigated based on the finite element method in this study.On this basis,the evolution laws of the key physical parameters of these two types of planar steel trusses under each collapse mode were studied,and a three-level early-warning method for fire-induced collapse was proposed based on the displacement and displacement velocity at the key joints and the temperature of the truss members.In order to predict the remaining time before the truss collapse accurately,two dimensionless parameters were introduced,namely,the early-warning time ratio and the remaining time ratio before collapse.The values of the two parameters with reliability significance,which can be taken into practical application directly,were obtained by Monte Carlo method.The proposed fire collapse warning method and time ratio were verified by real fire collapse tests and numerical examples.The results show that the collapse modes of planar triangle and Warren trusses include rotation pin,slide surface,post-buckling rotation pin,post-buckling slide surface and rebalance.The remaining time before collapse can be predicted accurately if the guarantee rate of early-warning time ratio is 70%-80%.