Early-warning method for fire-induced collapse of planar triangle and Warren trusses
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％.
planar steel trussfireearly warning of collapsedisplacementdisplacement velocityreliability
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