An approach for early-warning collapse of planar steel trapezoid trusses exposed to fire

This paper presents an approach for early warning of the fire-induced collapse of planar steel trapezoid trusses based on real-time measurement of displacements and displacement velocities of key nodes. Firstly, a three-dimensional finite element model is validated by a full-scale fire test of a steel roof truss structure. Secondly, numerical simulations on the collapse process of planar steel trapezoid trusses under fire are conducted. Four collapse modes are summarized based on systematic parametric analyses. By exploring the variation laws of displacements and displacement velocities of key nodes, the early-warning characteristic points are determined, and a three-level early-warning method is proposed for identifying the collapse mode and collapse state. To improve the generality of the proposed method, dimensionless early-warning time ratios are introduced, and their values, with reliability significance, are determined by the Monte Carlo method. Then the accuracy of this proposed method is validated against an existing fire test. Finally, a numerical case study is presented to illustrate the effectiveness of the method for actual planar steel trapezoid trusses in real fire conditions. The accuracy of the proposed approach is validated with a satisfactory agreement between the precise remaining safety time and that early warned.