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Steel and Composite Structures
  Volume 36, Number 4, August25 2020 , pages 383-398

Progressive collapse of steel-framed gravity buildings under parametric fires
Jian Jiang, Wenyu Cai, Guo-Qiang Li, Wei Chen and Jihong Ye

    This paper investigates the progressive collapse behavior of 3D steel-framed gravity buildings under fires with a cooling phase. The effect of fire protections and bracing systems on whether, how, and when a gravity building collapses is studied. It is found that whether a building collapses or not depends on the duration of the heating phase, and it may withstand a \"short-hot\" fire, but collapses under a mild fire or a \"long-cool\" fire. The collapse time can be conservatively determined by the time when the temperature of steel columns reaches a critical temperature of 550C. It is also found that the application of a higher level of fire protection may prevent the collapse of a building, but may also lead to its collapse in the cooling phase due to the delayed temperature increment in the heated members. The tensile membrane action in a heated slab can be resisted by a tensile ring around its perimeter or by tensile yielding lines extended to the edge of the frame. It is recommended for practical design that hat bracing systems should be arranged on the whole top floor, and a combination of perimeter and internal vertical bracing systems be used to mitigate the fire-induced collapse of gravity buildings. It is also suggested that beam-to-column connections should be designed to resist high tensile forces (up to yielding force) during the cooling phase of a fire.
Key Words
    progressive collapse; gravity building; parametric fire; cooling phase; fire protection; bracing system
Jian Jiang, Wei Chen and Jihong Ye: Jiangsu Key Laboratory of Environmental Impact and Structural Safety in Engineering,
China University of Mining and Technology, Xuzhou 221116, China
Wenyu Caiand Guo-Qiang Li:College of Civil Engineering, Tongji University, Shanghai 200092, China

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