Failure of Building Structural Members During the Cooling Phase of a Fire

Fires in buildings are characterized by a heating phase followed by a cooling phase, but the effects of the cooling phase on structures are not well researched. This work presents an analysis of the behavior of different structural members under natural fires, with the aim to characterize their delayed failure in the cooling phase of a natural fire. Thermo-mechanical numerical simulations based on the nonlinear finite element method (SAFIR code) are conducted. Results show that, for all the studied members (column, beam) and materials (reinforced concrete, steel, steel-concrete composite), structural failure during the cooling phase of a fire is a possible event. The time structures fail can be up to 250 min later than the time maximum temperature in room reaches. The major factors that affect delayed failure time of structural members are the duration of heating phase of the fire, the applied load ratio, and the thickness of thermal insulation material (including concrete material). This work enhances the understanding of the structural behavior in the cooling phase of a fire and gives information for the safety of the fire fighters and people in a natural fire.