Fire Behaviors of double-layer grid structures under a new temperature-time curve

Double-layer grid structures with long span are widely applied by complex buildings such as airport terminal halls, super high-way train stations, conference & exhibition halls, sport studios, warehouses and so on. As the area of the fire source located in the large volume space is rather smaller than that of floor, this kind of fire scenario is named as localized fire with non-uniform temperature distribution. In present paper, a new temperature-time curve has been firstly developed to describe the transient non-uniform temperature distribution in localized fire, which is dependent on the space size, heat release rate of fire source. Then, the mechanical behaviors of global double-layer grid structures subjected to localized fire have been investigated by using numerical method. As a part of the structure is subjected to heating strongly and the heated members are restrained by the adjacent members which are heated slightly, some chords hold the characteristic of axially restrained members. The mechanical behaviors of chords with different axial restraint stiffness due to different non-uniform temperature distribution which can be described by the new temperature-time curve have been deeply studied. The initial imperfection can strongly improve the buckling resistance for axially restrained chords. An analytic method has been developed to estimate the fire resistance of double-layer grid structures exposed to localized fire.