An Analytical Method of Deflection Behavior Concerning Three-dimensional Steel Frame Exposed to Fire which takes Account of the Thermal Expansion of a Floor Slab

Abstract

It is natural to treat a building structure as a 3D body when concerning its behavior in a fire, because fire is a phenomenon involving 3D thermal expansion. The influence that the floor slab in a fire compartment exposed to fire has on the behavior of the building structure during a fire may be extremely large, therefore, it is necessary to explore how the floor slab affects the structure when exposed to fire. In this study, the end restraint force and the displacements of the adjacent substructures are formulated by dividing structures into unitary substructures, as an approach to the problem of the increase in the number of nodes which occurs in the 3D analysis taking account of the slab. Since no basic data is available for concrete under 2D stress exposed to elevated temperatures, the thermal expansion of a floor slab is considered by conceiving the slab as a grid of intersecting beams. A method of 3D coordinate transformation, which takes the effect caused by the principal axis of component section moving from time to time into account, is proposed. Under these assumptions, an analytical method of deflection behavior concerning 3D steel frame exposed to fire that takes account of the thermal expansion of a floor slab is constructed. The theoretical results agree well with those recorded in experiments in which a full-scale frame was exposed to vehicle fire.