Effect of support conditions on the fire behaviour of steel and composite beams

Abstract

AbstractThe fire behaviour of a structural steel beam or a steel and concrete composite beam in a fire compartment depends on many factors including the nature of the supports at the ends of the beam.This paper describes a detailed analytical investigation into the effects of support conditions on the fire performance of steel and composite steel‐concrete beams exposed to linearly increasing temperature with time, as well as to standard and parametric fires.The support conditions include simply supported, fully fixed, and a range of intermediate cases, providing varying levels of axial and flexural restraint. In each case, a comparison of the deflected shape with the evolving internal forces shows unusual but predictable behaviour, strongly dependent on the stress–strain relationship of the steel. In addition to the standard support conditions, a spring was used to simulate the effect of axial restraint provided by adjacent spans of a multi‐span beam. This case showed that the spring stiffness had a very considerable influence on the behaviour of the beam and the time to failure under an increasing fire temperature.This paper gives new insight into the structural performance of steel and composite beams, observed in recent fires such as the eight storey steel frame at Cardington. There are major implications for structural designers. Copyright © 2004 John Wiley & Sons, Ltd.