The effect of stress–strain relationships on the fire performance of steel beams

The behaviour of a steel beam in a fire depends on many factors including the properties of the steel and the type of supports at the ends of the beam. This paper describes a detailed analytical investigation into the effects of stress–strain relationships on the fire performance of steel beams and composite steel–concrete beams exposed to uniformly increasing temperatures on three sides. The support conditions include simply supported, pin–pin, fixed sliding and fully fixed. 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 structural steel. 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.