PERFORMANCE-BASED SIMPLIFIED MODEL FOR A STEEL BEAM AT LARGE DEFLECTION IN FIRE

摘要

This paper presents a simple model for a heated steel beam at large deflection taking into consideration the effect of the catenary action against the surrounding cold structure. This model can be used to predict the mid-span deflection and the tensile axial force of the heated steel beam at large deflection induced by the catenary action. This tensile axial force at large deflection can lead to integrity failure, and consequent fire spread, if sufficient strength and ductility are not designed into key elements such as beams and connections. However, provided that this can be done in particular cases, then it may be possible to achieve much greater real fire resistance than is estimated by the simple calculation methods currently used. The study highlights the effect of the axial horizontal restraints. However, for a heated steel beam within steel construction, catenary action, which may help the beam to hang to the surrounding cold structure, can prevent the run-away deflection when the tensile axial force of the beam has been overcome. The nature of this phenomenon has been investigated in a joint project between the University of Sheffield where the numerical analysis has been curried out, and the University of Manchester where the furnace tests were conducted. The prime objective of this study was to study computationally and analytically how different levels of restraint from surrounding structure, via catenary action in beams, affect the survival of steel framed structures in fire.