Stability of lightweight structural sandwich panels exposed to fire

Sandwich panels comprising thin flat metal faces and a lightweight structural core are increasingly used as walls and ceilings in buildings where their long-span capabilities, high thermal insulation, clean design, rapid installation and low maintenance often make them the preferred choice of designers and building owners. The fire performance of sandwich panels can be excellent if the correct core material is used and, importantly, if the metal facings are adequately restrained. For example, fire resistance in excess of 2 h can be easily achieved using panels with sheet steel faces and a non-combustible rock wool core. Where sandwich panels are used in cold stores there is the potential problem of cold-bridging between the facings wherever there is a metallic through-fixing, and this has led to designs which work well in normal conditions but allow panels to collapse very early when exposed to fire because the facings are not tied back to the supporting structure. Such collapse is a fire hazard to fire-fighters as proven in the 1993 fire in the Sun Valley poultry factory in Hereford, United Kingdom in which two firemen lost their lives. The paper describes what can happen if panel facings are not mechanically restrained with steel fastenings. It then introduces a fire safety engineering method for assessing the stability of ceiling sandwich panels exposed to fire. The method assumes that the ends of panels are restrained and the panel behaves as a catenary after delamination. The paper quantifies the variation of catenary force as fire develops and takes account of the initial beneficial sag which is present at the time of delamination. The method is currently being considered in the work of European committee CEN TC 127 on the development of rules for extended applications for construction products. Copyright (C) 2004 John Wiley Sons, Ltd.