Fire Safety Science Digital Archive

Developments in design methodologies and practices for structures in fire has for the last decade focussed on the horizontal stability of structures in fire. In this field there have been a number of developments of significance including the acceptance of membrane action as a viable load carrying mechanism under the large vertical displacements of floor systems which often occur during a fire. This research has focussed on two scenarios – simply supported floor systems and laterally restrained floor systems. Despite the large horizontal forces which the supporting structure must resist as a result of the adoption of these mechanisms in addition to the original vertical mechanical forces which were applied, very little research has been carried out into the consequences to the surrounding structure of the adoption of these mechanisms. These consequences were illustrated sharply by the collapse of the world trade centre twin towers on September the 11th 2001, where fires which raged inside of two tall steel structures ultimately brought about their collapse. The analysis of tall structures in fire is often seen as the domain of large consultancies or groups with access to high performance computing facilities or expensive software packages. However, a simple analytical technique is derived here which allows for a quick assessment of the forces acting on a perimeter column given both single and multiple floor fires. Based on this analysis, a simple assessment methodology is proposed which allows for a quick design check of tall buildings exposed to multiple floor fires.