Determination of Fire Induced Collapse Mechanisms of Multi-Storey Steel Framed Structures

Abstract

Following the events of September 11th 2001, understanding the performance of multi-storey buildings during large-scale fires has assumed greater importance. These events have highlighted the possibility of large uncontrolled fires lasting for several hours (WTC-7). Owners of high-rise buildings are seeking assurance that integrity can be maintained during similar elevated temperature situations. This work is part of a much larger study to evaluate the performance of high-rise steel-framed structures in the event of large uncontrolled fires, using primarily a computational approach. Given a building and its operating conditions, different fire scenarios are established. The choice of scenarios is established on the basis of probability of occurrence and also as a function of damage potential. Computational fluid dynamics models are used to predict critical conditions within pre-determined areas of the building. Emphasis is given to establish a proper thermal boundary condition for the structural elements. A three dimensional numerical model of the structure provides the basis for a structural finite element analysis to be carried out under combined static and thermal loading. Full investigation of the temperatures and stresses generated on structural members due to the design fire chosen are considered. Particular attention to detail is given to those members that are thought likely to contribute to total collapse through localised failure. This is done by combining CFD codes with finite element models. This paper will present a selection of results from the aforementioned investigation, with particular emphasis on the conditions that cause total collapse for the chosen case study.