A Study on the Effect of Compartment Fires on the Behaviour of Multi-Storey Steel Framed Structures

In order to ensure safe evacuation of occupants and safe access for fire-fighters, current fire precautions aim to prevent fire spreading beyond the compartment where it started. The focus of this study is to assess the stability of structural components when localised fires occur in unprotected steel buildings. A three-storey three-bay symmetrical steel frame representing a typical office building was analysed using a finite element computer program. The influence of six different localised fire scenarios was investigated. For each fire scenario, the variation in deflections, bending moments and axial forces, as the temperature increases, were monitored up to failure of the structure. The results indicate that thermal expansion of the heated beams, leading to lateral movement of surrounding structural components, is an important factor. The resistance to this movement by the columns and general surrounding elements, which are not exposed to the fire, has a great influence on the redistribution of internal stresses. In general, this may lead to instability of columns, catenary action developing in beams, and eventually failure of the structure as a whole. The study suggests that critical localised fire scenarios are those where all the ground floor columns are affected, or where a whole bay through the height of the frame is heated. However, it has been shown that fire survival under any localised fire scenario is improved in comparison to that when the whole frame is heated. Therefore, fire compartmentation does not only provide safe means of escape, it is also beneficial for enhanced structural fire resistance.