Residual load bearing capacity of structures exposed to fire

When fire occurs in buildings, depending on the relative severity of the fire, there might be fire-induced damage which affect the performance of building elements. While collapse of buildings, in fires, may be rare events it is not uncommon to have damage or distortion in various structural elements. The extent of damage to a structure is dependent on the fire intensity, duration of fire, geometry, materials used in construction and the load intensity. In many cases the structural members might have substantial strength and often can be restored to its original shape through repairs. Before undertaking such repairs an assessment of the building has to be carried out to determine the extent of damage and the residual load-bearing capacity of structural members. In this paper, the application of computer program SAFIR for determining the residual load bearing capacity is illustrated though three case studies; a simply supported beam, a column and a restrained beam. The three elements were modeled in two configurations, steel and reinforced concrete, and were designed to have the same fire resistance ratings. The analysis was carried out in a scenario that includes heating under a natural fire, cooling down to ambient temperature and then loading to failure. Results from three case show that the load bearing capacity was hardly modified, by the fire damage, in a simply supported beam, was increased by the effect of an axial restraint, especially in the concrete beam, and was reduced in the column, especially in the concrete column.