Problems of application of steel and reinforced concrete bearing structures for tall buildings with respect to their fire resistance

Abstract

The most common emergency that causes damage to structures high-rise buildings, is a fire. On the fire in high-rise, the 62-storey building in Los Angeles in 1988, even if not triggered the sprinkler fire-fighting system, thanks to the successful fire protection of load-bearing elements of the steel structure of the skyscraper withstood a three-hour exposure to flame. In a fire at a 106-metre 32-storey office building “Windsor Tower” in Madrid in 2005, an external unprotected steel frame collapsed on 6 upper floors. The results of the investigation of the consequences of a terrorist attack at the World Trade Center in the US showed high reliability designed steel structures, which could withstand impacts of planes at high speed, but shows a low level is applied to the active and passive protection of structures and buildings from fire. On the basis of a comprehensive study is not given negative evaluations of a particular material of load-bearing structures or fire protection or a carrier system and a constructive solution. Traditionally it is considered, that concrete construction is better than steel, retain their stability in a fire. This approach does not take into account a number of features. Fire resistance of reinforced concrete structures occurs when the heating of the concrete in the calculated cross section above its critical temperature and when heating of the working bars in the structure to the critical temperature. Thus, for steel structures, and reinforced concrete structures, fire resistance is determined by the time of reaching the critical temperature of steel elements. The only difference is that the concrete already laid, “fire-resistant” layer of concrete, and for steel structures it is necessary to provide separately. With the use of special fire resistant materials to steel structures, it is possible to achieve fire resistance up to 240 minutes, reduced structural weight compared to similar fire-resistant layer of concrete, the lack of explosive destruction. Thus, the choice of material of supporting structures should be based on modern concepts about fire protection with efficiency in mind. Currently, work is underway on implementation of structures made of steel-concrete which combines the features of two materials.