Investigation of the behavior of the multi storey steel buildings under fire

The strength of engineering materials decrease with increasing temperature. This deduction is also valid for steel, however the advantage of steel is its property of uncombustibility. It can recover its strength completely after fire. During fire, steel absorbes a considerable amount of heat energy and after fire when it was cooled to the ambient temperature, it recovers itself. During these cycles of heating and cooling, the steel elements, individually, can be bent or damaged and therefore lose its characteristic of bearing the whole structure of the building. Upon review of the current fires, fire resistance of unprotected steel members on the subject of the experiment and calculation methods have been studied.Besides, the steels of particular specifications have been developed for the fire safety of steel structures. These types of steels are named as "Fire Resistant Steels (FRS)". These steels are thermomechanically treated, so it can perform better than the ordinary structure steels. The FR steels have the same structure of perlite-ferrite as the ordinary steels but the presence of molibdenum and chromium stabilizes the structure even at 600 °C. These steels exhibit at least the two thirds of their yield strength when exposed to heat. From this point of view the FR steels have a natural protection against fire.The fire protection depend essentially on the fire load, the intensity of fire and the types of sthe structural elements. The structural resistance can be provided by dying of steel columns and beams, coating with protective substances of steel columns and beams, immersing of steel columns and beams in concrete, covering of steel columns and beams with plaster plates, covering and coating of steel columns and beams with isolating plates.Keywords: Fire and steel, fire resistant steels, fire load, fire protection