Fireproof properties of steel structure

Steel is a non-flammable building material, it has the characteristics of earthquake resistance and bending resistance. In practical applications, steel can not only increase the load capacity of buildings, but also meet the needs of architectural design aesthetics. It also avoids the defects of concrete and other building materials that cannot be bent or stretched. Therefore, steel is favored by the construction industry. The use of steel in single-story, multi-story, skyscrapers, factories, warehouses, waiting rooms, and departure halls is common. However, steel as a building material has some unavoidable defects in fire protection. Its mechanical properties, such as yield point, tensile strength and elastic modulus, will drop sharply due to the increase in temperature.　　

Steel structure usually loses load-bearing capacity at a temperature of 450～650℃, and undergoes great deformation, which causes the steel column and steel beam to bend. As a result, the steel structure cannot be used due to excessive deformation. Generally, the steel is not protected. The fire resistance limit of the structure is about 15 minutes. The length of this time is also related to the speed at which the component absorbs heat.　　

　　 In order to make steel structure materials overcome the shortcomings of fire protection in practical applications, fire protection must be carried out. The purpose is to increase the fire resistance limit of steel structures to the limit specified in the design code. There are various measures to prevent the steel structure from heating up rapidly and causing deformation and collapse in a fire. The key is to adopt different methods according to different situations, such as using heat insulation and refractory materials to block the flame and directly burn the steel structure to reduce the speed of heat transfer. Delay the time of temperature rise and strength weakening of steel structure, etc. But no matter what method is adopted, the principle is the same. The following introduces several fire protection measures for different steel structures. (Guide: The substantial difference between anti-loosening thread and self-locking thread)

　　 One. Outer layer. It is to add an outer coating on the outer surface of the steel structure, which can be cast-in-place or sprayed. The cast-in-place solid concrete outer layer is usually reinforced with steel wire mesh or steel bars to limit shrinkage cracks and ensure the strength of the outer shell. The spraying method can apply sand pumps to the surface of the steel structure at the construction site to form a protective layer. The sand pumps can be lime cement or gypsum mortar, or mixed with perlite or asbestos. At the same time, the outer cover can also be made of perlite, asbestos, gypsum or asbestos cement, and light concrete to make a prefabricated board, which is fixed on the steel structure with adhesives, nails, and bolts.　　

　　 Two, water filling (water jacket). Water filling in the hollow steel structure is the most effective protection against fire. This method can keep the steel structure at a low temperature in the fire, and the water circulates in the steel structure to absorb the heat of the material itself. The heated water can be recycled after being cooled, or cold water can be introduced through the pipe to replace the heated water.　　

　　 Three, shielding. The steel structure is arranged in a wall or ceiling composed of refractory materials, or the components are hidden in the gap between two walls. As long as a little refractory material is added or not, the purpose of fire prevention can be achieved. This is one of the most economical fire prevention methods.　　　　

Fourth, expansion materials. The steel structure fireproof coating is used to protect the components. This method has the advantages of good fireproof and heat insulation performance, and the construction is not restricted by the geometric shape of the steel structure. Generally, auxiliary facilities are not required, and the coating is light in quality and has a certain beautiful decorative effect. It belongs to modern advanced fire protection technology measures.　　

　At present, there is an increasing number of high-rise steel structure buildings, especially some super high-rise buildings, using steel structure materials more widely. Once a fire accident occurs in a high-rise building, the fire cannot be extinguished in a short time. This requires us to increase the fire protection of building materials during building design to enhance its fire resistance limit, and to formulate necessary emergency response in the building. Program to reduce casualties and property losses.

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