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Fireproof properties of steel structures

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Steel is a non-combustible building material that is resistant to earthquakes and bending. In practical applications, steel can not only increase the load capacity of buildings relatively, but also meet the needs of architectural design aesthetics, and avoid the defects of concrete and other building materials that cannot be bent and stretched. Therefore, steel is favored by the construction industry. Single-story, multi-story, skyscrapers, factories, warehouses, waiting rooms, waiting halls, etc. are all made of steel. However, as a building material, steel has some unavoidable defects in fire protection. Its mechanical properties, such as yield point, tensile strength, and modulus of elasticity, will drop sharply due to the increase in temperature.

The steel structure usually loses its bearing capacity at a temperature of 450-650 ° C, and a large deformation occurs, causing the steel column and steel beam to bend. As a result, it cannot be used due to excessive deformation. The limit is around 15 minutes. The length of this time is also related to the speed at which the component absorbs heat.
To overcome the deficiencies in fire protection of steel structure materials in practical applications, fire protection treatment must be carried out, the purpose of which is to increase the fire resistance limit of steel structures to the limit range specified in the design specifications. There are various measures to prevent the steel structure from rapidly heating up 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 temperature rise of steel structure, the time of strength weakening, etc. But no matter which method is adopted, the principle is the same. The fire protection measures for several different steel structures are introduced below.

1. Outer cladding. It is to add an outer cladding on the surface of the steel structure, which can be cast in place or sprayed. The cast-in-place solid concrete cladding is usually reinforced with wire mesh or steel bars to limit shrinkage cracking and maintain the strength of the shell. The spraying method can apply a sand pump to the surface of the steel structure at the construction site to form a protective layer. The sand pump can be lime cement or gypsum mortar, or it can be mixed with perlite or asbestos. At the same time, the outer cladding can also be made of perlite, asbestos, gypsum or asbestos cement, and light concrete to make prefabricated panels, which are fixed on the steel structure with adhesives, nails, and bolts.
Second, water-filled (water jacket). Filling the hollow steel structure with water is the most effective protection against fire. This method keeps the steel structure cool during a fire, and water circulates within the steel structure, absorbing heat from the material itself being heated. The heated water can be recirculated after being cooled, or cool water can be piped in to replace the heated water.
Three, shielding. The steel structure is set in the wall or ceiling made of refractory materials, or the components are enclosed in the gap between two walls, and the purpose of fire prevention can be achieved only by adding little or no refractory materials. This is one of the most economical fire prevention methods.
Four, expansion material. 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 limited by the geometric shape of the steel structure. Belongs to modern advanced fire prevention technical measures.

At present, there are more and more high-rise steel structure buildings, especially some super high-rise buildings, which use 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 in the building design to enhance its fire resistance limit, and to formulate necessary emergency measures inside the building. programs to reduce casualties and property damage.




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