Steel is a kind of incombustible building material, which has the characteristics of earthquake resistance and bending resistance.In practical application, steel can not only increase the load capacity of buildings, but also meet the needs of aesthetic modeling of architectural design, and avoid the building materials such as concrete that can not be bent and stretched. Therefore, steel is favored by the construction industry, single-layer, multi-layer, skyscraper, workshop, warehouse, waiting room, waiting hall and other steel are very common.However, as a building material, steel has some unavoidable problems in fire protection. Its mechanical properties, such as yield point, tensile strength and elastic modulus, will decrease sharply with the increase of temperature. 

The steel structure in usually loses its bearing capacity in the temperature range of 450 ℃ - 650 ℃, and great deformation occurs, resulting in the bending of steel columns and steel beams. As a result, the steel structure cannot continue to be used due to excessive deformation. The fire resistance of the steel structure without protection is generally about 15 minutes.The length of this time is also related to the heat absorption rate of the component.In order to overcome the shortcomings of fire protection in practical application of steel structure materials, fire prevention treatment must be carried out, whose purpose is to increase the fire resistance limit of steel structure to the limit range specified in the design code.There are various measures to prevent deformation collapse of steel structure caused by rapid temperature rise in the fire. The key is to adopt different methods according to different situations, such as using heat insulation and refractory materials to block the flame to burn steel structure directly, reducing the speed of heat transfer and delaying the time of temperature rise and strength weakening of steel structure.But no matter what method is adopted, its principle is consistent.Therefore, the author thinks that four kinds of fire protection measures of steel structure must be paid attention to in reality.

    1、 Outsourcing layer.As the name implies, it is to add an outer coating on the surface of the steel structure and apply the spraying method.The special spraying equipment is used to spray “steel structure fireproof slurry (single component)” on the steel structure surface to form a protective layer. According to the fire protection requirements, the thickness of fireproof slurry can be designed to meet the fire resistance limit of more than 2-3 hours. It is a fireproof slurry with good performance and high cost performance in the market at present.

    2、 Water filled jacket.Water filling in hollow steel structure is an effective protective measure against fire.This method can make the steel structure keep a lower temperature in the fire, water circulates in the steel structure, and absorb the heat of the material itself.After cooling, the heated water can be recycled or cold water can be introduced into the pipeline to replace the heated water. 

    3、 Shielding.The steel structure is set in the wall or ceiling composed of refractory materials, or the components are wrapped in the gap between the two walls. As long as a little refractory materials are added or not, the purpose of fire protection can be achieved.This is an economical way to prevent fire. 

    4、 Expansion material.Steel structure fireproof coating is used to protect components. This method has the advantages of good fireproof and heat insulation performance, construction is not limited by steel structure geometry and so on. Generally, it does not need to add auxiliary facilities, and the coating quality is light, and it also has a certain role of aesthetic decoration. It belongs to the modern advanced fireproof technical measures.

    At present, there are more and more high-rise steel structure buildings, especially some super high-rise buildings.Once a fire accident occurs in a high-rise building, the fire can not be put out in a short time, which requires us to increase the fire protection of building materials in the architectural design, so as to enhance its fire resistance limit, and make necessary emergency plans inside the building to reduce casualties and property losses.