Because the steel member itself can not reach the fire resistance limit required by the code, it is necessary to take corresponding fire-resistant protection measures for steel members. The common fire-resistant protection measures include fire-retardant coating method, foam fire-retardant paint method and external fire-proof layer method.
1. Fire retardant coating method
The fire retardant coating method is to spray fire retardant coatings on steel structure to improve its fire resistance. At present, China's steel structure fire retardant coatings are mainly divided into two types: thin coating and thick coating, that is, thin (B, including ultra thin) and thick (H). The thickness of thin coating is below 7mm. It can absorb heat and expand foam in fire disaster, and form a foam carbonized insulation layer, thereby preventing heat from transmitting to the steel structure. Its main advantages are: thin coating, light load on steel structure, good decoration, easy coating on small area of complex shape steel structure surface than thick type; thick coating thickness is 8-50 mm, the coating is not foamed when heated, and its low thermal conductivity is used to delay the temperature rise of steel structure, Both of them have different performance characteristics and are suitable for different occasions. However, no matter what kind of products are tested by national testing institutions, they can be selected.
2. Foaming fire retardant paint method
Foamed fire retardant paint is a kind of flame retardant coating made of film-forming agent, flame retardant, foaming agent and other materials. Compared with general paint, fire-retardant paint has basically the same physical properties. The difference is that after drying, the film itself is not easy to burn, and in case of fire, it can delay the flame burning to the combustible materials, According to the test: the general paint and fire-retardant paint are respectively painted on the wood board, and after drying, they are baked with the same flame. The wood plate coated with general paint will scorch with the paint in less than 2 minutes; while the board coated with non expansive fire retardant paint only has smoldering phenomenon after 2 minutes, and it will extinguish immediately after standing for 30 seconds; for the board coated with intumescent fire retardant paint, even if it is baked for 15 minutes, It can be seen that fire-retardant paint applied to the surface of objects can prevent the spread of fire and protect the surface of objects in a certain time in case of fire, so as to take valuable time for extinguishing fire.
3. The method of external fireproof layer
The method of external fire-proof coating is to add an outer layer on the surface of steel structure, which can be cast-in-place or sprayed. The outer layer of cast-in-place solid concrete is usually strengthened with steel mesh or reinforcement to limit the shrinkage cracks and ensure the strength of the shell. The spraying method can spray lime cement or gypsum mortar on the surface of steel structure to form a protective layer at the construction site, At the same time, the outer layer can also be made of perlite, asbestos, gypsum or asbestos cement, light concrete, and fixed on the steel structure with adhesives, nails and bolts.
