Steel has high seismic performance and avoids the defects of concrete and other construction materials that cannot be stretched, so it has been favored by the construction industry. However, as a construction material, steel also has some unavoidable defects in terms of fire prevention. Its mechanical properties, such as yield point, tensile strength, and elastic modulus, will sharply decrease with the increase of temperature. Steel structures usually lose their load-bearing capacity and undergo significant deformation at temperatures ranging from 450 to 650 ℃, resulting in bending of steel columns and beams. As a result, they cannot continue to be used due to excessive deformation. The two main problems of steel structures are corrosion prevention and fire prevention. Corrosion is a chronic hazard for steel structures, and a fire can blow up a steel structure in about 15-20 minutes. The loss of life and property caused by a fire is extremely significant. The external audit requires fire protection design for the construction of steel structures. The Technical Standard for Fire Protection of Steel Structures (GB51249-2017) provides rules for the fire protection design of steel structures.

Fire protection type

To increase the fire resistance limit of steel structures to the limit scale specified in the design standard rules, different methods can be adopted according to different conditions, such as outsourcing, water filling (water jacket), shielding, and spraying fireproof coatings. Spraying fireproof coatings is currently widely used as a fire prevention measure for steel components in China. The fireproof coatings in China are mainly divided into two types: thin coating (expansion type) and thick coating (non expansion type). When the thickness of thin coating is less than 7mm, it absorbs heat and expands and foams in the fire to form a foam like carbonized thermal insulation layer, thus preventing heat transfer to the steel structure. The thickness of the thick coating is 8-50mm, and the coating does not foam when heated. Relying on its low thermal conductivity to delay the temperature rise of the steel structure, it plays a protective role. The beams and columns are mainly thick coated, while the roof support stairs are mainly thin coated.