The purchasing skills of steel for structural steel shall follow the following principles

　　(1) Choice of quality grade

　　①If it is a general non-welded steel structure, the forehead pit should be selected from Grade A steel.

　　②If it is welded structural steel and subjected to static load, B grade steel should be selected; when subjected to dynamic load, C, D, E grade steel structure or special grade steel should be selected according to the ambient temperature of the structure. In this way, the brittle transition temperature of the steel can be lower than the ambient temperature of the structure.

　　③If laminar tearing will occur in the stressed structural part and the steel plate is thick, it needs to have the ability to resist laminar tearing.

　　④For joint structures or heavy welded steel structures with complex working conditions and harsh working environment conditions, the steel quality standard requirements should be improved.

　　(2) The choice of strength grade

　　①If it is ordinary steel structural steel, the strength grade is generally Q235 or Q345.

　　②If it is heavy or super heavy structural steel, its strength grade is Q345, Q390 or Q420, or higher.

　　③If it is a cold-formed thin-walled light steel structure, Grade A is optional for non-welded and Grade B for welded.