Steel structure material selection, construction and use safety of steel structure projects

　　The selection of steel materials is crucial for the construction and safety of steel structures, thus necessitating specific selection standards. Refer to the introduction by the Nantong steel structure construction team for details!

　　1. Strength

　　Steel strength indicators include elastic limit σe, yield limit σy, and tensile limit σu. Design is based on the yield strength of the steel. High yield strength reduces structural weight, saves steel, and lowers costs. Tensile strength σu is the maximum stress a steel material can withstand before failure. At this point, the structure loses its usability due to significant plastic deformation, but the large deformation doesn't cause collapse, meeting the requirements for structural resistance to rare earthquakes. The value of 'σu/σy' can be considered a parameter for steel strength reserve.

　　2. Plasticity

　　Steel plasticity generally refers to the property of exhibiting significant plastic deformation without fracture after stress exceeds the yield point. The main indicators for measuring the plastic deformation capacity of steel are elongation and reduction of area.

　　3. Cold Bending Performance

　　The cold bending performance of steel measures its resistance to cracking during plastic deformation from bending at room temperature. It's tested using a cold bending test to examine the steel's ability to withstand a specified degree of bending deformation.

　　4. Impact Toughness

　　Steel impact toughness refers to its ability to absorb mechanical energy during fracture under impact loads. It measures the steel's resistance to impact loads and the potential for brittle fracture due to low temperatures or stress concentration. It's generally obtained through impact testing of standard specimens.

　　5. Weldability

　　Steel weldability refers to obtaining high-quality welded joints under specific welding conditions. Weldability can be divided into weldability during the welding process and weldability in terms of performance. Weldability during the welding process refers to the sensitivity of the weld and the metal near the weld to the generation of hot cracks or cooling shrinkage cracks. Good weldability means that under certain welding conditions, neither the weld metal nor the nearby base material will crack.

　　6. Structural Form and Steel Thickness

　　In structures using lattice structures, stress concentration may occur at the joints between the struts and members, and welding is required at these points, so the material properties are higher than those of solid-web members. For important tensile and bending welded components, due to the existence of residual tensile stress from welding, a multi-directional tensile stress field often appears. When the steel thickness of the component is large, the number of rolling times is small, and the number of pores and inclusions in the steel is more than that of thin plates, and there are more defects. Therefore, for tensile and bending components with larger steel thickness, higher material property requirements should be considered.

　　Steel durability should also be considered. This requires protective measures to prevent corrosion and rust, regular paint maintenance, the use of galvanized steel, and special protective measures in environments with strong corrosive media such as acids, alkalis, and salts.