The strength index of steel consists of elastic limit σe, yield limit σy, and tensile limit σu. The design is based on the yield strength of the steel. The high yield strength can reduce the weight of the structure, save steel, and reduce the cost. The tensile strength σu is the large stress that the steel can withstand before failure. At this time, the structure loses its performance due to large plastic deformation, but the structure is large without collapse, meeting the requirements of the structure to resist rare earthquakes. The value of ‘σu/σy can be regarded as a parameter of steel strength reserve.
The plasticity of steel generally refers to the property of significant plastic deformation without breaking after the stress exceeds the yield point. The main indicators to measure the plastic deformation ability of steel are the elongation δ and the reduction of area ψ.
3, cold bending performance
The cold bending performance of steel is a measure of the resistance of steel to cracks when it is bent at room temperature to produce plastic deformation. The cold bending performance of steel is to use the cold bending test to test the bending deformation performance of the steel with the specified degree of bending.
4, impact toughness
The impact toughness of steel refers to the ability of steel to absorb mechanical kinetic energy during the fracture process under impact load. It is a mechanical property that measures the resistance of steel to impact load, which may cause brittle fracture due to low temperature and stress concentration. Generally, the impact toughness index of steel is obtained through the impact test of standard specimens.
5, welding performance
The welding performance of steel refers to obtaining a welded joint with good performance under certain welding process conditions. Welding performance can be divided into welding performance in the welding process and welding performance in use performance. The welding performance in the welding process refers to the sensitivity of the welding seam and the metal near the welding seam without thermal cracks or cooling shrinkage cracks during the welding process. Good welding performance means that under certain welding process conditions, neither the weld metal nor the nearby base metal will crack.
6. Configuration and steel thickness
Using the structural form of lattice type component, because the stress concentration phenomenon may occur at the connection between the fitting and the limb, and the place needs to be welded, the material properties are higher than the solid web type component. For important tensile and bending welded components, due to the existence of welding residual tensile stress, multi-directional tensile stress fields often appear. When the thickness of the steel of the component is large, the number of rolling is less, and the pores and slag inclusions in the steel are higher than those of thin plates. There are many defects, so the requirements for material properties should be higher for the tensile and bending members with larger steel thickness.
Steel must also pay attention to durability. To do this, protective measures must be taken to prevent steel from corrosion and rust. Regular maintenance of steel paint, galvanized steel, and special corrosion mediums such as acid, alkali, salt, etc. Protective measures.