What are the characteristics of steel structure
1. The material has high strength and light weight. Steel has high strength and high modulus of elasticity. Compared with concrete and wood, the ratio of its density to yield strength is relatively low. Therefore, under the same stress conditions, the steel structure has a small cross-section and light weight, which is convenient for transportation and installation. It is suitable for large spans, high heights, and heavy loads. Structure.
2. Steel has toughness, good plasticity, uniform material, and high structural reliability. Suitable for impact and dynamic loads, with good seismic performance. The internal structure of steel is uniform, close to isotropic homogeneous body. The actual working performance of the steel structure is more in line with the calculation theory. Therefore, the reliability of the steel structure is high.
3. The manufacturing and installation of steel structure has a high degree of mechanization. Steel structural components are easy to manufacture in factories and assemble on site. The factory mechanized manufacturing of steel structural components has high precision, high production efficiency, fast assembly on site, and short construction period. Steel structure is the most industrialized structure.
4. The steel structure has good sealing performance. Since the welded structure can be completely sealed, it can be made into high-pressure vessels, large oil pools, and pressure pipes with good air and water tightness.
5. The steel structure is heat-resistant and not fire-resistant. When the temperature is below 150°C, the properties of the steel will change little. Therefore, the steel structure is suitable for hot workshops, but when the surface of the structure is subjected to heat radiation of about 150 ° C, it must be protected by a heat shield. When the temperature is 300°C-400°C, the strength and elastic modulus of the steel decrease significantly, and when the temperature is around 600°C, the strength of the steel tends to zero. In buildings with special fire protection requirements, steel structures must be protected with refractory materials to increase the fire resistance rating.
6. The steel structure has poor corrosion resistance, especially in the environment of humid and corrosive media, it is easy to rust. Generally, the steel structure needs to be derusted, galvanized or painted, and it needs to be maintained regularly. For offshore platform structures in seawater, special measures such as "zinc block anode protection" are required to prevent corrosion.
7. Low-carbon, energy-saving, green and environmentally friendly, and reusable. The demolition of steel structure buildings hardly produces construction waste, and steel can be recycled and reused.

Material requirements for steel structures
1. Strength
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 steel. High yield strength can reduce the weight of the structure, save steel and reduce the cost. The tensile strength σu is the maximum stress that the steel can withstand before failure. At this time, the structure loses its performance due to large plastic deformation, but the structure does not collapse due to large deformation. It should be able to meet the requirements of the structure to resist rare earthquakes.
2. Plasticity
The plasticity of steel generally refers to the property of having significant plastic deformation without fracture after the stress exceeds the yield point. The main indicators to measure the plastic deformation ability of steel are elongation δ and reduction of area ψ.
3. Cold bending performance
The cold bending performance of steel is a measure of the steel's resistance to cracks when it undergoes plastic deformation during bending at room temperature. The cold bending performance of steel is to use the cold bending experiment to test the bending deformation performance of the steel to withstand 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 the action of impact load. It is a mechanical property to measure the resistance of steel to impact load, which may lead to brittle fracture due to low temperature and stress concentration. Generally, the impact toughness index of steel is obtained through the impact test of standard test pieces.
5. Welding performance
The welding performance of steel refers to obtaining welded joints with good performance under certain welding process conditions. Welding performance can be divided into two types: welding performance in the welding process and welding performance in use performance. Welding performance in the welding process refers to the sensitivity of the weld and the metal near the weld to not produce 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 produce cracks. Welding performance in terms of usability refers to the impact toughness of the weld and the ductility in the heat-affected zone. It is required that the mechanical properties of the steel in the weld and the heat-affected zone should not be lower than those of the base metal. Our country adopts the welding performance test method of the welding process, and also adopts the welding performance test method of usability and usability.
6. Durability

There are many factors that affect the durability of steel. First of all, the corrosion resistance of steel is poor, and protective measures must be taken to prevent corrosion and rust of steel. The protective measures include: regularly maintain the steel paint, use galvanized steel, and take special protective measures in the presence of strong corrosive media such as acid, alkali, and salt. For example, the offshore platform structure adopts "anodic protection" measures to prevent jacket corrosion. Zinc ingots are fixed on the jacket, and the seawater electrolyte will automatically corrode the zinc ingots first, thereby achieving the function of protecting the steel jacket. Secondly, under the action of high temperature and long-term load, the failure strength of steel is much lower than the short-term strength, so for the steel under long-term high temperature, the durable strength should be measured. Steel will automatically harden and become brittle over time, which is the phenomenon of "aging". For steel under low temperature load, its impact toughness should be tested.