First, what are the characteristics of steel structures:
1. High material strength and lightweight. Steel has high strength and high elastic modulus. Compared with concrete and wood, its density-to-yield strength ratio is relatively low. Therefore, under the same stress conditions, the steel structure has a small cross-section, is lightweight, easy to transport and install, and is suitable for structures with large spans, high heights, and heavy loads.
2. Steel has good toughness, plasticity, uniform material, and high structural reliability. It is suitable for bearing impact and dynamic loads and has good seismic resistance. The internal structure of steel is uniform and close to an isotropic homogeneous body. The actual working performance of steel structure is more in line with calculation theory. Therefore, the steel structure has high reliability.
3. The degree of mechanization of steel structure manufacturing and installation is high. Steel structure components are easy to manufacture in factories and assemble on-site. The finished products of mechanized steel structure components manufactured in factories have high precision, high production efficiency, fast assembly speed on-site, and a short construction period. The steel structure is a structure with the highest degree of industrialization.
4. Steel structures have good sealing performance. Since the welded structure can be completely sealed, it can be made into high-pressure containers, large oil pools, pressure pipes, etc. with good airtightness and watertightness.
5. Steel structures are heat-resistant but not fire-resistant. When the temperature is below 150°C, the properties of steel change little. Therefore, steel structures are 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 heat insulation boards. When the temperature is 300°C-400°C, the strength and elastic modulus of steel both decrease significantly. When the temperature is around 600°C, the strength of steel tends to zero. In buildings with special fire protection requirements, steel structures must be protected by refractory materials to improve the fire resistance level.
6. Steel structures have poor corrosion resistance, especially in humid and corrosive media environments, and are prone to rust. Generally, steel structures need to be rust-proofed, galvanized, or painted, and 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 will hardly generate construction waste, and steel can be recycled and reused.
Second, 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 construction costs. The tensile strength σu is the maximum stress that the steel can withstand before it is damaged. At this time, the structure loses its usability due to large plastic deformation, but the structure deforms greatly without collapsing and 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 breaking after the stress exceeds the yield point. The main indicators for measuring the plastic deformation capacity of steel are elongation δ and cross-sectional shrinkage ψ.
3. Cold bending performance: The cold bending performance of steel is to measure the resistance of steel to cracks when plastic deformation is generated by bending processing at room temperature. The cold bending performance of steel is to use cold bending tests to test the bending deformation performance of steel under a specified bending degree.
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 steel’s resistance to impact load and may cause brittle fracture due to low temperature and stress concentration. The impact toughness index of steel is generally obtained through impact tests on standard specimens.
5. Welding performance: The welding performance of steel refers to the ability to obtain a welded joint with good performance under certain welding process conditions. Welding performance can be divided into welding performance during welding and welding performance in terms of usability. Welding performance during welding refers to the sensitivity of the weld and the metal near the weld to not produce thermal cracks or cooling shrinkage cracks during welding. Good welding performance means that under certain welding process conditions, no cracks are generated in the weld metal and the nearby parent material. Welding performance in terms of usability refers to the impact toughness at 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 are not lower than those of the parent material. My country adopts the welding performance test method of the welding process and also adopts the welding performance test method of usability.
6. Durability: Many factors affect the durability of steel. First of all, the corrosion resistance of steel is poor, and protective measures must be taken to prevent steel from corroding and rusting. The protective measures include: regular maintenance of steel paint, use of galvanized steel, and special protective measures under conditions of strong corrosive media such as acids, alkalis, and salts. For example, the offshore platform structure adopts “anodic protection” measures to prevent the corrosion of the jacket. 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, because the destructive strength of steel is much lower than the short-term strength under high temperature and long-term load, the lasting strength of steel under long-term high temperature should be measured. Steel will automatically become hard and brittle over time, which is the “aging” phenomenon. The impact toughness of steel under low-temperature load should be tested.
Post time: Jan-22-2025