2. Steel toughness, good plasticity, uniform material, high structural reliability. Suitable for bearing impact and dynamic loads, with good seismic performance. The internal structure of steel is homogeneous and nearly isotropic. The actual working performance of the steel structure is more in line with the calculation theory. Therefore, the reliability of steel structure is high.
3. High degree of mechanisation in the manufacture and installation of steel structures. The steel structure is easy to be manufactured in the factory and assembled on site. The finished steel structure is manufactured in the factory with high precision and high productivity, and the site assembly is fast and short-lived. Steel structure is one of the most industrialised structures.
4. Steel structure sealing performance is good, because the welded structure can be completely sealed, can be made into gas-tight, water-tight are very good high-pressure containers, large oil pools, pressure pipelines, etc..
5. Steel structure heat resistance is not fire resistance, when the temperature is below 150 ℃, the nature of steel changes very little. Therefore, the steel structure is suitable for hot workshop, but when the surface of the structure is subjected to heat radiation of about 150℃, heat insulation board should be used to protect it. When the temperature is 300℃-400℃. The strength and modulus of elasticity of the steel drop significantly, and at around 600°C the strength of the steel tends to zero. In buildings with special fire protection needs, steel structures must be protected by fire-resistant materials to improve the fire resistance level.
6. Steel structure corrosion resistance is poor, especially in the environment of moisture and corrosive media, easy to rust. Generally steel structures should be descaled, galvanised or painted, and maintained regularly. For marine platform structures in seawater, special measures such as “zinc block anodic protection” should be adopted to prevent corrosion.
7. Low-carbon, energy-saving, green and environmentally friendly, reusable. The dismantling of steel structures produces almost no construction waste, and the steel can be recycled and reused.
The strength index of steel consists of elastic limit be, yield limit by, and tensile limit au. The design is based on the yield strength of steel, which can reduce the weight of the structure, save steel and reduce the cost. Tensile strength au is the maximum stress that the steel can withstand before damage, the structure at this time due to plastic deformation is very large and lost performance, but the structure deformation is large and does not collapse, should be able to meet the requirements of the structure to resist rare earthquakes.
Plasticity of steel generally refers to the stress exceeds the yield point, with significant plastic deformation and does not fracture the nature. The main indicator of the ability to measure the plastic deformation of steel is the elongation δ and section shrinkage rate ψ.
Cold bending performance of steel is a measure of steel at room temperature bending process to produce plastic deformation of the resistance to cracking. Cold bending performance of steel is used to test the cold bending test to test the steel bending deformation performance of the specified degree of bending.
Impact toughness of steel refers to the steel under impact loading, fracture process to absorb mechanical kinetic energy of a capacity, is a measure of steel resistance to impact loading, may be due to low temperature, stress concentration, and lead to brittle fracture of a mechanical property. Generally through the impact test of standard specimens to obtain the impact toughness of steel indicators.
The welding performance of steel refers to the welding process under the – certain conditions, to obtain good performance of the welded joint. Welding performance can be divided into welding performance and welding performance in the welding process on the use of two kinds of performance. Welding performance in the welding process refers to the sensitivity of the weld and the metal near the weld not to produce thermal cracks or cooling not to produce cooling shrinkage cracks during the welding process. Good welding performance means that under certain welding process conditions, both the weld metal and the nearby base material do not produce cracks. The use of performance on the welding performance refers to the impact toughness at the weld and heat-affected zone ductility performance, the mechanical properties of the weld and heat-affected zone steel is not lower than the mechanical properties of the parent material. China uses the welding process of welding performance test methods, but also the use of the nature of the use of welding performance test methods.
Many factors affect the durability of steel. The first is the poor corrosion resistance of steel, must take protective measures to prevent steel corrosion and rust. Protective measures include: regular maintenance of steel paint, the use of galvanised steel, in the presence of acid, alkali, salt and other strong corrosive media, the use of special protective measures, such as marine platform structure using “anodic protection” measures to prevent corrosion of the conduit frame, fixed on the conduit frame zinc ingots, seawater electrolytes will automatically first corrode the zinc ingots, so as to achieve the protection of steel This protects the steel conduit frame. Secondly, as steel is subjected to high temperatures and long-term loads, its breaking strength decreases more than its short-term strength, so for steel subjected to long-term high temperatures, the lasting strength is measured. Steel will automatically harden and become brittle over time, i.e. the “ageing” phenomenon. For steel subjected to low temperature loading, its impact toughness should be tested.