Detailed explanation of large-span truss construction1

Steel buildings are an extremely cost-effective and versatile solution for businesses in all industries.While using steel structure buildings such as steel structure warehouses and steel frame buildings, we also need to understand what factors affect the steel structure materials.

1、Chemical composition

• Carbon: the main component of steel strength. Carbon content progress, the steel strength progress, but together with the plasticity of steel, resistance, cold bending function, weldability and resistance to rust and corrosion can be reduced, especially at low temperatures under the impact resistance will also be reduced.
• Manganese and silicon: favorable elements in steel, are deoxidizers, can improve strength, but not too much plasticity and impact resistance.
• Vanadium, niobium, titanium: alloying elements in steel, both to improve the strength of steel, but also to maintain outstanding plasticity, resistance.
• Aluminum: strong deoxidizer, with aluminum to make up for the deoxidation, can further reduce the harmful oxides in steel.
• Chromium and nickel: alloying elements to improve the strength of steel.
• Sulfur and phosphorus: impurities left in the steel during exercise, harmful elements. They reduce the plasticity, resistance, weldability and fatigue strength of steel. Sulfur can make steel "hot brittle", phosphorus makes steel "cold brittle".
• "Hot brittle": sulfur can generate easy to melt iron sulfide, when hot work and welding to make the temperature up to 800 ~ 1000 ℃, so that the steel presents cracks, brittle appearance.
• "Cold brittle": at low temperatures, phosphorus makes the steel impact resistance decreased dramatically in the phenomenon.
• Oxygen and nitrogen: harmful impurities in steel. Oxygen can make steel hot brittle, nitrogen can make steel cold brittle.

2、Impact of metallurgical shortcomings

Common metallurgical drawbacks include segregation, non-metallic admixture, porosity, cracks, delamination, etc., all of which deteriorate the function of steel.

3、Steel hardening

Cold drawing, cold bending, punching, mechanical shear and other cold work so that the steel has a great plastic deformation, and then improve the yield point of steel, together with a decline in the plasticity and resistance of steel, this phenomenon is known as cold hardening or strain hardening.

4、temperature effect

Steel is appropriately sensitive to temperature, and both increases and decreases in temperature cause changes in steel function. In contrast, the low temperature function of steel is more important.

In the positive temperature scale, the general trend is to follow the rise in temperature, steel strength decreases, deformation increases. About 200 ℃ within the steel function does not change greatly, 430 ~ 540 ℃ between the strength (yield strength and tensile strength) a sharp decline; to 600 ℃ when the strength is very low can not bear the load.

In addition, 250 ℃ near the blue brittle phenomenon, about 260 ~ 320 ℃ when there is a creep phenomenon.