Selection of basic materials for steel structure
1. the main properties of steel
The main properties of steel include three important mechanical properties of steel, that is, yield point, tensile strength and elongation, but also includes cold bending properties and impact toughness. In addition, the technical properties and chemical composition of steel is also an important part of the performance of steel. Steels used as steel structures must have the following properties:
1 higher strength, i.e., tensile strength Fu and yield point FY are relatively high.
2 sufficient deformation capacity, that is, good plasticity and toughness. Plastic structure deformation before failure obviously to reduce risk of brittle failure; good toughness in dynamic loads at failure to absorb more energy, and also reduce the risk of brittle failure.
3 good processing performance, both suitable for cold and hot processing, but also has good weldability, not because of these processing and strength, plasticity and toughness to bring greater harmful effects.
Two, the choice of steel points
Selection of steel to be safe and reliable structure, economic and reasonable, in order to select the steel should consider the following factors:
(1) the importance of structure or component;
(2) load properties (static or dynamic);
(3) connection method (welding, riveting or bolting);
(4) working conditions (temperature and corrosive medium).
Commonly used steel structure types are: carbon structural steel, low alloy structural steel, high strength steel, fire-resistant weathering steel. The light steel structure is usually made of carbon structural steel and low alloy structural steel.
(1) carbon structural steel
According to the quality of steel, carbon structural steel can be divided into A, B, C, D four grades, from A to D that the quality from low to high. Different quality grades on impact toughness (Charpy V - I=I deficiency test) requirements are different. The provisions of Grade A without impact; the B level provides 20 degrees of impact energy for Ak = 27J (vertical); C level 0 DEG C when impact energy Ak = 27J (vertical); D level required to 20 DEG C when the impact energy of k = 27J (vertical). According to the deoxidation method in smelting, steel can be divided into three types of boiling steel (F), Z and special killed steel (TZ).
(2) low alloy structural steel
Generally, Q235A steel is suitable only for structures that are not directly subjected to dynamic loads. When used for welding, the quality certificate shall indicate that the carbon content is not more than 0.2%. For the need to check the fatigue of the welded structure, should be used with room temperature impact toughness guaranteed B grade steel. When this kind of structure is in a low temperature environment in winter, if the working temperature is between 0 and, the Q235 and Q345 should be selected C grade steel, Q390 and Q420 should be selected with a grade of 20 D. If the working temperature is not higher than 20 C, the quality level of steel and improve the level of Q235 and Q345 by D and Q390 and Q420 grade steel with E grade steel. Non member welding brittle fracture of welded structure is more dangerous than smaller, material requirements than the welding structure appropriate to relax, but requires checking fatigue components should be used to ensure the grade B steel impact toughness at room temperature. When the working temperature is not higher than 20 C, Q235 and Q345 should be used to grade C steel, Q390 and Q420 should be used in grade D steel.
The steel used in the steel structure is mainly hot-rolled steel plate and steel, cold-formed thin-walled steel, etc..
(1) steel plate
Steel plate mainly thick steel plate, thin steel plate and steel (steel).
Thick steel plate: thickness 4.5 ~ 60mm, width of 600 ~ 3000mm, length of 4 ~ 12m;
Thin steel plate: thickness 1 ~ 4mm, width of 500 ~ 1500mm, length of 0.5 ~ 4m;
Flat: the thickness of 3 ~ 60mm, width 10 ~ 200mm, 3 ~ 9m in length.
Mainly used for welding thick steel plate beam column web and flange and gusset plate, thin steel plate is mainly used in the manufacture of cold-formed steel, flat steel can be used as a node plate and a connecting plate etc..
(2) hot rolled section steel
Steel structure commonly used for hot-rolled steel pipe, angle steel, channel steel, I-steel and wide flange I-section steel etc.. Wide flange steel can be used for the light steel structure in compression and bending members, other steel sections in the light steel structure is generally used for auxiliary structure or supporting structure.
(3) thin-walled steel
The section size of the thin-walled steel can be designed according to the reasonable scheme, which can give full play to and utilize the strength of the steel and save the steel. The wall thickness of thin wall steel is generally 1.5 ~ 5mm, but the wall thickness of the bearing component should not be less than 2mm. The commonly used thin-walled steel sections have groove shape, groove shape (C shape), Z shape and so on. The light steel structure in structural components such as purlines generally adopts thin-walled steel.
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