Eight basic knowledge of steel structure

Characteristics of steel structure

1. The weight of the steel structure is relatively light

2. The stability of steel structure is relatively high

3. building steel seismic (shock), impact resistance is good

4. High degree of modernization of steel structure manufacturing

5. the steel structure can be installed accurately and quickly

6. very easy to be made into a sealed structure

7. the steel structure is easy to etch

8. steel structure flame retardant poor common steel grade and performance

1. Alloy structural steel of carbon plant: Q195, Q215, Q235, Q255, Q275, etc

2. alloy structural steel high strength structural steel

3. High quality carbon steel and alloy tool steel

4, the main purpose of professional steel raw materials using standard steel structure material principle is to ensure the bearing capacity of the bearing structure and avoid brittle damage under certain conditions, according to the necessity of the structure, load characteristics, structural type, stress state, connection mode, building steel thickness and office environment and other factors are fully considered. "Steel structure design Standard" GB50017-2003 proposed four kinds of steel models are "appropriate" to use the model specifications, to the first selection after the approval of the standard, and is not strictly prohibited the application of other models, only the use of building steel to meet the provisions of the code can be. Key technical content

(1) high-rise residential steel structure technology. According to the building density and design points, the structure, the structure support point, the tube section and the oversized frame shear wall are selected respectively. The precast members can be made of steel, reinforced concrete or filled steel tube. The steel members are light and ductility, and can be welded by electric welding channel steel or cold rolled channel steel, which is suitable for the construction of very high construction layer. Strong concrete precast member has high bending stiffness, good fire safety performance, suitable for middle and high-rise buildings or bottom structures; Concrete filled steel tube engineering construction is simple, only used for column structure.

(2) indoor steel structure technology. The steel structure in the interior space has light weight, large bending stiffness, beautiful shape design, and faster construction speed. The tablet computer spherical mesh with seamless steel pipe as the component, double layer spherical mesh with variable section and reticulated shell are the most used structural forms of steel structure in indoor space in China. It has the advantages of large bending stiffness in indoor space, low steel quantity, in design, construction and inspection procedures, and can provide complete CAD. In addition to the grid, the space layout has long span suspension cable structure, tensioned membrane structure and so on.

(3) light steel structure technology. With light color steel plate made of wall and flat roof structure composed of new structure type. By 5mm steel plate welding or cold rolled large section thick wall H type steel wall beam and steel purlin, round steel made of soft terminal software and high strength bolt connection composed of light steel structure management system, column distance can be 6m to 9m, span can reach 30m or larger, the relative height can reach more than ten meters, and can be set up light hanging four. The amount of steel used is 20 ~ 30kg/m2. It has standardized design procedures and specialized production companies, with good product quality, faster assembly speed, light weight, less investment, engineering construction will not be limited by the season, suitable for all kinds of light plant.

(4) steel concrete composite structure technology. The beam and column bearing structure composed of steel or steel management and concrete engineering is the composite structure of steel and concrete structure, which has been increasingly applied in recent years. Composite structure has the advantages of both steel and concrete, overall high strength, good stiffness, excellent seismic grade performance, when selected for outsourcing business concrete structure, more has good fire and corrosion resistance. Structural components can generally reduce the amount of steel used by 15 ~ 20%. It also has the advantages of less formwork support or no formwork support, convenient and rapid engineering construction, and has great marketing and development potential. It is suitable for frame column, column and frame structure of double or multi-story building with relatively large load, public building column and densely ribbed floor.

(5) High toughness bolt connection and welding technology. High strength bolt is the friction force to convey the ground stress, by the bolt, screw and sealing ring three parts. High-strength bolt connection engineering has the advantages of simple construction, easy disassembly, high bearing capacity, fatigue relief performance, strong locking, and high safety. It has replaced riveting and partial electric welding in engineering projects, and has become the main connection method in steel structure manufacturing and installation. For steel members manufactured in the production workshop, automatic multi-wire arc submerged welding should be adopted for thick steel plate, and melting tip electroslag welding should be adopted for box column baffle. In the on-site construction and installation, semi-automatic welding technology, gas shielded welding wire and self-maintenance wire technology should be adopted.

(6) Steel structure safety protection technology. The safety protection of steel structure includes fire safety, corrosion prevention and rust prevention treatment. Generally, it is necessary to use rust prevention after fireproof material treatment, but there is corrosion gas in the building to be treated. There are many types of fire-resistant materials in China, such as TN series products and MC-10, among which the fire-resistant materials of MC-10 include alkyd enamel, chlorinated rubber paint, fluorine adhesive building coatings and chloro-sulfonated materials.

In the process of construction should be according to the steel structure form, fire grade requirements and environmental conditions to use appropriate building coating and coating thickness.

Overall objective and countermeasures Steel structure engineering projects involve a wide range of areas, high technical level, in the popularization and use of the need to follow the technical standards of our country and industry. Construction administrative departments all over the country should attach great importance to the basic construction of the systematic stage of steel structure engineering projects, organize good quality inspection team training, and summarize the work practice and new technology in time. Colleges and universities, technical departments and construction enterprises should speed up the molding of steel structure engineers and technicians and the marketing and promotion of steel structure CAD with mature technology. The members of public organizations should cooperate with each other in the development of steel structure technology, vigorously carry out academic forums and training courses around the world, and actively promote the overall level of steel structure design, manufacturing, construction and installation technology in the near future.

The connection method of steel structure has three kinds: weld connection, bolt connection and bolt connection.

(1) Weld connection Weld connection is caused by the heat caused by electric arc welding material and workpiece partial melting, condensation into a weld through refrigeration, so as to connect the welding parts into one. Advantages: do not weaken the cross section of prefabricated components, save construction steel, simple structure, convenient production and manufacturing, connection bending stiffness, good sealing performance, easy to choose automation technology under certain conditions, production and manufacturing efficiency. Defects: The heat-affected zone of the construction steel around the weld due to the continuous high temperature effect of electric welding may cause some materials to become brittle; In the welding process, the pipes are exposed to uneven high temperature and refrigeration, which causes the welding residual stress and deformation of the structure, and has certain influence on the bearing capacity, bending stiffness and service performance of the structure. Because of the large bending stiffness of welded structure, partial cracks are easy to expand to the whole, especially at ultra-low temperature. The plasticity and flexibility of the weld connection are weak, which may produce shortcomings during welding, so that the impact toughness is reduced.

(2) Bolt connection Bolt connection is made of bolts such as standard parts to connect the connector into one. Bolt connection is divided into general bolt connection and high toughness bolt connection two kinds. Advantages: simple construction technology, convenient assembly, especially suitable for construction site assembly and connection, but also easy to disassemble and assemble, suitable for must be installed and disassembled structure and temporary connection. Defects: Holes need to be punched and assembled in parts, which increases the amount of manufacturing tasks and requires high precision of manufacturing. The bolt hole also makes the cross section of the line weak, and the connected parts often need to be connected to each other or to assist the connecting plate (or Angle iron), so the structure is more complex and cost more materials.

(3) Bolt connection Bolt connection is to put one end of the bolt containing a semi-circular prefabricated member nail head, the nail rod is burned red and quickly inserted into the joint of the connector, and the other end is riveted into a nail head with a rivet gun, so that the connection can be tightened. Advantages: Reliable riveting force transmission, plasticity, ductility are good, quality is easy to check regularly to ensure, suitable for super heavy and bear dynamic load structure. Defects: The riveting process is complicated, the production and manufacturing time and material cost, and the working intensity is high, so it has been basically replaced by electric welding and high toughness bolt connection. Electric welding welding joint

The common welding process of steel structure is arc welding, including arc welding, automatic or semi-automatic arc welding and gas shielded welding. Arc welding is a common welding process in steel structure. Its machines and equipment are simple and convenient to use. However, the working conditions are poor, the production capacity is lower than that of automatic or semi-automatic welding, and the specificity of weld quality is large, which lies in the technical strength of the welder to a certain extent. The weld quality of the automatic welding machine is stable, the internal structure of the weld is less, the plasticity is good, the fracture toughness is good, suitable for electric welding welding long immediate weld. Semi-automatic welding due to manual control, suitable for welding curves or random shape of the weld. Automatic and semi-automatic welding shall adopt the electrode and flux suitable for the main metal materials, the electrode shall meet the provisions of the national industry standards, and the flux shall be defined according to the welding process requirements. Gas shielded welding should use rare gas (or CO2) air as the protective substance of electric arc, so that the molten metal material and air barrier, in order to keep the welding process smooth. Gas shielded welding arc heating centralization, welding speed, melting depth, so the weld compressive strength is higher than manual welding. And good plasticity and corrosion resistance, suitable for carbon steel plate welding.

According to the mutual parts of the connected prefabricated members, the weld connection can be divided into four ways: connection, reinforcement lap, T-joint and Angle joint. The weld used for this connection has two basic methods: joint weld and fillet weld. In the specific application, should be based on the support of the connection, the integration of manufacturing, installation and welding standards to choose.

(3) Weld structure 1, joint weld joint weld force transmission is immediate, stable, and there is no significant stress condition, so the bearing performance is excellent, relative to the static and dynamic load bearing prefabricated member connection are applicable. However, due to the high quality requirements of the joint weld, the welding gap in the middle of the welding part is more strict, generally used in factory manufacturing connections. 2, fillet weld fillet weld form: fillet weld according to its length direction and the bearing of external force, can be divided into parallel to the direction of force action side fillet weld, perpendicular to the direction of force action of positive face fillet weld and force bearing Angle of oblique fillet weld and girth weld. Fillet weld cross section mode is divided into general type, gentle slope type and deep penetration type. hf refers to the size of fillet weld foot in the figure. The general cross section welding hole side ratio is 1:1, infinite close to isosceles right triangle, the bending of the force transmission line is strong, so the stress is more serious. For the structure bearing dynamic load at the same time, in order to ensure the smooth force transfer, the positive face fillet weld should adopt the gentle slope type with the size ratio of two welding angles 1:1.5 (long side along the internal power orientation), and the side fillet weld should adopt the deep penetration type with the ratio of 1:1. Bolted connection

(1) The structure of general bolt connection

1, the general form and specifications of the bolt model steel structure adopts the general way for large hexagonal head type, its number with the English letter M and nominal pressure and aperture (mm) indicated. M18, M20, M22 and M24 are common in engineering. According to the national standard, bolts are represented by bolt performance levels, such as "Class 4.6" and "Class 8.8". The digit before the decimal place indicates the minimum compressive strength of the bolt raw material. For example, "4" indicates 400N/mm2, and "8" indicates 800N/mm2.

The number after the decimal point (0.6, 0.8) indicates the strong bending of the bolt material, that is, the ratio of the yield limit to the minimum compressive strength. According to the dimensional accuracy of bolts, general bolts are divided into A, B, C three levels. Class A and B bolts (special bolts) are made of 8.8 grade materials and machined by CNC lathes. They have smooth surfaces and accurate specifications, and are suitable for class Ⅰ holes (namely, bolt holes are drilled or redrilled on well-installed prefabricated members, with smooth edges and accurate holes).

Because of its high dimensional accuracy, close contact with the hole side, its connection deformation is small, good bearing performance, suitable for bearing relatively large shear stress and tensile strength of the connection. But the production and installation is time-consuming, the cost is relatively high, so it is less used in the steel structure. Class C bolts (overbuilt bolts) are made of 4.6 or 4.8 grade steel. The production and processing are not smooth and the specifications are not accurate enough. Only class Ⅱ holes are required (that is, bolt holes are punched in individual parts at one time or drilled without machine tool fixtures.

The general aperture is 1~2mm larger than the bolt rod diameter). In the transmission of shear stress, the connection deformation is large, but the transmission of tensile resistance performance is good, the actual operation does not use unique machines and equipment, low cost. It is mainly used to bear the tensile bolt connection and bear the load of foundation pile or simply bear the dynamic load structure of the primary and secondary shear connection.

2. The arrangement of the sort bolts of the general bolt connection should be simple, unified and close, to achieve the bearing capacity provisions, effective structure and convenient assembly. There are two kinds of arrangement, side by side and staggered, as shown in the figure below. Side by side is simpler and the rows are tighter.

(2) Bearing characteristics of general bolt connection

1. Shear bolt connection

2, bending bolt connection

3, tensile shear bolt connection

(3) Bearing characteristics of high toughness bolt connection according to the design and bearing capacity provisions can be divided into friction type and pressure type two. Friction type connection in the bearing of cutting, the external shear stress to the parts may occur between the greater friction resistance for the limit state; When it exceeds the relative movement between the parts, that is, the connection has failed and destroyed. When the pressure bearing connection is shear, the sliding friction is allowed to get rid of and the relative movement between the parts is generated. Then the external force can continue to increase, and the ultimate failure of the lead screw cutting or the hole edge under pressure is the limit state.