1、Characteristics Of Steel Structure
① The steel structure is light in weight
② The reliability of steel structure work is high
③ Steel has good vibration resistance (seismic) and impact resistance
④ The degree of industrialization of steel structure manufacturing is relatively high
⑤ Steel structures can be assembled accurately and quickly
⑥ Easy to make a sealed structure
⑦ Steel structure is easy to corrode
⑧ Steel structure has poor fire resistance
2、The Grades Of Steel Commonly Used In Steel Structures
① Carbon structural steel: Q195, Q215, Q235, etc.
② low alloy high strength structural steel
③ High-quality carbon structural steel and alloy structural steel
④ special purpose steel
3. Principles Of Material Selection For Steel Structures
The principle of material selection for steel structures is to ensure the load-bearing capacity of the load-bearing structure and prevent brittle failure under certain conditions. According to the importance of the structure, load characteristics, structural form, stress state, connection method, steel thickness and working environment and other factors, comprehensive consideration of.
The four types of steel proposed in the "Code for Design of Steel Structures" GB50017-2003 are "suitable" models to be used. They are the first choice when conditions permit. The use of other types is not prohibited, as long as the steel used meets the requirements of the specification. .
4. Main Technical Content Of Steel Structure
High-rise steel structure technology
According to the building height and design requirements, the frame, frame support, cylinder and giant frame structure are adopted respectively, and its components can be steel, stiff reinforced concrete or steel tube concrete. Steel components are light in weight and good in ductility, and can be welded steel or rolled steel, which is suitable for super high-rise buildings; rigid reinforced concrete components have high rigidity and good fire resistance, and are suitable for medium and high-rise buildings or bottom structures; steel pipe concrete is easy to construct, For column structures only.
Space steel structure technology
The space steel structure has light weight, high rigidity, beautiful appearance and fast construction speed. Ball-joint flat grids, multi-layer variable cross-section grids and reticulated shells with steel pipes as rods are the structural types with the largest amount of space steel structures in my country. It has the advantages of high spatial rigidity and low steel consumption, and can provide complete CAD in accordance with the design, construction and inspection regulations. In addition to the grid structure, the space structure also includes a long-span suspension cable structure and a cable-membrane structure.
Light steel structure technology
Accompanied by a new structural form consisting of walls and roof enclosures made of light colored steel plates. Large-section thin-walled H-shaped steel wall beams and roof purlins welded or rolled by steel plates above 5mm, a light steel structure system composed of flexible support systems made of round steel and high-strength bolt connections, the column distance can be from 6m to 9m, and the span can reach 30m or more, the height can reach more than ten meters, and the steel consumption is 20-30kg/m2. Now there are standardized design procedures and specialized production enterprises. The product quality is good, the installation speed is fast, the weight is light, the investment is small, and the construction is not limited by seasons. It is suitable for various light industrial plants.
Steel Concrete Composite Structure Technology
The beam and column load-bearing structure composed of section steel or steel management and concrete members is a steel-concrete composite structure, and its application range has been expanding in recent years. The composite structure has the advantages of both steel and concrete, and has high overall strength, good rigidity, and good seismic performance. When the outsourcing concrete structure is used, it has better fire resistance and corrosion resistance. Composite structural members can generally reduce steel consumption by 15-20%. Composite floors and steel tube concrete members also have the advantages of less or no formwork, convenient and rapid construction, and have great potential for promotion. It is suitable for frame beams, columns and floors of multi-storey or high-rise buildings with large loads, industrial building columns and floors, etc.
High Strength Bolt Connection and Welding Technology
High-strength bolts transmit stress through friction and consist of three parts: bolts, nuts and washers. High-strength bolt connection has the advantages of simple construction, flexible dismantling, high bearing capacity, good fatigue resistance and self-locking performance, and high safety. It has replaced riveting and partial welding in engineering and has become the main connection method in steel structure fabrication and installation. For steel components manufactured in the workshop, automatic multi-wire arc submerged welding shall be adopted for thick plates, and electroslag welding and other technologies shall be adopted for box-shaped column partitions. During on-site installation and construction, semi-automatic welding technology, gas-shielded welding flux-cored wire and self-shielded flux-cored wire technology should be used.
Steel structure protection technology
Steel structure protection includes fire protection, anti-corrosion, and anti-rust. Generally, anti-rust treatment is not required after fire-resistant coating treatment, but anti-corrosion treatment is still required in buildings with corrosive gases. There are many types of domestic fire-resistant coatings, such as TN series, MC-10, etc. Among them, MC-10 fire-resistant coatings include alkyd enamel paint, chlorinated rubber paint, fluorine rubber paint and chlorosulfonated paint. During the construction, the appropriate coating and coating thickness should be selected according to the steel structure type, fire resistance level requirements and environmental requirements.
5. Goals And Measures Of Steel Structure
Steel structure engineering involves a wide range of areas and is technically difficult, so national and industry standards must be followed in promotion and application. Local construction administrative departments should pay attention to the construction of steel structure engineering in the professional stage, organize the training of quality inspection teams, and summarize work practices and new technology applications in a timely manner. Universities, design departments and construction enterprises should speed up the training of steel structure engineering technicians and promote the mature technology of steel structure CAD. Mass academic groups should cooperate with the development of steel structure technology, carry out extensive academic exchanges and training activities at home and abroad, and actively improve the overall level of steel structure design, production, construction and installation technology, and can have incentives to improve in the near future.
6. Connection Method Of Steel Structure
There are three connection methods for steel structures: weld connection, bolt connection and rivet connection.
Weld connection
The welding seam connection is that the welding rod and the weldment are partially melted by the heat generated by the arc, and then condensed into a weld after cooling, so that the weldment is connected into one.
advantage
It does not weaken the section of the component, saves steel, has a simple structure, is convenient to manufacture, has high connection rigidity, and has good sealing performance. It is easy to adopt automatic operation under certain conditions, and the production efficiency is high.
shortcoming
The heat-affected zone formed by the welding high temperature of the steel near the weld may be that some parts of the material become brittle; the steel is subjected to unevenly distributed high temperature and cooling during the welding process, which causes the structure to produce welding residual stress and residual deformation, which affects the bearing capacity of the structure. , stiffness and performance have a certain influence; due to the high stiffness of the welded structure, once a local crack occurs, it is easy to spread to the whole, especially at low temperature, it is prone to brittle fracture; the plasticity and toughness of the weld connection are poor, and may occur during welding. Defects reduce the fatigue strength.
Bolted
Bolt connection is to connect the connecting parts into one through the fasteners such as bolts. There are two types of bolted connections: ordinary bolted connections and high-strength bolted connections.
advantage
The construction process is simple and the installation is convenient. It is especially suitable for installation and connection on the construction site, and it is also easy to disassemble. It is suitable for structures that need to be assembled and disassembled and temporary connections.
shortcoming
It is necessary to open holes on the plates and align the holes during assembly, which increases the manufacturing workload and requires high manufacturing precision; the bolt holes also weaken the component cross-section, and the connected parts often need to overlap each other or add auxiliary connecting plates ( Or angle steel), so the structure is more complex and more expensive steel.
Rivet connection
Rivet connection is to use a rivet with a semicircular prefabricated nail head at one end, insert the nail rod into the nail hole of the connecting piece quickly after burning red, and then use a rivet gun to rivet the other end into a nail head to make the connection tight. solid.
advantage
The riveting force is reliable, the plasticity and toughness are good, the quality is easy to check and guarantee, and it can be used for heavy-duty and directly bearing dynamic load structures.
shortcoming
The riveting process is complex, labor-intensive and wasteful, and labor-intensive, so it has been basically replaced by welding and high-strength bolt connections.
7、 Welding Connection
Welding method
The commonly used welding method for steel structures is arc welding, including manual arc welding, automatic or semi-automatic arc welding, and gas shielded welding.
Manual arc welding is the most commonly used welding method in steel structures. Its equipment is simple and its operation is flexible and convenient. However, the working conditions are poor, the production efficiency is lower than that of automatic or semi-automatic welding, and the variability of weld quality is large, which depends to a certain extent on the technical level of the welder.
The weld quality of automatic welding is stable, the internal defects of the weld are less, the plasticity is good, and the impact toughness is good, which is suitable for welding long direct welds. Semi-automatic welding is suitable for welding curves or welds of any shape due to manual operation. Automatic and semi-automatic welding shall use welding wire and flux suitable for the main metal. The welding wire shall comply with the provisions of the national standard, and the flux shall be determined according to the requirements of the welding process.
Gas shielded welding uses inert gas (or co2) gas as the protective medium of the arc to isolate the molten metal from the air to keep the welding process stable. The arc heating of gas shielded welding is concentrated, the welding speed is fast, and the penetration depth is large, so the weld strength is higher than that of manual welding. It has good plasticity and corrosion resistance, and is suitable for welding thick steel plates.
Weld form
According to the mutual position between the connected components, the welding seam connection form can be divided into four types: butt joint, lap joint, T-shaped joint and fillet joint. There are two basic types of welds used for these connections, butt welds and fillet welds. In specific applications, it should be selected according to the force of the connection, combined with manufacturing, installation and welding conditions.
Weld construction
① butt weld
The force transmission of the butt weld is direct, smooth, and there is no significant stress concentration phenomenon, so the mechanical performance is good, and it is suitable for the connection of components bearing static and dynamic loads. However, due to the high quality requirements of butt welds, the requirements for welding gaps between weldments are relatively strict, and they are generally used in factory-made connections.
② fillet welds
The form of fillet welds: fillet welds can be divided into side fillet welds parallel to the direction of force action and front fillet welds perpendicular to the direction of force action and oblique to the direction of force action according to their length direction and direction of external force action. oblique fillet welds and perimeter welds.
The cross-section form of fillet weld is divided into ordinary type, flat slope type and deep penetration type. The ratio of welding leg to edge of ordinary cross-section is 1:1, which is similar to an isosceles right-angled triangle. The force transmission line bends sharply, so the stress concentration is serious. For the structure directly bearing the dynamic load, in order to make the force transmission smooth, the front fillet weld should adopt the flat slope type with the ratio of two fillet sides 1:1.5 (the long side follows the direction of internal force), and the side fillet weld should adopt the ratio of 1:1 deep melting formula.
8. Bolt Connection
The structure of ordinary bolted connection
① Form and specification of ordinary bolts
The common form adopted by the steel structure is a large hexagonal head type, and its code name is represented by the letter M and the nominal and diameter (mm). M18, M20, M22, M24 are commonly used in engineering. According to international standards, bolts are uniformly expressed by the performance grade of bolts, such as "4.6 grade", "8.8 grade" and so on. The number before the decimal point indicates the minimum tensile strength of the bolt material, such as "4" means 400N/mm2, "8" means 800N/mm2. The numbers after the decimal point (0.6, 0.8) indicate the yield ratio of the bolt material, that is, the ratio of the yield point to the minimum tensile strength.
According to the machining accuracy of bolts, ordinary bolts are divided into three grades: A, B, and C.
A and B grade bolts (refined bolts) are made of 8.8 grade steel, turned by machine tools, with smooth surface and accurate size, and equipped with type I holes (that is, bolt holes are drilled or expanded on assembled components) , the hole wall is smooth and accurate to the hole). Because of its high processing precision, close contact with the hole wall, its connection deformation is small, and its mechanical performance is good, it can be used for connections that withstand large shear and tension. However, manufacturing and installation are labor-intensive and costly, so they are rarely used in steel structures.
C-level bolts (coarse bolts) are made of 4.6 or 4.8-grade steel, with rough processing and inaccurate dimensions. Only type II holes are required (that is, the bolt holes are punched on a single part at one time or drilled without a drilling jig. Generally, the diameter of the bolt is smaller than that of the bolt. The rod diameter is 1~2mm larger). When transmitting shear force, the connection deformation is large, but the performance of transmitting tension force is still good, no special equipment is required for operation, and the cost is low. It is often used in bolted connections bearing tension and secondary shear connections in structures bearing static loads or indirectly bearing dynamic loads.
② Arrangements of ordinary bolted connections
The arrangement of the bolts should be simple, uniform and compact to meet the force requirements, and the structure should be reasonable and easy to install. There are two types of arrangement, parallel and staggered. Side by side is simpler, and staggered is more compact.
Stress Characteristics of Ordinary Bolted Connections
1> Shear bolt connection
2> tension bolt connection
3> tension shear bolt connection
Stress characteristics of high-strength bolts
According to design and force requirements, high-strength bolt connections can be divided into friction type and pressure-bearing type. When the friction connection is subjected to shear, the external shear force reaches the maximum friction resistance that may occur between the plates as the limit state; when the relative slip occurs between the plates when the external shear force exceeds it, the connection is considered to have failed and is destroyed. When the pressure-bearing connection is sheared, the friction force is allowed to be overcome and the relative slippage between the plates occurs, and then the external force can continue to increase, and the final failure of the screw shear or the pressure of the hole wall occurs as the limit state.
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