I. features of steel structure:
1. Light weight of steel structure
2. High reliability of steel structure work
3. Anti-vibration and impact resistance of steel
4. The degree of industrialization of steel structure is high
5. Steel structure can be assembled accurately and quickly
6. Easy to seal structure
7. Steel structure is easy to corrode
8. The steel structure is not fireproof
The number and performance of steel used in steel
1. Carbon structural steel: Q195, Q215, Q235, Q255, Q275, etc
2. Low-alloy high-strength structural steel
3. High quality carbon structural steel and alloy structural steel
4. Special purpose steel
3. Material selection principle of steel structure
Material selection of steel structure principle is the guarantee of the bearing capacity of the bearing structure and prevent appear brittle failure under certain condition, according to the importance of the structure, load characteristics, structure, stress state, the connection method, the thickness of the steel and the work environment factors taken into account.
Specification for design of steel structure GB50017-2003) put forward four kinds of steel model used is "appropriate" model, is the first choice of when conditions permit, does not prohibit the use of other types, as long as the use of steel to meet the requirements of the specification.
Technical contents of main steel structure:
(1) high-rise steel structure technology.According to the building height and design requirements, the frame, frame support, barrel body and giant frame structure are adopted respectively. The components can be used for steel, strength reinforced concrete or steel tube concrete.Steel components are light ductility, can be used in welding section steel or rolled steel, suitable for supertall building;The stiffening reinforced concrete member has a large rigidity and good fireproof performance. It is suitable for middle and high - rise buildings or the bottom structure.Steel tube concrete construction is simple and only used for column structure.
(2) space steel structure technology.The space steel structure has light weight, large rigidity, beautiful shape and fast construction speed.It is the largest structural type of steel structure in China, with steel pipe as the ball node, the mesh frame of multi-layer variable cross section and the mesh shell.With large space stiffness and low steel capacity, the design, construction and inspection procedures can provide complete CAD.Besides the structure of the net frame, the spatial structure has a large span suspension structure and the cable membrane structure.
(3) light steel structure technology.A new structural form of wall and roof enclosure with light colored steel plate is used.By more than 5 mm steel plate welding or rolling the thin-wall h-beam wall beam with large section and roofing purline, round steel made of flexible support system and high strength bolt connection of light steel structure system, column distance from 6 m to 9 m, span up to 30 m or more, up to a dozen meters high, and can set four light.The steel amount is 20 ~ 30kg/m2.Now has a standardized design program and professional production enterprises, products of good quality and fast installation, light weight, less investment, construction season without limit, suitable for all kinds of light industrial workshop.
(4) steel and concrete composite structure technology.Girder and column bearing structure of steel or steel management and concrete components are steel mix structure, and the application scope has been expanded in recent years.Has both the advantages of steel and concrete composite structure, the overall strength, good rigidity, good seismic performance, when using outsourcing concrete structure, a good fire and corrosion resistance.Composite structural components can generally be reduced by 15 ~ 20% of steel.The composite building and steel tube concrete members have the advantages of short - supporting or unsupported modules, convenient construction and fast development.It is applicable to the frame girder, column and floor, industrial construction column and floor cover of multi-storey or high-rise buildings with larger loads.
(5) high strength bolt connection and welding technology.The high strength bolt is passed through the friction force to deliver the stress, which consists of bolt, nut and gasket.High strength bolt connection construction simple, demolition of flexible, high bearing capacity, good fatigue resistance and self-locking, high security, etc. The project has replaced the riveting and part in welding, become the main connection of steel structure production and installation.The steel components made in the workshop should be soldered by automatic multi-wire arc welding, and the box column should be used for the welding technology.In the construction of the site, semi-automatic welding technology and gas shielded flux cored wire and self-protected flux coring technology should be adopted.
(6) steel structure protection technology.Steel structure protection includes fire prevention, anticorrosion and rust prevention. It is generally used in the treatment of fire retardant coating, but it needs to be treated as a preservative in the building with corrosive gas.There are many kinds of domestic fire retardant coatings, such as TN series, Mc-10, etc., of which Mc-10 fire retardant coating has alkyd enamel, chlorinated rubber paint, fluorine rubber coating and chlorine sulfonated coating.Suitable coating and coating thickness should be selected according to the type of steel structure, fire resistance level and environmental requirements.
5. Objectives and measures of steel structure:
Steel structure engineering involves wide range and technical difficulty, which must conform to national and industry standard norms in promotion and application.The administrative departments of construction shall pay attention to the construction of the professional stage of steel structure engineering, organize the training of quality inspection teams, and summarize the work practice and application of new technology in time.Colleges and universities, design departments and construction enterprises should accelerate the training of steel structure engineers and promote the mature steel structure CAD.Academic societies should coordinate the development of steel structure technology, extensive domestic and international academic exchange and training activities, and actively put the installation technology of steel structure design, production and construction of the overall level, in the near future will have a reward.
The connecting method of steel structure
The connection method of steel structure has three kinds: weld joint, bolt connection and rivet connection.
(1) weld joint
The weld joint is the heat generated by the arc to melt the electrode and the welding parts locally, and then the weld joint becomes one.
Advantages: not weaken the component section, save the steel, construct simple, make convenient, the connection rigidity is large, the sealing performance is good, under certain conditions easy to adopt automatic operation, the production efficiency is high.
Disadvantages: the thermal influence zone of the steel near the weld due to high temperature is likely to be brittle in some parts.During the welding process, the steel is subjected to uneven distribution of high temperature and cooling, resulting in the welding residual stress and residual deformation of the structure, which has certain influence on the bearing capacity, rigidity and performance of the structure.Due to the large rigidity of the welding structure, the local crack can easily be extended to the whole, especially at low temperature.The plasticity and toughness of weld joints are poor, and the defects can be produced when welding, which can reduce the fatigue strength.
Bolted connections are bolted fasteners to connect the joints to one.Bolt connections are divided into ordinary bolted and high-strength bolts to connect two types.
Advantages: the construction process is simple and easy to install, especially suitable for site installation and connection. It is also easy to disassemble. It is suitable for assembling and dismantling structure and temporary connection.
Disadvantages: it is necessary to open holes and assemble the holes in the plate, increase the manufacturing workload, and have higher precision requirements for manufacturing.The bolt holes also weaken the section sections and are often connected to each other or add a secondary board (or Angle steel). Therefore, the structure is more complicated and more cost steel.
(3) rivet connection
Rivet connection is will end with a semicircular prefabricated screw head rivet, insert the nail rod quickly after burn red fitting nail holes, then the other end with a rivet gun also play riveting hammer head, to make the connection to tighten.
Advantages: the riveting transmission is reliable, the plasticity and toughness are good, the quality is easy to check and guarantee, can be used in heavy and direct bearing dynamic load structure.
Disadvantages: the riveting process is complicated, the manufacturing cost is high, and the labor intensity is high. Therefore, it has been replaced by welding and high strength bolt connections.
Vii. Welding connection
(1) welding method
The welding method commonly used in steel structure 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 structure. Its equipment is simple and easy to operate.But the labor condition is poor, the production efficiency is lower than automatic or semi-automatic welding, the variation of the weld quality is large, to a certain extent depends on the technical level of the welder.
The weld quality of automatic welding is stable, the weld internal defects are less, the plasticity is good, the impact toughness is good, suitable for welding the long direct weld.Semi-automatic welding due to manual operation, suitable for welding curves or any weld of any shape.Automatic and semi-automatic welding shall be used with the welding wire and flux of the main metal, and the wire shall conform to the national standard, and the flux shall be determined according to the welding process.
Gas shielded welding is used as an arc protection medium using inert gas (or CO2) gas, which insulates the molten metal from the air to keep the welding process stable.Gas shielded welding arc heating concentration, fast welding speed, deep penetration, so the weld strength is higher than manual welding.Good plastic and corrosion resistance, suitable for thick steel plate welding.
(2) weld form
The joint form of weld joints can be divided into four forms: butt joint, lap joint, t-shaped connection and Angle joint according to the mutual position between the connected members.The weld seams used in these connections have two basic forms of butt weld and fillet weld.In the specific application, the choice of manufacturing, installation and welding conditions should be made according to the stress situation of the connection.
(3) weld construction
1. Butt weld
The connection of welding seam is direct, smooth and without significant stress concentration. Therefore, the force performance is good, and the connection of the member with static and dynamic load is applicable.However, due to the high quality of the butt weld, the welding gap between welding pieces is stricter, and it is usually used in the connection of factory manufacturing.
2. Fillet weld
Fillet weld form: fillet weld according to the length direction and the direction of the external force is different, can be divided into is parallel to the direction of the profile Angle of weld and fillet weld is perpendicular to the direction of the front and force direction of oblique oblique Angle of welding seam and the weld.
The fillet form of fillet weld is divided into ordinary type, plain slope type and deep melting.The hf is called the welding foot size of the fillet weld.The ratio of normal cross section welding feet is 1:1, which is similar to the isosceles right triangle. The bending of the power line is more severe, so the stress concentration is serious.Structure of directly under dynamic loading, to make power transmission smooth, positive fillet weld size appropriate USES two solder side ratio 1:1. 5 flat slope type (long side along the direction of internal force), side fillet weld should adopt the deep melting type of ratio of 1:1.
(1) construction of common bolt connections
1. The form and specification of ordinary bolts
The normal form of the steel structure is the big hexagonal head type, which is represented by the letter M and the nominal and diameter (mm).In engineering, M18, M20, M22, M24 are commonly used.According to international standards, bolts are used in the performance rating of bolts, such as "4.6" and "8.8".The number before the decimal point indicates the minimum tensile strength of the bolt material, such as "4" for 400N/mm2, "8" means 800N/mm2.The number after the decimal point (0.6, 0.8) indicates the ratio of the strength of the bolt material, i.e. the ratio of the yield point to the lowest tensile strength.
According to the machining accuracy of bolt, ordinary bolts are divided into A, B and C.
A and B grade bolts bolts (refined) made of 8.8 grade steel by the machine tool turning processing and become, the surface is smooth, precise size, and with Ⅰ class hole (namely the bolt hole drill into or in assembly good members in, reaming hole wall is smooth, the hole accurate).Due to its high machining accuracy, it is closely connected with the hole wall, and its connection deformation is small, and its mechanical properties are good, which can be used to bear the connection of large shear force and pull.But manufacturing and installation are more expensive, so it is less used in steel structure.
C grade bolts (unfinished bolts) with 4.6 or 4.6 on the Richter scale steel production, rough machining, size is not accurate, only ask Ⅱ class hole (i.e. last rushed into the bolt hole in a single parts or don't have to drill into the diamond.Normal aperture is 1~2mm larger than bolt diameter.In the transmission of shear force, the connection deformation is large, but the performance of the transmission tension is good, the operation need not special equipment, the cost is low.A bolt connection that is often used to bear tension and a secondary shear connection under static load or indirectly under dynamic load structure.
2. Arrangement of common bolt connections
The arrangement of bolts should be simple, uniform and compact, meet the requirements of force, construct reasonable and easy to install.The arrangement is arranged in two categories (as shown).The parallel is simpler, the wrong column is more compact.
(2) characteristics of normal bolt connections
1. Connect the shear bolt
2. Connected by pull bolt
3. Pull bolt connection
The force characteristics of high strength bolts
High strength bolt connections can be divided into two types: friction type and pressure type according to design and mechanical requirements.
When the friction connection is subjected to shear, the shear force can reach the maximum friction resistance which can occur between the plates.When a relative slip occurs between the plates, it is considered that the connection has failed and is destroyed.
Pressure type connection when shear, allows friction be overcome and the relative slip between panel, and then the external force can continue to increase, and then the shear or screw hole wall pressure eventually damage for the limit state.