What is a steel structure
What is a steel structure?
Steel structure refers to a structural form that can bear and transfer loads by using steel plates and hot-tied, cold-formed or welded sections connected by connectors. Steel structure system has the comprehensive advantages of light weight, factory manufacturing, quick installation, short construction period, good seismic performance, fast investment recovery, and less environmental pollution, etc. Compared with reinforced concrete structure, it has the unique advantage of developing in three aspects of “high, large and light”. In the field of construction, steel structures are widely and reasonably used.
Steel structures are widely used in various engineering constructions, such as steel bridges, steel plants, steel gates, various large pipeline containers, high-rise buildings and tower-track institutions.
Steel structure is a structure composed of steel materials and is one of the main types of building structures. The structure is mainly composed of steel beams, steel columns, steel trusses and other components made of steel sections and steel plates, etc., and uses rust removal and rust prevention processes such as silanization, pure manganese phosphating, washing and drying, and galvanization. Each component or part is usually connected by welding, bolts or rivets. Because of its light weight and easy construction, it is widely used in large plants, arenas, super high-rise and other fields. Steel structures are prone to rust and corrosion. Generally, steel structures should be descaled, galvanized or painted, and maintained regularly.
Basic introduction of steel structure
Definition of steel structure
Steel is characterized by high strength, light weight, good overall stiffness and strong resistance to deformation, so it is particularly suitable for the construction of large span and super-high and super-heavy buildings; good homogeneity and isotropy of the material, which is an ideal elastomer and best meets the basic assumptions of general engineering mechanics; good plasticity and toughness of the material, which can have large deformation and can well withstand dynamic loads; short construction period; high degree of industrialization, which can be High degree of mechanization of specialized production.
Steel structure should study high-strength steel, greatly improving its yield point strength; in addition to rolling new varieties of steel sections, such as H-beam (also known as wide flange steel) and T-shaped steel and pressed steel plates to adapt to the needs of large-span structures and super high-rise buildings.
In addition, there is a light steel structure system without thermal bridge. The building itself is not energy-saving, and this technology solves the hot and cold bridge problem of the building with clever special connections; the small truss structure makes the cables and water and sewage pipes cross from the wall, and the construction and decoration are convenient.
Characteristics of steel structure
The structure made mainly of steel is one of the main types of building structures. Steel is characterized by high strength, light weight and high stiffness, so it is especially suitable for the construction of large span, super high and super heavy buildings.
Material homogeneity and isotropic good, is the ideal elastomer, the most consistent with the basic assumptions of general engineering mechanics; material plasticity, toughness, can have a large deformation, can well withstand the dynamic load; construction period is short; its high degree of industrialization, can be mechanized to a high degree of professional production; processing precision, high efficiency, good confinement, so can be used to build gas tanks, oil tanks and transformers, etc..
Its disadvantage is that the fire resistance and corrosion resistance is poor. It is mainly used for the load-bearing skeleton of heavy workshops, plant structures subject to dynamic loads, plate and shell structures, towering TV towers and mast structures, large-span structures such as bridges and warehouses, high-rise and super high-rise buildings, etc.
Steel structure should be studied in the future high-strength steel, greatly improving its yield point strength; in addition to rolling new varieties of steel sections, such as H-beam (also known as wide flange steel) and T-shaped steel and pressed steel plates to adapt to the needs of large-span structures and super high-rise buildings.
Steel structures are also divided into light and heavy steel. There is no unified standard for determining them, and many experienced designers or project managers often cannot fully understand them, so they can be considered and judged by some data.
- 1. Steel structure is lighter in weight
- 2. High reliability of steel structure work
- 3. Good vibration (shock) resistance and impact resistance of steel materials
- 4. High degree of industrialization of steel structure manufacturing
- 5. The steel structure can be assembled accurately and quickly
- 6. Large indoor space of steel structure
- 7. Easy to make sealed structure
- 8. Steel structure is easy to corrode
- 9. Steel structure has poor fire resistance
- 10. Steel structure can be recycled
- 11. Steel structure has shorter construction period
Development history of steel structure
Although China had outstanding achievements in iron structures in the early days, it stayed at the level of iron buildings for a long time. It was not until the end of the 19th century that China began to adopt modern steel structures. After the founding of New China, the application of steel structures has developed greatly, both in terms of quantity and quality, far exceeding the past. The floor of light steel structure is composed of cold-formed thin-walled steel frame or combined beam, floor OSB structural slab, support and connection parts. The materials used are oriented strand board, cement fiber board, and plywood. Loads of 316 to 365 kg per square meter can be carried on these lightweight floors.
The number of steel buildings marks the economic strength and economic development of a country or a region. After 2000, China’s national economy has grown significantly, and the national strength has increased significantly, and the steel production has become a world power, so that the “active and reasonable use of steel” has been proposed in the construction, which has thrown off the shackle of “restricting the use of steel”, and the steel structure buildings have gradually increased in economically developed The number of steel buildings in economically developed regions has gradually increased. Especially around 2008, under the impetus of the Olympic Games, there was a boom of steel structure buildings, and the strong market demand pushed the rapid development of steel structure buildings, and a large number of steel structure stadiums, airports, stations and high-rise buildings were built, among which, some steel structure buildings have world-class production and installation technology, such as the national stadium of the Olympic Games and other buildings.
After the Olympic Games, steel structure buildings have been popularized and developed continuously, and steel structures are widely used in buildings, railroads, bridges and residences, etc. There are tens of thousands of steel structure enterprises of various scales, and the world’s advanced steel structure processing equipment is basically complete, such as multi-head multi-dimensional drilling machines, steel pipe multi-dimensional coherent line cutting machines, corrugated plate automatic welding machine tools, etc. And now hundreds of steel structure enterprises have the world advanced level of processing and production, such as steel structure making special and first-class enterprises. In recent years, the steel production is as much as 600 million tons per year, and the steel varieties can fully meet the construction needs. Steel structure design specifications, steel structure material standards, steel structure engineering construction quality acceptance specifications, and various professional specifications and enterprise work methods are basically complete.
Steel structure downstream industries have a greater traction and driving effect on the development of the steel structure industry, and their demand changes directly determine the future development of the industry.
1. Upstream industry of steel structure is the raw material supply industry such as steel
The steel industry is the material basis for the development of the steel structure industry, and the technological progress of the steel industry has created favorable conditions for the application of steel structure. Some large enterprises in the domestic steel industry have started the research and development of steel varieties and technologies for building structures, and have successively developed high-strength steel and steel for fire resistance, weather resistance, seawater resistance, laminar tear resistance and low temperature resistance, as well as H-beams, high-performance color coated steel sheets and cold-formed steel, which have laid a good application foundation for the development of the steel structure industry.
2. Upstream and downstream influence on this industry
The upstream of steel structure is mainly the steel industry, and the price fluctuation of steel products directly affects the procurement cost of this industry. On the whole, the upstream industry is basically a competitive industry, producing various steel plates, steel pipes, steel sections and other steel used in steel structures, of which H-beams and medium thick plates are the most commonly used products in steel construction. Industry insight research data 2011 crude steel production reached 696 million tons, production is relatively saturated, the raw materials required for the production of steel structures can get a stable supply.
Downstream industries have a greater traction and driving effect on the development of the steel structure industry, and their changes in demand directly determine the future development of the industry. With its comprehensive advantages of high strength, light weight, good seismic performance, high industrialization, short construction cycle, high plasticity, energy saving and environmental protection, steel structure has been widely used in industrial plants, municipal infrastructure construction, cultural, educational and sports construction, electric power, bridges, offshore oil engineering, aerospace and other industries, and the market space is gradually expanding. In addition, once the residential steel structure market makes a breakthrough and gradually replaces the traditional building form into the residential construction field, the steel structure industry will lead to explosive growth.
Applications of steel structure
It is composed of roof frame, structural OSB panels, waterproof layer, light roofing tiles (metal or asphalt shingles) and related connections. The appearance of roofing with Maitreya Construction’s light steel structure can have various combinations. There are also a variety of materials. With waterproofing as a technology guaranteed, the appearance has many options to choose from.
The walls of a light steel structure house are mainly composed of wall frame columns, wall top beams, wall bottom beams, wall supports, wall panels and connectors. Architectural light steel structure residential generally uses the inner horizontal wall as the load-bearing wall of the structure, and the wall columns are C-shaped light steel members, whose wall thickness depends on the load applied, usually 0.84 to 2 mm, and the wall column spacing is generally 400 to 600 mm. This wall structure arrangement of architectural light steel structure residential can effectively bear and reliably transfer vertical loads, and is convenient to arrange.
Classification of steel structure
The steel structure industry is usually divided into five major subcategories: light steel structure, high-rise steel structure, residential steel structure, space steel structure and bridge steel structure.
Heavy steel structure
- 1. Lifting weight of plant truss: ≥25 tons.
- 2. Steel consumption per square meter: ≥50KG/㎡.
Light steel structure
It refers to the light steel structure made of round steel and angles less than L45×4 and L56×36×4. National norms and technical documents do not have a heavy steel.
The Code for Design of Steel Structures GBJ17-88 has been abolished since December 1, 2003, and the Code for Design of Steel Structures GB50017-2017 is now in effect.
Precision steel structure
The processing and production of precision steel structure is between ordinary structural parts (with low processing requirements) and precision machining (with fine processing requirements), using welding or bolting connections, so it belongs to the category of steel structure. It is usually used for structures with special use requirements, higher precision requirements and higher connection requirements, such as crane welded beams, equipment towers, large equipment supports, various tanks such as oil tanks, gas storage tanks, etc.
Equipment steel structure
Equipment steel structure refers to the steel structure part of large equipment, according to the experience of technical personnel, the following structures should be classified as equipment steel structure: the tower steel structure of the bridge machine, crane lifting beam, crane body, large equipment bracket, etc., belongs to one of the precision steel structures with high requirements for precision, material, connection, etc. For complete sets of equipment, it is the most important force-bearing part and plays a structural role in function.
Fabrication of equipment steel structure
The processing and production of equipment steel structure is similar to precision steel structure, between ordinary structural parts (not high processing requirements) and precision mechanical processing (requiring finer processing), using welding or bolting connection method.
Meanwhile, the main types of steel structure are: row frame structure for plant, frame structure for multi-story building, frame and shear wall structure, frame and cylinder structure, flat grid structure and curved top grid structure for large space, etc. The building function is different, the structural form used is also different. Steel structure design should implement the national technical specifications to achieve advanced technology, economic and reasonable, safe and practical, and ensure quality. Therefore, we should pay attention to the following requirements when designing and producing the structure:
- 1. First of all, according to the functional requirements of the building, adopt the corresponding reasonable structural system. To achieve advanced technology, novel structure, to achieve the unity of architecture and structure.
- 2. Steel structures (except containers) are mainly made of rods, so the size of the rods is modulized and standardized as much as possible to facilitate mechanized manufacturing, transportation, installation and increase productivity.
- 3. The use of high-efficiency steel with high economic indicators.
- 4. The nodes of the steel structure are crucial, and appropriate connection methods should be used to make the node design consistent with the simplified model of structural calculation. In the past, the majority of structural damage occurred at the nodes, so the nodes should be carefully designed and carefully constructed. Use advanced and reliable connection methods.
Requirements of equipment steel structure
Equipment steel structures usually have special requirements or higher requirements in the following areas.
- Structural parts: material, surface roughness, tolerance, surface treatment, straightness (or curvature).
- Connection: hole deviation, bolt grade; welding method, welding standard, welding material; air tightness, requirement for non-destructive testing, liquid penetration testing, etc.
- Overall structure: verticality, levelness, etc.
- Packaging: packaging materials, packaging methods.
- Storage: ambient temperature, ambient humidity.
- Transportation: loading and unloading, placement in vehicles, placement in containers, etc.
Material requirements of steel structure
Steel structure in the process of use will be subject to various forms of action (load, uneven settlement of the foundation, temperature, etc.), so the requirements of steel should have good mechanical properties (strength, plasticity, toughness) and processing properties (hot and cold processing and welding properties) to ensure the safety and reliability of the structure. There are many types of steel, in line with the requirements of steel structures are only a few, such as carbon steel in Q235, low alloy steel in l6Mn, for high-strength bolts of 20 manganese vanadium steel (20MnV), etc.
Steel strength index by the elastic limit σe, yield limit σy, and tensile limit σu, designed on the basis of the yield strength of steel, high yield strength can reduce the weight of the structure, save steel, reduce the cost. Tensile strength σu is the maximum stress that the steel can withstand before damage, the structure at this time because of plastic deformation and lost performance, but the structure deformation is large and does not collapse, to meet the requirements of the structure to resist rare earthquakes. ‘σu/σy value of the size of the steel can be seen as a parameter of the strength reserve.
Plasticity of steel generally refers to the stress exceeds the yield point, with significant plastic deformation without fracture of the nature. The main indicator of the plastic deformation capacity of steel is the elongation δ and section shrinkage ψ.
3. Cold bending properties
Cold bending properties of steel is a measure of steel bending process at room temperature to produce plastic deformation of the resistance to cracking. Cold bending properties of steel is used to test the cold bending experiment to test the steel bending deformation performance of the specified degree of bending.
4. Impact toughness
Impact toughness of steel refers to the steel under impact loading, fracture process to absorb mechanical kinetic energy of a capacity, is a measure of steel resistance to impact loading, may be due to low temperature, stress concentration, and lead to brittle fracture of a mechanical property. Generally through the impact test of standard specimens to obtain the impact toughness of steel indicators.
5. Welding properties
The welding performance of steel refers to the welding process under – certain conditions, to obtain good performance of the welded joint. Welding performance can be divided into welding performance and welding performance in the welding process on the use of two kinds of performance. Welding performance in the welding process refers to the sensitivity of the weld and the metal near the weld not to produce thermal cracking or cooling not to produce cooling shrinkage cracking during the welding process. Good welding performance means that under certain welding process conditions, both the weld metal and the nearby base material do not produce cracks. Welding performance on the use of performance refers to the impact toughness and heat-affected zone ductility properties at the weld, the mechanical properties of the weld and heat-affected zone steel is not less than the mechanical properties of the parent material. China uses the welding process of welding performance test method, but also the use of the nature of the use of welding performance test method.
Many factors affect the durability of steel.
- The poor corrosion resistance of steel, must take protective measures to prevent steel corrosion and rust. Protective measures include: regular maintenance of steel paint, the use of galvanized steel, in the presence of acid, alkali, salt and other strong corrosive media, the use of special protective measures, such as marine platform structure using “anodic protection” measures to prevent corrosion of the conduit frame, fixed on the conduit frame zinc ingots, seawater electrolytes will automatically first corrode the zinc ingots, so as to achieve the protection of steel The seawater electrolyte will automatically corrode the zinc ingots first, thus achieving the function of protecting the steel conduit frame.
- Since the strength of steel under high temperature and long term loading decreases more than the short term strength, the lasting strength of steel under long term high temperature should be measured. Steel over time will automatically harden, become brittle, that is, the “aging” phenomenon. For low-temperature loading of steel to test its impact toughness.
Advantages and Disadvantages of Steel Structures
Advantages of Steel Structures
Compared with other constructions, steel structure has advantages in use, design, construction and comprehensive economy, low cost and can be moved at any time.
- Steel structure houses can better meet the requirements of flexible separation of large openings on the building than traditional buildings, and can improve the area utilization rate by reducing the cross-sectional area of columns and using light weight wall panels, and the effective usable area inside the house is increased by about 6%.
- Good energy-saving effect, the wall adopts light energy-saving standardized C-shaped steel, square steel, sandwich panel, good heat insulation performance, good seismic degree. Energy-saving 50%.
- The steel structure system can be used for residential buildings can give full play to the good ductility of steel structure, plastic deformation capacity, has excellent seismic and wind resistance performance, greatly improving the safety and reliability of residential. Especially in the case of earthquake and typhoon disaster, steel structure can avoid the collapse of the building damage.
- The total weight of the building is light. The self-weight of the steel structure residential system is light, about half of that of the concrete structure, which can greatly reduce the foundation cost.
- The construction speed is fast, and the construction period is at least one-third shorter than that of traditional housing system, a building of 1000 square meters only takes 20 days and five workers to complete.
- The environmental protection effect is good. Steel structure housing construction greatly reduces the amount of sand, stone and ash, and the materials used are mainly green, 100% recycled or degraded materials. When the building is dismantled, most of the materials can be reused or degraded and will not cause garbage.
- With flexibility and abundance. Large openings are designed, and the space inside the house can be divided in multiple schemes, which can meet different needs of users.
- In line with the requirements of residential industrialization and sustainable development. Steel structure is suitable for mass production in factories, high degree of industrialization, and can collect advanced finished products such as energy saving, waterproof, heat insulation, doors and windows in one, complete set of applications, integrate design, production and construction, and improve the level of construction industry.
- Compared with ordinary reinforced concrete structure, steel structure is superior in its homogeneity, high strength, fast construction, good seismic resistance and high recovery rate. Steel has many times higher strength and elastic modulus than masonry and concrete, so the mass of steel members is light under the same load condition. From the aspect of being destroyed, the steel structure is in advance a large deformation foreshadowing, belongs to the ductile damage structure, can be found in advance of the danger, so as to avoid.
Steel structure plant has the advantages of overall lightness, saving foundation, less material, low cost, short construction period, large span, safe and reliable, beautiful shape, stable structure, etc. Steel structure workshop is widely used in large-span industrial plants, warehouses, cold storage, high-rise buildings, office buildings, multi-storey parking lots and residential buildings and other construction industries.
Disadvantages of steel structure
Quality problems in steel structure engineering
The complexity of construction quality problems in steel structure projects is mainly manifested in the wide range of factors that trigger quality problems and the complexity of the causes of quality problems, even for quality problems of the same nature, the causes are sometimes different, thus increasing the complexity of analysis, judgment and treatment of quality problems. For example, welding cracks, which can occur both in the weld metal, but also in the parent material heat influence, both on the surface of the weld, but also inside the weld; crack direction can be parallel to the weld channel, but also perpendicular to the weld channel, the crack may be both cold cracks, but also may be hot cracks; the causes are also improper selection of welding materials and welding preheating or post-heating improperly.
The seriousness of construction quality problems of steel structure projects is manifested as follows: in general, it affects the smooth progress of construction, causing delays and cost increase, and in serious cases, the building collapses, causing personal injury or death, property damage and causing adverse social impact.
Steel structure engineering construction quality problems will also continue to develop and change with external changes and time, quality defects gradually reflected. For example, the weld of the steel member due to changes in stress, so that the original crack-free weld cracks: due to the role of hydrogen activity in the weld after welding can produce delayed cracks. Another example is that if the member is overloaded for a long time, the steel member should be produced under the arch bending deformation, producing hidden problems.
(iv) Frequent occurrence
As China’s modern buildings are mainly concrete structures, the managers and technicians engaged in building construction are relatively rusty in the production and construction techniques of steel structures, and the specific construction personnel mainly civilian workers do not know the scientific construction methods of steel structure engineering, which leads to accidents in the construction process from time to time.
Steel structure is easy to corrode
Steel structure must pay attention to protection, especially thin-walled members, therefore, buildings in a strong corrosive medium should not use steel structures. Steel structures should be thoroughly descaled before painting, and the quality of paint and coating thickness should meet the requirements of relevant specifications. The structure should be designed to avoid moisture and rain leakage, and the structure should be constructed to avoid the existence of dead ends for inspection and maintenance. Newly built steel structures generally need to be repainted at certain intervals, and the maintenance cost is high. At home and abroad are developing a variety of high-performance coatings and weathering steel that is not easy to rust, the problem of poor corrosion resistance of steel structures is expected to be solved.
Steel structure heat resistance is not fire resistance
When the temperature exceeds 250 ℃, the material changes significantly, not only gradually reduce the strength, but also occur blue brittle and creep phenomenon. Temperature up to 600 ℃, the steel into the plastic state can not continue to carry, steel strength is almost zero.
Steel structure fracture
Steel structure at low temperatures and under certain conditions, brittle fracture may occur, as well as laminar tearing of thick plates, should draw the special attention of designers.
Steel is more expensive
The use of steel structure will slightly increase the cost of the structure, which often affects the choice of the owner. In fact, the cost of the superstructure accounts for a very small proportion of the total project investment, with an increase of about 10%. And in the case of high-rise buildings, for example, the increase is less than 2%. Obviously, the structure cost of a single factor should not be used as the basis for deciding what materials to use. If all factors are taken into account, especially the advantages of the construction period, the steel structure will be increasingly important.
Technical measures for reinforcement of steel structure
Steel structure is also damaged at times, we have to find out instantly to solve the problem immediately, the main factors of steel structure damage are.
- 1) Insufficient structural load-bearing capacity due to load changes, over-service, code and regulation changes.
- 2) Deformation, distortion, disability, depression, etc. caused by various accidents, resulting in weakening of the cross-section of the member, warping of the rod, cracking of the connection, etc.
- 3) Deformation, cracking and warping of members or connections caused by temperature difference.
- 4) Corrosion due to erosion of chemical substances and electrochemical corrosion resulting in the weakening of the cross-section of the steel structure members.
- (5) Other including design, production, construction errors and service period in the use and operation of irregularities.
There are three main technical measures for reinforcement of steel structures.
- 1) section reinforcement method: in the local or along the full length of the member to steel reinforcement, connected to the whole so that the common force.
- 2) Change the calculation sketch: add additional supports, adjust the load distribution, reduce the internal force level, force displacement on the super-static structural bearings, and reduce the stress peak.
- 3) Prestressed cable method: using high-strength cables to strengthen structural weak links or improve the overall structural bearing capacity, stiffness and stability.
Construction technology of steel structure
Preparation work before steel structure installation and welding
The test steel includes Q345GJC-Z15 (wall thickness 70mm), Q345GJC-Z15 (wall thickness 40mm), Q345C (flange thickness 28mm), and the welding positions are column-column transverse welding, column-beam flat welding (including truss beam upper and lower flange flat welding), and T-angle vertical welding. The bevel form and size are according to the design requirements. After passing the post-welding appearance and ultrasonic inspection, the samples were taken for mechanical and physical tests.
The test results of the tensile strength of the joint reached the standard value of the tensile strength of the parent material, the joint bending 180 ° without cracks. The technical conditions of the welding materials and welding equipment used should be in line with national standards and excellent performance. Slag cleaning, air planing, welding rod drying and insulation devices should be complete and effective.
Manual arc welding and CO2 gas welding consumables and equipment
- (1) The welding rod should be dried in a high-temperature drying box, the number of times the drying of welding rod shall not exceed twice.
- (2) Welding wire packaging should be intact, such as damage and lead to wire pollution or bending, disorder should be partially abandoned.
- (3) CO2 gas purity should be not less than 99.9% (volume ratio), water content should be less than 0.05% (weight ratio), and the bottle should be stopped when the high pressure is lower than 1MPa.
- (4) The voltage of the welding machine should be normal, the ground wire should be pressed firmly and contacted reliably, the cable and welding pliers should not be damaged, the wire feeder should be able to feed the wire evenly, and the gas pipe should have no air leakage or blockage.
The installation of welding procedures and general provisions
The general order of welding is: pre-welding inspection → preheating and rust removal → welding pad and arc guide plate → welding → inspection
- 1. Check the bevel angle, blunt edge, gap and the amount of misalignment before welding, the rust spot, oil, iron oxide etc. in the bevel and on both sides should be cleared.
- 2. Preheating. Use gas welding or special baking gun to evenly heat the base material within 100mm on each side of the bevel and its sides before welding, and measure the temperature with a surface thermometer to prevent the temperature from not meeting the requirements or local oxidation of the surface and preheat the temperature.
- 3. Re-check the preheating temperature, if the temperature is not enough, it should be reheated to make it meet the requirements.
- 4. Install the welding pad and lead arc plate, its surface cleanliness requirements and bevel surface, pad and base material should be tight, lead arc plate and base material welding should be solid.
- 5. Welding: the first layer of welding should seal the connection between the base material and the pad within the bevel, and then weld layer by layer until the bevel is filled, and after each weld, the welding slag and spatter must be removed, and welding defects should be ground and repaired in time.
- 6. An interface must be continuously welded, such as a last resort and stop welding in the middle, should be heat preservation slow cooling treatment, before welding again, should be re-heated according to the provisions.
- 7. In case of rain, snow days should stop welding, members of the weld around and above the wind, rain shelters, wind speed greater than 5m/s should stop welding. When the ambient temperature is lower than zero degrees, preheating and post-heating measures should be taken in accordance with the provisions of construction.
- 8. Carbon structural steel should be cooled to ambient temperature in the weld, low-alloy structural steel should be completed 24h later, the weld flaw detection inspection.
- 9. Welders and inspectors should fill out the operation record sheet carefully.
The welding sequence and process parameters of the canonical node
- (1) The upper and lower columns without trunnion side by two welders on both sides of the symmetrical welding to 1/3 of the plate thickness, cut off the trunnion.
- (2) Then two welders on both sides of the trunnion side are symmetrically welded to 1/3 of the plate thickness.
- (3) Then two welders will undertake the welding of two adjacent sides respectively.
- (4) The joints of the weld channel between each two layers should be staggered from each other, and the joints of the weld channel welded by the two welders should also pay attention to the staggering of each layer, and the interlayer temperature should be detected during the welding process.
- (5) welding process parameters.
CO2 gas welding: wire diameter Φ1.2mm, current 280 – 320A, welding speed 350 – 450mm/min.
Wire outreach length: about 20mm, gas flow 25 – 80L/min.
Voltage 29-34V, interlayer temperature 120-150℃.
Column – beam, beam – beam node
- (1) Weld the lower flange of the beam first, and keep the flange welding channel on both sides of the beam web to be welded symmetrically.
- (2) When the lower flange is finished, then weld the upper flange.
- (3) If the thickness of the flange is more than 30mm, the upper and lower flanges should be welded in rotation.
- (4) Welding process parameters.
CO2 gas welding: wire diameter φ1.2mm, current 280 – 360A, welding speed 300 – 500mm/min.
Wire outreach length of about 20mm, gas flow 20 – 80L/mm.
Voltage 30-38V, interlayer temperature 120-150℃.
The difference between heavy steel structure and light steel structure
There is really no unified standard for judging the structure as heavy steel and light steel structure, and many experienced designers or project managers often cannot fully understand, but we can take some data into consideration and judge.
- 1. The lifting weight of the crane of the factory: greater than or equal to 25 tons, can be considered as heavy steel structure.
- 2. The amount of steel used per square meter: greater than or equal to 50KG/㎡, can be considered as heavy steel structure.
- 3. Thickness of steel plate of main components: greater than or equal to 10MM, light steel structure is used less.
In addition, there are some reference values: such as the cost per square meter, maximum component weight, maximum span, structural form, eave height, the above can provide empirical data in determining whether the plant is heavy steel or light steel, of course, many buildings are light and heavy steel. But there are some we can say with more certainty is heavy steel: such as: petrochemical plant facilities, power plant plants, large-span stadiums, exhibition centers, high-rise or super high-rise steel structures.
In fact, the national code and technical documents do not say heavy steel, in order to distinguish the light housing steel structure, perhaps it is more appropriate to call the general steel structure as “ordinary steel”. Because the scope of ordinary steel structure is very wide, can include a variety of steel structures, regardless of load size, even including many elements of light steel structure, light housing steel structure technical regulations only for its “light” characteristics and provide some more specific content, and the scope is limited to single-story portal frame.
Light steel is also a relatively ambiguous term, generally can have two kinds of understanding. One is the current “Code for Design of Steel Structures” (GBJ17-88) in Chapter 11, “Light Steel Structures of Round Steel and Small Angles”, which refers to light steel structures made of round steel and angles smaller than L45*4 and L56*36*4.
It can be seen that the difference between light steel and heavy steel is not in the lightness of the structure itself, but in the lightness of the enclosure material, but in the concept of structural design is still the same.
Installation of steel structure
The prefabrication and assembly of steel members are carried out on the steel platform in accordance with the installation sequence and process requirements, to ensure the quality of welding production.
The spacing between the splicing joints of the flange plate and the splicing joints of the web should be more than 200㎜. The splicing length of flange plate should not be less than 2 times of plate width; the splicing width of web plate should not be less than 300㎜ and the length should not be less than 600㎜.
For the convenience of welding and to ensure the welding quality, try to group and weld the reinforcement plate, connection plate, pad plate and pick beam (beam) on the column and cross beam on the ground steel platform according to the size of the construction drawing.
In addition to the production and assembly of prefabricated steel members on the steel platform according to the construction drawings and specification requirements, the craftsmanship of on-site installation and changes in installation dimensions should also be considered.
Installation quality control of steel structure
- ① Before installation, the construction unit should check the product certificate of conformity, design documents and pre-assembly records of the members, and recheck the dimensions of the recorded members. The deformation and defects of the steel structure exceeding the allowable deviation shall be handled.
- Before installation, a detailed measurement and correction process shall be prepared, and the welding of thick steel plates shall be carried out before welding and installation to simulate the process test of the product structure and prepare the corresponding construction process. A certain degree of arching should be preset for the assembled roof frame.
- ② After the steel structure is lifted into position, the component positioning axis, elevation and other design requirements control points should be measured and marked, and the quality of the lifting butt joint should be checked before welding. Install temporary supports and steel cables to make the steel roof frame safe and stable in the construction process.
- ③ When the steel structure is installed, the construction unit shall submit the elevation size, welding and painting of each beam after lifting to the supervisor for acceptance respectively.
Installation points of steel structure
- (1) Friction coefficient: where F is the force measured by the anti-slip test that causes the initial slip of the test piece, nf is the number of friction surfaces, and is the sum of the measured values of the tightening pre-tension of the high-strength bolts corresponding to F.
- (2) Torque factor: where d is the nominal diameter of the high-strength bolt (mm), M is the applied torque value (N M), P is the bolt preload. 10.9 grade high-strength hexagonal bolt connection must ensure that the average value of the torque factor K is 0.110-0.150. The standard deviation should be less than or equal to 0.010.
- (3) the initial screwing torque: in order to reduce the impact of the deformation of the steel plate during the tightening of the bolt, the second tightening can be used to reduce the mutual impact between the successive tightening of the bolt. The first screwing of high-strength bolts for the first screwing, so that its axial force should reach 60% to 80% of the standard axial force.
- (4) Final torque: The final tightening torque of high-strength bolts is the final torque. Considering the loss of various pre-stress, the final torque is generally 5% to 10% larger than the torque value calculated theoretically according to the design pre-stress.
Source: China Steel Structure Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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