What is Steel Structure?
Steel Fabricated Structure Steel structure is generally composed of steel beams, steel columns, steel trusses and other components made of steel profiles and steel plates; each component or part is connected by welds, bolts or rivets
Some steel structures are also made up of steel strands, steel cables or cable bundles, and cast steel.
Featuresuniform textural structure of steel close to the isotropic homogeneous material, steel, and therefore the theoretical calculations more realistic force conditions; high strength steel, high modulus of elasticity; good ductility and toughness of steel, suitable for withstanding vibration and shock loads; The apparent density of steel to strength ratio is generally lower than that of concrete and wood, so the weight of the steel structure is light; the steel structure is easy to machine, high precision and easy to install
It is the most industrialized structure in engineering structure The construction is faster and the economic benefits of the investment can be put into play as soon as possible The sealing performance of the steel structure is good, but the corrosion resistance is poor and it is requires frequent maintenance; fire resistance is also poor
Scope of applicationSteel structures are often used in various engineering structures with long spans, high heights, large loads and large dynamic effects, such as load-bearing structures and crane beams of industrial plants, long-span roof structures (Figure 1 ), high-rise building frames, long-span bridges, crane structures, tower and mast structures, petrochemical equipment frames, offshore oil production platforms and work platforms, pipeline supports, hydraulic gates, etc.
; they are also commonly used in structures that can be assembled and dismantled, such as temporary exhibition halls, housing on site, concrete formwork, etc. Light steel structures are often used in various houses with small spans and light ceilings, automated warehouses for high-rise, etc. In addition, the vessel frame, furnace frame and large-diameter pipes are also usually made of steel
Figure 1 Steel Structure Roof of Xi’an Lintong Terracotta Warriors Exhibition Hall
History China is one of the first countries to build structures with iron
Sichuan province (Figure 2) has a clear span of 100 meters and a width of 2.7 meters and was built in the 45th year of Kangxi in the Qing dynasty (1706). In addition, there are many monumental buildings, such as the present Tower of East Iron of Guangxiao Temple in Guangzhou, built in the 10th year of Dabao of the Southern Han Dynasty (967) It has 7 floors and a height of 6.35 meters; There is also the West Iron Tower built in 963 Only 3 floors left; the iron tower of Yuquan Temple (1061) built in Dangyang county, Hubei province by the Song dynasty, the tower is 17.9 meters high with 13 stories (see color), and the iron tower is 9 stories built in the Iron Tower Temple in Jining City, Shandong Province (1105),
The iron tower of Yuquan Temple, the tallest existing cast iron tower in China, imitating a wooden pavilion, was built in 1061
In Western countries, the first bridge built entirely of cast iron appeared in Colebrookdale, England in 1779, with a span of 30.5 meters
At the end of the 18th century, with the rise of the Industrial Revolution, metallurgical technology and construction followed the development of a combination of wrought and raw iron structures. The rivet connection appeared in the 1920s and 1930s, and the processes Converter casting and flat furnace were successively invented in the 1950s and 1960s With the use of rolled profiles, the scope of application of steel structures continued to expand, and the structural system, span and height were relatively high Great development like the Eiffel Tower in Paris
Since the 20th century, the increase in varieties of steel, the improvement of manufacturing methods, and the development of calculation theory and design specifications have made steel structures more widely used in industrial and civil buildings and other engineering structures For example, the Sears Tower is currently the tallest high-rise building; the Humber Bridge in England is the largest steel bridge to date
After the founding of the People’s Republic of China in 1949, steel structures have been widely used in bridges, large-scale heavy-duty factories, large-scale public buildings and high-rise structures.
For example, Nanjing Yangtze River Bridge; Shanghai Boiler Factory’s heavy container workshop built in 1977, the main span is 36 meters, the height is 40 meters, and the crane capacity is 400/80 tons It is the largest plant in China; Beijing Capital International Airport hangar was built in 1983. The roof structure adopts steel truss with 72-meter span and 10-ton multi-pivot suspension crane; the roof structure of the Shanghai Gymnasium built in 1975 adopts a flat steel grid (see grid structure); the total height of the Shanghai Television Tower built in 1972 210 55 meters; Beijing Environmental Meteorological Tower,
The Empire State Building, built in 1931, has held a height record (378 meters, 102 stories) for 40 years
It comprehensively represents the level of construction science and technology in the 1930s It is located in New York City, USA
The largest steel structure hangar built in Beijing Capital International Airport
Grid structure: China’s aid to the large stadium of the Moroccan Sports Center (span of 100.8 meters)
The triangular lattice mast of the Beijing Environmental Meteorological Tower (Air Pollution Monitoring Tower), 325 meters high, is currently the tallest structure in China
Chongqing Yangtze River Bridge, the rigid-structure prestressed concrete bridge T-shaped with the largest span (174 meters) in China, completed in 1980
Structural design The strength and stability of all types of steel structures must be calculated and, if necessary, the stiffness and fatigue resistance must also be verified
The strength of the various stresses in the net section of structural steel members and their connections shall not exceed the corresponding design strength of the steel.
For elements that are subjected to static loading in bending, tension and compression, if they meet certain structural requirements, the development of plastic deformation of the section can be considered when calculating the resistance.
Stability Axial compression members, eccentric compression members, and bending members may lose overall stability, and components (webs and flanges, etc.)
) of these elements may also lose local stability The general stability of these components and the local stability of their components must be verified during design When necessary, the general stability of the entire structure must be verified
Stiffness The entire steel structure and each component have certain stiffness requirements.
The design must make it meet the stiffness requirements specified in the code, such as strain and slenderness ratio, etc. It must not exceed the maximum allowable value.
Fatigue resistanceFor steel structures or steel elements and their connections directly supporting repetitive dynamic loads (see load), when the number of cycles of stress changes is frequent, fatigue calculations should be made so that the stress range do not exceed the corresponding allowable
Steel structure steel should be based on the importance of the structure, load-bearing characteristics, connection method, working temperature and other different conditions, select the appropriate steel
The commonly used steels are ordinary low carbon steel and ordinary low alloy steel, and the carbon content should generally be less than 0.22%; otherwise, plasticity and weldability will be reduced For structures subjected to heavy loads, especially dynamic loads, and at low temperatures, No. 3 killed steel or manganese 16 steel, manganese 16 bridge steel, carbon vanadium steel are often used. manganese 15, etc.
Hot rolled steels include plate steel, angle steel, channel steel, I-beam, tube steel, square steel, round steel, etc.
(see hot-rolled steel) Cold-formed thin-walled steel is formed by cold-formed or cold-rolled steel strips or steel plates with a small thickness (usually 1 5-6 mm), which can be made into angle steel, crimped angle steel, ribbed steel, crimped channel steel, crimped edge Z-shaped steel, square tube, round tube, etc (see cold-formed steel)
The steel used in the steel structure must guarantee the tensile strength, elongation, yield strength and the limit content of sulfur and phosphorus, and the limit content of carbon must be guaranteed for the welded structure
For major structures and components that need to be cold formed, the cold bending test must be qualified; for important structures directly supporting dynamic loads, the corresponding impact toughness at normal temperature or low temperature must be ensured according to the calculated temperature of the structure
The yield point is generally considered as the limit value of steel strength calculation and is the main basis for determining the design strength of steel; the tensile strength indicates the strength reserve of the steel after yielding; and the elongation indicates the yield index of plastic steel
The cold bending test can reflect the ability of the steel to resist the specified bending deformation and can detect the defects of the internal structure of the steel. The impact toughness indicates the ability of the steel to resist brittle fracture under stress concentration and impact. ; temperature decreases, impact toughness decreases
Anti-corrosion: If the surface of the steel structure is not protected, it will rust under the action of the surrounding environment.
The rate of corrosion is related to temperature, humidity and the content of harmful substances in the surrounding environment. The most widely used anti-corrosion method is protection with paint, etc.; it can also be protected with a metallic coating such as galvanized; or it can be protected by chemical oxidation treatment such as phosphating The use of alloy steel containing copper, chromium, nickel and other elements can improve corrosion resistance
Flame retardantAlthough steel is non-combustible, it is not fire resistant
When the temperature exceeds 300°C, the yield strength, tensile strength and elastic modulus begin to decrease significantly and almost drop to zero when it reaches 600°C The common fire prevention method is to line concrete masonry or brick outside the steel structure, or spray a layer of cement grout containing vermiculite, asbestos or other materials on the surface of the component When the surface of the steel structure is exposed to radiant heat greater than 150°C during long time, it should be protected with a layer of thermal insulation
OutlookWith the development of production and science and technology, steel structures will also develop accordingly.
Production will place increasingly complex requirements on steel structures, requiring research and development of new structural forms and high-strength steel grades suitable for steel structures.
The application of electronic computers provides a means for the accurate calculation of steel structures and creates conditions for the application and optimal design of more complex structural systems (such as space structures); design calculation theories for steel structures and components, such as stability calculations (including plate
The load-carrying capacity of parts after buckling), plastic plate calculations, reliability analysis, and performance under dynamic loads will progress Profiled steel plates, have the advantages of light weight, reduced use of steel and fast installation, and have been developed in recent years.
The combined steel and concrete structure gives full play to the characteristics of the two materials, and the scope of application is gradually expanded In addition to the further development of high-strength bolt connection and welding, the steel structure connection will also have other connection methods The degree of industrialization of steel structure manufacturing will be further improved with the development of new technologies and more stringent requirements will be put on the standardization of steel structures