The Application Of Steel Structure In High Rise Buildings
I. Steel Structure Materials and Types
There are three types of steel for high-rise building steel structure: ordinary carbon steel, ordinary low-alloy steel and heat-treated low-alloy steel. Ordinary carbon steel is still widely used. At present, Q355 and Q235 steel is the most commonly used in construction steel structure in China. Based on the importance of high-rise steel structure, cold bending test, impact toughness, yield point, tensile strength and elongation are listed as the five basic requirements of steel mechanical properties, and only those steels that are qualified for these five indicators can be used. For seismic high-rise steel structures, the yield ratio of steel should not be less than 1.2, and for steel structures with fortifications above 8 degrees, the yield ratio should not be less than 1.5. There is an obvious yield step, the elongation should not be less than 20%, and it should have good ductility and weldability. For steel columns, in order to prevent laminar tearing of thick plates, the content of sulfur and phosphorus needs to be further controlled and should not exceed 0.04%.
II. The Advantages of High Rise Building Steel Structure
1. Can reduce the area occupied by the structure in the building. For high-rise buildings with reinforced concrete structures built in the 30th to 40th floors in the earthquake zone, the size of the column section often depends on the limit of the axial compression ratio, reaching 1.8m×1.8m～2.0m×2.0m. The core tube is at the bottom. The wall thickness will reach 0.6m to 0.8m to meet the requirements of the lateral stiffness of the structure and the displacement between floors. The area of these two structures is about 7% of the floor area of the building. If a steel structure is adopted, the column cross-section will be greatly reduced. When the core tube adopts steel columns and steel supports, including the exterior decoration methods, its thickness is still much thinner than that of the tube wall, and the corresponding structural area is generally about 3% of the building area. It can be reduced by about 4% compared with the reinforced concrete structure.
2. It can reduce the weight of the structure and reduce the cost of the basic project. In general high-rise buildings with reinforced concrete frame-shear structure, when the outer wall adopts glass curtain wall or aluminum alloy curtain wall panel, and the inner wall adopts light weight partition wall, the total gravity load of the upper building structure including floor live load is about 15kN/m2 ～17kN/m2, of which the self-weight of beams, slabs, columns and shear walls is about 10kN/m2～12kN/m2. If a steel structure is used under the same conditions, the total gravity load is 10kN/m2～12kN/m2, and the structural dead weight of steel structure and concrete floor slab is about 5kN/m2～6kN/m2. It can be seen that the ratio of the structural deadweight of the two types of structures is 2:1, the ratio of the total gravity load is about 1.5:1, which is equivalent to the upper gravity load of a 30-storey steel structure high-rise building, and can be equivalent to a 20-storey reinforced concrete structure high-rise building. The large difference in load value determines that the foundation load will inevitably be reduced, and the difficulty of basic technology processing and the project cost will be greatly reduced.
3. The seismic performance is significantly better than that of reinforced concrete structures. Under the action of earthquake force, steel structure has good ductility. It can not only weaken the earthquake response, but also has the ability to resist the deformation of strong earthquake, because it is an ideal elastoplastic structure. However, the tensile and shear strength of concrete is low, and the ductility is also poor. The bearing capacity and deformation capacity of concrete members after cracking will decrease rapidly, and the seismic capacity is weaker than that of steel structures.
4. Ability to shorten the construction period. The construction feature of the steel structure is that the steel components are made in the factory and installed on-site. During installation, there is no need to set up a large number of scaffolding. At the same time, the profiled steel plate can be used as a permanent formwork for the concrete floor and no additional formwork is required. The construction of the concrete floor can be crossed with the installation of the steel structure. Practice has proved that the steel structure construction speed is 20%-30% faster than the reinforced concrete structure, the corresponding construction period will be greatly shortened, and obvious economic benefits will be obtained.
5. The cost of steel structure engineering has dropped significantly. Studies have shown that the cost of the upper high-rise steel structure (excluding the foundation and basement structure) is generally 15% to 20% of the project cost (the total structure cost and building decoration, elevators, electromechanical equipment, etc.), while the general project cost is about It is 50% to 70% of the total project investment (including demolition, land purchase and municipal facility expansion costs, etc.), and the corresponding upper steel structure cost is about 8% to 15% of the total project investment. Therefore, the total project investment difference between steel structure and reinforced concrete structure is about 5% to 10%. At the same time, it also reduces the cost of the foundation due to the reduced structural weight, increases the building area and shortens the construction period, so as to achieve the purpose of improving the comprehensive benefits of the project.
III. The Installation of Steel Structure
1. The installation of high-rise steel structure shall be carried out in accordance with the installation sequence, mechanical selection, approach and classification of components, or inspection and acceptance of the foundation positioning axis, top elevation, and anchor bolt positioning dimensions. The requirements of the drawings and the approved construction organization design are carried out.
2. During installation, minimize the number of lifting operations at heights to improve the quality of structural installation; use special spreaders to prevent permanent deformation of components; large components (such as beams and columns) should be corrected immediately after installation. One section of the positioning axis should be directly drawn from the ground control axis to avoid error accumulation and ensure that the deviation of the entire column is within the allowable range. The installation of steel components and the construction of the concrete floor should be carried out successively; the construction load on the floor should be strictly limited; the installation, calibration, bolting and welding of the same unit are all completed and inspected before the installation of the next unit can be started.
3. Connection and fixation of steel structures. Welding process tests should be carried out on the main welding joints; high-strength bolts should be subjected to construction tests before use to calculate the average and deviation values of the retest torque coefficient, and determine the construction torque based on the average ; Bolt-welded mixed joints of high-rise steel structure beam-column connections should be constructed in the order of first tightening the high-strength bolts on the web and then welding the beam flange welds; studs should be tested before welding.
4. The installation and acceptance of high-rise steel structure projects should be carried out by a combination of phased acceptance and final completion acceptance. After the welding, bolting and concealment works are accepted, check the allowable deviation value in accordance with the regulations of the high-rise steel structure.
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