This paper briefly introduces the structural system of high-rise and super-high-rise buildings, analyzes the main problems faced by localization in steel, design, construction and supervision through the investigation of steel structure localization of high-rise buildings in China, and puts forward some suggestions for the development of steel structure of high-rise buildings.
Keywords: high-level; General situation; Development; System; build
High-rise steel structure buildings have a history of 1 10 years abroad. 1883, the earliest high-rise steel structure building rose in Chicago, USA. After World War II, high-rise and super-high-rise buildings developed rapidly due to the rising land price and rapid population growth, as well as the improvement of the structural system of high-rise and super-high-rise buildings, the development of computing technology and the continuous improvement of construction technology.
First, the application of steel structure in architecture
1 Layout and structural selection
The steel structure is suitable for the building plane with regular and symmetrical layout and less concave-convex changes, but not for the residential plane with many staggered axes, large distance between centroid and centroid, and easy to produce large torsion.
The design of steel structure residence needs to control the horizontal displacement under wind load and earthquake load, so it is very important to consider the lateral force resisting structure. In the structural design of residential buildings, the walls of stairwells and elevators are often designed to resist lateral forces. If the displacement cannot be controlled within the allowable range, the partition walls between units or some walls (immobile walls) in kitchens and bathrooms can also be used as lateral force resisting structures.
2 Discussion on deformation limit value
The lateral force resisting structure can be steel structure or reinforced concrete structure. When the steel truss is used as a lateral force resisting structure to form a pure steel structure, the code stipulates that under the action of wind, the story displacement is 1/400 and the vertex displacement is1/500; Under the earthquake, the interlayer displacement is 1/250, and the vertex displacement is 1/300. Therefore, using steel truss as lateral force resisting structure may greatly improve the steel consumption index, thus increasing the cost.
If the overall stiffness of the structure is controlled according to the limit value of steel structure 1/300, the reinforced concrete shear wall has been destroyed when the steel structure participates in the work in the earthquake, which is not safe enough.
If the overall stiffness of the structure is controlled according to the limit value of reinforced concrete shear wall 1/800, the sections of steel beams and columns will increase greatly due to the increase of seismic force.
3. Determination of the number and height of floors
Any structural form has its scope of application and the best building height. Steel structure has unique advantages in high-rise and super-high-rise buildings. Because of the seismic fortification of high-rise residential buildings, although the cross section of beams and columns is much smaller than that of reinforced concrete beams and columns under the same conditions, the existence of beams and columns is still very embarrassing in ordinary people's rooms. In contrast, we think that steel structure has certain advantages when it is used in multi-storey and "small high-rise".
Determination of column network and selection of column section type
The determination of column network is generally based on the division of surface, combined with the position and section height of beam and the hidden way of steel beam. The column spacing of the outer wall is the key to determine the column network. If the height relationship between the steel beam along the external wall and the window epithelium of the external wall is properly handled, the column network will be basically determined.
The cross-section types of steel columns can be roughly divided into three types: circular tube columns, square tube (box) columns and H-shaped steel columns. Among them, the concrete filled steel tubular column is formed by pouring concrete in the column, which greatly improves the bearing capacity compared with the reinforced concrete column, so the steel consumption is less. In the joint construction method, the square chord structure is simple and reasonable. However, the upper and lower flanges of the pipe string must be provided with partitions to form straight-through joints, which increases the processing difficulty and thus increases the engineering cost. H-shaped steel columns form steel reinforced concrete columns when they are wrapped in reinforced concrete. The processing and construction of H-shaped steel columns are convenient, but the steel columns use more steel.
5 Connection structure of steel structure
The joint structure directly affects the steel consumption, so we concentrate on solving the joint practice of two parts in the pilot residence.
(1) Rooting position of column foot
The basement structure of the pilot project is considered as reinforced concrete frame-shear wall structure, and the column foot is located at the elevation of the basement roof, and the column foot is connected with the embedded steel plate of the roof through high-strength bolts. The reinforced concrete outer column of the first floor supermarket is considered as steel reinforced concrete frame-reinforced concrete shear wall structure, and more than two floors are considered as steel framed-reinforced concrete shear wall structure.
(2) The connection between steel beam of steel frame and reinforced concrete shear wall (core tube)
In order to ensure the safety and reliability of the pilot project, the simple connection mode of embedding steel plates in the shear wall was not adopted in the design. Instead, I-core columns are set from the column foot elevation at the end of the shear wall and the corner of the core tube, and steel trusses are used as the transverse connection between the core columns at the height of the steel beam to ensure that the working state of this part of the joints is consistent with the calculation assumptions.
6 structural system selection
(1) Frame system or frame support system can be used for floors below 5-6, and frame support system or frame-concrete shear wall (core tube) system can be used for floors above 6. Multi-storey houses mostly adopt double systems.
(2) Frame columns include H-shaped steel columns, concrete filled steel tubular columns and steel reinforced concrete columns, and the latter two are composite columns. In small and high stories, composite columns save more steel than H-beam columns.
(3) The ductility of shear wall is lower than that of steel support, and the seismic force with low ductility is greater than that with good ductility in large earthquakes. From the seismic performance, steel brace is superior to concrete shear wall.
(4) The steel frame-concrete shear wall system is a mixed structure, and the research on its seismic performance is not enough at present, and it has not been included in the seismic code. Although it is widely used now, we should choose it carefully. The core tube should be reinforced with small steel columns, which is also beneficial to installation. Second, the steel structure production and installation
1, Installation of steel column
Steel column is the main vertical component that determines the height and total height of high-rise and super-high-rise buildings, and it must meet the acceptance standards of current codes when processing and manufacturing.
Super high-rise steel columns with a height of 100m are generally divided into 8 ~ 12 members. The shrinkage deformation of weld and the compression deformation caused by vertical load should be considered in the process of making steel columns, so the length of steel columns is not equal to the design length, even if it is only a few millimeters. Moreover, when the sections of the upper and lower steel columns are completely equal, they are not allowed to be interchanged. Each steel column is required to have a different number and be installed correctly.
The welding of stiffening plates in rectangular or square steel columns should be based on the requirements of current codes, and other forms such as opening holes in box plates and slot plug welding are not allowed.
There are usually two methods to control the elevation of steel columns:
(1) Make and install according to the relative elevation. The length error of steel column should not exceed 3mm, regardless of the shrinkage deformation of weld and the compression deformation caused by vertical load. As long as the total height of the building reaches the total allowable deviation of each column and the total compression deformation of steel columns, it is qualified. This kind of fabrication and installation is generally below 12 floor, and the height control is not very strict.
(2) according to the design elevation production and installation. Generally, for floors with high accuracy requirements above 12, the bottom elevation of the first steel column should be installed according to the civil elevation, and the cumulative total size of each steel column should meet the design requirements. The processing length of each steel column should be added with the shrinkage deformation at the joint of each column and the compression deformation caused by vertical load.
2. Fabrication and installation of frame beam
In order to ensure the good ductility, connection reliability and high accuracy of the connection area between the frame beam and the steel column, a cantilever beam (short support) is set at the position of the frame beam during factory manufacture, and the upper and lower flanges of the cantilever beam are connected with the steel column by through welds, and the web is made by fillet welds. The frame beam is connected with the cantilever beam (short bracket) of the steel column, the upper and lower flanges are connected by the full penetration weld of the lining plate (also the arc striking plate), and the webs are connected by high-strength bolts.
Because the allowable deviation of reinforced concrete construction is far greater than the precision requirement of steel structure, when the frame beam is connected with reinforced concrete shear wall or reinforced concrete tube wall, the connecting plate of the web plate can be opened with oval holes, and the length of the oval holes should not be greater than 2d0(d0 is the diameter of bolt holes), and the requirements of hole allowance should be guaranteed.
The cutting length of frame beam is not equal to the design length, so welding shrinkage deformation should be considered. Welding shrinkage deformation can be calculated by empirical formula and checked after actual machining to determine the exact length of sample turning and blanking.
The upper and lower flanges of the frame beam can be connected by high-strength bolts or welding. At present, most of them are connected by full penetration welding of liner. During construction, first weld the lower flange, then weld the upper flange, first spot weld one end, then weld the other end.
The webs are connected by high-strength bolts, so it is necessary to fully understand whether to use friction-type or pressure-bearing high-strength bolts in the design. The friction coefficient of friction type high strength bolts should be reasonable.
When using high-strength bolt group connection, the accuracy of hole position is very important. At present, template drilling and multi-axis CNC drilling are generally used to make holes. The former has low accuracy and the latter has high accuracy, so the latter should be given priority. When using formwork to make holes, the accuracy of formwork should be ensured to ensure the accuracy requirements of high-strength bolt assembly holes and field installation holes. If the hole position is partially deviated, only reaming with reamer is allowed. It is forbidden to use gas cutting to enlarge the hole. If gas cutting reaming is adopted, it should be treated as a major quality accident.