In the long-span steel structure, the more scattered the fulcrum of the steel structure, the stronger the constraint on the plane layout and spatial combination; on the contrary, the more concentrated the supporting points of the steel structure, the greater its flexibility.
Main structural forms of long span steel structure
a. Reticulated shell structure
Curved grid structure is called reticulated shell structure, which can be divided into single-layer and double-layer latticed shell. The main materials of reticulated shells are steel latticed shells, wood latticed shells, reinforced concrete latticed shells, etc. The main structural forms are spherical reticulated shell, hyperbolic reticulated shell, cylindrical reticulated shell, hyperbolic paraboloid reticulated shell and so on.
The reticulated shell structure has the main characteristics of both the rod system structure and the thin shell structure. The members are relatively simple and the stress is relatively reasonable. The structure has large rigidity and large span capacity. It can be assembled into large space with small components, and the small components and connection nodes can be prefabricated in the factory. It is easy to install, does not need large machinery and equipment, and has good comprehensive economic indicators. It has a rich and colorful shape, No matter it is the architectural plane or the space curved surface shape, may according to the creation request arbitrary choice.
b. Grid structure
The spatial structure connected by several members through nodes according to a certain rule of geometry is called grid structure, and the double-layer or multi-layer flat grid structure is called grid structure or grid structure. It is usually made of steel pipe or section steel. The main forms include: (1) grid structure composed of plane truss system; (2) grid structure composed of quadrangular cone; (3) grid structure composed of triangular cone; (4) grid structure composed of hexagonal cone.
The main characteristics of grid structure are space work, simple force transmission, light weight, high stiffness, good seismic performance, simple construction and installation, easy finalization and commercialization of grid members and nodes, and mass production in the factory, which is conducive to improving production efficiency. The plane layout of grid structure is flexible, and the roof is flat, which is conducive to ceiling, installation of pipes and equipment; The architectural shape of the grid is light, beautiful and generous, which is convenient for architectural treatment and decoration.
c. Membrane structure
Membrane structure, also known as fabric structure, is a new type of large-span spatial structure developed in the middle of the 20th century. The membrane surface is supported by the air pressure in the membrane, or the membrane is pre tensioned by the flexible steel cable or rigid supporting structure, so as to form a structural system with certain rigidity and covering large space. The main structure forms include air supporting membrane structure, tension membrane structure and skeleton supporting membrane structure.
The main characteristics of membrane structure are light weight, large span; free and rich architectural modeling; convenient construction; good economy and high safety; good light transmission and self bonding; poor durability.
d. Suspension structure
The suspension structure is a kind of structure system which takes the tension cable as the basic load-bearing component and arranges the cables according to certain rules. The suspension roof structure usually consists of three parts: suspension system, roof system and support system. The structural forms mainly include: one-way single-layer suspension structure, radial single-layer suspension structure, bidirectional single-layer suspension structure, unidirectional double-layer prestressed suspension structure, radial prestressed suspension structure, bidirectional double-layer prestressed suspension structure, prestressed cable network structure, etc.
The mechanical characteristics of the suspension structure are that only through the axial tension of the cable to resist the external load, there is no bending moment and shear effect in the structure, so the strength of the steel can be fully utilized; the suspension structure has various forms, flexible layout, and can adapt to a variety of building plans; because the self weight of the steel cable is very small, the roof structure is light, and the installation does not need large lifting equipment, However, compared with the conventional structure, the analysis and design theory of suspension structure is more complex, which limits its wide application.
e. Thin shell structure
Shell structures in construction engineering are mostly thin shell structures (the shell with T / R ≤ 1 / 20 is defined as thin shell). Thin shell structure can be divided into rotating shell and moving shell according to curved surface; according to construction materials, it can be divided into reinforced concrete thin shell, brick thin shell, steel thin shell and composite material thin shell.
The shell structure has a very good bearing performance and can bear a considerable load with a very small thickness. The strength and stiffness of the shell structure is mainly based on the rationality of its geometric shape. The material is directly pressed to replace the bending internal force, so as to give full play to the potential of the material. Therefore, the shell structure is a kind of economical and reasonable structure with high strength, high rigidity and material saving.
