Several structural types of steel structures and conditions for their application

1、 Steel structures generally have structural methods such as frame, plan truss, spherical grid (shell), cable membrane, light steel structure, tower and mast.

1. Steel structure

2. Truss

H é ng frame (ji à) (truss): a structure formed by connecting the rods with screws on both sides. The truss consisting of metal rods generally has a triangular element plan or indoor space structure. The key of the truss rods is to bear the radial tensile resistance or working pressure, so the material strength can be flexibly used. When the span is large, raw materials can be saved compared with the solid web beam, and its own components can be relieved and the bending stiffness can be expanded.

The advantage of truss is that the key point of the member is to bear the tensile force or working pressure, which can make full use of the effectiveness of raw materials, save raw materials and alleviate the net weight of the structure. The common ones are steel truss, concrete structure truss, prefabricated concrete truss, wood truss, steel and wood truss, steel cement soil truss.

3. Spherical space truss

The interior space structure is formed by connecting multiple members according to certain grid diagram method and connecting points. The basic units that form the grid structure include triangular pyramid, triangular cube, truncated pyramid, etc. The basic units can be used to form the triangular, quadrilateral, hexagonal, annular or any other shape of the plan. It has the characteristics of indoor space bearing capacity, light weight, large flexural stiffness, good seismic ability, etc; It can be used for roof trusses of stadiums, cinemas, exhibition halls, waiting halls, stadium grandstands, hangars, two-layer column spherical grid structures and production workshop buildings. The main disadvantage is that there are a large number of rods in the connection point, and the fabrication and assembly are more complicated than those in the plan.

4. Chordal membrane

The cable membrane structure system started from the outdoor tents (housing buildings composed of support rods, ropes and furs) for human survival in ancient times. After the 1970s, the birth of membrane materials with high strength, moisture-proof, light transmittance, smooth surface, easy cleaning and aging resistance, coupled with the rapid development of scientific and rational engineering calculation, the cable membrane engineering building structure system has started again. Now, many of them have been used in commercial buildings in coastal tourism, expositions, literary and artistic styles, sports and other major regions.

5. Light steel structure

Light steel structure is a young and vigorous steel structure system, which has been widely used in general industrial and agricultural, commercial service and service-oriented engineering buildings, such as office buildings, single family villas, warehouses, sports venues, games and entertainment, vacation and tourism engineering buildings, and low and high rise residential and construction industries.

Light steel structure is also an ambiguous word, which can be generally understood in two ways. One is Chapter XI "Light steel structure with round steel and small angle steel" in the current standard "Steel Structure Planning Standard" (GBJ 17-88), which refers to the light steel structure made of round steel and angle iron lower than L45 * 4 and L56 * 36 * 4. It is mainly used to not recommend the use of concrete structure to produce small structures when building steel is in short supply, Most of the steel structure planning standards have been removed in this revision.

6. Tower mast structure

For structures with large relative height and small cross section, level load (especially wind load) is an important basis for structure customization. According to its structural method, it can be divided into independent vertical structure and guyed mast structure, so the towering structure is also called tower mast structure.

With the development of industrial production technology, various types of towering structures have emerged. In 1889, the Eiffel Tower was built for the Paris Expo in France, with an absolute height of 300 meters. After 1921, wireless communication antennas and television antennas were installed on the tower, with a total height of 321 meters.

2、 When selecting the structure model, attention should be paid to the characteristics of different structure methods.

In the plant, when there is a certain suspension load or large-scale moving load, it can be considered to give up the portal steel frame and use the spherical grid frame.

In areas with large snow load, the roof curve should be conducive to snow sliding (no snow load needs to be considered beyond 50 degrees of the broken line). For example, the dolomite warehouse shed in the chemical plant uses a three center circular shell, and nearly half of the total snow load is released compared with the sloping roof. Areas with large precipitation are similarly considered. When the engineering building allows, the layout of support points in the frame structure is more reasonable than that of the structure just connected with simple connection points.

For buildings with large span covered by flat roof, suspension bridge or cable membrane structure system with prefabricated members as the main body can be selected. In the steel structure planning of high-rise residential buildings, steel concrete is often used to form the structure. In high-rise residential buildings with high seismic fortification intensity or very irregular seismic fortification intensity, the method of adding frame tubes with poor seismic grade can not be selected simply for economic development. The nearby super large SRC column should be selected, and the key is the structural system relying on the structure. In China, more than half of such high-rise residential buildings are of the former type, which is not good for earthquake resistance.

The layout of the structure should be fully considered according to the system characteristics, load distribution characteristics and types. In general, it is required that the bending stiffness is symmetrical, the mechanical model is clear, and the influence degree of large load or moving load should be limited as far as possible, so that it can be transmitted to the basic by the most intuitive route. The division of the fire shadow lateral support in the early generation should be symmetrical, and its centroid should be close to the efficacy line of the lateral force (wind, earthquake) as far as possible, otherwise, attention should be paid to the distortion of the structure, The lateral resistance of the structure should be protected by multiple procedures. For example, for the support point structure, the column should be able to bear at least 1/4 of the total horizontal force independently,

The layout of frame beams in the floor plan of a building with a frame structure can sometimes adjust its load transmission direction to meet different needs. Generally, in order to reduce the cross section of the frame beam along the short direction, the main beam section will be added, reducing the floor height of the building, and sometimes the high-rise frame columns will also be unbearable. At this time, the frame beam support point on the short bearing beam can give up the frame beam to save the bearing beam and column.