Design Analysis and Application of Large Span Closed Cylindrical Grid Structure
I. General Description of Large Span Spatial Structures
Large-span spatial structures are mostly used in spatial grid structures. The reticulated shell structure is a curved grid structure. It has the characteristics of simple structure of the rod structure and reasonable force of the thin shell structure. Its appearance is beautiful and the force performance is good. Good economy and convenient construction, it is a large-span spatial structure with broad development prospects. Cylindrical reticulated shell structure, as one of the reticulated shell structures, is the most widely used in the field of closed bulk cargo yards, coal storage, mining industry shed, etc. The construction technology is the basis for the realization of the design results of the large-span grid structure. The common construction methods of the large-span grid structure include the high-altitude bulk method, the divided (striped) block installation method, the high-altitude sliding method, and the overall lifting method.
II. Design of Large Span Enclosed Cylindrical Grid Structure
1. Dead load and live load
The dead load mainly includes the self-weight of the grid structure, purlins, roof panels and other overlying materials. Live loads mainly include: roof live load, snow load, wind load, temperature effect, and earthquake effect. The roof live load and snow load are directly taken according to the provisions in the load code. Large-span structures are most sensitive to wind load effects, and the current load codes in my country lack design data for this type of structure, which should be determined by wind tunnel tests in actual projects. The temperature effect should be calculated from the temperature at the time of installation, and the maximum positive temperature difference and negative temperature difference should be calculated. Seismic actions include horizontal and vertical seismic actions. In areas with a fortification intensity of 7 degrees, vertical seismic action calculations are not required for reticulated shell structures, but horizontal seismic actions must be calculated.
2. Structural geometric parameters
The geometric design of the large-span cylindrical grid structure mainly includes the ratio of rise to span, grid thickness and grid size. The design of the actual structure should be comprehensively considered from the aspects of economy and force performance, and the thickness and size of the grid should be optimized.
3. Support conditions and joint design
There are usually three ways to support the reticulated shell structure: upper chord, lower chord and upper and lower chords are supported together. Compared with the bottom chord support, the upper chord support reduces the peak internal force by 34%, and the internal force of the rods is evenly distributed. Therefore, the top chord support method is widely used in the large-span cylindrical grid structure. The design of the bearing nodes should be as close as possible to the actual boundary conditions. The fixed hinge bearing is generally used in the reticulated shell structure, and its force is reasonable, the calculation model is basically the same as the actual force, and the amount of steel is small. Large-span grid structures usually use bolted ball joints, which are characterized by only axial force in the rods, no bending moments, and fast construction speed. When working at high altitudes, the construction quality is easier to guarantee.
III. Construction Method
The construction method directly affects the quality, schedule and cost of the project. Commonly used construction methods for large-span grid structures include high-altitude bulk method, split (strip) block installation, high-altitude sliding method, and overall lifting method. The high-altitude bulk method requires a large amount of high-altitude operations and requires too much material to build the assembly platform; the grid structure unit after the division (strip) block installation method should have sufficient rigidity itself, otherwise temporary reinforcement should be adopted Measures: The high-altitude sliding method can reduce a large number of high-altitude operations and ensure the quality and safety of structural construction; the advantage of the overall lifting method is that it can ensure the quality of the nodes and the accuracy of assembly, but it has higher requirements for lifting equipment.
