Dapeng Town Industrial Park, Tongshan District, Xuzhou City, Jiangsu Province, China
Space structures have many forms, and the selection of their structures is a complex issue. In structural design, the factors affecting the selection of Space structures mainly include: building shape, building plane shape, span size, support conditions, load form and size, stiffness requirements, roof structure and materials, and grid manufacturing and installation methods.
Several important aspects to measure whether the selection is appropriate and reasonable are: technical and economic indicators of grid structure, construction technology level such as manufacturing and installation, and the required construction period.
The manufacturing method takes the nodes of the grid as an example. When the nodes are welded nodes, the cross truss system grid composed of plane truss systems is more convenient to manufacture than the space truss system grid composed of pyramids; the two-way orthogonal grid is more convenient than the three-way grid; the four-corner pyramid grid is more convenient than the triangular pyramid grid.
1.Installation method
When the installation method of the grid is to install in strips or blocks, or to use the high-altitude sliding method, rather than overall lifting or hoisting, it is more advantageous to use three types of orthogonal grids, such as two-way orthogonal grids, upright tetrahedral grids, and upright evacuated tetrahedral grids, than to use oblique grids. Because when the latter is hoisted in strips or blocks, temporary supports are often added due to insufficient rigidity or geometric variability, which is uneconomical.
2.Steel usage index
The steel usage index of the grid structure itself is an important index for measuring the selection of grids. When peripheral support is used and the plane is close to a square, the oblique tetrahedral grid and chessboard tetrahedral grid use less steel by comparing through the full stress optimization design method. Because the upper chord of these two types of grids is a compression member, its grid is small, the rod is short, and the stable bearing capacity of the compression rod is close to the section strength during the stability verification, and the material utilization rate is high; the lower chord is a tension member, its grid is large, the tension member is long, the number of nodes and rods is small, so the amount of steel used is saved. When the side length ratio of the same four-sided support plane size is greater than 1.5, due to the relationship between stress distribution, the orthogonal grid uses less steel than the oblique grid under the same conditions. The amount of steel used in some hollow pyramid grids is generally less than that of non-hollow pyramid grids, but the internal force of the rods of the hollow pyramid grid changes more than that of the non-hollow, and the requirements for the design of nodes and rods are high and relatively complex.
3.Span size
Generally, for grid structures, the large span is more than 60m, the medium span is 30~60m, and the small span is less than 30m. Comprehensive analysis of factors such as cost shows that the span size has little effect on the selection of grids. However, large-span grids are generally important buildings. At present, the grid structures composed of plane truss systems such as two-way orthogonal grids, two-way orthogonal oblique grids and three-way grids are more commonly used in my country. Because these types of large-span grids have rich design and construction experience and are more skilled. Three-way grids, triangular pyramid grids, and hexagonal pyramid grids are generally more complex in structure and use a large amount of steel, so they are rarely used in small and medium spans.
