Selection of space frame structure

Factors affecting the selection of space frame mainly include space frame production, installation method, steel index, span size, rigidity requirements, plane shape, support conditions, etc. The production of space frame is more convenient than that of quadrangular cone, if the nodes are welded.  

1.If the nodes are welded, the net rack composed of plane truss system, its production is more convenient than the net rack composed of quadrangular cone; two-way orthogonal net rack is more convenient than two-way diagonal net rack and three-way net rack; quadrangular cone net rack is more convenient than triangular cone net rack.  

2.When the installation method of the space frame is not used as a whole lift or hoisting, but the use of strip or block installation, or the use of high-altitude skidding method, the choice of two-way orthogonal orthogonal space frame, orthogonal orthogonal cone space frame, orthogonal orthogonal four-cone space frame, four-cone space frame and other three types of orthogonal orthogonal space frame than the choice of inclined to put the type of space frame is advantageous. Because the latter in the slitting or block lifting, often due to insufficient rigidity or children’s variability and to set up additional temporary support, which is not cost-effective.  

3. The space frame itself with steel index is a measure of the space frame selection of an important symbol. Such as peripheral support and plane close to the square space frame, through the full stress optimization design comparison, diagonally placed quadrangular cone space frame, checkerboard-shaped quadrangular cone space frame steel consumption is more provincial. Because of these two kinds of space frame of the upper chord space frame is small, the rod is short, compression rod stability calculation section folding reduction, material utilization rate is high; The lower chord space frame is large, the tensile rod is long, the number of nodes and rods is small, so the amount of steel is provincial. If the side length ratio is greater than 1.5, due to the distribution of internal forces, the orthogonal orthogonal space frame in the same conditions than the diagonal put class space frame of steel saving some. Some of the pumping angle cone space frame of the amount of steel is generally more than not pumping cone space frame to save; but pumping angle cone space frame rod internal force than not pumping when the magnitude of the change is large, on the node design and the selection of rod unfavorable.  

4.Calculation shows that the span size (for the space frame structure, more than 60m can be called big span, less than 30m can be called small span, 30~60m is medium span) has little influence on the selection of space frame. However, large-span frame is generally an important building. At present, in our country, the two-way orthogonal orthotropic space frame, two-way orthogonal diagonal space frame and three-way space frame and other kinds of planar truss system composed of space frame structure are used more often.Because the design and construction experience of these large-span space frame is rich and the technology is skillful, three-way space frame, triangular cone space frame and hexagonal cone space frame are generally more complicated in structure and use a large amount of steel, so it is better to be used in small and medium-sized spans.  

5. The stiffness of the space frame is much better than the plane roof frame, but a variety of space frame, whether it is the horizontal stiffness or vertical stiffness, the difference is not small. Such as diagonally placed quadrangular cone space frame, it is geometrically variable in itself, in the addition of edge members or a strong ring beam to ensure its geometric invariance. Generally speaking, the number of nodes and the number of rods is more network frame, such as triangular cone network frame, hexagonal cone network frame, three-way network frame, positive release quadrangular cone space frame, its stiffness is larger, on the contrary, such as diagonal release quadrangular cone network frame, tessellated quadrangular cone network frame, pumping triangular cone Ⅰ, Ⅱ type network frame, cellular triangular cone network frame, its number of nodes and rods is smaller, it is also smaller stiffness.  

6.The plane shape for the circular, hexagonal and polygonal polygonal frame, from the plane layout and architectural design, it is more appropriate to use three-way space frame, hexagonal cone space frame, triangular cone space frame, evacuated triangular cone Ⅰ, Ⅱ type space frame and honeycomb triangle cone space frame. Especially when the plane shape is positive hexagonal, the space frame of these kinds of space frame is regular. Rod type is less, the construction is convenient; if other types of racks are used, the space frame near the boundary is not regular, more chaotic, the rod type increases, the construction is inconvenient.  

7. Multi-point support space frame, the choice of orthogonal orthogonal put class space frame is more appropriate. Because of the multi-point support, this orthogonal orthogonal put class space frame force performance than inclined put class space frame is reasonable, deflection is also small, after the four-point support space frame calculations show that, in the case of the same conditions, two-way orthogonal orthogonal space frame and two-way orthogonal diagonal space frame of the maximum internal force ratio of about 5/7, the deflection ratio of about 6/7, and the diagonally placed type of space frame has to be equipped with additional edge bars for sealing the edge at the free boundary, increasing the number of rods and the amount of materials. The number of rods and material consumption are increased. It is also suitable to use orthogonal orthogonal type of space frame for the space frame with opening on one side of three sides of support. Peripheral support and multi-point support combined with the space frame, can be used orthogonal orthogonal put type space frame, can also choose oblique put type space frame, but generally should not be used in three-way space frame and triangular cone, hexagonal cone composed of the space frame.  

8.The span is not greater than 40m multi-storey building floors and spans not greater than 60m roof, can be used to replace the steel chord of the reinforced concrete plate combination of space frame; combination of space frame should be used to put the quadrangular cone combination of space frame, put the pumping quadrangular cone combination of space frame, two-way orthogonal orthogonal combination of space frame, diagonal put quadrangular cone combination of space frame and cellular shape triangle cone combination of space frame.  

In general, the space frame selection is a more complex problem, must be based on the principle of practical and economic, multi-program comprehensive analysis and comparison to determine. The above mentioned factors affecting the selection of the most important consideration should be given to the construction of the production and steel indicators of these two factors.