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Large-span space frame structure design

space frame roof design

1 Space Frame Introduction

Among the types of spatial structures, space frame structures are widely used, and are suitable for some large, medium, and small-span buildings. The space frame structure mainly includes single-layer, double-layer, and multi-layer types. Among them, the double-layer structure is more commonly used. If the span is large (greater than or equal to 100m), a 3-layer space frame can be used. Compared with some other space structures, the space frame structure has unique advantages, so its use range is very wide.

2 Choice of space frame structure

The space frame structure is a spatially hinged rod structure, and geometric deformation is not allowed. Therefore, when choosing a space frame structure, the geometric variability of the structure should be considered. Triangular and quadrangular pyramids are geometrically invariant elements commonly used in space frame structures. At present, many space frame structures at home and abroad use triangular pyramid elements and quadrilateral pyramid elements. There are many types of space frames, which should be combined with specific projects in the process of use, and then the structure type should be selected reasonably. In the process of selecting the type of space frame, it is necessary to comprehensively consider the plane size, load, shape, support method, and roof structure of the building, and follow the principles of economy and practicality. Under normal circumstances, several structural forms should be selected for scheme design, and then the schema comparison and selection should be carried out to finally determine the best scheme. In the process of optimizing the design, it is necessary to consider not only the amount of steel used but also comprehensive economic indicators, such as the cost difference between rods and joints, the installation cost of roofing materials and envelope structures, etc. From the point of view of material consumption, if the plane is close to a square, you can only place the quadrangular pyramid space frame at the opposite corners to save the use of materials; when the structural plane is close to a rectangle, you can choose the quadrangular pyramid space frame placed diagonally, and the four corners can be evacuated. Cone space frame or chessboard-shaped quadrangular pyramid space frame; if the plane is a circle or a polygon, you need to use a three-way space frame, an empty triangular pyramid space frame, and a triangular pyramid space frame.

3 Advantages of space frame structure

3.1 Good integrity and high rigidity

Each rod in the space frame structure is not only a force rod, but also a support rod, and work together with each other. Therefore, it has large spatial rigidity and good integrity, and can carry concentrated loads, asymmetric loads, and dynamic loads. Advantage.

3.2 Strong adaptability

The space frame structure can be adapted to the requirements of industrial plants and public buildings with different supporting conditions, and the shape of the building plane is not high. It is suitable for polygons, squares, circles, triangles, sectors, and various planes combined therefrom. The shape of the building can be used in both long-span roofs and small-span roofs. Facilities such as pipes, lamps, suspended ceilings, and maintenance horse paths can also be set in the internal space of the space frame. Regarding the large-span workshop, the setting of the suspended crane can be completed along the vertical and horizontal directions, which is better suited to the process requirements.

3.3 Good seismic performance

The space frame structure has a uniform texture, is lightweight, has very good ductility, can absorb a large amount of seismic energy, and has good overall stability. Therefore, its seismic performance is strong.

3.4 The degree of industrialization of production and installation is relatively high, and the construction period is short

The size and shape of a large number of nodes and rods in the space frame structure are consistent, which is convenient for mass production in industrialization, and the on-site assembly is relatively simple, which can improve the construction speed and shorten the construction period, thereby creating conditions for improving the economic benefits of the project.

3.5 The building is beautiful in appearance

The space frame structure has the advantages of a beautiful appearance, lightweight, strong decoration, and convenient construction. For example, the use of relatively large overhangs in public buildings can not only enrich the shape of the building but also ensure that the force of the space frame components is more reasonable. . The use of space frame roofs (four-point support leakage) in sports buildings can make the majesty and stiffness of sports buildings manifest. In addition, the exposed or directly exposed part of the specific space frame of the ball joint of the steel pipe member can show the regularity of the geometric figures, and finally, form a relatively unique structure with rhythmic beauty.

3.6 Simple design and calculation

At present, there are many general design programs and space frame structure analysis software in China, and some units are already using targeted software, which can directly complete the drawing of construction drawings. In terms of structural calculation, there are also many approximate calculation charts suitable for the decoupling design of different types of space frames. All these provide favorable conditions for the calculation and design of the space frame structure. In addition, due to the singleness of the nodes and members of the space frame, the number of structural construction drawings is also small, so the workload of engineering designers can be reduced.

4 The form of the space frame structure

Common space frame structures include the following forms: (1) two-way orthogonal inclined space frames and two-way orthogonal positive space frames, etc. composed of a plane frame system; Cone space frames, positive quadrangular pyramid space frames, oblique quadrangular pyramid space frames, chessboard-shaped quadrangular pyramid space frames and star quadrangular pyramid space frames; (3) Evacuated triangular pyramid space frames, triangular pyramid space frames composed of triangular pyramids frame and honeycomb triangular pyramid space frame, etc.

5 Drainage of space frame structure roof

5.1 space frame arching

The arching of the space frame is designed above the roof, mainly to keep the upper and lower chord members of the space frame parallel, and attention should be paid to raising the entire space frame in the middle of the span, and the height of the arch needs to be determined according to the roof drainage slope. This design method can Improve the seismic performance of the structure. However, it should be noted that if the camber angle is high, it will have a certain impact on the internal force of the rod.

5.2 The upper set of the small column of the winding node

Columns can be set at the top chord nodes of the space frame to form a drainage slope. As long as the height or arrangement of the small columns is changed, a double-slope, four-slope or another complex multi-slope drainage system can be formed. The structure of the small column is relatively simple, and it is a very commonly used method for finding slopes. However, if the span of the space frame is relatively large, the height of the small column will also increase, but the seismic performance of the slender small column is weak. Therefore, when the small column is used in the seismic zone, it is necessary to carry out stability inspection and calculation.

6 Node design of space frame structure

6.1 Use of Symmetry in Computation

The space frame structure is a high-order statically indeterminate system, but the interior of the members and the displacement of the nodes need to be controlled by the final load state. If the structural system itself and the loads it bears have symmetry, in order to reduce the computational workload, 1/2n of the entire space frame can be selected for analysis.

6.2 Network frame node structure The rationality of the node structure will have a certain impact on the work performance, project cost and installation quality of the network frame.

At present, steel plate joints and ball joints are more commonly used, and ball joints mainly include bolt ball joints and welded hollow ball joints. 1) Steel plate joints. The characteristics of steel plate joints include many parts, complex forces, and many welds. If the internal force of the chord is large, it cannot be connected with an external cover plate, and the force transmission can only be carried out on the basis of the gusset plate. This will make the internal force distribution of the gusset plate more complicated. In the welded steel plate joints, if the strength of the fillet welds is relatively poor, the connection design joints based on fillet welds and slot welds can be used to ensure that the centers of gravity of the intersecting members meet at one point. At the same time, it is necessary to ensure that the bars The center of the section of the member and the center of the connecting weld of the member are coincident to avoid eccentric force. 2) Weld the hollow ball node. Welded hollow spherical joints are widely used in various space frames of steel pipe members. The advantages include: the sphere has no directionality and can be connected with rods in any direction so that the steel pipe is perpendicular to the axis, the connection with the hollow ball node is easy to center, without eccentricity, and the node force is very clear. 3) Bolt ball joint. Bolt ball joints are small, lightweight, and very aesthetically pleasing. Each node can connect up to about 18 members. The welding workload at the nodes is less, the installation is very simple, and certain disassembly can be implemented. It can be used in all kinds of space frames, especially in space frames composed of quadrangular pyramids and triangular pyramids. However, this kind of joint still has some disadvantages: high price, complicated sphere processing, poor rust resistance, internal and external galvanizing, and the bolt ball joint belonging to the corresponding hinge.

7 Conclusion

In a word, the space frame structure is a relatively basic type of space structure, and its use range is very wide. With the continuous improvement and development of technology, it is believed that in the future, it will continue to develop in the direction of reducing the weight of the structure and increasing the span of the structure, further promoting the development of the construction industry.