Structural Design of Large-Span Space Pipe Truss

In recent years, the application of steel pipe structures in industrial and civil buildings has become increasingly widespread. Large-span stations, airports, stadiums, etc. mostly use steel pipe truss structures. In the design of the Daqing Jurassic Park indoor playground, the main building is. space truss structure with 128 meters x 112 meters.

1. Overview of the truss project

The single building of this project is octagonal, with a construction area of 13,475.74 square meters, a one-way vaulted roof, a length of 128m, a sag height of 12.8m, and a net height of the vault of 28.5m. The maximum span of the truss is 64 meters. The indoor landscape amusement facilities are complicated and the ground is undulating. The walls around the building are installed with scenery designed by American companies. The whole building has high requirements for beauty and space. Therefore, in addition to the columns around the whole building, only four columns are allowed in the middle to support the whole roof system. A long catwalk is arranged in the triangular truss of the roof, which is used as performance lighting and cable bridge, making reasonable use of the building space.

2. Introduction to Truss

2.1 The shape of the truss:

From the truss shape (ie, from the chord type), it can be divided into linear and curved tube truss structures. In order to meet the requirements for the beauty and function of the building, as well as the diversity of space modeling, the pipe truss structure is mostly made into various curved shapes to enrich the three-dimensional effect of the structure. When designing a curved pipe truss structure, sometimes in order to reduce the processing cost, the rod is still processed into a straight rod, and the curve is replaced by a broken line approximation. If the requirements are high, the pipe bending machine can be used to bend the steel pipe into a curved pipe. The construction effect is good, but the processing technology is required to be high.

2.2 Advantages of tube trusses

Because of its beautiful appearance, reasonable stress characteristics, and superior economy, the steel pipe structure has been widely used in modern industrial plants, gymnasiums, exhibition halls, venues, terminals, stations, hotels, and other buildings, such as Shanghai Steel pipe structures are used in large-scale projects such as the stadium, the new terminal building of the Capital Airport, the Guangzhou New Baiyun and Long Terminal Buildings, the Guangzhou International Convention and Exhibition Center, and the Shanghai New International Expo Center. The engineering practice shows that the steel pipe structure can not only meet the building requirements well, but also make the structure reach the performance indicators such as safety, applicability, and economy, and conform to the latest design concept of steel structure.

2.3 The members of the chord and web chord of this building are all-round steel pipes, so the advantages of the steel pipe section are mainly in the following aspects:

 (1) The tube wall of the round tube and the square tube is generally thin, and the radius of gyration of the section is large, so the compressive and torsional performance is good. The symmetrical section form makes the moment of inertia of the section the same for each axis, which is beneficial to the stable design of a single member. The closure of the section increases the torsional stiffness, and the closed section is also superior to the open section with the cantilevered plate for the local stability of the plate. In many occasions, architects are also willing to express their architectural intentions by using the simple appearance of steel pipes.

 (2) Among the profiles with the same cross-sectional area, the outer surface area of the steel pipe is the smallest, which makes the contact area between the steel pipe and the atmosphere the smallest. In addition, the steel pipe is often closed at both ends, and the interior will not rust, which greatly reduces the anti-corrosion and fire-proof coating. material consumption and painting effort. Moreover, the steel pipe structure is easier to clean and paint, so maintenance is more convenient.

(3) The hydrodynamic characteristics of the steel pipe section are good. When subjected to loads such as wind or water flow, the effect of the load on the steel tube structure is much lower than that of other cross-sectional structures.

(4) The steel pipe is convenient to process. With the development of multi-dimensional CNC cutting technology, the intersecting line cutting of steel pipes is no longer a problem, and many domestic steel structure processing manufacturers have mastered this technology.

Although in terms of material unit price, the price of steel pipe is higher than that of ordinary open-section steel, but the combination of the above advantages, the steel pipe structure is still one of the preferred basic structural forms among many structural forms.

3.The essentials of the structural design of this amusement park:

3.1 The building is 128m long and 112m wide, with a single-story, one-way curved roof and a vault height of 28.5m.

Due to the functional requirements of the building, except for the surrounding columns, there are only 4 columns in the middle to support the entire roof system. The column grids of this building are all square grids of 8mX8m. Considering factors such as building use requirements and economy, through multiple verifications and comparisons, the final roof adopts an inverted triangular space tube truss system, and the width and height of the trusses are both 4 meters. The east-west trusses are 32-64-32 meters, with a truss set at an interval of 16 meters, and the north-south brackets are 40-32-40 meters, with a distance of 64 meters. A truss is set at an interval of 16 meters between the two brackets, and the main truss and brackets intersect on the four columns of the atrium. The elevation of the two-way truss intersection is the same, the components are shared, and the final coordinated deformation and joint stress. The maximum lower chord of the main truss is Ф500×25, the upper chord is Ф351X16, and the two upper chords and the upper chord web form a plane truss. The roof purlins are made of rectangular tubes with a maximum span of 12m and a spacing of 2m. Welded to the top chord. The entire roof is provided with horizontal cross bracing to increase the in-plane rigidity of the roof structure, prevent out-of-plane instability of the roof truss, and coordinate structural deformation to reduce torsional deformation and lateral displacement of the structure.

3.2 The surrounding columns of the building are made of 1mX1m rectangular steel tubular concrete columns;

there are 4 concrete columns with a diameter of 2m in the middle. The concrete-filled steel tubular column adopts the pumping and jacking pouring method. It is advisable to add an appropriate amount of micro-expansion agent when pouring the concrete, the dosage should be controlled within 5%, and the grouting pressure should be controlled within 12MPa.

For rectangular concrete-filled steel tubular columns, the strength, stability, and deformation of the empty steel pipe shall be checked according to the load during the construction stage, and the axial compressive stress of the empty steel pipe during the construction stage shall not be greater than 60% of the design value of the steel compressive strength.

3.3 The structural calculation software is PMSAP software, considering the complexity of the force of the space structure,

The stress of all members is controlled within 0.8, and the displacement is based on the single-layer frame without bridge crane in the steel structure specification. control. The loads are all acting on the nodes, and the temperature loads are also considered. The maximum stress member of this building is the lower chord of the truss and bracket connected with the four central columns. After calculation, the section is Ф500X25. At the same time, the axial force of the 4 web rods in this position is relatively large, which is later increased to Ф325X16. After the calculation is completed, the overall modeling of the 3d3s space tube truss is used to review the calculation, and the above scheme is finally determined.

4. Key technical issues

4.1 The main truss, secondary truss, and bracket joints of this project are all the joints of pipes, which require high precision and are difficult to install.

It is necessary to study the technical problems such as production and processing technology, hoisting technology, and splicing of high-altitude tubular components to solve the problems of spatial correlation. The technical difficulties of loft cutting and splicing through the curved surface ensure the quality of production, processing, and installation.

4.2 For the pressure grouting of concrete-filled steel tubular columns, pay attention to the aggregate and water-cement ratio, the control of slump, and the control of pumping pressure, and strictly prevent the occurrence of steel plate swell or concrete hollow.

4.3 The hoisting and installation are difficult, and the overall stiffness of the truss and the strength at the hoisting point need to be checked, and the hoisting weight and turning radius of the crane must be strictly controlled.

During the whole process of fabrication, transportation, and installation, the stress of different working conditions must be analyzed, and the temporary buttresses and temporary reinforcement measures must be designed and optimized to ensure quality and safety.

The use of space steel tube trusses as the roof structure has many advantages, not only meeting the requirements of the large span of the amusement park but also as a structural system, it meets the development needs of the large-span space structure, creating a perfect combination of aesthetics and mechanics. design concept.