Shougang Jingtang Iron and Steel United Co., Ltd. pellet yard renovation and closure project is located in Caofeidian Industrial Zone, Hebei Province. In accordance with the design concepts of energy conservation, environmental protection and green production, the project realizes fully enclosed production management of materials and controls dust pollution through the construction of a new arched steel structure greenhouse above the open-air raw material plant in the plant area of Shougang Jingtang Iron and Steel United Co., Ltd. The main structure of the greenhouse adopts the tension chord arch truss structure system, the main cross-section of the round steel pipe truss is triangular, the cable is covered with semi-parallel steel wire bundle PE, and the bearing adopts spherical hinge bearing. The overall span of the project is 245 meters, the length is 650 meters, and the highest elevation is about 63.7 meters.
Fig.1 Caofeidian pellet yard stretched string arch truss closed greenhouse
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Cable structure system
1) The cable of the project adopts semi-parallel steel wire bundle steel cable, the steel wire is a low-relaxation hot-dip galvanized steel wire with a strength level of 1670MPa, and the steel cable adopts a cold-cast anchor and a double-layer sheath.
2) Because the steel truss span of the project is extra-large, and the structural volume is large, the vertical load and horizontal thrust borne by the arch truss are larger, based on the consideration of structural stability, construction safety, etc., the cable installation point distance is designed according to the super large cable distance of 191 meters, and the cable design range within 150 meters of the conventional large, medium-span prestressed steel truss structure is broken. See Figure 2~Figure 5.
The main components are shown in Table 1.
Fig.2. Location of the cable
Fig.3. Schematic diagram of the cable
Fig.4. Schematic diagram of the cable clamp
Figure 5 Schematic diagram of the cable installation node
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Cable structure construction
1) Calculation of cable stress value
Considering the characteristics of the truss structure and the characteristics of the truss slip construction process, in order to ensure the stability and operation safety of the truss structure during the construction process, the Midas Gen finite element simulation analysis technology (Fig. 6) was used in the early stage of construction to simulate and analyze the structural deformation and tension changes of the truss cable during the construction process, and the optimal tensile force value of the truss cable was determined.
Fig.6. Diagram of the tension design model of the cable
2) Erection of aerial work support system
In order to ensure the safety and convenience of truss work at height and the stability of truss slip tire, a multi-purpose support system with integrated synchronous sliding device was developed to ensure the installation and construction of extra-large span tension chord arch truss structure (Fig. 7). The support system integrates safety passages, aerial work platforms, synchronous sliding devices, cable installation platforms and other purposes. During cable construction, the 1.5-meter overhanging cantilever platform at the top of the support system (Fig. 8) can be used to carry out the high-altitude traction installation and in-situ tensioning operation of the cable body.
Fig.7. Schematic diagram of the multifunctional support system
Fig.8. Schematic diagram of the structure of the 1.5-meter overhanging platform
3) Cable installation at high altitude
The truss of the project is innovatively installed by using the two-way combined sliding construction technology, and after the truss structure is assembled on the support system, it is slid to the position of the 1.5-meter overhanging cantilever platform for the installation and construction of the cable. Adopt cable high-altitude traction installation technology, during construction, through the use of winch, cable disc and truss lower chord pull set up wire rope, pulley group and other devices, the cable from one end to the other end of the high-altitude traction installation (Fig. 9), the installation process pay attention to prevent the collision of the cable body and the support system.
Fig.9. Schematic diagram of cable traction installation
4) Stretching the cable at high altitude
The high-altitude in-situ tensioning technology of the cable was adopted, the stress value was calculated according to the simulation of the cable, and the tensioning equipment was used to carry out the high-altitude tensioning of the cable at the position of the 1.5-meter overhanging cantilever platform at the top of the support system (Fig. 10). Before tensioning, check whether the equipment and instruments used in cable tensioning are within the effective measurement period, and whether the centroid of the tensioning equipment coincides with the centroid of the cable, so as to ensure that the prestressed cable does not produce eccentricity during tensioning. The tensioning operation of the cable is carried out in two stages, the first stage is stretched to 70% of the design value, and the second stage is stretched to 5% when the design tension of the cable is reached. At the same time, ensure that after the tension is completed, the cable force deviation is not greater than 5% of the design cable force.
Fig.10 High-altitude tensioning construction of the cable
5) Construction process monitoring
In order to ensure the stability of the truss structure after the tire is discharged, the digital total station is used to track and measure the whole construction process, and the installation accuracy and stability of the overall structure are ensured by observing the deflection of the five points of the lower chord of the truss, and the allowable deviation value of the design is compared in real time by observing the deflection of the five points of the lower chord of the truss (Fig. 11).
Fig.11. Schematic diagram of the layout of the deflection observation points under the truss
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Project photos
Figure 12 Diagram of cable installation nodes
Fig.13 Cable construction drawing
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bibliography
[1] Wu Xiaolong, Zhang Yuan.Design and construction of 245m super-large span arch prestressed tension string truss structure[J].Building Science,2022,38(7):141-149
[2] Li Weixue, Li Wensong, Wu Xiaolong, Cao Kai.Application of reverse cumulative slip method in prestressed pipe truss[J].Shanxi Architecture,2021,1(47):43.)