The steel structure engineering of the station is composed of two parts: the steel structure of the station house and the steel structure of the awning. The total steel used is about 20,845t. The station house is a reinforced concrete frame structure, and the roof of the station house is a steel pipe space frame structure. The space frame unit is mainly an orthogonal square rectangular cone unit. The maximum size of the overall steel structure roof plane is 210m×438m, the typical space frame size is 4.8m × 4.2m, and the height is 3.6-7m. According to the expansion joints, the whole steel roof is divided into A, B, and C three lifting areas. The weight of the space frame in zone A and C are both about 1 700T, and the total weight of the space frame in zone B is about 2 500T. The lifting height is 20 ~ 40m.
The steel roof of the station is raised by sub-unit cumulative lifting and mid-span prestressed cable tensioning technology. The whole construction process of steel roof is simulated and analyzed, the unloading process is optimized, the excessive deformation of CFST column in construction is reduced, the construction quality is improved and the design requirements are satisfied.
2.1 Cumulative improvement of sub-units
The steel roof of the station is raised in units. Both low-span unit 1 and high-span unit 2 of the space frame were integrated on the ground first. The height of the tire rack of unit 2 was more than 9m, with poor stability and a lot of temporary measures. Therefore, the construction method of accumulative lifting by unit was adopted, that is, unit 2 was raised about 9m to dock with side span unit 1, and then unit 1+ Unit 2 was raised as a whole. The cumulative lifting construction method has lower requirements for site assembly, reduces the amount of overhead work, has better safety, is easy to ensure the quality of installation and welding, and has fewer temporary measures.
2.2 Prestressed cable tension
The steel roof space frame of the station is rigidly connected with the column, and the mid-span structure is arched. The joint force with the column is small. In the lifting construction, there is only a vertical constraint at the lifting point of the space frame, which is released horizontally, and the arch effect disappears. The maximum deflection of the space frame is about 400mm, which exceeds the requirements of the code. When the space frame is lifted, a cable is set between the two lifting points below the lower string. During the lifting operation, it is loaded synchronously with the hoist to reduce the mid-span deflection and reduce the stress ratio of the lower chord member. In practice, the maximum pull of the cable is about 1 580kN. The tensioning cable is locked with a cylinder pre-tensioning anchor. The oil cylinder is placed in the cable hanging cage, and its end is connected with the lower hanging point pin shaft through the ear plate. The other end of the cylinder is connected with the cable spreader through a steel strand. The cable spreader is connected with the lower lifting point pin at the other end through the lug plate. The material of the hanging cage and sling is Q345B. According to the arch structure characteristics of the steel space frame, the prestressed cable is set at the hanging point at the end of unit 2, so that unit 2 can be inverted and the axial force of upper and lower strings of unit 2 can be reduced. By adopting this method, the deflection of the steel space frame is reduced to 145ram, which is reduced by 60% and meets the requirements of the code.
By adopting horizontal pretensioning cable, the technical requirements of the cumulative lifting of sub-units are met. Using this construction technology, the middle part of the space frame span is also assembled at 500m height on the ground, which can reduce the number of temporary measures by about 100T. It can reduce the overhead operation of workers, with better safety and greatly reduced labor cost; It can speed up the construction progress and shorten the time by at least 1 month, meeting the construction period requirements of the general contractor.