Key Techniques for Welding of Steel Structure Engineering in Sea Platform of Hangzhou Bay Bridge
I. Overview of the Steel Structure
The sea-crossing platform of the bridge is situated 150 meters downstream from the K66 + 120 mark of the Hangzhou Bay Bridge. The platform has an elliptical shape, with the upper structure designed as a "Dapeng Wings" style. The total construction area of the platform is 36,616.73 square meters, consisting of six floors and reaching a height of 24 meters. Located on the eastern side of the platform, the sightseeing tower has a total construction area of 5,100.42 square meters, featuring 16 floors above ground and standing at a height of 145.6 meters. This is illustrated in Figure 1.
The main structural system of the platform is a steel frame support structure. The column grid is arranged in two different patterns: 6m × 8m and 12m × 8m. The columns are made of round pipe sections with a diameter of 800mm and a thickness of 32mm. The bottom three levels feature concrete-filled steel tube columns. The frame supports are located along axes 10, 11, 17, 25 and E, F, G, J, K, L. From the top of the platform to the top of the structure, the floor plan transitions from an elliptical shape to an irregular one. The main beams have various H-sections, including H750×400×18×25, H750×450×18×25, and H750×450×20×30. The floor slabs are made of reinforced concrete.
The roof is constructed using a welded grid structure. The cantilevered section uses a three-layer grid, while the rest of the roof employs a two-layer grid. The grid is supported by multiple points on the lower chord, and diagonal bracing is provided at the bird’s tail section. A skylight frame is installed in the center of the grid and connected via a pipe truss.
The sightseeing tower is a cylindrical structure, composed of eight columns and inter-column braces evenly distributed around a circle with a radius of 4.6 meters, forming an octagonal layout. The column sections include φ800mm and φ1600mm, with a variable section column in the middle. At the top of the tower, there is a mast that stands 18.84 meters tall, fixed at the water tank level of the tower.
II. Welding Characteristics and Challenges
1. Welding Construction Characteristics
(1) The node design is complex, making welding operations challenging. (2) Quality control for welding of steel castings and dissimilar steel (Q345) is critical. (3) Controlling welding deformation is essential and poses significant difficulties.
2. Difficulties in Welding Construction
(1) It is difficult to manage welding deformation and residual stress in steel structures. (2) Both round and elliptical tubes require all-position welding, which demands high technical expertise and makes quality control more complex. (3) The high humidity in the Shanghai sea area can lead to hydrogen accumulation in the weld metal, increasing the risk of cold cracks.
3. Welding Methods
Considering the welding efficiency and practical challenges on-site, CO2 gas shielded welding is used for the platform and grid structure. For the sightseeing tower, CO2 gas shielded welding is applied below 21.9 meters, while electrode arc welding or flux-cored self-shielding welding is used above this height.
For more detailed information, please refer to the attached documents or read “Metal Processing (Hot Processing)†No. 18.
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