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 structure is elliptical in shape, with the upper part designed as a Dapeng Wing. The total construction area of the platform is 36,616.73 square meters, featuring six floors and a height of 24 meters. On the eastern side of the platform, there is a sightseeing tower. This tower has a total construction area of 5,100.42 square meters, spans 16 floors above ground, and reaches a height of 145.6 meters, as shown in Figure 1.

The main structural system of the platform is based on 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 pipes with a diameter of 800mm and a thickness of 32mm. The bottom three levels use concrete-filled steel tube columns, while the frame support is located at 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 sections such as H750×400×18×25, H750×450×18×25, and H750×450×20×30, and the floors are constructed using reinforced concrete. The roof is composed of a welded grid structure. The cantilevered section uses a three-layer grid, while the rest of the structure uses a two-layer grid. The grid is supported by multiple points on the lower chord, and diagonal supports are installed at the bird’s tail section. A skylight frame is placed in the center of the grid, connected via a pipe truss. The sightseeing tower is a cylindrical structure, consisting of eight columns and inter-column supports 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 with a height of 18.84 meters, fixed at the water tank level of the tower.

II. Welding Characteristics and Challenges

1. Welding Construction Features

(1) The node design is complex, making welding difficult. (2) Quality control for welding of steel castings and dissimilar Q345 steel is challenging. (3) Controlling welding deformation is crucial and technically demanding.

2. Difficulties in Welding Construction

(1) It is hard to manage welding deformation and residual stress in steel structures. (2) Both round and elliptical tubes require full-position welding, which demands high technical skills and strict quality control. (3) Due to the high humidity in the Shanghai coastal area, hydrogen can accumulate in the weld metal, increasing the risk of cold cracks.

3. Welding Methods

Considering the efficiency and difficulty of on-site welding, COâ‚‚ gas-shielded welding is used for the platform and the grid. For the sightseeing tower, COâ‚‚ gas-shielded welding is applied below 21.9 meters, while electrode arc welding or flux-cored self-shielding welding is used above that height. For more detailed information, please refer to the attached content or read "Metal Processing (Hot Processing)" No. 18.

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