I. Project Overview

The Songpu Bridge, spanning the Songhua River in Harbin, is a single-tower, double-cable-stayed steel bridge located in the high-altitude northern region of China (see Figure 1). The bridge features a main span of 268 meters, side spans of 208 meters, and an overall length of 476 meters. Its total deck width reaches 39.3 meters, with a total steel weight of approximately 7,000 tons. The steel beam structure consists of a main longitudinal beam, secondary beams, small longitudinal beams, and two side beams. The main longitudinal beam is designed as a box-shaped section, with anchor boxes welded to the outer flanges. Except for the box-section beams at the auxiliary piers, most of the beams are working sections. The small longitudinal beams and pick-up beams are constructed using I-shaped cross-sections, and shear studs are welded onto the main girders, secondary beams, and small girders. Most connections between steel components are made through bolting, although certain critical sections such as LZ0–LB0, LB14–LB19 of the main longitudinal beams are fully welded. Some other beams, like HL3 and HL10, are also welded to the main longitudinal beams.

There are 36 pairs of steel anchor beams installed on the bridge tower, as shown in Figure 2. Each pair measures 4.5 meters in length and weighs between 6.98 and 8.86 tons, contributing to a total weight of approximately 270 tons. The primary structural materials used are Q345qE and Q370qE steel plates, with thicknesses ranging from 10 to 50 mm.

II. Challenges in Welding

During the steel fabrication process of the Songpu Bridge, several welding challenges were encountered:

(1) The bridge has a unique structural design, with the main longitudinal beam featuring a large-box section and cable-stayed anchor boxes. All of these components are fabricated using welding, which creates limited access for welding in the anchor box and steel anchor beam areas. Most of the welds require full penetration, making them particularly challenging to execute.

(2) The primary materials used are Q345qE and Q370qE steel plates, which demand a welded joint with a low-temperature impact absorption energy of at least 34 J at -40°C. This results in very high toughness requirements for the weld joints.

(3) Due to the large cross-sectional dimensions of the main steel box girder, along with large force-bearing components such as the long longitudinal steel plates, anchor boxes, and steel anchor beams (with a maximum thickness of 50 mm), significant welding distortion occurs during the process.

(4) The main longitudinal beams, secondary beams, and the cable tower are primarily connected using bolts at the construction site, requiring high installation accuracy and strict control over welding deformation. Sections such as LZ0–LB0 and LB14–LB19 of the main longitudinal beams are fully welded on-site, presenting complex and technically demanding welding conditions.

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