Rongjiang Bridge: The World’s Longest Bridge of Rigid Girder and Flexible Arch

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The Rongjiang Bridge is a part of the Xiamen-Shenzhen high-speed railway route constructed in the Jieyang City of Guangdong Province, China. It is the longest bridge in the world with a main span of 660 m between two flexible steel arches and rigid girders.

Rongjiang Bridge is considered the most challenging long-span bridge that has ever been constructed for a high-speed railway network. This is because of the innumerable construction problems faced, the scale of the project, and the need for highly specialized components.

In this article, we discuss the structural elements of the Rongjiang Bridge, key factors associated with its design, foundation details, and the construction procedure.

1. Structural Components of the Rongjiang Bridge

The structural components of the Rongjiang Bridge are the main girder, gusset plates, and the deck system. The main girder is made up of four continuous spans of steel truss girders and two components of steel arches. The approach bridges are made up of prestressed concrete beams of 32 m in length and constructed on simple supports. The steel truss girder weighs approximately 15,000 tons and the single beam weighs about 70 tons.

Q370-qE steel was utilized in the main bridge for all the steel components, which are thicker than 40 mm. In addition, Q370-qD steel was used for the more slender steel components, like the supporting frameworks. Concrete of strength grades C30, C35, and C40 were chosen, for pile foundations, piers, and pile caps, respectively.

1.1 Main Girder of the Rongjiang Bridge

Two components of N-type triangular truss were adopted with vertical bars for the construction of the main girder. The main trusses were separated by 15 m from center to center with an internode distance of 11 m. A total of 20 and 10 internodes were provided in the middle and side span, respectively.

The height of the steel truss was restricted to 15 m and 30 m in the middle span and at the supports, respectively. Steel arches were introduced on the main girder to expand the range of the main bridge. The steel arch was in the shape of a parabola to provide greater flexibility to the main bridge. 

The span and height of the flexible arch were 220 m and 44 m, respectively. Thus, a rise to span ratio of 1/5 was achieved. The main truss beam consisted of three members named the lower chord, the upper chord, and the diagonal chord. These members were joined with the gusset plates by high-strength bolts. The box shape and H-shaped cross-sections were adopted for the truss members and for the connecting rods, respectively.

1.2 Gusset Plate

The gusset plates were utilized in most parts of the Rongjiang Bridge. One of the basic gusset plates was named E-11, which is chosen to represent the properties of the gusset plate in detail in this article. The E-11 gusset plate was provided at the junction between the flexible arch and the steel truss girder.

The stress condition on the E-11 gusset plate is complex as a total of ten members were connected to it. The entire E11 gusset plate comprises of five types of steel plates. These steel plates were named N1, N2, N3, N4, and N5. The thickness of N1 is 50 mm while that of N2 and N3 is 42 mm, and that of N4 and N5 is 40 mm.

1.3 Deck System of the Rongjiang Bridge

The deck arrangement of the Rongjiang Bridge is a ballasted track. It was provided for the first time for any high-speed railway network in the world. The track was made out of three sections, specifically, ballast bed, cushion and steel deck. The center to center spacing between the two tracks is 4.6 m and the width of the sidewalk and ballast tank are 1.3 m and 9 m, respectively.

A light cushion was provided between the steel deck and the ballast bed. The CAP high adhesion layer was used to make the lightest possible cushion. The waterproofing for the cushion was provided using the MMA system. A layer of C40 polypropylene fiber mesh concrete with a thickness of 38 mm and 12 mm thickness of AP high adhesion pad were provided for CAP high adhesion lightweight, protective layer.

The steel deck was connected to the lower chord with a spacing of 11 m between the transverse beams to provide more rigidity. The connection was provided in such a way that at each main transverse connection, three minor connections were provided at a spacing of 2.75 m.

An inverted T-shaped cross-section was chosen for the transverse beam connection. Also, an orthotropic bridge deck system was provided by arranging the U-type ribs and I-type ribs on the deck panel of the bridge.

2. Design Criteria of the Rongjiang Bridge

The Rongjiang Bridge was designed for a high-speed railway network. The following points describe the design criteria adopted for the Rongjiang Bridge:

1. The design speed is restricted to 250 km/h.
2. The longitudinal radius of the curve is 4500 m.
3. The maximum slope is restricted to 6%.
4. ZK live load (as per Chinese codes) was chosen to design the railway track.
5. Standard load cases were selected according to global standards for wind load, earthquake load, and dead load.

3. Foundation Details of the Rongjiang Bridge

Pile foundation was adopted for the construction of the Rongjiang Bridge. A total of three types of steel support pier were provided, namely middle span pier support, side span pier support, and auxiliary pier support. The design capacities of middle span pier support and side span pier support are 10,000 tons and 7500 tons, respectively. Whereas for auxiliary pier support, the design capacity is 1500 tons.

A hollow pier was adopted for construction due to its excellent performance in dynamic loading for high-speed railways. The maximum height of the bridge pier is 45 m. A circular cross-section was adopted for the pile foundation, and two types of piles having diameters of 2 m and 2.8 m were provided. The maximum depth of the pile foundation is 110 m. 

4. Construction Procedures

V-shaped stiffening chords were provided for the main bridge to form a continuous steel girder. Also, flexible steel arches were used to connect the other spans of the bridge. However, the connection of flexible steel arches with the steel truss girder proved to be a challenging task.

To overcome the connection problems, the scheme of making the erection of the continuous steel truss girder with flexible arch on various levels and implementing the staged closure was prepared. In this manner, the continuous steel truss beam was constructed before constructing the flexible steel arch structures.

Four dewing derrick cranes were used to construct the steel truss girder on four different platforms. The cranes were provided at such a location that one crane was able to finish the task up to the mid-span of the two main spans.

The flexible steel arches were successively raised by two dewing derrick cranes from the external edge of the two flexible arch ribs to the focal point of the main bridge. The butt joint was provided at the intermediate pier to mark the closing operation of the derrick cranes. The construction of the Rongjiang Bridge was finished by following the above steps.

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