On January 12, the Lu'an Zhou Special Navigation Channel Bridge of the Changtai Yangtze River Bridge, surveyed and designed by China Railway Major Bridge Reconnaissance & Design Institute and constructed by units including China Railway Major Bridge Engineering Group, was successfully closed.

With this, both special navigation channel bridges of the Changtai Yangtze River Bridge have been fully closed. The project will next enter the stage of dismantling the cable-stayed suspension system and installing ancillary structures.

Viewed from afar, the two completed special navigation channel bridges echo the main bridge under construction—one high and one low, one rising and one dipping. The diamond-shaped main tower in the middle of the river stands like a precious vase, while the special navigation channel bridges on both sides lie horizontally like ruyi scepters, and the grand silhouette of the bridge is taking shape.

Zheng Qinggang, deputy chief engineer of China Railway Major Bridge Reconnaissance & Design Institute and project leader of the Changtai Yangtze River Bridge, said that there is a Class I-(3) navigation channel on both the north and south sides of the bridge site, which must meet the two-way navigation requirements of 5,000-tonne seagoing vessels entering and leaving upstream. Taking into account factors such as the navigation channel and the location of the embankment, both special navigation channel bridges adopt a road-rail dual-purpose steel truss arch bridge scheme with a main span of 388 meters, crossing the navigation channel waters in a single span. This also makes the two special navigation channel bridges the world's largest-span road-rail dual-purpose steel arch bridges.

"Both special navigation channel bridges are composed of steel members in different forms," said Li Shaojun, head of the special navigation channel bridge of the Changtai Yangtze River Bridge at China Railway Major Bridge Reconnaissance & Design Institute. The arch rib axis of the special navigation channel bridge is a multi-segment polyline that "replaces curves with straight lines." At each main truss node, lateral diagonal members and cross braces are needed to connect two non-coplanar planes. If the traditional design method were used, the lateral bracing gusset plates would need to be bent multiple times to accommodate the space requirements for connecting bolts, resulting in oversized gusset plates and cramped space, which would inconvenience welding and coating.

Is there a method that can not only make the connections of the bridge members simpler, but also make welding and coating during construction more convenient?

Inspired by the design team, the project team envisioned: why must the lateral bracing system line be coplanar with the main truss system line? If an independent lateral bracing system line were constructed, it could solve the problem of multiple bends in the lateral bracing gusset plates and also keep the additional bending moment caused by the lateral bracing offset within a very small range. The BIM forward design method for steel truss girders that the team had always used could precisely make this complex spatial geometry problem simple and clear.

Based on these conditions, the design team proposed "a design method for a variable-height truss bent node structure," successfully solving this problem.

On one side of the Changtai Yangtze River Bridge is Changzhou, one of the birthplaces of Wu culture and a famous cultural city with more than 3,000 years of history; on the other side is Taizhou, the gateway to central Jiangsu connecting south and north, known since ancient times as a "key land and water hub, throat commanding the prefecture." The name "Changtai" not only represents the connection between Changzhou and Taizhou, but also embodies the traditional cultural meaning of "always enjoying prosperity and peace."

As early as the start of the design work, the design team of China Railway Major Bridge Reconnaissance & Design Institute agreed that the Changtai Yangtze River Bridge is of great significance for shaping local cultural symbols and spreading a positive local image. Therefore, the design of the bridge must meet functional needs and also focus on achieving deep integration of bridge aesthetics with structural modeling and traditional culture, profoundly reflecting the local humanistic spirit of advancing with the times and the urban philosophy of courageous innovation.

Yu Lu, head of the bridge architectural modeling project for the Changtai Yangtze River Bridge at China Railway Major Bridge Reconnaissance & Design Institute, said that the overall shape of the main navigation channel bridge tower is like a "precious vase," meaning eternal safety; the special navigation channel bridges are arch bridges shaped like "ruyi," meaning good fortune and auspiciousness; and the overall bridge design symbolizes "peace and ruyi, always enjoying prosperity and peace."

In Yu Lu's view, bridge aesthetics is an extension and manifestation of structural mechanics, and the pursuit of aesthetics must be built on a mechanical foundation. For example, in designing the steel truss arch curve of the special navigation channel bridge, the design team analyzed and studied various rise-to-span ratios and arch heights for the special navigation channel bridge and, combined with structural force requirements and bridge aesthetic requirements, ultimately selected a scheme with an arch height of 11 meters and a rise of 55 meters. The proportions are balanced and harmonious, giving the entire special navigation channel bridge a rounded, transparent, and smooth landscape effect.

The Changtai Yangtze River Bridge began full-scale construction in October 2019 and is scheduled to be completed in the first half of 2025. Once completed, it will be of great significance for advancing the construction of the "Belt and Road" intersection point, better serving the integrated development of the Yangtze River Delta and the development strategy of the Yangtze River Economic Belt, and improving the regional road network layout.