Qiansimen Jialing River Bridge: Engineering Analysis of a Combined Road-Rail Cable-Stayed Bridge

1. Project Overview and Positioning

The Qiansimen Jialing River Bridge is a river crossing that connects Yuzhong District and Liangjiang New Area in Chongqing, spanning the Jialing River waterway. It is an important component of the urban secondary trunk road system in northern Chongqing. The bridge is a cable-stayed bridge, a combined road-rail bridge, and a mega bridge. The total route length is 1,647.47 meters, the main bridge length is 720 meters, and the main span is 312 meters. The upper deck carries a two-way, four-lane urban expressway with a design speed of 40 km/h. The lower deck carries a dual-line urban rail transit, serving Chongqing Rail Transit Line 6. The highway deck width ranges from 24 to 36.9 meters, and the rail deck width is 13 meters. The bridge starts at Cangbai Road in the south, connecting smoothly with the Qiansimen Tunnel and the Dongshuimen Yangtze River Bridge, and ends at Jiangbeicheng Main Street South in the north. The managing authorities are the Chongqing Urban Management Bureau and Chongqing Rail Transit Operations Co., Ltd.

From an engineering classification perspective, this bridge combines three attributes: cable-stayed structural system, shared road-rail transit corridor, and extra-large span. Its design and construction complexity far exceeds that of a single-purpose river crossing. Understanding this type of bridge requires examining four dimensions: construction history, structural system, road-rail coordination, and operation and maintenance management.

2. Construction History and Key Milestones

The construction of the Qiansimen Jialing River Bridge went through a complete cycle from groundbreaking to opening and then to functional expansion. The key milestones are as follows:

• December 29, 2009: Construction began, entering the substantive construction phase.
• January 2, 2013: Bridge tower topping-out was completed, marking the completion of the main vertical structure construction.
• July 21, 2013: Stay cable installation was completed, and the cable-stayed system initially took shape.
• November 25–29, 2013: Closure engineering was carried out and completed, achieving structural continuity of the main bridge.
• April 22, 2014: Asphalt paving was carried out, entering the bridge deck system construction phase.
• May 2014: The main bridge and Jiangbeizui ramps were completed.
• June 24, 2014: Acceptance inspection was passed, and the bridge met traffic opening conditions.
• April 2, 2015: Ramps A and B on the Yuzhong side passed acceptance inspection.
• April 29, 2015: The bridge officially opened to traffic.
• September 26, 2023: The urban observation deck officially opened, extending the bridge’s function from transportation to public space.

From these milestones, it can be seen that the bridge took approximately five and a half years from groundbreaking to opening. The period from tower topping-out to closure was about ten months, and from closure to opening was about one and a half years. This sequencing reflects the typical logic in cable-stayed bridge construction: “main structure first, deck second, ancillary works last.” For developers, this phased delivery approach is highly analogous to the iterative strategy in software systems of “core services first, peripheral capabilities gradually filled in.”

3. Structural System and Mechanical Characteristics

The Qiansimen Jialing River Bridge adopts a cable-stayed bridge structure with a main span of 312 meters, placing it in the large-span bridge category. The core load-bearing logic of a cable-stayed bridge is: through stay cables, the main girder loads are transferred to the bridge towers, and then from the towers to the foundations. Its structural system can be broken down into the following layers:

1. Bridge towers: As the primary compression members, they bear the vertical and horizontal components transmitted by the stay cables.
2. Stay cables: They transfer main girder loads to the towers in the form of tension while providing elastic support to the main girder.
3. Main girder: It bears vehicle loads, rail train loads, and its own dead load, and works in coordination with the towers through the stay cables.
4. Foundations: They spread the loads transmitted from the towers to the ground.

For a combined road-rail bridge, the load combinations are more complex. Highway loads and rail loads differ in time distribution, dynamic characteristics, and application positions. The following combination scenarios must be considered in design:

• Highway fully loaded + rail unloaded
• Highway unloaded + rail fully loaded
• Highway and rail simultaneously fully loaded
• Eccentric effects caused by single-side rail loading

These scenarios require the structure to meet code requirements in terms of strength, stiffness, and stability. Stay cable force adjustment becomes a key means of controlling main girder alignment and internal forces. During construction, stay cables must be tensioned in stages to gradually establish the design cable force state. After bridge completion, fine-tuning of cable forces based on actual monitoring data is also required.

4. Key Aspects of Road-Rail Coordinated Design

The core challenge of a combined road-rail bridge lies in “one structure, two sets of load standards.” The upper deck of the Qiansimen Jialing River Bridge is a two-way, four-lane urban expressway, and the lower deck is a dual-line rail transit. The two are arranged in layers spatially and influence each other mechanically. The following aspects require special attention in design:

4.1 Vertical Stiffness Matching

Highways and rail transit have different requirements for vertical stiffness. Rail trains have higher requirements for track smoothness, and excessive vertical deflection can affect operational safety and ride comfort. Therefore, the main girder design must use rail stiffness requirements as the governing condition while also accommodating highway driving needs.

4.2 Dynamic Response Control

Rail train operation generates periodic dynamic loads that may cause bridge resonance. Vehicle-bridge coupled vibration analysis must be conducted during design to ensure that harmful resonance does not occur within the train design speed range. The dynamic effects of highway vehicles are relatively random and are typically considered using impact factors per code.

4.3 Track and Deck Deformation Compatibility

The track structure is laid directly on the lower deck, and deck deformation is transmitted directly to the track. Therefore, longitudinal and transverse deformations of the deck under loads must be controlled to prevent track geometry from exceeding limits. This requires the deck system to have sufficient overall stiffness and reasonable force-transfer and adjustment mechanisms between the track and the deck.

4.4 Construction and O&M Interface Division

Construction of a combined road-rail bridge often involves interface management between the bridge structure and the rail system. After opening, the highway and rail are managed by different authorities, requiring clear O&M interfaces and coordination mechanisms. For example, bridge structural monitoring data must serve both highway maintenance and rail safety assessment.

5. Operation and Maintenance Management and Functional Expansion

After the Qiansimen Jialing River Bridge opened to traffic, its function did not stop at being a transportation corridor. On September 26, 2023, the urban observation deck officially opened, marking the bridge’s transition from a single transportation facility to a composite “transportation + public space” function. This change imposes new requirements on O&M management:

• Load management: The observation deck introduces crowd loads, requiring assessment of their impact on structural forces and, if necessary, crowd flow control.
• Monitoring expansion: In addition to traditional structural monitoring, crowd density and railing load monitoring items must be added.
• Emergency evacuation: Public spaces require emergency evacuation routes and signage systems coordinated with the bridge’s original traffic flow lines.
• Maintenance coordination: Maintenance of the observation area and the traffic area must be planned in a unified manner to avoid mutual interference.

From a technical perspective, this functional expansion reflects the concept of “full-lifecycle management” for infrastructure. A bridge is no longer a static asset built once, but a dynamic system that continuously evolves with urban needs.

6. Lessons for Engineering Practitioners

The construction and operation practices of the Qiansimen Jialing River Bridge provide transferable experience for similar combined road-rail cable-stayed bridges:

1. Structural system selection must match functional requirements: Cable-stayed bridges are suitable for large spans and shared road-rail scenarios, but dedicated design is required for stiffness, dynamics, and deformation control.
2. Construction sequencing affects the completed bridge state: Staged tensioning of stay cables and closure sequence directly affect completed bridge internal forces and alignment. Construction control is needed to ensure the target state is achieved.
3. Road-rail coordination must run through design, construction, and O&M: From load combinations to interface division, road-rail coordination is not a single-phase task but a full-cycle requirement.
4. Functional expansion requires structural adaptability assessment: When adding non-transportation functions such as public spaces, load and safety impacts must be re-evaluated.
5. O&M data should form a closed loop: Monitoring data is not only for safety warnings but should also feed back into maintenance decisions and structural assessment.

For developers working on infrastructure digitization, structural health monitoring, or engineering management platforms, the O&M needs of such bridges can be abstracted into general technical problems: multi-source data collection and fusion, load scenario identification, structural state assessment, and early warning rule engines. These capabilities can be implemented through general-purpose data platforms, message queues, time-series databases, and monitoring and alerting components, rather than relying on vendor-specific proprietary solutions.

7. Summary

As a combined road-rail cable-stayed bridge, the Qiansimen Jialing River Bridge has technical implications far beyond the simple designation of “river crossing.” From groundbreaking in 2009 to opening in 2015, and then to the observation deck opening in 2023, it has gone through a complete cycle of construction, operation, and functional expansion. Its practices in structural systems, road-rail coordination, construction control, and O&M management provide valuable references for similar projects. For engineering practitioners, the key to understanding this bridge is not memorizing specific parameters but mastering the systemic thinking that “function determines structure, construction affects the completed state, and O&M runs through the full lifecycle.”