Improving bridge stress control with advanced monitoring

A recent article in Scientific reports An overview of new construction practices, short prestressing units for long-span bridges with improved strength and precision of stress control, specifically targeting potential hazards.

Improving bridge stress control with advanced monitoring
Extensometers in passive reinforcement of Tajo Bridge arch: (a) extensometer in reinforcement of stay piers; (b) Extensometer in reinforcement of half arches. Image Credit: https://www.nature.com/articles/s41598-024-61873-y

Background

Cable stays or suspensions are commonly used in the design of long-span bridges. The durability of these solutions is limited by fatigue and/or corrosion damage caused by dynamic loads such as traffic and wind. The impact of fatigue and corrosion and damage to cables in service is often assessed by monitoring axial stress.

Various direct and indirect methods and devices have been developed to measure the tension in bridge cables. Direct strain measurement devices include load cells, fiber optic Bragg grating sensors, and elasto-magnetic strain sensors. Alternatively, vibrating wire methods are commonly used to estimate indirect and instantaneous stresses in bridge cables.

Substructural elements used during bridge construction, such as temporary stay cable towers, also experience high instantaneous prestress losses. Therefore, it is very important to monitor their stress pressure and the time variation of this stress to ensure that the element is performing as desired.

methods

Researchers presented a review of systems currently used to monitor stresses in bridge abutments and prestressing units during the construction phase of the Tajo Bridge, Spain’s unique high-speed infrastructure designed and built between 2012 and 2016.

Tajo Bridge has been carefully planned to meet high speed, performance and safety standards through advanced engineering and provide modern aesthetics. To experimentally investigate the structural response of the central arch span of the bridge, the researchers designed a structural health monitoring system (SHMS) that includes several devices and systems.

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The Project Management and Coordination System (M&USP) includes project databases provided by the bridge’s design and construction teams and a Sensor System (SS) consisting of 114 sensors installed at different locations on the bridge. For example, load cells on rail gauges in suspension cables and anchorage and half-arch reinforcements of stay cable towers.

A data acquisition and processing system (DA&PS) for different sensor systems is included in the SHMS. Additionally, the Data Management and Processing System (DM&PS) was designed and planned. It was used for data transmission, visualization and storage and establishment of early warning systems.

Finally, a Structural Safety and Assessment System (SS&AS) was developed. It consisted of all organizations involved in bridge construction, including technical and management teams. This subsystem enabled monitoring of instrumental data and comparison with theoretical data of the project. Comparison results are updated in M&USP databases and fed to SHMS.

The proposed SHMS was used to monitor the deformation caused by the reinforcement of half arches, stay piers and stay towers. Also, the acceleration of the northern semi-curve, the thermal gradient in different structural sections and the wind phenomenon in the structure were monitored.

Results and discussion

Based on the Tajo Bridge experience, researchers reimagined new monitoring systems for stress management. Load cells for active anchors can accurately characterize the total axial force transmitted by the bridge stay or prestressing unit and must provide a robust solution for extreme environments, shocks and impacts.

Additionally, they should provide direct measurement without the need for signal integrators. Accordingly, the designed load cell consisted of a metal ring that allowed the bridge to rest or the prestressing unit to pass through. It can be anchored in the structure and positioned between the distribution plates.

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Three devices were simultaneously installed to monitor the bridge stays, including load cells on the active anchors, unidirectional strain gauges on a strand forming the stays, and piezoelectric accelerometers on the stays. These have enabled detection of various structural phenomena during construction, including stress variations in bridge stays, stress variations derived from the concrete of adjacent sections, analysis of force variation due to stress on different cables, and force variations from load restoration operations. Suspension gold cables.

Also, a new synchronized multi-strain gauge load cell network is proposed for monitoring short prestress units in each stay tower. This ensured proper pre-stressing and accurate measurement of the losses caused by the pre-stressed joint.

Conclusion

Overall, this study focuses on improving stress management for bridge stays, suspension cables and short prestressing units, emphasizing one integral parameter: stress. Advanced load cells are designed and installed in active anchors for robust and precise stress control. Furthermore, the implementation of a novel synchronized multi-strain gauge load cell network for compact prestressing units was critical in situations where prestressing losses could reach significant levels.

To verify these developments, the researchers presented the practical experience and results obtained by applying these methods to monitor the structural response during the construction of Tajo Bridge using the cable-stayed cantilever technique. These methods help to calculate the prestress losses exceeding 10% in Tajo Bridge and to plan new stress functions in such critical structures.

Journal Note

Gaute-Alonso, A., Garcia-Sanchez, D., Ramos-Gutierrez, Ó. R., & Ntertimanis, V. (2024). Improving the accuracy control of pressure gauges in the construction of long-span bridges. Scientific reports, 14(1), 10961. https://doi.org/10.1038/s41598-024-61873-y, https://www.nature.com/articles/s41598-024-61873-y

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