Chetwynd Bridge is a Grade II* listed three-arch cast-iron bridge in Staffordshire, UK, and the largest surviving pre-1830 cast-iron arch bridge in England, (second largest in the world). Built in the early nineteenth century, it represents one of the most significant surviving examples of cast-iron arch bridge construction worldwide. Following a comprehensive programme of restoration to its ironwork and protective coating, Staffordshire County Council, (SCC), with Amey acting as asset manager. Amey consulting undertook a comprehensive structural assessment of the bridge involving load testing and a vision-based sensing to monitor movement. Based on recorded results mirrored by finite element modelling Amey showed the cast iron arches were being loaded beyond available capacity which resulted in the bridge being restricted to 7.5 Tonnes.
Amey reached out to trusted specialist supply chain partner Terra Measurement on behalf of SCC. This led to a structural monitoring scheme being commissioned to better understand the bridge’s behaviour under operational traffic loading while fully preserving the historic and architectural significance of the structure.
Terra Measurement, a UK-based geospatial surveying and consultancy practice specialising in monitoring and measurement of complex structures, was appointed to design and deliver the monitoring solution. A central requirement of the commission was that the system should be entirely non-invasive, reversible, and visually unobtrusive, providing reliable long-term data without introducing any permanent alteration or risk to the historic fabric.
To meet these requirements, Terra Measurement adopted a technology-led but consultant-defined approach, selecting wireless structural health monitoring equipment supplied by Move Solutions. Move Solutions develops wireless monitoring systems for civil infrastructure and built assets, with a focus on non-invasive installation, long-term autonomy, and cabling-free deployment, supported by remote data management through its MyMove cloud-based platform. As part of the monitoring programme, Move Solutions carried out the modal frequency analysis based on vibration data acquired from the accelerometer network, while Terra Measurement reviewed and interpreted the results for the client.
This collaborative approach brought together Terra Measurement’s responsibility for monitoring strategy, installation methodology, and client-facing interpretation with Move Solutions’ sensor technology, data platform, and specialist analytical capability.
Monitoring strategy and heritage constraints
Before defining the monitoring layout, Terra Measurement undertook a detailed engineering and site assessment to establish the most relevant structural parameters to observe and to identify the constraints imposed by the bridge’s heritage designation, environment, and operational use. Particular attention was given to the dynamic response of the cast-iron arches under traffic loading, alongside environmental influences such as temperature variation and river-related flood risk.
Based on this assessment, Terra Measurement defined the monitoring objectives, sensor locations, acquisition strategy, and installation methodology in consultation with SCC and Amey. The monitoring strategy focused on capturing meaningful, high-quality structural behaviour data while fully complying with heritage and environmental constraints, including the prohibition of drilling, bonding, or permanent attachments, and the requirement that the bridge’s visual appearance remain unchanged.
Technology partnership and system configuration
The monitoring system was designed to observe the dynamic response of one arch of the bridge under operational traffic and environmental actions. The focus was on vibration, displacement, and tilt measurements, complemented by video monitoring to correlate structural response with vehicle passages.
The system comprises a network of fully wireless sensors, eliminating the need for cabling and minimising installation complexity.
The deployed instrumentation includes:
- 36 wireless triaxial accelerometers for vibration measurement and modal analysis
- 9 dynamic displacement sensors for real-time displacement monitoring
- 15 wireless tiltmeters for angular variation measurement
- 2 gateways for local data collection and cloud transmission
- 3 complementary video cameras for synchronised visual monitoring
Move Solutions supplied the monitoring instrumentation and MyMove platform, enabling continuous data acquisition, remote access, and long-term data storage. Modal frequency analysis was led by Move Solutions using vibration data collected from the accelerometer network and delivered through the MyMove platform, establishing a baseline dataset for future comparison, with Terra Measurement responsible for the technical review and client-facing interpretation.
Installation methodology
Strict heritage constraints governed the installation process. No drilling, bonding, or permanent attachment was permitted, and all equipment had to be fully reversible. In addition, the bridge spans a river subject to flooding, requiring all devices to be installed above historical flood levels.
Installation was carried out by Terra Measurement using non-invasive magnetic mounting for all sensors. Magnetic mounting provides stable mechanical coupling to the cast-iron elements while remaining fully reversible, ensuring reliable vibration transmission without introducing stiffness discontinuities or permanent damage. Each mounting arrangement was tested to confirm resistance to vibration, temperature variation, and weather exposure prior to final deployment.
Maintaining the bridge’s visual integrity was critical. All sensors were painted to match the surrounding painted cast-iron surfaces, ensuring that they remain unobtrusive to bridge users and fully compliant with heritage authority requirements. This allows the system to operate continuously without drawing attention.
The installation was completed without the need for traffic management, scaffolding, or structural modification. Magnetic mounting allowed rapid placement and immediate verification of signal quality, while remote wireless calibration further reduced on-site intervention.
Power supply and data management
Powering monitoring systems on heritage structures presents particular challenges. Solar panels were not permitted for aesthetic reasons, and the installation of new power infrastructure was prohibited. To address this, the system was connected to an existing 24-volt street-lighting circuit, which charges a dedicated backup battery to ensure continuous operation during temporary power interruptions. This battery-powered, cabling-free setup minimizes physical impact and maintenance requirements while guaranteeing reliable, uninterrupted monitoring.
All monitoring data is transmitted wirelessly to the MyMove cloud platform via cellular gateways, providing real-time access to measurements, automated alerts when predefined thresholds are exceeded, and secure long-term storage for trend analysis.
Acceleration, displacement, and tilt data are synchronised with video recordings, allowing structural responses to be directly correlated with individual vehicle crossings. This integrated dataset enables objective, evidence-based engineering assessment without the need for frequent on-site inspections.
Outcomes and engineering value
Since installation in September 2023, the monitoring system has continuously recorded the dynamic behaviour of one arch of the bridge. Key outcomes include the successful identification of every vehicle crossing, including overweight vehicles that pose particular risks to cast-iron structures.
The modal frequency analysis outputs established baseline dynamic characteristics for the monitored arch, enabling future changes in behaviour to be detected and assessed objectively. Terra Measurement reviewed these outputs and, over time, identified subtle variations in structural response that would not be apparent through visual inspection alone.
These insights provide SCC and Amey with a robust evidence base to support asset management decisions, maintenance planning, and long-term preservation strategy. In particular, the monitoring data contributes to informed decision-making regarding future intervention, strengthening the technical justification for strategic options even where visible deterioration is limited.
Engineering significance
The Chetwynd Bridge project demonstrates the practical value of continuous, non-invasive structural monitoring for sensitive heritage infrastructure. When combined with a carefully defined monitoring strategy and close collaboration between client, consultant, and technology provider, advanced monitoring technology can deliver high-quality engineering data without compromising historic fabric or appearance.
The project highlights several transferable lessons:
- Magnetic mounting is effective for reliable vibration measurement on metallic heritage structures
- Visual integration is essential in protected environments
- Leveraging existing power infrastructure enables autonomous operation
- Wireless networks reduce installation complexity and long-term maintenance requirements
- The digital platform trigger levels notified SCC and Amey of potential damage due to overloading events.
- Continuous monitoring provides insights unavailable through periodic inspection alone
- Historical digital data captured could potentially be used to model bridge deterioration.
These lessons provide a framework for similar applications on historic bridges and protected structures worldwide.
Conclusion
The structural monitoring of Chetwynd Bridge illustrates how a consultant-led, technology-enabled approach can successfully safeguard a nationally significant historic structure. Terra Measurement’s monitoring strategy and delivery, supported by Move Solutions’ wireless instrumentation and collaborative support, MyMove platform, and modal analysis capability, has resulted in a robust, non-invasive monitoring system aligned with heritage, operational, and engineering requirements. The technical partnership and collaboration between the two teams has been as successful on many other infrastructure projects.
The project provides a reference model for the monitoring of historic bridges and protected structures worldwide, demonstrating that preservation objectives and high-quality structural monitoring can be achieved together.
