Bridges, tunnels and other civil engineering structures form the backbone of modern rail infrastructure. Every day, they must withstand rising train numbers, higher axle loads and increasing climatic stresses. At the same time, demands on safety, availability and cost-effectiveness are rising. Whilst traditional structural inspections remain indispensable, they are increasingly reaching their limits in the face of ageing infrastructure and growing traffic volumes. With Structural Health Monitoring (SHM), TÜV SÜD is expanding traditional structural monitoring to include continuous, digital condition assessment – thereby opening up new opportunities for operators to implement condition-based maintenance.

Infrastructure under constant strain

The challenges facing infrastructure operators are constantly growing. Many railway bridges and tunnels were built decades ago and are approaching the end of their planned service life. At the same time, traffic volumes are steadily increasing, meaning that these structures are permanently exposed to higher levels of stress. Closures for inspections or unplanned repairs have a direct impact on rail operations and result in significant economic consequences.

To date, structural monitoring has been based predominantly on regular inspections. In the railway sector, these are carried out in accordance with the infrastructure operators’ specifications and are often guided by the provisions of DIN 1076. Major inspections are generally carried out every six years, whilst routine inspections take place at three-year intervals. In addition, special inspections may be required, for example following floods, fires or accidents. However, these procedures only ever provide a snapshot of the structure’s condition. Changes that occur between two inspections often go undetected.

Continuous condition assessment instead of periodic snapshots

With Structural Health Monitoring, TÜV SÜD is therefore pursuing a complementary approach. Sensors continuously record measurement data directly on the structure. This information is digitally collated, analysed and evaluated from an engineering perspective. This provides a virtually continuous picture of the actual condition of the infrastructure.

“With our Structural Health Monitoring, we are supplementing traditional inspection methods with the continuous digital recording and structured evaluation of structural data,” explains Holger Bach, an expert in measurement data and data analysis at TÜV SÜD’s Rail Business Unit. “In doing so, we create transparency regarding the actual condition of railway structures, support condition-based maintenance planning and make an important contribution to improving the safety and reliability of railway infrastructure.”

Unlike a single visual inspection, SHM enables long-term changes and load trends to be identified. Uncertainties in condition assessment are reduced, and decisions regarding maintenance or refurbishment can be made on the basis of a significantly broader data set.

Side note: TÜV SÜD’s range of services – more than just sensor technology and data acquisition

Structural Health Monitoring encompasses far more than the installation of individual sensors. TÜV SÜD takes a holistic approach that covers the entire life cycle of a structure – from the initial feasibility analysis to long-term condition forecasting.

At the start of a project, the experts conduct a feasibility study to assess whether, and to what extent, a structure is suitable for continuous monitoring. They then develop a bespoke monitoring concept tailored to the specific structure, the loads it is subjected to, and its operational requirements. On this basis, suitable measurement systems are selected, and their technical planning, installation and commissioning are carried out.

Depending on the structure, different sensors are used to record, for example, deformations, vibrations, temperature trends or other structure-relevant parameters. The data collected continuously is then not only stored but also analysed by experts and contextualised within the overall structural framework. This enables changes in load-bearing behaviour or material stresses to be identified and assessed at an early stage.

Another component of the range of services is the provision of forecasts regarding the remaining service life and future maintenance requirements. This provides operators with reliable insights into how their structures may develop under various operating conditions. Furthermore, the system enables the simulation of different scenarios – such as the effects of speed restrictions, reduced axle loads or structural reinforcement measures. On this basis, investments can be prioritised in a targeted manner and maintenance measures planned cost-effectively.

At the same time, TÜV SÜD continues to offer all standard structural inspections in accordance with DIN 1076. These include main and routine inspections, special inspections following exceptional events, structural recalculations, material and strength tests, non-destructive testing methods, as well as damage analyses and rehabilitation recommendations. The combination of traditional engineering inspections and digital monitoring thus creates a comprehensive basis for the safe operation of railway infrastructure.

More data – better decisions

A key advantage of Structural Health Monitoring lies in the continuous availability of reliable condition data. Operators not only receive information on the current condition of a structure, but can also track developments over months or years.

This transparency enables significantly more precise planning of maintenance measures. Repairs can be carried out as and when required, rather than solely following fixed inspection intervals. At the same time, monitoring helps to determine the optimal time for refurbishment measures and to make better use of the remaining service life of existing structures.

Early warning system for critical changes

Whilst traditional structural inspections often only reveal damage at the next scheduled inspection, Structural Health Monitoring operates continuously. If defined thresholds are exceeded, warning or alarm messages can be triggered immediately.

This results in a significant safety benefit, particularly for safety-critical infrastructure. Potential damage or unusual loads can be detected and assessed at an early stage, before they lead to more serious problems. At the same time, unplanned closures can be reduced and maintenance measures planned more effectively.

Digitalisation complements statutory inspection requirements

Although digital monitoring systems are becoming increasingly sophisticated, they do not replace the statutory structural inspections. Major, routine and ad hoc inspections remain an indispensable part of structural monitoring.

Structural Health Monitoring (SHM) instead expands these procedures by providing a continuous information base between individual inspections. This results in a more complete picture of a structure’s life cycle and the stresses it is actually subjected to.

From repair to predictive maintenance

For railway infrastructure operators, a paradigm shift is increasingly coming into focus. Instead of rectifying damage only after it has occurred, data-driven, condition-based maintenance concepts are gaining in importance.

Through continuous condition monitoring, maintenance measures can in future be tailored more closely to the actual condition of the structure. Repairs are no longer carried out exclusively at fixed intervals, but rather when measurement data indicates a specific need for action. This approach not only improves cost-effectiveness but also helps to reduce closure periods and sustainably improve the availability of the infrastructure.

Data is becoming a safety factor

Digitalisation is fundamentally transforming structural monitoring. Sensor technology, data analysis and engineering assessment are increasingly merging into an integrated, holistic system. Individual snapshots are being replaced by a continuous assessment of the structure’s condition throughout its entire life cycle.

Structural Health Monitoring is thus evolving into a key component of modern asset management strategies. Particularly in the face of ageing transport networks, rising mobility demands and limited maintenance budgets, continuous condition monitoring offers the opportunity to manage investments more effectively, identify risks at an early stage and sustainably increase the availability of critical rail infrastructure.

For operators, this represents a fundamental shift in perspective: away from merely reacting to damage – towards a proactive, data-driven infrastructure strategy. The structure is thus no longer assessed only at regular intervals, but is monitored continuously. The traditional snapshot is transformed into a digitally supported, dynamic representation of reality – a decisive step towards the intelligent rail infrastructure of the future.