Steel bridges: safety and service life of existing infrastructure

Fatigue

Many existing steel bridges are approaching the end of their originally intended service life, while also facing increasing traffic loads. Fatigue is a critical issue for these bridges: cracks can develop over time, posing a risk to the reliability of the structure.

At the same time, full replacement is often costly and socially disruptive. Asset managers are therefore exploring strategies to ensure safety while responsibly extending the service life of bridges.

From around the 1950s onwards, welded connections increasingly replaced riveted joints in Dutch steel bridges. This was a major innovation, as welding is much simpler and enables more slender designs. However, a drawback is that welded connections are more susceptible to fatigue under repeated loading, due to higher stress concentrations.

'The question we address for Rijkswaterstaat is: how can we arrive at a more accurate assessment of the structural strength? In other words, how can we demonstrate that these structures are stronger than previously assumed.' - Adri Vervuurt.

Adri Vervuurt, Senior Scientist Structural Safety at TNO: 'A key characteristic of fatigue is that it manifests over the service life by formation of cracks, well before the structure ultimately fails. The “advantage” of crack formation is that the effects of fatigue can be identified during the service life, for example through monitoring and measurements. The question we address for Rijkswaterstaat is: how can we arrive at a more accurate assessment of the structural strength? In other words, how can we demonstrate that these structures are stronger than previously assumed.'

Why TNO?

For decades, TNO has worked with organisations such as Rijkswaterstaat and ProRail on the assessment and management of existing infrastructure.

Based on modelling, Rijkswaterstaat can estimate when crack initiation will occur in a steel bridge. As a result, a higher probability of failure can be accepted up to the next inspection than would otherwise be justified.

In other words, TNO’s model has enabled Rijkswaterstaat to plan its activities more effectively and reduce unnecessary inspection costs, without compromising road user safety. Asset managers actively use the model to define inspection intervals for structures.

Our expertise is relevant to:

• asset managers at Rijkswaterstaat, provinces and municipalities
• engineering and consultancy firms
• asset managers of bridges and other civil structures
• policymakers involved in infrastructure and replacement/renovation

Working together on future-proof infrastructure

Through the smart use of data, models, and expertise, TNO enables the safe life extension of existing steel bridges. In doing so, we contribute to an affordable, reliable, and sustainable infrastructure in the Netherlands. TNO supports organisations at various stages:

• analysis of existing bridge structures
• model development and validation using data
• risk and service life assessment
• advice on inspection, maintenance and renovationimplementation in guidelines and policy

Would you like to know more about how to extend the service life of your bridges? Please contact our experts or explore our projects and case studies.