A stronger future for our bridges
New research and engineering insights from Arup are helping to overcome metal fatigue and improve bridge lifespans, redefining how we deal with ageing transport assets
With aging bridges used in ways they often were not designed for—facing intensifying stress from environmental factors and the increased average weight of electric vehicles—the implications for bridge endurance and safety are growing concerns. As many bridge engineers would confirm, the issue of metal fatigue and its impact on bridge decks is a key design dimension that hasn't been understood in sufficient detail or approached with nearly enough rigor.
The positive news is that engineers are developing deeper insights into metal fatigue and examining how the adoption of circular economy principles, such as reusing materials during refurbishment, can extend this infrastructure’s lifespans in sustainable ways. We’ll explore those solutions in more detail below.
Growing awareness of a widespread problem
Although there is a lack of consistent global data on bridges, in Europe, most steel railway and road bridges are within the 50 to 100-year age range. If we focus on steel railway bridges, a (Dinas 2017) survey found that 75% were over 50 years old, and almost 35% were over 100 years old. We also know that 45% of bridges in the United States are more than 50 years old.
For many decades, it was assumed that major cracks in bridge decks were unlikely during the infrastructure’s design life. Research in 2008 (de Jong 2007) demonstrated that in reality, cracking can start as soon as seven years into a bridge’s lifespan. Given the widespread expectation that a bridge will last the design life of 50 to 120 years, this number represents a wake-up call for the whole industry.
Importantly, steel decks are used on everything from short-span lifting bridges to long-span bridges. For example, in China, the Yichang Yangtze River Highway suspension bridge had extensive cracking despite being constructed in 2001 (Shiqiang Qin 2023).
A central issue is that metal fatigue has never been seen as a primary risk for new bridges—in engineering terms, the governing load is usually traffic weight, wind, or seismic activity. Historically, there are also no well-defined guidelines for dealing with the threat of metal fatigue, leading to a lack of awareness. It’s an issue compounded by a lack of physical visibility, the complexity of carrying out rigorous analysis and testing, and fear of the implications of bridge closures—all of which produce a reluctance to face this issue head-on.
A new approach to bridge renovation
Engineers and designers of transportation infrastructure have learned a lot more about metal fatigue in the last 15 years, and these insights are shaping new approaches to our bridge design and maintenance practices. These insights not only determine the overall quality of assets like roads and bridges but help us maintain a dialog between transportation authorities, regulators and standards bodies, and the wider public.
Our work on bridges in the Netherlands—a central node of European trade with some of the busiest roads and bridges on the continent—has provided us with unique insights into metal fatigue. Working as a partner to the Dutch highways authority, Rijkswaterstaat, we have been addressing this growing issue by developing inspection, repair, and strengthening (both local and global) measures to extend the life of these bridges.
In the Netherlands, this work is informing a new Euro-code supplement (Technical Specification TS 1993-1-901). This improved set of fatigue classifications and design rules will provide a more accurate and clearly defined approach to the design of steel bridge decks. The result for new bridges will be thicker deck plates to ensure the full design life is achieved. But codes alone aren’t enough—these insights need to shape understanding and drive development by bridge designers. Every bridge is unique in terms of typical load, location, and usage—understanding how metal fatigue will manifest in each context is vital.
Assessing existing bridges presents a wide variety of challenges that require different approaches to solve depending on the circumstances. As an aid to manage these challenges, we have also developed new guidelines for the assessment of steel bridges for fatigue for National Highways in the UK. Our work has established a systemic approach to bridges’ vulnerability to metal fatigue—an assessment and inspection that leads to a pragmatic and contextual fix.
Circular principles, extended lifespans?
One of the busiest bridges in the Netherlands is the Van Brienenoordbrug, a key connection to the Port of Rotterdam. The twin bridges carry about 230,000 vehicles daily. Like so many bridges built decades ago, the renewal challenge was considerable for such a key part of the region’s transportation network. Our approach was meticulous and prioritized circularity, with the planned reuse of 3,200 tons of steel while maintaining the bridge in its original form. That’s an almost 50% reduction in lifetime carbon emissions.
The approach for the Van Brienenoordbrug is to remove the older, eastern bridge and replace it with the newer, refurbished western bridge, while a new bridge is constructed off-site and installed to replace the western bridge. This approach will add 100 years of life to both halves and mean the bridge is only closed completely for six weeks, rather than facing partial closure for 1.5 years. The conclusion we draw from this example is that adopting circularity can drive operational benefits and efficiencies as well as sustainability performance.
Action – a balance of timing and funding
While it’s true that no one wants to spend unnecessarily on pre-emptive maintenance, materials science suggests this is a widespread issue and one that’s only likely to grow.
Inspections should happen promptly, not because every bridge will require immediate repair, but because knowing the condition of an asset allows it to keep operating safely and enables operators to plan. Thoughtfully designed systems of embedded digital sensors make this practical and cost-effective, as we proved in our work on Queensferry Crossing.
Thoughtfully designed systems of embedded digital sensors make this practical and cost-effective, as we proved in our work on Queensferry Crossing.
With a structured inspection regime, you can design a monitoring system that can rigorously assess crack development and asset longevity. This knowledge lets you set realistic timelines, phase capital expenditure sensibly, and combine public safety with sustainability through timely repair and refurbishment.
Metal fatigue is an issue that requires industry and government to work together, based on shared understanding and recognition of the issue. Delivering a sustainable approach to bridge renovation at scale will take collaboration between technical experts and asset owners, with shared responsibility for solutions (and their funding) driving ultimate success. In our wider work, as we help national agencies and transport operators deal with interlocking issues posed by ageing transport assets, we also need to be transparent about the size of challenge, and collaborative as we tackle bridge renewals.
To explore how Arup can support your bridge renewal or maintenance, contact us.
