Researchers at Lund University have developed a new framework that can lead to the Öresund Link, thanks to the right maintenance at the right time and smart monitoring, having a total lifespan of 200 years. This is twice as long as envisaged when the bridge was inaugurated 25 years ago.
The results come from the interdisciplinary research project EXTEND, which is led by Sebastian Thöns and Ivar Björnsson, both from the Division of Structural Engineering at LTH. The project team has developed new methods for how large infrastructure facilities can be kept safe, efficient and sustainable far beyond their intended lifespan.
"For more than a decade, we have developed utility-based decision analysis originally rooted in economics, and adapted it to engineering contexts such as bridge infrastructure. We have used these unique methods for the Öresund Link," says Sebastian Thöns.
Scientific models for a long life
When the Öresund Bridge was inaugurated in the year 2000, its technical lifespan was estimated to be 100 years. Since then, more than 150 million cars and 1.5 million trains have travelled across the bridge. This, combined with the strong impact of weather, means that the bridge is constantly worn down.
In 2021, the operators of the Öresund Bridge (Øresundbron Konsortiet) initiated a scientific review of the bridge's prospects for extending its service life. The goal was to investigate whether the link, which consists of a bridge, a tunnel and an artificial island, can be kept running until the year 2200 - technically, environmentally and financially.
The research within the EXTEND project is based on a combination of scenario-based life expectancy analysis, structural reliability with so-called degradation models, as well as inspection and monitoring data. By simulating how materials such as steel and concrete degrade over time and how different maintenance strategies affect the structure's durability, the researchers can identify cost-effective and sustainable ways to extend the bridge's safe service life.
"We have developed methods that show how the lifespan can be extended by deploying measures where they really make the biggest difference. It's about understanding why and how the structure comes to a service life end - and monitoring and acting in a targeted manner to tackle the service life limiting scenarios," says Sebastian Thöns.
Focus on the bridge's most critical parts
The work has focused on the parts of the bridge that are most service life relevant, technically and economically - especially the steel truss, the inclined cables and the tunnel section.
The large oblique cables, which support the main span of the bridge, are subjected to great stress and are crucial for the safety of the bridge. According to the researchers, cable replacements must be planned very carefully, but new technology for monitoring as well as maintenance can greatly extend their lifetime.
"The suspension cables are some of the most critical components. They are subjected to high loads and stress over time, and their maintenance requires both precision and care. By using sensors and continuous monitoring, and updating our models with the collected data, we can determine when an intervention is really needed," says Ivar Björnsson.
The tunnel under the Öresund has also been analysed. Here, the researchers have modelled how chemicals penetrate the concrete and affect the reinforcement. By updating these models with chemical ingress measurements, a significant service life extension for this specific scenario could be justified.
The EXTEND project was driven by both the research methods and the ambitious, professional and demanding project management by Torbjörn Arland and Bengt Hergard the Øresundbron Konsortiet.
"Without the critical interaction with the bridge operators, we would not have come this far," states Ivar Björnssson.
The results show that both the tunnel and the bridge can live on for 200 years, provided that they are inspected and maintained according to the strategies proposed by the EXTEND project.
Digitalization and sensors for the future of maintenance
The research has also laid the foundation for a new generation of data-driven maintenance. The Öresund Bridge Consortium has already installed over 5,500 sensors along the bridge, which register vibrations, temperature, humidity and movement. With the EXTEND project it is demonstrated how specific data can be used to update service life extension models so that they have so-called information value.
"Through our models, we can, among other things, calculate how environmental conditions at the bridge and tunnel affect the structure. It can be modelled how long it takes for chemicals to diffuse through the concrete and how fast corrosion in the reinforcement occurs," says Ivar Björnsson.
The usage of both the sensors and the models make it possible to analyse and to predict the condition of the bridge, and to plan and act in time. However, the sensors need to deliver relevant data for the service life limiting scenarios. This is crucial for maintenance to be planned with higher precision and lower costs than before.
A model for the infrastructure of the future
At the end of the service life, it will not be economically viable to replace parts or to repair the bridge, or it will be too difficult. Building new infrastructure is one of the most resource-intensive activities in society. Demolishing a bridge or a tunnel costs an enormous amount of money. The environmental impact is also very large considering the amount of concrete and other materials involved.
"Doubling the lifespan of the Öresund Bridge does not only mean technological progress - it is also an important contribution to the climate transition. By extending the life of existing structures, emissions, material consumption and costs can be drastically reduced. This is what we quantified,"says Sebastian Thöns, and Ivar Björnsson agrees.
The hope is that the methods developed within EXTEND can be applied to other infrastructure and contribute to modernizing how society as a whole plans, assesses and extends the life of large structures.
