TU Delft researchers take a close look at the condition of the Zeelandbrug

By Linda Bak

TU Delft will spend the next two years investigating the condition of the Zeelandbrug between Zierikzee and Kats. The sixty-year-old bridge will soon need renovation or replacement. For the research, the field lab Monitoring Zeelandbrug has been set up. In it, the Province of Zeeland, TU Delft, HZ University of Applied Sciences, engineering firm Witteveen+Bos, and the World Class Maintenance Foundation are working together.

Eliz-Mari Lourens is one of the researchers involved in the field lab. She is an assistant professor of Structural Monitoring and Identification at TU Delft and has worked for years on algorithms to help monitor infrastructure. “To take decisions about renovating bridges and other structures, it is crucial to know the condition of a structure. A lot of research is being done on infrastructure monitoring using specially designed sensor networks combined with smart algorithms,” Lourens outlines.

Safety first

That’s also the case in the Zeeland Bridge field lab. “The goal is to ensure a safe connection for the next 15 to 20 years,” states the scientist. In addition, the field lab is a good way for researchers and companies to gain practical knowledge. With this, they can strengthen the Dutch business sector and improve education about similar constructions. “After the research, it is up to the province to make the final decision on the future of the Zeeland Bridge,” she said.

From the lab to practice

Installing monitoring systems on full-scale structures is essential for the researchers. “We are deploying different types of software and hardware – such as sensors. We know after laboratory studies that the methods work in theory and on a small scale in controlled conditions. But to make a real impact, we must go into the field,” Lourens states. The Zeeland Bridge then also poses significant challenges. The bridge is five kilometers long and is an essential connection for many Zeelanders. More than 15,000 vehicles cross the bridge daily.

“Various conditions slowly affect the bridge, such as the weather, traffic load, and salty seawater. These conditions are linked to failure mechanisms that can eventually cause a bridge component to fail.” The latter rarely happens, Lourens emphasizes. “In constructing bridges and other infrastructure, design codes stipulate large safety margins and periodic inspections.”

Accurate measurement with cables

How exactly do the researchers monitor the Zeeland Bridge? “Because the bridge is so long, we must carefully consider the sensor technology we use. Sensors that measure local behavior must be cleverly placed. We use optical fibers to map the global behavior of the bridge, among other things. In that case, we lay a cable that takes a measurement every few centimeters”, explains the researcher. Information from the various data streams is integrated with physical knowledge about the behavior of the bridge to arrive at an accurate prediction. 

Optical fibers are durable: the cables often last longer than many alternative sensors. These are also things we consider when setting up this type of field lab,” says Lourens.

A reliable model

The researchers aim to have a model that can make reliable recalculations in two years. Of the Zeeland bridge to begin with, but in the future, the technology can be used for similar bridges, too. “Now, the models we use are often partly based on assumptions, so we must deal with uncertain factors. We want to eliminate those as much as possible,” Lourens states.

That’s very important for the Zeeland Bridge and the rest of the Dutch infrastructure. Many bridges and roads were built between 1950 and 1970 and are now beginning to show wear and tear. This is evident, among other things, from TNO’s report ‘De staat van de infrastructuur’ presented last year. In addition, traffic has increased and become heavier in recent years —think of more and larger trucks.

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Different materials, different hazards

Many different problems can occur in bridges and other forms of infrastructure. It depends on the materials and how they are used. Concrete and steel can crack, for example, but chemical processes such as corrosion and carbonization can also affect materials, compromising the safety of a bridge. “With concrete, you are dealing with different hazards than with steel. Each material behaves differently and thus poses different risks,” says Lourens.

Man vs machine

Data-driven maintenance algorithms can only partially replace human physical inspections. “As more and more bridges need extra attention, these technologies offer opportunities to monitor on a structural basis and update mathematical models as needed. With physical inspections alone, that’s not possible. Still, physical inspections are also important. Technology only measures certain parameters (specific elements, ed.); physical inspections often provide additional information.”

The future of infrastructure

Currently, research focuses primarily on finding good ways to monitor bridges and other infrastructure. In the coming years, this will shift to developing new technologies to make renovations as innovative and sustainable as possible. Collaboration with industries such as engineering firms and construction companies will also become more critical. Lourens: “At the universities, we develop new technologies. Then it’s up to companies to implement it in practice.”