Drones are the inspection of the future: "The Great Belt bridge shall outlive most of us"

Mathias  Flindt

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Drones are the inspection of the future: "The Great Belt bridge shall outlive most of us"

The Great Belt Bridge has been in use since 1998 and must last for at least 100 years. Therefore, the bridge is continuously maintained and inspected for cracks and wear.

Until now the bridge has been maintained by people rappelling on ropes or by using a crane which transport people up and down the Great Belt bridge's enormous heights.

But gradually the rope and lift are being replaced with the inspection tool of the future, which is more climate-friendly and takes place with a joystick in hand.

Drones, sensors, and artificial intelligence are the new eyes and hands when it comes to making the Great Belt bridge outlive most of the rest of us.

Drones have already been used to find the cracks in the bridge, but now it has also become possible to investigate how deep the cracks are, so that it can be known more quickly which of the cracks need to be repaired.

This work is the result of an Odense Robotics collaboration between Sund & Bælt, the Danish Technological Institute (DTI), the Technical University of Denmark (DTU), the Danish Drone Network and Senseable. The project, called DroneDeploy, has examined the possibility of supplementing ropes and lifts with new technology.

- The drones are now being used for interactions and not just observations. Before, the drones took photographs and people still had to physically go to the cracks and find out if they were too deep and needed to be repaired. Now you can put pressure on the crack with the drone and see how deep it is and whether it is serious, says Mathias Flindt, Consultant at DTI.

A greener maintenance

The drones - and the fact that they can now interact with the bridge - may prove to add years to the life of the Great Belt bridge.


Finn Bormlund is project manager and engineer at Sund & Bælt. He has no doubt about what the drones can mean for the future of the Great Belt bridge.

- The bridge was designed to last about 100 years, but we are aiming for 200 years by providing better maintenance -- and the drones may help us achieve this, says Finn Bormlund enthusiastically.

But the extended lifespan not only saves time and money.

- The climate also benefit from the bridge getting extra birthdays. Building with new materials such as steel and concrete is expensive in terms of the CO2 footprint. Specifically, an extra 100 years will save 750,000 tonnes of CO2, says Finn Bormlund.

From free-flying to fixed-mounted

The drones are controlled to fly round and check the condition of the bridge by photographing the surface of the concrete. This can find the cracks in the concrete faster and easier than before.

An algorithm from Senseable analyzes image data and identifies cracks in the concrete surface.

But the new thing is that you can make the drone "get stuck" on the surface of the bridge, and in that way measure how deep the crack is.

- You can see immediately if it is a crack that needs to be repaired or if it is just a cosmetic crack that does not require repair, says Mathias Flindt.

Matteo Fumagalli, associate professor of robot technology and unmanned autonomous systems at DTU, is one of those who has developed the new type of drone for inspection of the Great Belt Bridge.

- The drone flies around the bridge structure looking for cracks using built-in sensors. Once a crack is detected, it first assesses whether a crack is critical using visual information from a built-in camera, he says.

The drone will then land and sit "fixed" on the wall - i.e. go from being free-flying to being "fixed".


DTU's software helps the drone to place the manipulator correctly on the concrete surface so that measurements are obtained in the right places.

- The drone uses a robot arm to inspect the crack depth using ultrasonic sensors, says Matteo Fumagalli and continues:

- Drones can not only be used to take remote measurements, for example with a camera, but also to use sensors and even tools that require a physical interaction with the environment. That's the new thing about this project.

Once the cracks are located, an algorithm from Senseable helps to calculate the correct positioning of the measuring equipment. 

Captures damage earlier

The entirety of the Great Belt bridge's construction is checked from sea to sky every five to eight years during a general inspection, which requires lifts, cranes, and a large crew.

- It requires a lot of manpower to carry out bridge inspections with a lift and rappelling, when the bridge needs to be checked. The lift must be able to reach a height of 254 meters and we must, among other things, block lanes and have a lot of staff available. Therefore, inspection is carried out continuously over several years and is a very time-consuming process, Finn Bormlund says.

- With the drones, we should be able to catch the damage earlier. Inspecting the cracks with a drone makes it possible to inspect the bridge more often, so that cracks are caught before they become so serious that a major repair is needed.

The project was carried out under the auspices of RoboCluster, which has now become part of Odense Robotics. The project is supported by the Ministry of Higher Education and Science and the Region of Southern Denmark.

Develop and test concepts together with DTI

DTI offers independent consultancy and hands-on experience with various drone technologies - reducing the amount of time and money that companies need to invest.

For more information, contact Mathias Flindt from DTI at mfl@dti.dk.