Monitoring preload

DYWIDAG is best known for forecasting technology. An increasingly important part of its services is monitoring. In other words, Life Span Management over the entire life span of a structure in order to get a better grip on the structure and to be able to carry out any repairs and reinforcements in a timely manner.

At least a thousand bridges in the Netherlands are past their initial lifespan. But what does that mean? What needs to be done? "Monitoring bridges provides insight into the current condition of a structure," says Jansen. "Our Life Span Management department can fully visualize changes in structures (not only bridges, but also quay walls, locks, etc.) by integrating sensors. This provides information not only about any deformation, but about displacement, elongation and shortening. We can also measure the prestressing force and how it changes with time. By mapping where exactly the bottlenecks are, we can actively intervene to prevent calamities. Unnecessary maintenance based on 'traditional protocols' is also a thing of the past."

Preload without attachment

"As an internationally based and operating company, we have the knowledge, resources and products in-house and also take our responsibility very consciously," Jansen continued. "We push very hard on the themes of sustainability and circularity. For example, we closely follow developments in printed constructions. Not only in terms of predictive techniques, but also in terms of monitoring solutions. For example, we deployed our expertise and systems for the world's first printed bicycle bridge, which went into service three years ago in Gemert in Brabant, and we are now closely involved in the development and monitoring of a printed bridge in Nijmegen. Printing larger structures generally means that several elements have to be connected together. The way of building up the prestress requires different techniques than the usual methods used in concrete. We offer the right solutions for that: prestressing without adhesion."

To measure is to know

To monitor the effect of loading on the prestress (without attachment) in (PCB) bridges, sensors are integrated. Jansen: "All kinds of assumptions are made in advance. By measuring effectively, we can check whether those assumptions are ultimately well-founded. The circular viaduct in Kampen is a demountable test bridge and composed of separate components. Sensors around the prestressing cables and under the bridge measure the deformation resulting from the load on the deck. In addition, temperature sensors are placed both above and in the deck and camera monitoring is in place to properly assess the nature of the traffic. The position of the bridge on the globe has also been precisely recorded with sensors to detect shifts. The bridge has since been dismantled again and has held up well. In the end, our assumptions even turned out to be a little too conservative and we could do with less preload. That's another conclusion you can only find out one way: measure."

Monitoring completes the circle, Jansen summarizes. "By knowing what is happening and how something is happening, you can take targeted action and engineer new projects. For example, for the PCB bridge in Nijmegen, a test bridge that is ultimately part of the complete bridge, we knew how to engineer the right preload. Here, too, the specific prestressing force was measured during the test process using sensors around the prestressing cables. The results were exactly in line with what had been calculated. By making structures smarter with sensors, we can ultimately engineer smarter as well."