Wrapping instead of welding boosts construction endurance
Structures constructed to produce energy offshore have to hold out in rough circumstances. The so-called jacket foundations made of large steel tubes that fixate windmills to the seabed are sensitive to fatigue loading, especially their welded connections. In the near future, the fatigue endurance of this steel construction can be a hundred times better thanks to an innovation by TU Delft of wrapping the joints with composite material, instead of welding them.
The rough conditions at the ocean are a serious issue for the endurance and demand improvement of the jacket support structures. The welded junctions are vulnerable for fatigue loading due to wind and waves and corrosion resistance is also put to test in the salt water.
![[Translate to English:] Wrapnode Impressie](https://filelist.tudelft.nl/News/2024/05_May/CiTG/WrapNode%20impressie%204.JPG)
The construction industry is used to utilise welds and bolds. According to Marko Pavlovic, assistant professor in Steel and Composite Structures at TU Delft, the brittle type of behaviour is not good. “Once a small tearing occurs, the whole structure fails.” He got inspired by trees to come up with something better. He now investigates a method to smoothly attach steel branches to each other, and reinforce the construction at places where there is the highest load, just like trees do. “The industry did not believe in this new structure. But tests and science say it can be a hundred times better.”
We are talking about the so-called WrapNode, a glass fibre composite connection. This composite material is wrapped around the steel tubes. Pavlovic explains with toilet rolls and tape: “It is just like duct-taping. I have one tube, and at the sides I would like to attach another two tubes. I put them together and wrap tape around the connection. Should I use some glue instead, the structure would break easily once I pull it, but with the tape it is really strong.”
![[Translate to English:] WrapNodes exposition](https://filelist.tudelft.nl/News/2024/05_May/CiTG/WrapNodes%20exposition2.JPG)
Tested on full scale
Because of this innovative construction method it was hard finding ways to conduct research and thoroughly test, model and calculate properties. Starting small in 2017 and after years of testing, the research group has now scaled it up to tubes with a diameter of one to two meters for connections in jacket foundations of 60 meter high. Pavlovic: “We tested the full scale junction. The bending test was an equivalent of, roughly, 25 years of use offshore. And we did see no damage at all.” Another benefit of this wrapping technique, is that once it starts to fail, it will not cause the whole structure to collapse. When the steel tubes partly slide out of the wrap due to forces, they will still stay in place because of the tight and firm wrapping.
![[Translate to English:] Failed WrapNode](https://filelist.tudelft.nl/News/2024/05_May/CiTG/Wrapnode%20failed.jpg)
Upscaling offshore energy
“To produce enough sustainable energy in the future, we have to expand the offshore energy production,” tells Pavlovich. “We cannot stick to existing methods of monopiles and jackets. We need to broaden the way of producing the constructions to keep up with the demand.” In 2017 Marko Pavlovic invented the composite joint at TU Delft. Now, the start-up Tree Composites aims to get this technology to the market. Tree Composites built the first full composite floating platform with WrapNodes for the SeaVolt consortium which installed this floater supporting solar panels in August 2023 off the coast in Oostende in Belgium. The implementation of WrapNode in full scale jacket support structures is expected to start in 2026.