The following is an excerpt.
Electricity pylon Alma has half the weight of her steel competitors. She just might signal the start of another victory for aluminium structures. Alma is made from fifteen different profiles. Eight of them are brand new. NTNU helped find the best.
Alma was duly christened, champagne bottle and all, by Statnett’s R&D Director Sonja Berlijn on 24 October. The ceremony took place at Kapp Aluminium, on the shore of Lake Mjøsa. In the weeks ahead the pioneer pylon will go through some severe testing, eventually leading to breakdown.
Potential new industry
Alma is not the first aluminium pylon produced in Norway. Hydro put up a series of them close to their production plant in Årdal 45 years ago, but stopped at that.
This time AluMast project owner Statnett is serious. Håkon Borgen, Executive Vice President for Technology and Development, puts it like this: “If we can get aluminium pylons at the same cost as steel, we will go for it. We will halve helicopter transport and reduce the need for assembly onsite. This will greatly improve working conditions.”
Statnett’s vision is to develop a pylon that can be put up without the need for workers climbing above ground level. As owners of 33 000 pylons, Statnett represents a significant potential for a new industry. A pylon lives for 70 years or more. Still, hundreds need to be replaced every year. New lines come in addition. A large percentage requires helicopter transport. Alma weighs 5.5 tonnes. That halves the 11 helicopter turns needed for an equivalent steel pylon.
When does she buckle?
Researcher Marius Andersen has been NTNU’s man on the project. After defending his PhD at SFI SIMLab, he was engaged by the AluMast project to work with the behaviour and modelling of aluminium columns. His has given special attention to the structural response of thin-walled aluminium tubes subjected to axial loading. The aim: to avoid buckling and collapse. In his work, Andersen has taken advantage of the numerical simulation methods and experimental techniques available at SIMLab.
His work was one of the factors that helped choose the fifteen best profiles to give Alma optimal properties. As sometimes happens, a successful research result is the scrapping of the solution you have investigated. In Marius Andersen’s case, his careful look at tubes showed that they were not the best choice for large parts of the structure. One important reason was the need for bolted joints. Therefore, half moon shaped tubes were preferred.
All the profiles are produced at Hydal in Raufoss, Norway’s largest pasta factory. Aluminium pasta, that is. The professional term for the production process when aluminium bars are heated to optimal temperature and formed into any imaginable form, is extrusion. The profiles are made from the same alloy, 6082, as the pylons produced 45 years ago.
Eight of Alma’s profiles have never been produced before. That says a great deal about the amount of research and development that has been put into the project. It also illustrates the pasta qualities of aluminium: only imagination limits the shapes and forms. In this context, the aim is for Alma to withstand any thinkable combination of stretching, compression, torsion, bending, vibration and temperature, while still keeping her sleek figure.
Will die young
Alma will die young. However, she will experience a lot on a way. The profiles have already undergone wind tests. Now, vibrations tests are waiting at Kapp Aluminium. After that, Alma will be dismantled and sent to Seville in Spain for further tests. In the final one, she will be brought to collapse.
The aim is to find out how much Alma can take. She must be able to tackle all the conditions she will experience in real life. At the same time, she shouldn’t be too strong. If she is, it means she can be made even lighter.
The AluMast project, that has produced Alma, is an IPN project. IPN is a funding scheme administered by the Research Council of Norway, directed towards innovation building projects for industry. The aim is to help industry through research.
AluMast comprises the whole chain typical for an IPN project, starting with the basic research performed by Marius Andersen and others. SFI CASA partner Hydro is an AluMast partner, supplying aluminium and expertise. SINTEF Raufoss Manufacturing has played an important role in pushing the project forward. At the other end of the chain, we find Statnett as customer and project owner. Their wish has been to bring about an aluminium pylon suited for the highest voltage levels and for the Nordic climate and topography.
At the christening ceremony, all partners stressed how useful it has been for the project that all parts of the chain have collaborated. It has been financed by in-kind contributions from the partners. In addition, the Research Council has granted ten million NOK. Statnett and Innovation Norway have also put in two million each.
If everything goes well, the first aluminium pylons will be installed in North Norway in a few years.