Complex design, ageless beauty

A modern greenhouse ETFE dome grows with the use of 3-D modeling software.

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The botanical gardens in Aarhus, Denmark, have a lot of history. They were first developed in 1875 as a way to showcase thousands of species to its visitors. In 1969, a greenhouse dome was constructed to allow for the greatest interior volume with the lowest possible surface area—a very energy-efficient design. The support structure consists of 10 steel arches, which fan out around a longitudinal and a transverse axis, creating a net of rectangles of varying sizes.

FormTL in Radolfzell, Germany, planned and designed a cover for these arches made mainly of double-layered ETFE cushions, which are affixed with biaxially bent profiles due to their complex structure. On the south-facing side, the cushions are made with three layers. Through changes in pressure, the relative positions of these foils can be adjusted. This adjustment can increase or decrease the translucence of the cushions, changing the light and heat input of the building as desired.

Manuel Neidhart, project engineer at FormTL, explained that the most challenging aspect of the project was the three-dimensional bent aluminum profiles, which make up the complex shape of the roof.

“The flat bended projection of the three-layer aluminum profiles was generated with self-programmed software, which generates the geometry in the two main axes—the X and Y axes—of the profile, and a torsion angle in the length axis—the Z axis—of the profile, so that a profile bending company could produce these special profiles. The geometry of these profiles was generated rectangular to the shape of this complex roof geometry with the software Rhino 5.0.” The 3-D modeling software was crucial for FormTL as they developed the design for the complex roof structure.

Another challenging aspect to the project was the three-layer cushions for shading the south side of the roof, and the air support system for moving the inner layer. “The middle layer of the moving cushion lets a layer of air move from the inner to the outer side," Neidhart explains. "If the roof is not shaded, air can flow between the space to dry the cushions." Quite a complicated method of moving air within the structure takes place so the structure can remain temperature-controlled.

"The air support system uses different pressures to move the shaded cushions," Neidhart explains. "This system has to be planned so that all cushions with the shading option can be filled with two different air support hoses. The tube system was placed at the main structure with no contact to the cushions; this prevents friction between tube system and cushion.” This complex design allows the structure to be temperature controlled.

Even though this project included many complexities, Neidhart cites the most rewarding aspect is being able to solve those problems that came with the complex design of the roof surface, "and to see the good result of this really nice and good-looking roof," Neidhart adds.

FormTL’s clients were impressed as well. “Our contractor says that the clients are all satisfied and happy about the new roof for their tropical plants.”

The structure has revamped the greenhouse, making it more energy-efficient and therefore more cost-effective to run. Aarhus remains a popular destination for locals and tourists alike, and now visitors will be able to visit the greenhouse for many years to come.

Kelly Frush is a freelance writer from Minneapolis, Minn.

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