13 September 2019
It is now easier to make complex, curved timber structures by harnessing wood’s tendency to swell and shrink in response to moisture. The technique has been used to make a large twisting tower in Germany.
Using wood to produce complex, curved shapesrequires a lot of energy and wasted timber. To try to minimise this, Markus Rüggeberg at the Swiss Federal Laboratories for Materials Science and Technology and his colleagues tried a new technique which involved manufacturing flat panels of timber that were designed to curve in specific ways as they dried.
This technique is different from traditional manufacturing, which typically involves drying the timber out before using powerful machinery to bend it into curved structures. Here, moisture is considered a drawback because changes can cause deformation and cracking in the timber.
The first proof-of-concept building made from the team’s self-shaping wood was erected in Germany in May. The Urbach Tower is a twisting, 14-metre-tall structure made from 5 metre by 1.2 metre spruce planks.
But for self-shaping wood to be practical for large scale designs, engineers first need to be able to predict how different wood responds under different conditions.
To do this, Rüggeberg and his colleagues tested the technique on 15- to 45-millimetre-thick planks made from an abundant hardwood, the European beech, and an abundant softwood, the Norway spruce, on computer models and in experiments.
The timber is constructed by glueing together two layers of plywood that run perpendicular to each other. These are manufactured with a wood moisture content of 18 per cent or more – higher than the 10 to 15 per cent wood moisture content that timber is typically manufactured at.
As the moisture content in the wood drops, one layer shrinks while the other stays the same, bending the wood.
Engineers program the wood to curve in different ways by adjusting the way it is layered. Once dry, the layers are bonded together locking in the curved state. This won’t change regardless of moisture in the atmosphere.
This technique could revolutionise masstimber production and building, says Rüggeberg. Without needing heavy machines to bend wood, it could be done less energy intensively.
Journal reference:Science Advances,DOI: 10.1126/sciadv.aax1311
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