"World-first" twisting tower is made from timber that bends itself into shape

Moisture is usually bad news for timber, at least if you plan to use it for building purposes. This is largely because it can cause the material to crack and warp as it dries out, features hardly conducive to the idea of structural integrity. But one group of researchers in Germany is investigating how this process can actually be harnessed for more efficient construction, manifesting in a magnificent tower made up of timber pieces that twisted themselves into shape.

Generally speaking, part of preparing timber for construction involves ridding it of moisture by drying it out in a kiln, or a machine with similar heating capabilities. This causes it to deform, but ultimately stabilizes it and makes it suitable for use. Researchers at the University of Stuttgart's Institute for Computational Design and Construction are exploring how they can interfere in this process to "program" the wood so that it transforms into desired shapes, just like you might program a robot to perform particular movements.

"By carefully understanding and digitally modeling the deformations that occur in the drying process we can arrange the wood before drying to produce specific deformations," team member and doctoral candidate Dylan Wood explains to New Atlas. "More specifically, we build flat wood bilayers plates (two layers with opposing grain directions) while the wood still has a relatively high moisture content. The plates are dried using industrial drying processes and they emerge curved. The species of wood, grain orientations, thickness ratios, and the change in moisture during the drying process are all parameters that affect the curvature."

The team says its so-called Urbach Tower is the first structure in the world to use self-shaped building-scale components. To begin, the bilayers were produced to contain 22 percent wood moisture content and were then dried to 12 percent, which Wood says is standard for this type of construction. Once dried and curved, the bilayers were stacked and glued together to lock their curvatures in place.

These warped Cross Laminated Timber (CLT) components were then transported by truck to a site at Remstal Gartenschau 2019, a garden show in the German city of Schorndorf. Here, a team of four craftsmen assembled the pieces into a striking 14-meter-tall (45-ft) tower in a single day, topping it off with a transparent roof. The tower was then finished with a protective facade of larch wood, and is also equipped with sensors that will track moisture content over the coming decade to try and keep tabs on any further warping.

"The elegant part here is that we don't need to add water as wood cut starts with a high moisture content, so in a way we are just strategically intervening in the drying process to use the shrinking forces rather than fighting them," says Wood.

Though Wood and his colleagues used spruce wood boards sourced from Switzerland, he says that this process can theoretically be applied to any species of wood, as it all shrinks and swells. And though the Urbach Tower certainly makes for an impressive spectacle, the hope is that it acts as a proof-of-concept for a form of self-shaping architecture that can make wood a more appealing material for different kinds of projects.

Not only is wood more sustainable than concrete or steel, contorting it into desired shapes through this method negates the need for energy-intensive mechanical forming that involves serious machinery, as the material itself does the heavy lifting. This also brings down the cost, and could make these kinds of curved CLT pieces viable options for load-bearing components in walls and long roof structures, for example. And according to Wood, the technology could even extend beyond the world of construction.

"Our research group at ICD is also studying similar self-shaping methods using wood and new materials combined with 3D printing where we can tune the shapes and speed for smaller parts with more complex movements," says Wood. "These parts have a range of applications, from building facades and roofs that open and close autonomously with the weather to clothing that vents when you sweat and seal when you are cold."

Source: University of Stuttgart