In recent years, scientists have created shape-shifting materials, which are often made from polymers that bend and twist when they’re exposed to some kind of external stimulus, such as heat or moisture. Now, researchers from the University of Stuttgart’s Institute for Computational Design and Construction have figured out how to bring similar shape-shifting properties to one of humanity’s oldest building materials: wood.
After three years of research alongside the Swiss Federal Laboratories for Materials Science and Technology and the Swiss Federal Institute of Technology Zurich, the designers have created a striking, 46-foot-tall twisted wooden tower as an architectural prototype of what their new technique can achieve. Each of the 12 wooden components of the tower was made by laminating two pieces of wood with different levels of moisture. Then, when the laminated pieces of wood dried out, the piece of wood curved naturally–no molds or braces needed.
As the environmental cost of building with glass and steel becomes increasingly apparent (New York City Mayor Bill DiBlasio recently decried the carbon emissions of traditional glass skyscrapers), some architects, designers, and scientists are hailing timber as the building material of the future. This is in part due to the rise of cross-laminated timber, a building material that reinforces the weaknesses of individual wood pieces by laminating it together with other timber. The Institute for Computational Design and Construction’s research is part of this growing trend, especially as wooden skyscrapers start to pop up around the world.
But while timber is a great building material, there are hurdles to using it in creative ways. In the past, to make wood curve, architects have to apply moisture to the material and then use often expensive and time-consuming molds and rigs to hold the wood in place by force until it dries. The institute’s new technique will be much less expensive and allow for more variation in what types of curves are produced, because no external force is required: just the clever alignment of wood with different grain directions and levels of moisture. From there, the wood dries into a new, curved shape.
Warping wood using moisture isn’t a new idea, but knowing exactly what the curvature would look like on the other side is. Using computer simulations, the researchers were able to calculate the exact amount of moisture each piece needed to have, along with which direction the grain of each piece of wood should go, to predict how exactly each length of wood would curve. If the moisture differential between the two laminated pieces is large, the wood curves more, while if the moisture differential is smaller, the wood curves less. In some experiments, the researchers designed the wood to bend so much that it had a radius of 3.3 feet.
Almost as important as the direction of the grain was the realization, after many experiments, that if the grains of the two pieces are perpendicular to each other, then the final curved wooden piece will begin to twist as well as curve.
The technique is based on the way that wood holds moisture: It’s why wooden chests’ drawers don’t always fit perfectly in different seasons, because the wood will absorb any water that’s in the air. “Usually in timber manufacturing or engineering, this is seen as a problem,” says Achim Menges, the director of the Institute for Computational Design and Construction at Stuttgart University, who led the research project. “What we have done is basically used this assumed deficiency as an advantage to shape the material.”
For decades, furniture makers and architects have used curved wooden shapes in their designs. Creating the wood forms always required using moisture, along with some kind of mold or brace, to create the desired effect. But since this new technique does not require the use of any kind of mold, it’s far cheaper to create different curved shapes with wood. “We no longer rely on always having the same curvature because we need to use the same mold,” Menges says. “Just by playing with grain direction and moisture content, we can program the material itself to take a particular shape.”
Additionally, the technique doesn’t require tools beyond two that are already a part of standard manufacturing facilities: moisture readers and industrial ovens (timber factories already have these machines, since all fresh timber has to be dried before it can be used as a building material).
As a result, Menges anticipates a wide range of applications, mostly in adding curved architectural elements to buildings–a detail that looks beautiful, but that also makes buildings more structurally sound and more environmentally friendly, to boot. “A curved element allows you build with less material,” Menges says. “If it was a straight cube or box, it would consume a lot more material.” He believes the technique adds “a truly sustainable forming process to an already really sustainable building material.”
There are challenges ahead: Menges says that while the curving process doesn’t require tools beyond what is already available in timber manufacturing facilities, the industry is still designed for flat pieces of wood, making logistics more difficult (you can’t fit nearly as many curved pieces of wood on a truck as you can flat pieces). But he doesn’t think it will be too difficult to overcome. After all, the 46-foot-tall tower was prefabricated in five days and only took five hours to assemble. The tower is currently on display at the Remstal Garden Show in Germany, which runs until October 20.