This novel spiral staircase was designed by researchers at ETH Zurich's Digital Building Technologies.
Intended for a building at EMPA (Swiss Federal Laboratories for Materials Science and Technology), it's made of concrete, but at a fraction of the material required if it were designed conventionally:
To create the staircase, the formworks for the concrete were 3D printed using a large format printer developed by Germany's BigRep.
Unsurprisingly, the mold is rather complicated:
BigRep notes that molds created in this manner can be re-used.
"Ultra-high-performance fiber-reinforced concrete is used for its excellent structural properties that enable very thin, complex shapes, otherwise impossible with regular reinforced concrete," writes EMPA. "Even though the innovation object is perceived as one coherent sculptural element, it is discretized into individual steps. The lightweight and structurally efficient elements are prefabricated and assembled on-site. The assembly is enabled by a state-of-the-art shape memory alloy post-tensioning system that provides the necessary reinforcement."
You can see more applications for concrete cast in 3D printed formworks in this BigRep video: