Innovative Construction: Active-Bending Structures

The Institute of Building Structures and Structural Design (ITKE) at the University of Stuttgart is pushing the use of materials and engineering systems to new limits. As part of ongoing research on Active-Bending structures the institute has built the Bend9 pavilion, which further explores the potential of engineering systems that use bending as a shape‐forming strategy.

Developed by ITKE engineer and researcher Riccardo La Magna, the pavilion focuses on the use of intelligent material for the construction of complex free-form surfaces. Specifically, the project engages with the challenges of building load‐bearing shell structures, arbitrary in shape and geometry, by simply exploiting the properties of bending.

Clearly, Bend9 presents an alternative mode of construction which departs from traditional building systems. Instead of using preformed elements, the pavilion takes advantage of the deformation qualities of planar sheets of material to achieve its overall shape. This logic of construction is directly informed by the mechanical features of the plywood employed for the project. The overall geometry is the result of a type of negotiation between the mechanical limits of the material and its deformation capabilities.

To fully exploit the large deformations that plywood allows for the thickness of the sheets is reduced to a minimum (the final choice being 3.5mm birch plywood). The overall shape of the shell provides additional stiffness, as the pronounced double‐curvature helps avoiding undesirable types of deformation in the pavilion.

Although a very elegant way to build large structures with minimal use of material, the high production costs and fabrication complexity of double‐curved components often renders their application in engineering prohibitive. However, the assembly strategy for the pavilion totally eliminates these issues and drastically reduces the fabrication complexity by resorting to exclusively planar components which make up the entire double‐curved surface.

As such, the pavilion is no longer the result of an assembly procedure of preformed pieces, but rather the outcome of a form‐finding process guided by the underlying construction logic. The tiling logic of the initial master geometry guarantees that each component can be bent into the specific shape required to construct the whole surface. This is achieved by strategically placing the voids into target positions, ensuring that the bending process can take place without prejudice for the individual components. Although initially flat, each element undergoes multi-directional bending and gets locked into position once neighbouring pieces are added. The supple 3.5mm plywood elements achieve consistent stiffness once assembled, although a discrete version of the initial shape, still retains substantial shell stiffness.

The pavilion employs 196 elements unique in shape and geometry and 76 connectors for a total of 156 exclusive compound mitres. The geometry of the elements is the result of the evaluation of the material properties and forming capabilities at the very early stage of design. Despite the large amount of individual custom components, the whole fabrication process was easily optimised as each element is cut flat and later assembled on‐site.

Overall, the Bend9 pavilion exemplifies the capacity of Active-Bending surface structures as part of a process of shape‐generation. For ongoing research, the building serves as a first prototype for the exploration of surface‐like shell structures that derive their shape through elastic bending.

Photo credit: “University of Stuttgart / Riccardo La Magna”. Material used in the preparation of this article has been drawn from ITKE.

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