The Spider's Lesson

The Spider’s Lesson

Some of the most interesting research into the architectural/structural use of composites continues to be done by the Institute for Computational Design (ICD) and the Institute of Building Structures and Structural Design (ITKE) at the University of Stuttgart. We featured their research pavilions from 2012-2013 and 2013-2014  previously here. They’re back again.

This group, under the leadership of Prof. Achim Menges and Prof. Jan Knippers, has again drawn on the “engineering” of the natural world to find structural efficiencies that can be scaled up and applied to architecture. They previously synthesized the structure of lobster shells and beetle wings, using robotic arms to create complex windings of polymer-saturated fibers that cure and harden into self-supporting shells.

This year’s pavilion is a new twist on their methodology. It is based not on the structural properties of a bug itself. Instead, they have investigated the method employed by one of the insect world’s most unusual engineers.

From the ICD/ITKE website:

The design concept is based on the study of biological construction processes for fiber-reinforced structures. These processes are relevant for applications in architecture, as they do not require complex formwork and are capable of adapting to the varying demands of the individual constructions. The biological processes form customized fiber-reinforced structures in a highly material-effective and functionally integrated way. In this respect the web building process of the diving bell water spider, (Agyroneda Aquatica) proved to be of particular interest. Thus the web construction process of water spiders was examined and the underlying behavioral patterns and design rules were analyzed, abstracted and transferred into a technological fabrication process.

“The water spider spends most of its life under water, for which it constructs a reinforced air bubble to survive. First, the spider builds a horizontal sheet web, under which the air bubble is placed. In a further step the air bubble is sequentially reinforced by laying a hierarchical arrangement of fibers from within. The result is a stable construct that can withstand mechanical stresses, such as changing water currents, to provide a safe and stable habitat for the spider. This natural production process shows how adaptive fabrication strategies can be utilized to create efficient fiber-reinforced structures.

To borrow this idea and recreate it in carbon fiber, they placed a robotic arm inside a large bubble, a “soft shell” of ETFE membrane initially supported by air pressure. The robotic arm then lays up strands of polymer-saturated carbon fibers around the inside of the bubble, very selectively. The paths the arm reinforces are determined by a computational form-finding process. It’s tricky work applying it, though, because the membrane is flexible and deforms as the pressure of fiber lay-up is applied to it.

“The changing stiffness of the pneumatic formwork and the resulting fluctuations in deformation during the fiber placement process pose a particular challenge to the robot control. In order to adapt to these parameters during the production process the current position and contact force is recorded via an embedded sensor system and integrated into the robot control in real time. The development of such a cyber-physical system allows constant feedback between the actual production conditions and the digital generation of robot control codes. This represents not only an important development in the context of this project, but more generally provides new opportunities for adaptive robotic construction processes.”

The development of this method included creation of a robotic tool that used integrated sensor data to guide placement of the carbon fibers.

“During production nine pre-impregnated carbon fiber rovings are placed in parallel. 45km of carbon roving were laid at an average speed of 0.6 m min on 5km of robot path. This additive process not only allows stress-oriented placement of the fiber composite material, but it also minimizes the construction waste associated with typically subtractive construction processes.”

There’s a good video about it on Vimeo.

The completed pavilion has a footprint of 40m2 (430 sf) and an internal volume of approx 130m3 (170 cy). It is 4.1m (13.5 ft) tall, and weighs just 260 kg (573lbs).

The idea of bubble formwork is intriguing, especially with the availability of a responsive layup robot.  It has real-world architectural potential.  The ICD/ITKE pavilion demonstrates how the function of formwork could be performed in an unfamiliarly flexible way through the inaction of the membrane and the responsive robot arm.  It also suggests that formwork might be minimized for a rapid form of construction. (Possibly more rapid than the ICD/ITKE pavilion itself  enjoyed.  Assuming the nine rovings placed in parallel were placed simultaneously, arithmetic says the pavilion took just under 6 days of robot time.)

Just imagining for a moment: The inflation of the membrane can bconstrained in various ways to achieve some control over the shape of the monocoque.  The inflated bubble could provide a form for just enough carbon-fiber strands to define a very minimalist shape when hardened, possibly even less of a continuous carbon fiber surface than the pavilion.  The resulting bubble/carbon fiber composite could, in turn, provide enough stiffness and shape to act as formwork for a fabric-based composite skin to be laid up on the outside of the membrane, using a lower-cost material such as glass-fiber.  This would limit the amount of robot-arm time needed. The glass-fiber fabric layup could be relatively rapid.  The final result would be durable, no longer dependent on the initial membrane for any of its shelter functions.  The membrane would be cut away at opening such as doors and windows.

Once again, the folks in Stuttgart are opening up a wealth of fascinating possibilities.

Images copyright ICD/ITKE