One of the great opportunities of our time is to do more with less, and therefore to provide a better life for more people. In the realm of building structures this is especially true because our capacity in the key parameter of information has expanded so greatly. Inputs to materials and energy can therefore be less and save everybody time, money and effort. In other words, it's much cheaper to move electrons doing precise structural calculations than to manufacture overbuilt concrete beams.
Capacity-building in the parameter of information comes from other sources besides increased computation. It also comes from increased understanding, through the domain of science, in the principles that govern our physical and biological world. This is the promise of bio-inspired design. Nowhere has this informational advantage been so elegantly demonstrated than in the building of thin shell structures.
Although this building process has fallen out of favor with architects, there are some key aspects of it that could be recombined with modular or air-inflated forming systems, and new concrete mixes that eliminate the need for traditional reinforcing steel for a new approach to some of our buildings. Most important would be the informed approach. The architects and engineers who built some of these structures had indeed learned the lessons of the egg:
1. That the shape itself is key to strength
2. That the form is, as D'Archy Thompson put it, “…a diagram of (the) forces (acting on it)”
3. That this form generally takes the path of least energy and material
Next time you are washing the dishes take a look at the raft of soap bubbles floating in the sink. You will be looking at a pure form example of all of the above concepts: A thin film surface maintained by constant pressure and forming a constant curvature and minimal surface. No doubt you will see consistently triple junctures at 120 degree angles where the bubbles meet. All because the particles of soap and water are more attracted to themselves than to the outside air, and the soap has made the normal surface tension of plain water (the “skin” on all droplets) weaker and more stretchable. (For an excellent explanation of bubbles, foam, and, for that matter, nature's patterns, see “The Self-Made Tapestry: Pattern Formation in Nature,” by Philip Ball)
Wise engineers and architects have learned from these phenomena to solve their problems in spanning space, and they have applied these lessons in one of two ways: Membranes and shells. Many, like architect Frei Otto, had done meticulous studies of soap films in order to design minimal surface structures like the Olympic Swimming Arena in Munich.
When the builders of the Eden Project (see photo above) in Cornwall, England, had to join two domes together, they knew that the geometry of intersecting bubbles always yields a shared vertical plane, and they could design a strong arch within that plane to support the opening. The geodesic dome by Buckminster Fuller (above) is another well-known exploration of minimal materials to enclose space, and unwittingly presaged shapes later found in nature, the icosohedron in bacteriophages and the sphere of the C60 molecule, appropriately named buckminsterfullerene.
These are all membrane structures, skins supported by cables or frames, but what I want to discuss now are shells. These are structures that have thin curved surfaces that translate loads to their supports by tension, compression and shear only: The buildings most emulating the egg. In this field all roads do initially lead to Rome (the dome of the Pantheon, 125 AD, is the world's oldest known concrete shell), but also, and more precisely, to Zurich and the Swiss Technical University.
It was there, in 1866, that professor Karl Culmann developed the seminal Graphische Statik in which outlines of a form were visually related to the forces keeping it in equilibrium. He once famously related the cross section of a femur with the structure needed to relieve the tension and compression stresses acting on a crane he was designing. He also is reputed to have influenced the design of The Eiffel Tower.
From this Swiss tradition have come the works of Robert Maillart, Heinz Isler, Othmar Amman, Christian Menn, Edward Torroja, Felix Candela, Pier Luigi Nervi, Oscar Niemeyer, and Santiago Calatrava. (See “The Art of Structural Design: A Swiss Legacy,” by David Billington)
It's not a bad list, if you are looking for elements of a “less is more” approach to building. In our case (aesthetics aside, for the moment) this means less material and energy, and more information. By the way, many of these forms were designed before the physical forces acting on them were very well understood.
Take Torroja's Zarzuela Hippodrome, started in 1935, in which hyperboloid umbrella shapes cantilever 42 feet out over the stadium seating and still offer protection and clear views for 17,000 spectators today. Its so called anticlastic form uses double curves of reinforced concrete in only 2-5-inch thickness to cancel out opposite forces, much as corrugated iron roofing or scallop shells exhibit strength from shape, not material.
Swiss engineer Heinz Isler perhaps best represents the search for a pure thin shell form based on natural forces. He has chased the Holy Grail of efficiency and beauty since 1954, when he realized from looking at his pillow that if he designed his building shapes from models that were determined purely by the forces acting on them, he could solve (nearly) every problem. Using formed earth, inflated rubber membranes and draped fabrics, he has emphasized form and stability and been able to scale up these shapes to building size. (See “Heinz Isler” by John Chilton)
Best known of his methods is the use of hung fabric to determine a shape by natural tension, then solidifying this shape with resin or freezing. Isler will then flip this form and thereby create a model in which all previous lines of tension forces are translated into pure compression. The model is now a perfect predictor of how the concrete shape will perform under most loads. These models are scaled up in design drawings and carefully built… over 1500 of them in the course of his career. They include the Chamonix Shells under Mont Blanc, the Norwich Sports Village Hotel, the Wyss Garden Center and the Flieger-Flab Museum in Dubendorf.
While Isler's three-legged shallow domes at the Dietingen Service Station on the Berne-Zurich highway (1968) are some of the most elegant organic forms ever built, their genesis was not from a study of biological forms, but the forces that tend to shape those forms. The impetus for them was stability and efficiency, and not conservation of resources, but we can still profit from their example and all of this building tradition.
Tom McKeag teaches bio-inspired design to at the California College of the Arts and University of California, Berkeley. He is the founder and president of BioDreamMachine, a nonprofit educational institute that brings bio-inspired design and science education to K12 schools.
Eden Project - CC license by Benjamin A'Lee; Geodesic dome - CC license by Paul Lowry