Diatoms → Geodesic Domes

Diatoms, defined in botanical language also as bacillariophyceae (“rod-shaped plants”), are algae of sea and freshwater plankton, which fabricate finely porous

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silicate skeletons. Figures 5.1 and 5.2 illustrate some forms and details captured by a classical transmission electron microscope (TEM). The petri dish-shaped forms usually have a diameter under a tenth of a millimeter and float freely in the plankton of the ocean or freshwater. They can additionally attach themselves to each other to form chains that can be anchored to the ocean floor. Such chain formations or other “Aufwuchs” (organisms that grow on open surfaces in aquatic environments) of diatoms form the brownish, slimy coating on stones in slowly flowing creeks in springtime. Under the microscope the structure reveals itself as a lacy, mesh-like skeleton (Fig. 5.1a). More intense magnification under the electron microscope shows that the apparently open pores are actually covered with another mesh layer, whose pores in turn can be covered in a sieve-like

man-Fig. 5.1  a–d TEM images of diatoms. (Adapted from Roland 1965, edited)

ner (Fig. 5.1b, 5.1c, 5.1d, Fig. 5.2). One ultimately finds a system of up to three fine layers nested inside of one another. The finest pores are actually open, but they are however already so small that they do not allow multi-molecular proteins to penetrate.

Closer observation shows a typical irregularity that suggests a strong role of random processes in the micromorphological formation.

Diatom → Train Station Shed The diatom Surirella is formed as an elongated ellipse (Fig. 5.3a). A central beam supports spanning arched ribs on both sides, onto

Fig. 5.2  a–e TEM images of diatoms. (Adapted from Roland 1965, edited)

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which a finely porous perforation system spreads itself. Its basic form is remarkably similar to a train station canopy designed by E. Torroja in the 1940s. It is not known whether the similarity of form is simply coincidental or whether the architect had actually been informed about diatom structures.

Diatom → Stadium In contrast to the previously mentioned diatom Surirella, which exhibits an elongated oval shape, the diatom Arachnoidiscus is circular in plan view; it belongs to the subgroup of “Centrales.” Its structure is correspondingly radially symmetric; radial ribs run from the center outwards supporting the fine mesh layer in between. The famous roof structure designed by P.C. Nervi for the Palazzetto dello Sport in Rome (Fig. 5.3c) can be viewed as an analogy for this case, although it is again uncertain whether the similarity is intentional or not.

Fig. 5.3  Similarities of form, diatom structures: a, b diatom Surirella and train station (E. Torroja), c diatom Arachnoidiscus and Palazzetto dello Sport, Rome (P.C. Nervi), and d diatom Thalassio-sira and Renaissance church, Rome. (Adapted from various authors from Nachtigall 1974)

Diatom → Renaissance Churches With stronger electron microscopic magnifi-cation the structural system of the shell of the diatom Thalassiosira reveals itself as a highly sculptured brace pattern that is equally unimportant for its structure as are the heavy articulations and artistic cornices on the ceilings of many Renais-sance churches (Fig. 5.3d). Although the similarity is purely superficial, even such comparisons are not completely meaningless, because in design and architecture it eventually comes down to pure form generation that need not always and every-where have a functional purpose. Even these comparative exercises can provide inspiration for creative activities.

Fat Droplet Hypothesis To explain the occurrence of the fine shell structures of diatoms (Fig. 5.7a) G. Helmcke developed the following hypothesis. When the plasma globule slips out from its auxospore, it is still naked. However, the shells rapidly form at this point. Fats had been previously detected on the outer surface.

According to Helmcke, the still shell-less diatom uses a metabolic process to form fat droplets that arrange themselves on its outer surface where they struggle for space, as they run into each other and deform (Fig. 5.4a). The interstitial spaces are then filled with liquid silicic acid in a single casting process. After it hardens, the fat droplets are broken down, and only the casted form remains (Fig. 5.4b). On touching surfaces of the former fat droplets circular openings emerge by mutual flattening of the spherical shape (Fig. 5.7a). Today this hypothesis is no longer sup-portable, though it still inspires much design work. Delicate building bricks were developed as a technical analogy to this principle (Fig. 5.7b).

If one were to press a soccer ball into a hexagonal box, cast the interstitial space with a hardening liquid, and remove the form, a hexagonal building block would remain with an empty void in its center and a circular opening on each side (eight in total) yet maintain a certain structural capacity. With these blocks one could build lightweight partition walls, for example; in the 1960s this was actually attempted (compare Fig. 5.4b).

Cast Concrete Shells For his doctoral thesis, architect T. Noser, whom G. Helmcke had mentored during his time in Berlin, attempted shell forms according to the

“Helmcke Principle.” This principle, as mentioned, was later proven as not entirely accurate; in detail the diatoms construct their shell differently. Though the fat drop-let hypothesis still developed as an entirely separate but important heuristic prin-ciple and provided many inspirations for unconventional building designs.

T. Noser pressed soccer balls between pressure plates and casted the form with plaster or polyester (Fig. 5.5a). It resulted in the previously stated hollowed hex-agonal frame form. Shells with sectional forms that follow a kind of catenary curve were also attempted (Fig. 5.5b). After evaluation and turning them upside-down, they were self-supporting. One could produce spans of up to several meters, which are preeminently suitable for roofs over swimming halls, for example. Covered with a film that can hold for a few years, they can defy surface stress due to wind or snow as well. Details can be found in the Figs. 5.6a, 5.6b, 5.6c, 5.6d, 5.6e; the legend provides information. Interestingly, one practically cannot distinguish between the image of a diatom shell and its replication in casted forms when they are photo-graphically compared at similar sizes.

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Lightweight Structures: Bell Towers An economical system was sought for the reinforcement of large surfaces, in which individual elements can be brought together that can sustain heavy wind forces (e.g., for the reinforcement of screens for open air theaters). Hexagons built of glass fiber-reinforced polyester, which correspond to the diatom-cast forms, have proved themselves useful for this task (Fig. 5.7c). As an analogy, F. Otto and M. Mahnleitner, who in Berlin in 1960 worked in continuous exchange with botanist G. Helmcke under the keywords

“biology and building,” welded tetragonal cube structures consisting of steel panels together (Fig. 5.7d), whose basic form has a similar biomimetic background. The cubes became components of a bell tower for a church in Berlin (Fig. 5.7e), which have several advantages: relatively lightweight construction, easy to erect as one piece, enough resistance against torsion to withstand the vibrations from the bell and wind forces, and ultimately simple to breakdown and completely renewable:

the disassembled structure can be melted down. The Mühlau-Mahnleitner minimal support structure of hexagonal honeycombs (Fig. 5.7c) proved itself in practice for a 500 m² movie theater screen for the Waldbühne in Berlin and the diatom-inspired bell tower of Otto-Mahnleitner for a church in Berlin.

Fig. 5.4  Diatom concrete cast forms, a fat droplet hypothesis of G. Helmcke, ca. 1956 and b result from a: diatom shell cavity. (adapted from Nachtigall 1987)

Steel-Reinforced Concrete Shells Diatoms with the form of an equilateral triangle (approximately Triceratium alternans, Fig. 5.8a) provided inspiration to the engi-neer and architect E. Torroja for the construction of large, triangular, reinforced concrete shells (Fig. 5.8b), which were to cover water reservoirs. If one structures them so that the vaults from the edges outwards are formed as sloped surfaces, they are self-supporting. Triangle configurations of this kind can be combined to form hexagonal structures, as J. Joedecke has shown with his diatom-like, experimental reinforced concrete shell (Fig. 5.8c).

Geodesic Domes Since the 1950s B. Fuller has become known for his geodesic domes, for example the canopy of a greenhouse (“Climatron”) in the Botanical

Fig. 5.5  Diatom-like, lightweight panels and shells: a principle of panel formation and b principle of shell formation. (adapted from Noser 1983)

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Gardens in St. Louis from 1953 (Fig. 5.9). The structure consists of a double shell with hexagonal grids that mutually support each other and are covered with trian-gular plexiglass panels.

There are diatoms, which are structured principally similar and also represent a doublelayered, self-supporting shell framework, whose cavities are lined with finely punctured silicic acid membranes. B. Fuller denied that he received his inspiration for his structure from nature; the similarities have only been discov-ered a posteriori. It seems strange, as it is well known that Fuller had occupied himself with small and microscopic life forms, though it may also be apparent that general influence resulting from these studies is completely unavoidable. In honor of the architect, soccer ball-like molecular cages of carbon were named

“Fullerenes”.

Fig. 5.6  Formation according to the diatom principle: a soccer balls arranged around a center, b soccer balls deforming to a hexagonal form, c, d “interstitial form” of diatoms and from b, and e hemisphere forms. (Adapted from Noser 1983)