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| Close-up photograph of a sea urchin skeleton showing its porous and lightweight structure |
Whereas bamboo is a relatively pure embodiment of tubular structural engineering, bones are more complex. Bones frequently reveal ways in which asymmetrical forces are resolved.
What we see is a precise match between the density of bone filaments and the concentration of stresses; where there is high stress, there is a proliferation of material and elsewhere there is a void.
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| Diagram showing the lines of stress passing through a bone |
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| X-ray through a bone showing the arrangement of bony trabeculae |
As biological mathematician D’Arcy Wentworth Thompson’s seminal 1917 book On Growth and Form documented, the vulture’s metacarpal is identical to a Warren truss. The vulture is an extreme case, where intense selective pressure to achieve high strength with minimal weight yields impressive results.
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| As a result of intense selective pressure for lightness, some birds have evolved remarkably efficient structural forms, like this vulture’s metacarpal, which is effectively identical to a Warren truss |
Birds in general have evolved in response to intense selective pressure on weight, with different species showing various expressions of the ‘materials are expensive and shape is cheap’ maxim.
Avian skulls, such as those of crows and magpies, are little short of engineering miracles. The effective thickness of the skull is increased while weight is decreased. The structure is similar to a space-frame in which two layers of structural members are connected with struts and ties. The bird skull goes one step further in forming a dome shape, with the associated efficiency benefits.
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| Section through the skull of a magpie showing thin domes of bone connected together with struts and ties |
It’s an astounding combination of shell action with space-frame technology – and all in a humble magpie. This principle was the inspiration for a canopy structure designed by architect Andres Harris.
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| Canopy structure designed by architect Andres Harris, using the same structural principles as those found in bird skulls |
The design resulted from a detailed understanding of the way in which bone tissue forms around pressurised cells, creating air voids between solid surfaces. The potential exists to construct the canopy in a way that is very similar to nature: using a web of inflated void formers, around which suitable materials could be cast.
Skeletons have been a source of inspiration for architects ever since Thompson demonstrated the parallels between structures such as the Forth Road Bridge and the form of dorsal vertebrae found in a horse.
Architect Santiago Calatrava is renowned for his love of skeletal structures; he created many of the most graceful bridges in the world.
While his exuberance is enjoyable, there is a sense in which the biomorphic extravagance occasionally occludes a rational structural basis for the schemes.
It could be argued that the beauty found in nature is derived from its economy, with the absence of the superfluous being part of the rigour that we perceive.
While his exuberance is enjoyable, there is a sense in which the biomorphic extravagance occasionally occludes a rational structural basis for the schemes.
It could be argued that the beauty found in nature is derived from its economy, with the absence of the superfluous being part of the rigour that we perceive.
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| Biomorphic exuberance in the Milwaukee Art Museum by Santiago Calatrava |
I made a grasshopper script for the Milwaukee Art Museum structure on my Gumroad here:
https://dana-krystle.gumroad.com/l/lFELu
https://dana-krystle.gumroad.com/l/lFELu
The sea urchin has inspired both simple biomorphic and thoroughgoing biomimetic architecture. The urchin skeleton (called a ‘test’) is made of interlocking plates (called ‘ossicles’) , each of which has the structure of a single calcite crystal.
If the calcite were solid, it would be heavy, but the ossicles have a sponge- like structure that is porous, lightweight and stiff due to its increased effective thickness.
Sea urchin skeletons provided a visual reference for the Doughnut House by Future Systems, although the structure, at a functional level, had very little in common with that of the marine organism.
A building that has deliberately come much closer to the structure of a sea urchin is the Landesgartenschau Exhibition Hall at the University of Stuttgart, Germany, where some of the most interesting and thorough research into biomimetic architecture is currently underway .
The project was the result of a collaboration between the Institute for Computational Design (ICD, Prof. Menges (PI)), the Institute of Building Structures & Structural Design (ITKE, Prof. Knippers) and the Institute of Engineering Geodesy (IIGS, Prof. Schwieger).
Sea urchin ossicles, and the way they interlock, were a source of inspiration for the building. It is made out of 50 mm thick plywood panels, connected with precise finger joints. Menges observed that ‘in comparison to man-made constructions, natural biological constructions exhibit a significantly higher degree of geometric complexity’.
Computational design was essential to resolve this complexity in finding the optimum form. Each panel was then robotically prefabricated. The structure covers an area of 250 m 33 and, in relative terms, is thinner than eggshell.
If the calcite were solid, it would be heavy, but the ossicles have a sponge- like structure that is porous, lightweight and stiff due to its increased effective thickness.
Sea urchin skeletons provided a visual reference for the Doughnut House by Future Systems, although the structure, at a functional level, had very little in common with that of the marine organism.
A building that has deliberately come much closer to the structure of a sea urchin is the Landesgartenschau Exhibition Hall at the University of Stuttgart, Germany, where some of the most interesting and thorough research into biomimetic architecture is currently underway .
The project was the result of a collaboration between the Institute for Computational Design (ICD, Prof. Menges (PI)), the Institute of Building Structures & Structural Design (ITKE, Prof. Knippers) and the Institute of Engineering Geodesy (IIGS, Prof. Schwieger).
Sea urchin ossicles, and the way they interlock, were a source of inspiration for the building. It is made out of 50 mm thick plywood panels, connected with precise finger joints. Menges observed that ‘in comparison to man-made constructions, natural biological constructions exhibit a significantly higher degree of geometric complexity’.
Computational design was essential to resolve this complexity in finding the optimum form. Each panel was then robotically prefabricated. The structure covers an area of 250 m 33 and, in relative terms, is thinner than eggshell.
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| Close-up photograph of a sea urchin skeleton showing its porous and lightweight structure |
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| The Doughnut House by Future Systems – biomorphic rather than biomimetic |
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| Landesgartenschau Exhibition Hall at the University of Stuttgart – made from interlocking plywood panels based on the structure of a sea urchin skeleton |
Another noteworthy aspect of sea urchins is the structure of their spines. These provide protection as well as locomotion and sensing.
As protection, considerable strength is required to resist impact onto the ends of the spines – or ‘axial loading’ as an engineer would describe it.
If the spines were monolithic, they would be very brittle. Instead, they have evolved in a porous form that blends calcite with proteins. The composite effect of these two materials is enhanced strength and flexibility. Are there applications in architecture that require high resistance to axial loading as well as flexibility? The sea urchin spine is a solution waiting for the right design opportunity.
As protection, considerable strength is required to resist impact onto the ends of the spines – or ‘axial loading’ as an engineer would describe it.
If the spines were monolithic, they would be very brittle. Instead, they have evolved in a porous form that blends calcite with proteins. The composite effect of these two materials is enhanced strength and flexibility. Are there applications in architecture that require high resistance to axial loading as well as flexibility? The sea urchin spine is a solution waiting for the right design opportunity.
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Close-up photographs showing the
remarkable structure of sea urchin spines |
If Buckminster Fuller had ever designed a fish, one wonders if it might have looked something like the boxfish (perhaps Lactoria cornuta or Acanthostracion polygonius). Their carapace is a remarkable geometrical composition of mainly hexagonal and pentagonal plates or ‘scutes’.
Each of these has a tough mineralised collagen outer layer with a raised pattern of reinforcing struts and a softer, un-mineralised collagen layer underneath. The struts serve to distribute piercing impacts over a wider area.
Finely interlocking seams unify the plates into an extremely strong skeleton – it is tempting to refer to it as an exoskeleton but it is actually an endoskeleton because it lies under a layer of skin. Some fish evolved faster swimming to avoid predation; boxfish developed a formidable defensive structure (and some toxicity for good measure).
Further protection comes from two pairs of horns – one pair at the front and one at the rear – which would make for uncomfortable swallowing by a predator. The horns have an intriguing structure of their own – an intricate hierarchy of ridges and ribs to provide high strength.
While buildings in the twentyfirst century generally don’t have to be designed to resist attack, the boxfish carapace could still provide clues for how to stiffen thin materials into a robust enclosure using a minimum of resources. Just as twentieth-century anthropologists were compelled to revise the widely held racist notion of ‘primitive’ societies, there are certain biological organisms that should encourage us to abandon the idea of single- or multi-celled life forms being in some way ‘lower’ than others.
One such example is the Venus’ flower basket glass sponge (Euplectella aspergillum), The structure of this marine organism is a complex assembly of spicules (fourpointed star-shaped elements made from silica) forming a tapered lattice tube .
This square grid is stiffened with diagonal bracing on alternate cells like a chequerboard, so that every node is braced and open cells allow for filter feeding. The scientists studying this organism have observed that it ‘shares features with the theoretical design criteria for optimized material usage in similar two-dimensional structures subjected to shear stresses’.
The number, and size, of spicules around the perimeter stays constant along most of the length (only increasing in the top few centimetres), so tapering is achieved by variations in the overlap of the spicules.
Each of these has a tough mineralised collagen outer layer with a raised pattern of reinforcing struts and a softer, un-mineralised collagen layer underneath. The struts serve to distribute piercing impacts over a wider area.
Finely interlocking seams unify the plates into an extremely strong skeleton – it is tempting to refer to it as an exoskeleton but it is actually an endoskeleton because it lies under a layer of skin. Some fish evolved faster swimming to avoid predation; boxfish developed a formidable defensive structure (and some toxicity for good measure).
Further protection comes from two pairs of horns – one pair at the front and one at the rear – which would make for uncomfortable swallowing by a predator. The horns have an intriguing structure of their own – an intricate hierarchy of ridges and ribs to provide high strength.
While buildings in the twentyfirst century generally don’t have to be designed to resist attack, the boxfish carapace could still provide clues for how to stiffen thin materials into a robust enclosure using a minimum of resources. Just as twentieth-century anthropologists were compelled to revise the widely held racist notion of ‘primitive’ societies, there are certain biological organisms that should encourage us to abandon the idea of single- or multi-celled life forms being in some way ‘lower’ than others.
One such example is the Venus’ flower basket glass sponge (Euplectella aspergillum), The structure of this marine organism is a complex assembly of spicules (fourpointed star-shaped elements made from silica) forming a tapered lattice tube .
This square grid is stiffened with diagonal bracing on alternate cells like a chequerboard, so that every node is braced and open cells allow for filter feeding. The scientists studying this organism have observed that it ‘shares features with the theoretical design criteria for optimized material usage in similar two-dimensional structures subjected to shear stresses’.
The number, and size, of spicules around the perimeter stays constant along most of the length (only increasing in the top few centimetres), so tapering is achieved by variations in the overlap of the spicules.
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| The carapace of the boxfish Acanthostracion polygonius showing its amazingly geometric arrangement of scutes |
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| Diagram of the scutes that form the boxfish carapace showing the arrangement of reinforcing ribs |
The glass sponge has a series of helical ridges and a rigid
top ‘filter plate’ that effectively stiffen the tube
against the kind of failure we described earlier.
The way
that the sponge attaches to the sea bed is also intriguing.
Materials scientist Professor Helga Lichtenegger has observed that anchoring can be achieved much more efficiently (in material terms) if the structure allows flexibility rather than rigidly resisting all lateral loads.
Saplings demonstrate this phenomenon and so does the glass sponge – there is considerable pliancy at the base (the very point at which the highest stress would accumulate in a more rigid structural attachment).
In the lower part of the sponge there is a longer and more fibrous type of spicule, approximately 200 of which extend down into the sediment of the sea floor to form a strong holdfast. Scanning electron microscopy has revealed these fibres to have smooth surfaces above sea bed level, barbed surfaces below and an anchor-shaped termination .
Materials scientist Professor Helga Lichtenegger has observed that anchoring can be achieved much more efficiently (in material terms) if the structure allows flexibility rather than rigidly resisting all lateral loads.
Saplings demonstrate this phenomenon and so does the glass sponge – there is considerable pliancy at the base (the very point at which the highest stress would accumulate in a more rigid structural attachment).
In the lower part of the sponge there is a longer and more fibrous type of spicule, approximately 200 of which extend down into the sediment of the sea floor to form a strong holdfast. Scanning electron microscopy has revealed these fibres to have smooth surfaces above sea bed level, barbed surfaces below and an anchor-shaped termination .
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| The glass sponge Euplectella aspergillum, made from silica at ambient temperature and pressure with five or more levels of hierarchy |
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| Illustration showing how the glass sponge is assembled from a complex arrangement of intersecting, cross-shaped spicules |
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| Magnified image of the filter plate that stiffens the top of a glass sponge |
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| Scanning electron microscope views of the fibrilar spicules that anchor the glass sponge in soft sediments. Above the sea bed the spicules are smooth, while below they are barbed and have a complex holdfast at the termination |
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