Biomimicry in Architecture

Michael Pawlyn

• Éditeur: RIBA Publishing
• Année: 2019
• ISBN:
  9781000701609
• Édition: 2
• Sujet: Architecture
• Sous-sujet: Architecture General

When searching for genuinely sustainable building design and technology - designs that go beyond conventional sustainability to be truly restorative - we often find that nature got there first. Over 3.5 billion years of natural history have evolved innumerable examples of forms, systems, and processes that can be applied to modern green design.

For architects, urban designers and product designers, this new edition of Biomimicry in Architecture looks to the natural world to achieve radical increases in resource efficiency. Packed with case studies predicting future trends, this edition also contains updated and expanded chapters on structures, materials, waste, water, thermal control and energy, as well as an all-new chapter on light.

An amazing sourcebook of extraordinary design solutions, Biomimicry in Architecture is a must-read for anyone preparing for the challenges of building a sustainable and restorative future.

Chapter One
How can we build more efficient structures?

8. X-ray image of an Amazon water lily leaf showing an example of how robust structures are created in nature with a minimum of materials. The network of ribs stiffens the large area of leaf without adding excessive thickness

In nature, materials are expensive and shape is cheap.

PROFESSOR JULIAN VINCENT ¹⁹

This observation captures the essence of biological structures. In technology, it is generally the shape that is expensive instead.²⁰ Nature makes extremely economical use of materials, often achieved through evolved ingenuity of form. Using folding, vaulting, ribs, inflation and other means, natural organisms have created effective forms that demonstrate astonishing efficiency. The many manifestations of this in natural organisms provide a rich sourcebook of ideas for structures that could be radically more efficient than those found in conventional architecture.

Why is nature this way? The pressures of survival in all its varied aspects – finding sustenance, thermoregulating, mating and avoiding predation, among many other factors – have, over aeons, ruthlessly refined the structures and other adaptations that genetic mutation and recombination has created. The process continues, of course, but what we can observe in nature today is many of the best structures, evolved throughout the history of life on earth. The principle for architecture that emerges from observing is: less materials, more design. Exploring this paradigm, we will see an array of examples showing how minimum materials can be used to maximum effect.

9. Sketch showing how four equally stiff structural elements can be made with varying degrees of efficiency. By using shape and putting the material where it needs to be, it is possible to use only 14 per cent of the material of a solid square section (after work by Adriaan Beukers and Ed van Hinte in Lightness: The Inevitable Renaissance of Minimum Energy Structures)

Hollow tubes

Nature builds simply and economically, often meeting both goals simultaneously by making hollow tubes. Nature is abundant in examples that demonstrate this structural principle, such as human bones, plant stems and feather quills. If one takes a square cross-section of solid material with a side dimension 24 mm (fig. 9), it will have the same bending resistance as a circular solid section of diameter 25 mm with only 81.7 per cent of the material. Similarly, a hollow tube with only 20 per cent of the material of the solid square can achieve the same stiffness. In engineering terms, material has been removed from areas close to the neutral axis and placed where it can deliver much greater resistance to bending – achieving the same result but with a fraction of the material.

One plant in particular shows how hollow tubes can be applied at larger scales in nature. Bamboo species can reach 40 m in height. How do they maintain strength over this length? One of the ways in which a tubular element can fail under loading is through one side of the tube collapsing in towards the central axis, leading to overall buckling. Bamboo solves this by interrupting smooth tubular growth with regular nodes, which act like bulkheads (fig. 10). The nodes provide great resistance to structural failure, and are part of what has facilitated bamboo’s lofty accomplishments. Bamboo is, by strict taxonomy, actually a species of grass which has achieved such wild success that it resembles the scale of a tree. This plant’s solution seems to apply so widely that it begs the question: why aren’t more trees hollow tubes? The answer derives from the different forms that they strive to grow into: trees generally create a canopy of cantilevering branches, rather than the multiplicity of stems characteristic of grasses. Bamboo offers solutions to tubular structural elements, while trees offer a biomimic further solutions to holistic structural issues, since they face different pressures than grasses.

10. The regular nodes in the stems of bamboo act like bulkheads stiffening the tube and preventing the normal way in which tubular structures fail

Trees: solid forms

Our understanding of trees and how lessons from them can be applied to engineering has developed enormously in recent years, particularly with the work of Claus Mattheck.²¹ In nature, biological forms follow a simple rule, which he describes as the axiom of uniform stress. In locations of stress concentration, material is built up until there is enough to evenly distribute the forces; in unloaded areas, there is no material. Trees also demonstrate the idea of optimised junction shapes that avoid stress concentrations and can adapt over time. The result approaches optimal efficiency, in which there is no waste material and all the material that exists is carrying its fair share of the load. By contrast, many steel and concrete structures are designed so that the most onerous load conditions (which only occur in specific locations) determine the size of the whole beam or column.

With his team at Karlsruhe Research Centre, Mattheck developed a design method that utilises two software processes (fig. 11) to create forms of biological design that are effectively identical to the refinements found in nature. The program allows designers to subject a rough structural computer model to the kind of forces that would be experienced in reality. These include snow, wind and seismic loading, as well as loads imposed by the building’s use. The first stage uses ‘Soft Kill Option’ (SKO) software to eliminate material in zones where there is little, or no, stress. Then a ‘Computer Aided Optimisation’ (CAO) program refines the shapes and, where necessary, builds up material at the junctions to minimise stress concentrations that could lead to failure. The designer is free to decide whether they like the output and find alternative ways to achieve structural integrity. Mattheck likens this process to starting with a roughly axed piece of timber, which is then carved to the near-final shape (the SKO stage) before being sanded and polished (CAO). The results can be surprisingly organic in form, and far more efficient than conventional structures.²² The designer Joris Larman used this to develop a number of elegant pieces of furniture and a bridge that is to be 3D printed and will span over a canal (fig. 12). We could do the same with buildings and achieve huge increases in material efficiency while producing more elegant and structurally legible forms.

11. Diagram showing Claus Mattheck’s design refinement process using ‘Soft Kill Option’ (SKO) and ‘Computer Aided Optimisation’ (CAO) software

The key difference between trees and bones is that, in the former, material cannot be removed whereas in bone tissue it can be. Trees consequently grow as solid forms. This might seem surprising, given the hollowness of many bones. The explanation probably lies in the fact that there is not the same selective pressure for lightness in stationary trees as there is in animals that must move at speed to either catch, or avoid becoming, prey. Most of the bulk of a tree is dead material (only the outer layers remain alive), whereas bones are continually being reformed and recycled. One other possible explanation is that the solid core of trees functions to some extent as a compression core to resist the tension created by the outer sapwood, which grows in helical patterns up and around the trunk. This structural form has some similarities with Future Systems’ Coexistence Tower (fig. 13).

12. 3D-printed bridge by Joris Larman Lab demonstrating the expressive and material-efficient results of designing with SKO software

13. Coexistence Tower by Future Systems. The compression core and the helical arrangement of tension members around the perimeter have functional similarities with the structure of tree trunks

14. Trees growing in the shallow soils of rainforests have evolved buttress roots that resist overturning

The root forms of trees could also inspire new approaches to creating foundations for buildings. The formation of a wide, stiff base effectively moves the pivot point some distance from the trunk and, on the opposite side, a branching network of roots m...