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.
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
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...