Prototyping Biomimetic Structures for Architecture

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3.8
Prototyping Biomimetic Structures for Architecture
Tobias Schwinn, Riccardo La Magna, Steffen Reichert, Frederic Waimer, Jan Knippers and Achim Menges i
Technology has always been a catalyst for design innovation in architecture. One example
of technical advancement that still has a profound impact on architectural design today is
the introduction of structural analysis in the second half of the 19th century. Since then,
almost all architectural structures are based on the paradigm of calculability. This has lead
to a certain set of construction typologies that are still predominant today, even though the
the development of its geometry and the calculation of internal forces or other functionalities.
It has its own boundary conditions and limitations that allow for solutions only within a
structural concerns. The introduction of computational design and digital fabrication offers
the technical means to break through these barriers, which raises the question about
a rigorous and systematic design strategy that allows the strategic exploration of new
systems beyond existing typologies (Knippers 2013).ii
Architects and master-builders have been using nature as a source of inspiration long
before the terms bionics or biomimetics were introduced, because structures in nature
are fundamentally different from any architectural or technical system. Not ruled by the
systems assembled from basic components that make up structures featuring multiple
have been used only to a very limited extent in architecture and building construction. While
there have been a considerable number of attempts to transfer characteristics from natural
to architectural systems in the twentieth century, they were profoundly limited by structural
calculability and the dominant constraints of serial production. With the recent advances
in design computation, structural simulation and robotic fabrication the boundary between
the underlying logics of ‘natural’ and ‘man-made’ structures can be rethought anew.
Given the rapidly changing and fundamentally different, post-industrial technological
present current research into the structural, architectural, and tectonic opportunities of
activating the performative capacities of biological structures within the architectural design
domain. The integrative and concurrent investigation of biomimetic design strategies,
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advanced digital simulation, and new modes of robotic fabrication converge in the design
of novel material systems that are subsequently evaluated with regards to their spatial
and structural capacities. The two research pavilions therefore not only demonstrate the
capacities of the respective material systems in full-scale but also the new opportunities
that can arise from prototyping new means and methods of contemporary architectural
production processes.
Case Study 1: Finger-Joint Plate Structure
Biomimetic design methodologies can be categorized by applying either a technological
pull or a biological push (Knippers & Speck 2012).iii While the former strategy approaches
nature looking for answers to technological questions, the latter is a bottom-up and open-
ended investigation of biological features, which, when abstracted, has the potential to
question existing technical solutions. The biomimetic design process that unfolded in this

meaningfully explore the ever-expanding possibilities provided by computer numerically
controlled (CNC) machinery in timber plate fabrication. The analysis of biological role

an integrative design and robotic fabrication process. The research aimed at integrating
the mechanical features of biological plate structures into architectural design and at
successively testing the spatial and structural properties of the newly developed material
system in a full-scale prototype. Researchers and students at the University of Stuttgart
developed the project in collaboration with biologists and palaeontologists at the Universities
of Tubingen and Freiburg, and completed the prototype in the summer of 2011.

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Robotic Fabrication of Finger Jointed Timber Plates
Finger joints are a common type of joinery in traditional woodworking and valued for
      

iv During the
industrialization period, a relatively crude mechanisation of formerly sophisticated manual


eventually also computer numerical controlled (CNC) routers were generally limited to the

such as 6- and more axis industrial robots and their associated kinematic freedom,
encouraged the development of a new robotic fabrication process as part of this research

at various angles (Krieg et al. 2011).v
3.8 Prototyping Biomimetic Structure for Architecture
Fig 3.8.2 Left: Manual fabrication of dovetail joints (J.
Baumgartner). Right: Finger joints are traditionally used as corner
joints to connect planar elements (Encyclopaedia of Wood Joints).

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Finger joints are a hinged connection type that performs extremely well under shear
forces, however only accommodates limited normal forces and no bending moments.
The overall plate arrangement utilized in the presented pavilion design therefore had to be


been conducted to verify the joint’s strength as well as to acquire empirical data to inform


geometric freedom provided by the 7-axis robotic fabrication process in combination with

the design freedom and even allows the design of non-load optimized structures. The
focus was set on the development of a modular structure, which, similar to its biological
role model, allows a high degree of adaptability and performance due to the differentiation
of its geometric components.
3.8 Prototyping Biomimetic Structure for Architecture
Fig 3.8.3 Seven-axis robotic fabrication facility the University of
Stuttgart.

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Biomimetic Design Principles and Transfer
During the analysis of biological role models with regards to structural plate behaviour,
the morphology of the sand dollar, a subspecies of the sea urchins Echinoidea, became of
particular interest and provided the basic morphological principles for the prototype that
was successively realised. The shell of the sea urchin is composed of a modular system of

1979).vi The plates of the sand dollar’s skeleton are organised following an overall geometric
principle according to which a maximum of three plates meet at one point. By following this
simple principle, any pure plate structure (i.e. systems composed of just plates and hinges
along the edges of connection) will be inherently stable, whereas any variation from this
arrangement pattern will result in a deformable and kinematic structure similar to origami
(Wester 2002).vii
3.8 Prototyping Biomimetic Structure for Architecture
Fig 3.8.4 Microscopic view of a plate edge showing the calcite


and tension forces in the structure.
From a mechanical point of view, thanks to this arrangement the plates are stabilised by
resisting internal forces that lie in the plate itself. Each face of a pure plate structure carries
plate forces only, i.e. plates must not rely on carrying bending moments and torsion for their
own stability. On the other hand, the lines of support enable the transmission of normal and
shear forces but no bending moments between the joints. This property allows the sea
urchins to grow without interfering with the transfer of stabilising forces, as the direction of
growth will be perpendicular to the shear lines, hence perpendicular to the direction of the
stabilising shear forces (Knippers et al. 2012).viii

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The structural morphology of the sand dollar can therefore serve as a role model for
modular shell structures of prefabricated components. Finger jointing is introduced as
a technological equivalent for the sand dollar’s plate joints providing similar structural
characteristics. Following the analysis of the sand dollar, the morphology of its plate
structure was translated into the design of a material system. Three plate edges always
meet together at just one point, enabling the transmission of normal and shear forces
but no bending moments between the joints, thus resulting in a bending bearing but yet
deformable structure. As the plates are mainly subjected to in-plane forces, the degree
of utilization of the material’s strength is maximized, guaranteeing an optimal structural


and tension forces in the structure.
3.8 Prototyping Biomimetic Structure for Architecture
Besides constructional and organizational principles, hierarchy is also a fundamental
property of biological structures. This principle was translated into the built prototype
  

bolt connection joins the cells together, facilitating the assembly and disassembly of the
prototype. Due to the arrangement of the bolts in the cells and the material characteristic
of plywood and its low stiffness, a transfer of bending moments between the cells could be
minimised by creating a hinged connection. Within each hierarchical level only three plates
- respectively three edges – meet at one point, therefore assuring bending-free edges for
both levels.

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
Digital and Robotic Prototyping
  
computational design framework as part of a generative rule set that informs the
parametric model, in addition to structural analysis and robotic fabrication (Menges 2011).
ix     
of the complex geometry constitutes a driver of the digital information model. The rules
           
structures, in turn, inform the local morphology of the case study, i.e. the relation between

      
By mathematically describing and algorithmically translating this dependency, it can be
directly integrated and activated within the computational design framework.
The large amount of unique building elements requires a generative approach to robotic
x
The aim therefore was to implement a strategy for automating the generation of the robotic
machine code directly from the parametric design model, thereby eliminating intermediate
software environments (Brell-Cokcan & Braumann 2010).xi 
paths for the fabrication of each plate are a function of the angles between the plate and
its neighbouring plates, which, depending on the angle can yield different structural and


15 to 165 degrees – a constraint that feeds directly back as a fabrication parameter into
the generative rule set (Schwinn et al. 2012).xii
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
plate’s outline with the tool shaft thereby ensuring co-planarity with the adjacent plate;
second, mitring a start and end segment of each edge with the tool axis aligned to the
bi-sector between the normal vectors of the adjacent plates resulting in the characteristic
            
fabrication sequence, where the plate’s edges are indented normal to the adjacent plate’s

Custom programmed routines are used to automatically generate these tool paths as
ordered point clouds for each edge of each of the case study’s 855 individual plates. The
Cartesian coordinates of the target points and tool vectors can then be extracted and
translated into machine code and ultimately into instructions for the control of the seven-

model is usually treated as a separate entity, in this custom process the fabrication data
model is tightly integrated into the geometry and design model (Menges & Schwinn 2012).
xiii
Fig 3.8.8 Top: Geometric relation between tool and work piece.
Bottom: Finger joint fabrication steps.

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Fig 3.8.9 Fabrication data model of the automatically generated
tool paths.
The custom integrative approach to fabrication programming is instrumental for the

of the plates on the university’s robotic fabrication system, the plates were combined into
modules and weatherproofed in the controlled environment of the workshop, before being
assembled on site.
Result
          
the design process can open up new performative design approaches. The analysis of

their transfer into generative and geometric rules formed the basis for the development
of a computational design tool integrating the sea urchin’s biomimetic principles, the
architectural and structural requirements and the fabrication constraints. Unlike traditional
lightweight construction, which can often only be applied to load optimized shapes, these
principles can be applied to any custom geometry. The ultra lightweight potential of this
approach is evident as the pavilion, despite its considerable size, could be built exclusively
out of extremely thin 6.5 mm sheets of plywood and therefore primarily needed anchoring
to the ground to resist wind suction loads. Plate action in today’s buildings is more or less
limited to the resisting of horizontal forces. The research pavilion showed how this principle
can be successfully implemented in a complex and expressive spatial system and how it
is possible to create an extremely light but at the same time very stiff supporting structure
only by the optimal arrangement of its constitutive elements.
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Besides, the 3-plate principle indicated new opportunities for the optimization of free-
form structures independently of the materiality (Waimer et al. 2013).xiv This fundamental
principle offers a powerful tool to investigate a wide range of structural morphologies by
simple equilibrium assumptions. Finally, the research pavilion offered the opportunity to
investigate methods of modular bionic construction using freeform geometry with different
geometric characteristics while developing two distinct spatial entities: one large interior
area with a porous inner layer and a big opening, facing the public square between the
University’s buildings, and a smaller space enveloped between the two layers that exhibits
the constructive logic of the double layer shell.
Fig 3.8.10 Aerial view of the built full-scale prototype.
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Fig 3.8.11 Interior view showing the two main spaces. The double-
layer structure responds to both structural and architectural
requirements.
Case Study 2: Fibre Composite Structure
The second case study, completed in the fall of 2012, is another example of an
interdisciplinary collaboration between architects and engineers of the University of
Stuttgart, and biologists of the University of Tubingen. In contrast to the biomimetic design
             
project is characterized by a biological push, that is performative principles of structural
     


design methodology resulted in an ultra lightweight, high-performing structure yielding new
architectural opportunities.
Biomimetic Design Principles and Transfer

Especially the exoskeletons cuticula of arthropods, such as the American lobster homerus
americanus, represent an interesting example since they evolved strong and lightweight
structural shells. Differentiation within the material in combination with geometric
differentiation allows the biological system to adjust its local properties to integrate different
tasks in a functionally graded material using the same material constituents (Fabritius et al.
2011).xv The cuticula varies its structural behaviour continuously between anisotropic and

of very pronounced arrangements: 1, for predicted loads in similar directions, unidirectional

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
(found e.g. along the legs of arthropods); 2, for wide areas with unpredicted forces that
        

a highly adaptable and functionally integrated structure.
In architecture functionality is still mainly achieved through addition of functionally discrete




design local material properties with the aim of producing functionally integrative, super
lightweight structural parts.
The concept of the presented pavilion explores the idea of a robotically fabricated full-scale

principles within the pavilion’s material design. The global design was developed as a
continuous and seamless shell with a pentagonal footprint and incorporating three open
sides functioning as entrances in addition to two closed sides. Such different architectural


               
transparency expresses the overall lightness of the structure.

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            
helicoidal arrangement found in the cuticula of arthropods whereas the dark and thicker

Directing the loads from the roof to the ground, the overall material thickness as well as
              

system.
Fig 3.8.13 Microscopic view of the exoskeleton (cuticula) of the
American lobster.
FRP Material System

based materials are suitable for moulding and shaping methods that enable the relatively
simple production of components with complex shapes. This offers great design freedom
but also at the same time risks of improper applications, as in architecture an appropriate


with polymers, one of the major challenges is to choose the right solution from the vast

components represent new and demanding responsibilities for architects and engineers
(Knippers et al. 2010). xvi   


     

these two materials are compared to steel or aluminium the advantages become clear. The

polymer matrix. A fracture in a laminate is generally caused by cracks in the matrix, which
in turn are caused by the maximum admissible strain in the polymer being exceeded.
Using a polymer with a high maximum permissible strain therefore increases the strength
of the entire composite component.
3.8 Prototyping Biomimetic Structure for Architecture

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3.8 Prototyping Biomimetic Structure for Architecture
Fig 3.8.14 Stress-strain curves of FRPs and conventional
lightweight materials.
The classical winding technique is typically used in the manufacturing of pipes, vessels,
tanks, and other rotationally symmetrical hollow components. The advantages of this method

composite wrapping, pretensioned rovings are wound around a rotating mandrel. The

  
series, reusable mandrels made from steel or aluminium are used depending on the batch
size and the geometry of the component. To ease de-moulding, mandrels are often slightly
conical in shape, or made from folding segments.

was adapted for robotic fabrication. The robotic winding process and the technological
              
calibrated to guarantee a continuous production. It was crucial to guarantee a constant
         

properties of the laminate as mentioned before, but also on the reliability of the process.


investigated by robotically wrapping 1:5 prototypes in the laboratory. The choice of the
resin system was dictated by the long manufacturing process, which required a resin with
high viscosity and pot life. Additionally, the resin system must have a low cure temperature
in order to allow the heat treatment for the given conditions. Parallel to that, unidirectional
laminate specimens were wrapped to determine through mechanical tests the material
properties, which were subsequently implemented in the FEA model.

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
winding prototype
Digital and Physical Prototyping
The design and robotic implementation of biologically inspired, high-performing, and
         

engineering, and architecture into one integrative computational design methodology. The



the structural system, along with scripted routines for the evaluation and optimization of
the local (material) and global (geometrical) stiffness of the system. Digital simulation of

  
and fabrication planning process. The biologically, materially and robotically informed
digital design and implementation suggests a new methodology of process prototyping


One of the initial goals was set on the fabrication of a seamless, continuously differentiated
 
winding process. The mechanical and architectural properties of the laminate are based
to a large extent on the interplay between winding support and winding logic. The winding
   
           becomes the
interface between design, analysis and fabrication through the algorithmic description of
             
            
winding sequence and the number of layers in the laminate. The syntax also serves as
input for the parametric generation of the robot tool paths, integrated simulation of the
robot kinematics and automated machine code generation. Initial physical models were

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used to explore architectural features such as openings, closed surfaces, and the various

      
quality of the bonding is a function of the pressure between the layers.
     
logic (syntax).
         
lay-up.

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The fabrication of complex geometries produced in FRP typically requires moulds
or custom formwork. The materially and time intensive subtractive fabrication of these
moulds is usually offset by high production runs. Consequently, an application of FRP in
architecture poses the inherent problem that it either requires moulds on an architectural
scale or many unique moulds for a potentially single use (Fischer 2012).xvii Minimizing the
mould requirement was therefore another central concern throughout the project and at the



            
winding process the industrial robot continuously lays resin-saturated glass and carbon


of negative Gaussian curvature as it naturally produces hyperbolic paraboloid geometry
consisting of straight lines.
A dedicated construction tent was set up on site to control the environment for the
3-component resin system and the 7–axis robotic fabrication setup consisting of a 6-axis
industrial robot installed on a two-meter high pedestal with a turntable as seventh external
axis. The continuous circular movement of the turntable maintained a constant feed of
  
calibrate the machine code, which was directly generated from the parametric design

and orientation of a rotationally symmetrical tool as in the example of robotic milling of the


placement end-effector and the orientation of the turntable.
Fig 3.8.18 Close-up view of the composite structure displaying
the directionality of the different layers and the inherent double-
curved surface geometry that results from the custom fabrication
process

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3.8 Prototyping Biomimetic Structure for Architecture
Fig 3.8.19 Robotic fabrication of the full-scale prototype showing

Result
The process described in this paper made it possible to produce a structure spanning
8.0 meters in diameter and reaching 3.5 meters in height by continuously winding more
 
order to achieve sound mechanical properties and to reduce the brittleness of the material.
Following the tempering process, the temporary steel frame could be safely disassembled
        

          
material design and robotic fabrication was made possible by the highly integrated
framework developed for the current project. The data exchange loop between designers,
engineers and fabrication experts enabled the creation of an integral work environment in

    
top-down approaches.

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For instance, the possibility of retrieving in thorough detail fundamental parameters for the
assessment of the mechanical response, offered a powerful means to actively design the
structural components by drawing fundamental decisions on the thickness of the lay-up

of architectural aspects and mechanical feedback enables the planning and fabrication of
highly customised components that completely meet the structural requirements of the
project, allowing for an optimisation of shape and geometry along with the local material
properties of the element itself. This is evident as the semi-transparent skin of the pavilion
weighs less than 320kg despite its considerable size and span, whilst still revealing the

Fig 3.8.20 Aerial view of the built full-scale prototype showing the
different structural zones.
Fig 3.8.21 The lighting accentuates the directionality of the
different layers and highlights the different functional zones of the
laminate.
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Conclusion
In both case studies, the concurrent integration of the biomimetic principles extrapolated
from the analysis of a biological role model – the morphology of the sand dollar’s plate
   
 
winding - within a robust computational design framework enabled a high degree of
structural performance and new opportunities in architecture. The synthesis of biology and
technology in architecture allows both the exploration of a new repertoire of architectural

The research presented above indicates that today, computational design, simulation and
digital fabrication processes open up new possibilities for approaching the transfer of
design principles from nature to architecture, as the technical requirements for doing so
can be met much more convincingly than even a very few years ago. It also shows that new
constructional systems provide for novel ways of reconciling structural and architectural
demands, offering novel tectonic qualities and spatial experiences while remaining very

for architects and engineers is more relevant today than ever before.
Acknowledgements
            
collaboration with the Plant Biomechanics Group in Freiburg (Professor Thomas Speck and
Dr. Olga Speck) and the Paleontology of Invertebrates Group (Professor James Nebelsick)
at the University of Tubingen. The research has been partly funded through a grant by
the European Regional Development Fund administered by the Department for food and
regional affairs as part of the “Cluster Forst und Holz” initiative of the state of Baden-
Wurttemberg (http://www.rwb-efre.baden-wuerttemberg.de).
The biological research of the second case study has been conducted in collaboration
with the Evolutionary Biology of Invertebrates (Prof. Oliver Betz) and the Paleontology
of Invertebrates Groups (Professor James Nebelsick) at the University of Tubingen.
The project was partly funded by the Competence Network Biomimectics (http://www.
kompetenznetz-biomimetik.de).
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