less material - more design
DESCRIPTION
Designer's manual for concrete structure optimization with fabric formworkTRANSCRIPT
LESS MATERIALMORE DESIGN
OPTIMIZED CONCRETE STRUCTURE WITH FABRIC FORMWORK
LESS MATERIAL - MORE DESIGN
OPTIMIZED CONCRETE STRUCTURES WITH FABRIC FORMWORK
written by:Bayu PrayudhiChris Borg CostanziSander van Baalen
a designer’s manual for AR0533Innovation and Sustainability Designer’s Manual (2014-2015 Q4)
TU DelftFaculty of Architecture and Built Environment
2015
Example projects page 22
Theory page 08
UHPCpage 14
Topological optimazationpage 10
Design Processpage 36
Unwrapping Geometrypage 50
Castingpage 62
Example projects page 22
Theory page 08
UHPCpage 14
Topological optimazationpage 10
Design Processpage 36
Unwrapping Geometrypage 50
Castingpage 62
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The image on the left is a scan of human bone at a microscopic level. This is one of basic principle of how nature builds its structural elements, ‘materials are expensive and shape is cheap’. As an inspiration for structural design, it represents a natural lightweight structure which has some very dynamic characteristic to fulfil the organism’s primary construction in extremely efficient way.
How can we, as a designer, architect and engineers learn from extraordinary system in natural organisms that has benefited from a 3.8-billion-year research and development period and improve the way we design our built environment?
This manual explains one of the many methods of design and fabrication of biomimicry design in structural element. Rethinking the way we design a column, by using topology optimization method to generate a material-efficient structure with a new innovative Ultra High Performance Concrete as a material and using an unconventional fabrication method with fabric form-work for concrete casting.
We will explain the process of design and fabrication in a simple step-by-step guides of a specific design problem which can be followed as a learning material. The intent of this guide is to become a case study, showing the possibilities and potential of a complex-form optimized structure with fabric form-work.
We hope this design manual will provoke interest for students and academics to do further research and inspire architects and designers to implement the methods in practical architecture projects.
Image (left) : Electron scanning microscope image showing osteoclast resorption of trabecular bone. Source : http://boneresearchsociety.org/resources/gallery/35/
Design
Construction Structural
Target grouppage 05
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Target Group
Topological optimization contemplates design, structural integrity and construction method of building elements. Therefore the target group of this manual is not limited to architects. This building method requires collaboration and integration, as does the software. Topological optimization requires an integrated process between;
• ARCHITECTS AND DESIGNERS
• CONTRACTORS
• STRUCTURAL ENGINEERS
Or as Mutsuro Sasaki puts it “topology optimization enables a shift from typological to topological design thinking, in which the need for empirical experience is exchanged for the need for a generic knowledge of the prerequisites of optimization.”1 This statement implicates that there must be a shared knowledge of design, creation (production technique) and structural behaviour from the beginning of a project. Design by optimization is based upon the collaboration, integration and shared parameters between the three mentioned fields. So ultimately that is the target group of this manual
1. R. Ponginan, (2015) Danish Team Uses HyperWorks to Prove the Value of Topology Optimization for Concrete Archi-tectural Structures, Altair University Hyperworks
1.THEORY
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The first chapter of the manual explains the basic theory of the process, in contains general informations of :
• Design process : Topology optimization
• Material of choice: Ultra High Performance Concrete
• Fabrication method : Fabric form-work
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1. Bendsoe, M., & Sigmund, O. (2003). Topology optimization: Theory, methods, and applications. Berlin: Springer.
2. Mattheck, C. (1998). Design in nature: Learning from trees. Berlin: Springer-Verlag.
TH
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Topology optimization method provides an answer to the following structural design question: Given a specified design domain including loads, supports and constraints; how should material be distributed such that the performance of the resulting structure is most efficient, relative to the aim of the optimization?
The method was originally developed by Prof. Martin P. Bendsoe and Noburu Kikuchi in 1988 for mechanical problems1, such as minimizing the weight of machine components while maintaining a high stiffness. Since its introduction, it has seen a wide application and international development.
The fundamental problems of mechanical engineering have been well understood at an early point within the field of topology optimization. However, the method has been left widely unexplored within architectural design and structure engineering.
The method of topology optimization mimics how skeletal forms in biology follow a simple rule described as ‘the axiom of uniform stress’2 : Material is built up in areas of stress concentration, until the forces is distributed evenly; in unloaded areas there is no material. The goal is perfect efficiency, with no waste material and all that exist is carrying its fair share of workload.
Topology optimization in structural design represents as an excellent result of a biomimicry approach as a design principle. It provides answer to one of the most crucial question of biomimetics design: How to radically improve resource efficiency? In the field of structural engineering, topology optimization will provide remarkable solutions in the future of architecture design.
LESS MATERIAL - MORE DESIGN
What is topology optimization?
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Examples of common topology optimization steps in 2D and 3D methods.Source : http://www.caess.eu/site/Software-Animations.html
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Huang, X., & Xie, Y. (2010). Evolutionary topology optimization of continuum structures methods and applications. Chichester, West Sussex: Wiley.
Millipede
http://www.sawapan.eu/
Books :
Softwares :
E, M., & Sigmund, O. (2003). Topology optimization: Theory, methods, and applications. Berlin: Springer.
TopOpt group
http://www.topopt.dtu.dk/
Further study on topology optimization
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Example uses topology optimization to gradually remove material from a solid volume chair on which the actions of a person seating are applied (ie. vertical and horizontal loads for the seating position)Source : http://www.liftarchitects.com/
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The complex geometry of the optimized structure design makes it very difficult to place a steel reinforcement in a conventional way of concrete construction. We need to use a special material which has the strength equal or better than the reinforced concrete. Ultra High Performance Concrete (UHPC) is our choice since it eliminates the needs of steel reinforcement.
UHPC, also known as reactive powder concrete (RPC), is a high-strength, ductile material formulated by combining portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers. The material provides compressive strengths up to 200 MPa and tensile strengths up to 48 MPa.
The materials are usually supplied in a three-component premix: powders (portland cement, silica fume, quartz flour, and fine silica sand) pre-blended in bulk-bags; superplasticizers; and organic fibers. The ductile behavior of this material is a first for concrete, with the capacity to deform and support flexural and tensile loads, even after initial cracking.
MATERIALIZATION
Ultra-High Performance Concrete
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2 cm thick of shell structure with UHPC in Shawnessy Light Rail Transit station, CalgarySource : https://buildcivil.wordpress.com/
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Fehling, E. (2014). Ultra-high performance concrete UHPC fundamentals, design, examples. Berlin: Ernst & Sohn.
Books :
Links :
Material properties:
http://www.cement.org/for-concrete-books-learning/concrete-technology/concrete-design-production/ultra-high-performance-concrete
Archdaily Material Minds: The Possibilities Of Ultra High Performance Concrete :
http://www.archdaily.com/630994/material-minds-the-possibilities-of-ultra-high-performance-concrete/
Ye, H. (2009). Ultra-high-pumpability and high performance concrete technology. Stafa-Zurich: Trans Tech Publications.
Further study on UHPC
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Top : Comparison of different material for the same structural performance of a beam. Source: http://www.taktl-llc.com/Bottom : Example project using UHPC for canopy roof. Source: http://www.constructionspecifier.com/introducing-g8way-dc-ultra-high-performance-concrete-has-it-covered/
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A variety of production methods for complex and topological optimized structures exist today;
• Fabric formwork
• CNC Milling
• Spay-up concrete
• 3D printing methods / additive manufacturing
• Traditional formwork methods
• Flexible moulds
The focus of this manual is placed upon Fabric formwork because of its sustainable aspects, low complexity (no need for complex equipment) and fast production. There is one limitation with this method, only the production of convex shapes is possible. The concrete mixture applies a pressure on the fabric and this force is solely transferred via tensile forces. Structurally this is an approach close to Gaudi’s methods of catenary arches, creating more optimal structures. But shape wise this may lead to design constraints.
Another small disadvantage of fabric formwork is the inaccuracy in the final design. Because of the forming of the fabric to the optimal shape the final shape might differ from the design. It is impossible to fully control the cast geometry only the supports are fixed. This a purely aesthetic demand that cannot be satisfied.
To understand fabric formwork a comparison with another promising construction method (CNC milling of EPS) elaborates the choice.
CNC milling of foam is relatively cheap compared to the previous named methods. The material EPS is inexpensive, only the CNC mill is a more complex instrument needed than with Fabric formwork. However CNC mills are widely used in the industry. The only limiting factors to CNC milling are the depth of the used mill and the demoulding of the structure. Using a mould that need to be separated in pieces requires a different design approach and can also complicate the process if more than two pieces are
FABRICATION METHOD
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used. But more advanced and complex shapes are possible with this method. Also the precision is high; tolerances are the same over the whole surface.
A disadvantage compared to fabric formwork is that the surface of the milled EPS needs to be treaded and smoothened with coatings. Also extensive amounts of EPS formwork are needed, especially when the projects become larger. And the formwork needs to be discarded after its use, creating more waste that fabric formwork. Asbjørn Søndergaard: “CNC milling disposes the EPS foam, however this can be recycled to minimize waste”1
The combination of both methods Fabric formwork and support of CNC-milled formwork can be an interesting option for complex shapes with convex and concave surfaces. At the University Of Manitoba (C.A.S.T.) CNC milled wooden frames are used to create beams and complex shapes. To replace these wooden formworks with CNC milled EPS might be a more sustainable solution.
1. Sproge, K., (2013) Topology optimization for reinforced concrete structure using large-scale rapid proto-typing technology. VIA University College, Horsens Denmark
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Fabric Formwork
“In order to hold wet concrete in place along a flat plane, conventional rectangular, panelised, formworks must resist bending moments.”1 Also minimalizing deflections is important to the structural quality. This results in more material and weight of the formwork. Also concentrated stresses are introduced in the edges and joints. The price that is paid to keep all the concrete in place and minimise the deflection, results in a lot of labour, craftsmanship and thus to high prices.
“A structural analysis of a cylindrical fabric column formwork reveals that the hydrostatic pressure of the wet concrete is taken by the horizontal (circumferential) fibers in tension. The mildly pretensioned vertical fibers of the fabric are essentially acting to hold the horizontal fibers in place, and to laterally stabilize the vertical column of wet concrete” 1 In this way all the forces applied on the material / fabric are transferred into the simplest and most efficient forces, tensile forces.
The fabric formwork consists if one-layered out of high density polyethylene scrim fabric (HPDE scrim fabric). And if applied two layered a more elastic inner layer out of spandex is covered in a outer polyethylene layer. These permeable membranes improve the surface finish and strength of the concrete. Because of their filtering capabilities they allow air and excess water to bleed out of the mixture. Therefore concentrations in the surface of gravel pockets and blow holes are prevented, and a high quality cement concentrated surface is created. Also the loss of water creates a more durable and stronger structure. When working with fiber reinforced concrete, concentrations of fibers in the surface of the concrete might occur. “these fibers were at least partly responsible for some surface finish problems encountered in this job. Large clumps with a very stiff, claylike consistency occurred amidst the otherwise properly plastisized concrete.”1 This can be prevented by shaking and vibrating the fabric when pouring.
Another issue to consider with fabric formwork is the hydrostatic pressure from the concrete mixture. This means that the freedom of shape in a column at the top is higher and easier to realise than in the bottom of the column.
1. West, M., 2002. Fabric-formed Concrete Columns for Casa Dent in Culebra Puerto Rico. Centre for Architectural Structures and Technology, University of Manitoba
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Rotated Column designed by students and constructed during the TEK1 workshop at the Royal Danish Academy of Fine Arts, School of Architecture. Source: http://concretely.blogspot.nl/2013/03/workshop-rotation-column.html
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Manelius, A. (2012). Fabric Formwork: Investigations into Formwork Tectonics and Stereogeneity in Architectural Constructions.
Books :
Links :
CAST Center for Architectural Structure and Technology University of Manitoba:
http://www.umanitoba.ca/cast_building/research/fabric_formwork/
International Society of Fabric Forming :
http://www.fabricforming.org/
Further study on Fabric Formwork
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Example of prototype project of fabric formwork concrete.Source: https://www.youtube.com/watch?v=29yLaYXSN9Y
2.CASE STUDIES
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This chapter shows six case studies projects which use either topology optimization method, UHPC, or fabric formwork for concrete. The case studies range from research project, prototype, to built architecture projects.
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SA new compression architecture
System of columns and plates that work as one element, constructed with fabric formwork.
2007
Winnipeg, Canada
University of ManitobaCentre for Architectural Structures and Technology (CAST)
Website:
http://www.umanitoba.ca/cast_building
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At the University of Manitoba this modular system is created. It exists out of an optimised column and plate that work as one element. The shape follows the flow of the forces.
The creation of these columns and plates or vaults (as they are called) is deducted from the same principle as Gaudi used. Basically the starting point for the creating of these shapes is the used fabrication technique, fabric formwork. With this technique a fabric I n the desired shape is cut and spanned into tension than it is filled with concrete. If the, by tension, created shape than is inverted or turned a compression element is realised.
This procedure of relaxing a membrane or a fabric is also done with domes and spheres to get opti-mal shapes, like Heinz Isler’s shells. But using this technique to create more complex shapes is new. Computer added design makes it possible to generate and predict the strength of these elements. Therefore it is possible to rationalize the shapes, curvatures and folds like in the examples from the University of Manitoba.
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SCrematorium in Kakamigahara
Structurally optimized 18 mm thick roof shell for most economical thickness to structural strength ratio. Created with wooden formfork
2004 - 2006
Kakamigahara, Gifu, Japan
Toyo Ito & Associates, Architects
http://www.toyo-ito.co.jphttp://www.detail.de
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The roof structure of this crematorium is designed by Toyo Ito & Assiciates in cooperation with Mutsuro Sasaki. The free flowing roof structure is supported by minimal amount of columns, with a thickness of 200 mm this is an impressive piece of engineering. With a maxima span of .. and height of 11.5 meters this shows that optimised concrete structures can exist out of bigger elements that beams and columns. Using dome shapes and columns to support this roof a balance between aesthetics, architecture and structural engineering is created, a very integrated approach and close collaboration between architect and structural engineer.
To build this roof structure a wooden formwork existing out of small laminated elements was used as shown in the pictures. The concrete also has reinforcement, which shows especially in the supporting columns. This cast in site project is an example of a modern design approach but a laborious construction method, which requires a lot of precision, material and craftsmanship.
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SUnika beton
This structure is created with CNC-milling of polystyrene blocks. The complex molds are produced in a fully digitized file-to-factory process.
January 2010
Aarhus Denmark
Per Dombernowsky, Asbjørn Søndergaard, Aarhus School of Architecture
Website:Mail:
http://[email protected]
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A project team from Aarhus School for Architecture created a 12 x 6 x 3.3 meters structures using topological optimization. This was coupled to robotic file to factory construction methods. With the use of CNC-milling with robotic arms a formwork out of polystyrene was created for concrete casting.
Interesting about this project is that the research was done from the optimization process to the building of the prototype itself. In the analysis the team figured out that 60% of material could be saved with the optimized design. But the notion that makes this type of design intresting is best explained by Søndergaard “new types of structures in which members are created in a continuous whole, eliminating such conventional sub-classifications of systems as beams, slabs and columns.” 2
Material wise they used self-compacting concrete to fill all the small gaps and elements in the form-work. Also they claim that the polystyrene could be reused. What in practice might be more difficult, as mentioned before in the theory.
2. Søndergaard. A., Dombernowsky P., 2009. ‘Three‐dimensional topology optimisation in architectural and structural design of concrete structures.’ In Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium, Valencia
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SAkutagawa River Side Project
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One of the first topological optimised projects to be realised.
Paper:
Computational Morphogenesis and its Applicationto Structural Design, Ohmori H, Futai H, Iijima T, Mutoh A and Hasegwa Y.
April 2004
Takatsuki City, Japan
F-tai Architect, IijimaStructural Design Office,and Mutoh Structural Design Office
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This building is one of the first examples of Topological optimization put in practice. The building consists of four stories and is relatively small for the amount of concrete used in the façade. Two of its walls facing south and west were optimized. I the process not only dead and live loads were used, because of Japan’s proneness to earthquakes also dynamic loads needed to be taken into account.
The realisation of this project is also done by methods that are not commonly used. To custom make a steel mould for such a small building and use it only one time is not a viable option for many pro-jects. Also a lot of steel reinforcement is used in the walls.
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SStade de Jean Bouin
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This project has a façade and covering of specially designed prefabricat-ed optimized UHCP elements, with glass cast in the gaps.
2007 - 2012
Paris, France
Architect, Rudy Ricciotti
http://www.rudyricciotti.com/sports-a-loisirs/stade-jean-bouin
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Website:
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The covering of this stadium and the facade are made up out approximately of 1900 respectively 1600 optimized UHPC triangles. The generated forms are different per panel but “resulting from an identical and repetitive manufacturing process.” 3 The triangles are prefabricated and made out of UHCP. They measure 8.4 meters in height and 2.4 meters in width. The optimization resulted in a 60% open cover/ façade, which is half filled with glass to protect the spectators.
The use of UHCP was profitable because of a couple of reasons. Firstly it reduced the material use considerably, creating the possibility of the open structure. Secondly it made a joining principle between the elements with cast in gutters possible saving a still connection principle. And lastly it created the possibility to cast in the glass in the elements. So no extra structure for the glass on top of the elements is needed. The UHCP has a sealing property including the glass in the gaps.
These elements are all prefabricated and transported to the side. Because of the precision of the process and the minimal material use a high lifespan of 50 to 100 years is expected for the façade and the covering.
3. Ter Maten, R.N., 2011. ‘Ultra High Performance Concrete in Large Span Shell Structure’ Delft University of Technol-ogy Retrieved from: http://repository.tudelft.nl/
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SCasa Dent
Project used to research the application of fabric formwork, whit realisa-tion 13 columns in a dwelling
2001
Culebra, Puerto Rico
University of ManitobaCentre for Architectural Structures and Technology (CAST)
Website:
http://www.umanitoba.ca/cast_building
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The 13 unique cast in site columns were sized from 2.9 to 3.8 meter and had a diameter of 34 cm. All these variations of shape and size were dealt with by rigging the formwork in a certain way. With fabric formwork “final geometry of the cast member is the result of the interaction between the flexi-ble tension membrane and the wet concrete it contains.”4 Because of this and that the formwork can be used multiple times the formwork can be used to create a lot of different shapes and sizes by just changing the way in which it is rigged. It is not mentioned how many times it is possible to reuse a formwork, but that it is dependent on the shape and the mixture of the concrete.
Because of the lightweight of the formwork it can be easily stored and transported ”The formworks for the Casa Dent columns are currently stored under a table in Winnipeg”4 It is generally fabricated from high density polyethylene scrim. But in this project a combination of an outer polyethylene jack-et and an inner stretch-knit (“Spandex”) line was used, mainly for aesthetic reasons.
4. West, M., 2002. Fabric-formed Concrete Columns for Casa Dent in Culebra Puerto Rico. Centre for Architectural Structures and Technology, University of Manitoba
3.DESIGN PROCESS
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This chapter explains step-by-step process of the design and modelling of the opti-mized column structure for a specific predetermined design case. The design process can be divided into three parts :
• Setting the design constraints
• Generative modeling for optimized structure
• Dynamic relaxation of the model
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INSTALLING REQUIRED PLUGINS
Download the Millipede plug-in from http://www.sawapan.eu/. The zip file also contains manual and example files. Copy all the files inside the Libraries folder into your Grasshopper library folder (accessible from grasshopper in Files > Special Folders > Components Folder and restart Rhino.
We recommend you to study the example files especially the 2D and 3D topology optimization and read the manual since it contains all the information of how to use all the available components and function in Millipede.
Other plugins which are required are Kangaroo, Weaverbird and uto’s MeshEdit. All of these plugins should be available for free in food4rhino website.
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Rhinoceros 5www.rhino3d.com
Grasshopperwww.grasshopper3d.com
Millipedewww.sawapan.eu
Kangarookangaroo3d.com
Weaverbirdwww.giuliopiacentino.
com/weaverbird
uto’s Mesh Editwww.grasshopper3d.
com/group/geco
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For this design guide, we modelled the ‘design area’ of the structure as a 3 x 3 x 3 m box. We put three point loads at the top surface and two point supports at the bottom surface. Basically, the structure design will act as a column which carry loads from the top surface to the bottom surface of the box.
Millipede recognizes loads and supports as volumes, therefore we created spheres as representative of these elements, the half part of the spheres which are intersected inside the box will be recognized as the loads and supports regions inside the whole design area.
We also added a void region which represent a restricted area for the structural design. This will inform millipede to avoid using these regions for the optimized design. These constraints should be pre-determined by the designer considering aspects such as architectural requirements.
MODELING THE DESIGN CONSTRAINT
Load Region
Support Region
Void Region
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3D Loads Region : accepts closed polysurfaces / Brep, the load input requires a unitized vector in N/m3, for this instance we will use 10 kN/m3 for each load.
3D Support Region : accepts closed polysurfaces / Brep, in this case we will use default fixed supports.
3D Boundary Region : accepts closed polysurfaces / Brep, this component determines the working design area of the structures, we will set the ‘IsVoid” input with boolean value ‘True’ for the void region.
DESIGN INPUTS FOR MILLIPEDE
3D Loads Region
3D Support Region
3D Boundary Region (Solid)
3D Boundary Region (Void)
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All the design inputs from the previous steps are connected to the Topostruct 3D Model, XR [Integer] is the number of cubic volume elements to generate along the x axis of the bounding box of the input geometries. The component basically creates a Finite Element system which will be calculated with the Topostruct 3D Solver, the main analysis component.
The important parameters are:
O [Integer]: Number of optimization iteration steps each time the user presses the “Step” button.
S [Number]: Smoothing factor applied at each iteration to avoid the generation of checker patterns. (0.0 to 1.0)
P [Number]: Penalization factor. The larger this number the fastest the optimization will converge to a black and white state.
T [Number]: Target Density percentage. A number from 0.0 to 1.0 designating the fraction of the overall material that should remain at the end of the optimization process.
RUNNING THE OPTIMIZATION
Topostruct 3D Model
Topostruct 3D Solver
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D [Number]: Deflection factor. This is used in order to exaggerate the deformation of the material at its equilibrium state. In this case we use 0.0 since we have a very small deflection which can be ignored.
Iso [Number]: contour value. This value is used in order to determine the density levels at which contours are drawn. For example a value of 0.5 means that a contour will be drawn that separates material densities less than 0.5 to material densities greater than 0.5.
Furthermore, we used Weaverbird’s Mesh Edges to show the edges of the mesh result.
DISPLAYING THE OPTIMIZATION RESULT
3D Iso Mesh
Weaverbird’s Mesh Edges
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The model result from the Millipede optimization is a very direct representation of the structural behaviour of the model assembly, the geometry is very rough and is not very suitable as an architectural elements. We need to refine the geometry to achieve a more pleasing geometry in terms of aesthetic and fabrication factor (in this case for fabric formwork casting).
The first step is to delete the top and bottom ‘cap’ (we have 5 parts) of the structure which are actually the slab connecting this structure. We need to bake the mesh result from Millipede, explode the mesh into individual mesh for each faces, delete the parts mentioned (highlighted in red border in the image above), and rejoin the mesh.
POST RATIONALIZATION
Top Surface
Bottom Surface
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The ReMesh component is one of the special component in kangaroo which runs its operation repeatedly (with timer component) until the mesh is fully refined. The important parameter is Edge Length, which control the target length of each edges of the mesh that will try to achieve.
MESH REFINEMENT (REMESH)
ReMesh (Kangaroo)
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The final step of the model optimization is to relax the mesh, to create a smooth surface representing a tensioned fabric formwork for the next fabrication process. We will use SpringsFromLine component in Kangaroo to apply the spring forces to each edges of the mesh to achieve a relaxed equilibrium state to the model. We will need a Kangaroo Physics Engine to run the operation.
First, we need to take the naked vertices of the mesh and use it as anchor points for the spring forces, we used kangaroo’s Naked Vertices component.
We took the edges of the mesh with Weaverbird’s Mesh Edges component and connect it to the Springs component. We need to specify the target length (rest length) of the edges which the forces will try to achieve. Since all the edges have different lengths, we multiplied the original length with a ratio number We will need to experiment a little with the parameters configuration to achieve the desired final design. After we satisfied with the result, we can bake the mesh and use the model for fabrication process.
MESH RELAXATION
Kangaroo Physics Engine
Kangaroo Naked Vertices
Weaverbird Mesh Edge
Kangaroo Springs From Lines
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Script overview (structure optimization process)
Design input (constraints) Topology optimization engine
Optimization parameters
Load direction and value
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Deflection factor
Result model and visualization
3D mesh model
contour (layers) views
cloud views
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mesh refinement
mesh relaxation
Spring forces (relaxation) parameters
Remesh parameters
Script overview (post rationalization process)
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Final design
Scan the QR Code on the left to download the rhino files and grasshopper scripts or simply use the following link (case sensitive): https://goo.gl/rrUYVj
4.UNWRAPPING GEOMETRY
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The next stage in the process is unwrapping the Digital 3D Geometry. This is done to prepare 2D ‘unfolded’ patterns which can be cut out in fabric and later stitched back together as a fabric 3D Geometry. This is done by first splitting up the digital model into manageable segments and then adding ‘cut seams’ to allow them to unfold – the same concept as cutting a paper cylinder to get a rectangle
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Open the 3D Coat UVW unwrapping software from the installed directory.
This will automatically load a prompt screen for the different modelling modes. Since the software will only be used for basic UV mapping, select the ‘UV Map Mesh’ mode. [alternatively, use File > Import > Model for Pixel Painting]
It is also recommended to keep the default import settings, as the software will only be used for basic exporting of UVW Maps.
LOADING THE SOFTWARE
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Once open, a number of panels, commands and options become available. Most of these will not be used and are irrelevant for what is needed.
MARK SEAMSThis is used to mark individual seams around the geometry.
EDGE LOOP This is used to mark continuous edge loops around the geometry. Par-ticularly useful for closed shapes
UV PATHThis draws the closest seam between two points. Particularly ueful for complex shapes
BASIC COMMANDS
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Once the geometry has been imported as described in STEP 1, it will be displayed with the mesh divisions as shown above.
The first thing that must be done is analyse the geometry and understand how it can be divided. There are two ways of seeing how this can be divided:
[a] a series of Cylinders: Dividing the geometry into multiple closed cylinders having an additional seam to cut them open
[b] Dividing into faces: Dividing the geometry into multiple faces which are relatively flat and open.
ANALYZING THE GEOMETRY
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There is no right or wrong strategy to dividing the geometry, however a basic rule is to have as simple geometry as possible as well as avoiding small divisions.
The Column method may result in a larger number of pieces though may also mean more manageable segments
DIVIDING THE GEOMETRY - COLUMN METHOD
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DIVIDING THE GEOMETRY - LARGER SEGMENTS
Alternatively, You may opt for larger pieces in lesser numbers. This, however, depends on the geometry being used and the limitations which come about from it.
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SAVING UNWRAPPED VECTOR
Once satisfied with the overall divisions, use the Apply UV Set command to save the unwrapped divisions in preparation for exporting.
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SAVING PATHS AS VECTORS
The paths created now need to be exported as Vectors so that they can easily be modified in CAD programs as well as having scalability without losing resolution. To do this, select ‘Textures’ > ‘Export’ > ‘Emissivity’.
This will export the emissivity layer of the unwrapped model.
Next, Open this file in Photoshop. Select the paths using ‘Select’ > ‘ Colour Range’ and from the Paths Menu, select the ‘Make Work Path’. This will automatically convert the selection into a path which can be exported as a Vector as needed.
To export, simply choose ‘File’ > ‘Export’ > ‘Paths to illustrator’
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The file paths are now saves as vectors and can be used for modifications needed prior to casting
FINAL PATHS
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The Final step in the preparation is to add an additional offset to the unwrapped geometry. This will be used as the area to join and sew the seams together.
This is done by importing the Vector File into any editing software (Autocad is Recommended) and creating an offset around the perimeter of the geometry that can be used as sewing area.
ADDITION OF DETAILS - LIPS
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5.CASTING
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The following chapter gives an overview of how to cast the final element using the fabric obtained in the previous chapter. The main steps can be divided into:
• Principle of Tensioning and Support Structure• Attaching fabric to support structure• Tensioning the fabric• Casting• Demoulding
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The basic principle for the support structure is to pre-stress the fabric to provide a rigid mould in which to cast the module as well as to get the basic casting form. This can be done by attaching the fabric to two plates [Top and Bottom] and increasing the distance between them; done by lengthening the corner rods shown in the figure above. This is a method described for pre-cast systems, however this is open to interpretation to different geometries; it is the basic pre-stressing principle that must be applied.
It must be noted that is method is described for members no higher than 3m in height - larger members would require more rigid tensioning systems
THE SUPPORT STRUCTURE
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Top
Bottom
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Given that the area of research is so new, there use of materials for fabric is still very open. For this example, however,
FORMWORK MATERIALS
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•Primary Casting Fabric: Hessein or any similar woven fabrics. •Reinforcing Jaket: Polyeurothane Fabric
Note, the system of using reinforcement jackets can be replaced by using a single-membrane as demonstrated in the Casa Dent project in case study section.
Reinforcing Jacket: Polyeurothane Fabric
Primary Casting Fabric: Hessein / woven fabric
Primary Casting Fabric: Hessein / woven fabric
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The bottom parts of the fabric can be attached using simple methods, one possibility is to sand-wich the fabric between a base and wooden guides as shown above.
ATTACHING THE FABRIC [BOTTOM]
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Similarly, the top part of the fabric can be attached to the top part of the support using pres-sure plates.
Fabric must first be pulled through the casting holes shown above.
ATTACHING THE FABRIC [TOP]
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Once the fabric has been attached to the support structure, pre-tensioning can beging. This is done by increasing the distance between the top and bottom plate - one method of achieving this would to have the top plate attached to adjustable rails and simply moving the plate upwards.
STRETCHING THE FABRIC
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Casting the concrete is simply a matter of pouring into open holes of the top support struc-ture. This should be done carefully and slowly so as not to overload the fabric instantaneously as well as to allow for even compacting, if necessary, the concrete fabric can also be slapped to encourage compacting as traditional vibrators are generally impossible to use.
A concrete mix having a good slump should be used to ensure that it is properly distributed and fills air gaps. Having a higher w:c ratio is not problematic as the permeable nature of the fabric allows excess water to bleed.
Once cast, demoulding can be done after at least 24 hours, depending on the size and rate of hydration of the member. Of course, in all cases, one’s own judgement should also be used.
CASTING AND DEMOULDING
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Dombernowsky P., Søndergaard. A., 2009. ‘Three dimensional topology optimisation in architectural and structural design of concrete structures.’ In Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium, Valencia
E, M., & Sigmund, O. (2003). Topology optimization: Theory, methods, and applications. Berlin: Springer.
Fehling, E. (2014). Ultra-high performance concrete UHPC fundamentals, design, examples. Berlin: Ernst & Sohn.
Manelius, A. (2012). Fabric Formwork: Investigations into Formwork Tectonics and Stereogeneity in Architectural Constructions.
Ohmori, H. et al., 2004. ‘Computational morphogenesis and its applications to structural design’ University of Cornwell
R. Ponginan, (2015) Danish Team Uses HyperWorks to Prove the Value of Topology Optimization for Concrete Architectural Structures, Altair University Hyperworks
Sproge, K., (2013) Topology optimization for reinforced concrete structure using large-scale rapid prototyping technology. VIA University College, Horsens Denmark
Ter Maten, R.N., 2011. ‘Ultra High Performance Concrete in Large Span Shell Structure’ Delft University of Technology Retrieved from: http://repository.tudelft.nl/
Veenendaal D., et al., 2011 ‘History and Overview of fabric formwork: using fabrics for Concrete casting’ Structural concrete 12 (2011) n03 doi:10.1002/suco.201100014
West, M., 2002. Fabric-formed Concrete Columns for Casa Dent in Culebra Puerto Rico. Centre for Architectural Structures and Technology, University of Manitoba
REFERENCES
Bayu Prayudhi - [email protected] Borg Costanzi - [email protected]
Sander van Baalen - [email protected]