Making Blobs with a Textile Mould Arno C.D.Pronk!and Rogier Houtman2 1 Department of Architecture,Building and Planning Technical University of Eindhoven P.O.box 513,NL-5600 MB Eindhoven,NL a.d.c.pronk@bwk.tue.nl http://www.blob.tue.nl 2 Department of Civil Engineering Laboratory of Building Engineering Delft University of Technology P.O.box 5048,NL-2600 GA Delft NL Tentech Design Engineering P.O.box 619,NL-2600 AP Delft NL rogier@tentech.nl http:/www.tentech.nl Summary.In the last decade compler buildings i.e.with unregular curved surfaces have been designed..The subject of this paper is the construction of those compler buildings.One of the main characteristics of a membrane structure is its geometrical complerity,which can be seen in multiple curved surfaces and complicated connection elements.Modern sophisticated computer technologies can be used to produce easily these compler three-dimensional shapes out of flat strips of fabric.Due to a lack of suitable production methods the erpression of the natural stress flow in supporting and connecting (rigid)structural elements is difficult.This paper assumes that it is possible to achieve the architectural desired free forms by manipulation of structural membranes.To prove that it is possible to achieve the architectural desired free forms different cases are described in which this technique is used.The first case describes the design of an indoor Ski run.The second and third case describes the building of a lightweight stage covering and an art pavilion.In all the three cases physical models have been used in the design phase.The structural design of the membrane mould has been engineered with the program easy.The rigidized structures have been analyzed using different FEM programs for each case.The transformation of a form- active structure (membrane)into a surface-active structure has been researched to make domes ore dome-like structures. Key words:Blobs,textile mould,free geometry architecture,tensile structures, pneumatic structures,formfinding,structural optimisation 305 E.Onate and B.Kroplin (eds.).Textile Composites and Inflatable Structures,305-322. 2005 Springer.Printed in the Netherlands
Making Blobs with a Textile Mould Arno C.D. Pronk1 and Rogier Houtman2 1 Department of Architecture, Building and Planning Technical University of Eindhoven P.O. box 513, NL-5600 MB Eindhoven, NL a.d.c.pronk@bwk.tue.nl http://www.blob.tue.nl 2 Department of Civil Engineering Laboratory of Building Engineering Delft University of Technology P.O. box 5048, NL-2600 GA Delft NL Tentech Design & Engineering P.O. box 619, NL-2600 AP Delft NL rogier@tentech.nl http:/www.tentech.nl Summary. In the last decade complex buildings i.e. with unregular curved surfaces have been designed. . The subject of this paper is the construction of those complex buildings. One of the main characteristics of a membrane structure is its geometrical complexity, which can be seen in multiple curved surfaces and complicated connection elements. Modern sophisticated computer technologies can be used to produce easily these complex three-dimensional shapes out of flat strips of fabric. Due to a lack of suitable production methods the expression of the natural stress flow in supporting and connecting (rigid) structural elements is difficult. This paper assumes that it is possible to achieve the architectural desired free forms by manipulation of structural membranes. To prove that it is possible to achieve the architectural desired free forms different cases are described in which this technique is used. The first case describes the design of an indoor Ski run. The second and third case describes the building of a lightweight stage covering and an art pavilion. In all the three cases physical models have been used in the design phase. The structural design of the membrane mould has been engineered with the program easy. The rigidized structures have been analyzed using different FEM programs for each case. The transformation of a formactive structure (membrane) into a surface-active structure has been researched to make domes ore dome-like structures. Key words: Blobs, textile mould, free geometry architecture, tensile structures, pneumatic structures, formfinding, structural optimisation 305 E. Oñate and B. Kröplin (eds.), Textile Composites and Inflatable Structures, 305–322. © 2005 Springer. Printed in the Netherlands
306 Arno C.D.Pronk and Rogier Houtman 1 Blobs In 1994 K.Michael Hays [10]writes that in reaction to fragmentation and contradic- tion there is a new movement in architecture,which propagates a combination not only of forms,but also between different media like film,video,computers,graphics mathematics and biology.He recognizes that architecture is influenced by the devel- opment of an increasing complexity of information and communication is changed into information and media.This has lead to a development that is being referred to as blob architecture (Figs.1,3).The characteristics of blobs are:smoothness, irregularity and a double curved skin. Fig.1.by Michael Bittermann Fig.2. Fig.3. Modeling by means of nylon stockings and balloons 2 Blobs with a Textile Mould The similarity between form active structures,like tent-and pneumatic structures on the one hand and blobs on the other hand is so striking that it is obvious to try to make blobs with techniques,that are being used for constructing tent-and pneumatic structures. In the past numerous possibilities have been examined.Frei Otto for example has demonstrated the possibilities of influencing the form of pneumatic structures by stretching nets and cables over them.Another possibility of manipulating a tensile form is the combination of cloth and a pneumatic structure into a blob design.An example is the floating theatre at the Expo 1970 in Osaka designed by Yutaka Mu- rata.One of the latest examples of transforming the shape of a pneumatic structure
306 Arno C.D. Pronk and Rogier Houtman 1 Blobs In 1994 K. Michael Hays [10] writes that in reaction to fragmentation and contradiction there is a new movement in architecture, which propagates a combination not only of forms, but also between different media like film, video, computers, graphics mathematics and biology. He recognizes that architecture is influenced by the development of an increasing complexity of information and communication is changed into information and media. This has lead to a development that is being referred to as blob architecture (Figs. 1,3). The characteristics of blobs are: smoothness, irregularity and a double curved skin. Fig. 1. by Michael Bittermann Fig. 2. Fig. 3. Modeling by means of nylon stockings and balloons 2 Blobs with a Textile Mould The similarity between form active structures, like tent- and pneumatic structures on the one hand and blobs on the other hand is so striking that it is obvious to try to make blobs with techniques, that are being used for constructing tent- and pneumatic structures. In the past numerous possibilities have been examined. Frei Otto for example has demonstrated the possibilities of influencing the form of pneumatic structures by stretching nets and cables over them. Another possibility of manipulating a tensile form is the combination of cloth and a pneumatic structure into a blob design. An example is the floating theatre at the Expo 1970 in Osaka designed by Yutaka Murata. One of the latest examples of transforming the shape of a pneumatic structure
Making Blobs with a Textile Mould 307 is the tensile structure of the Swiss pavilion(Figs.4,5)at the Expo 2002.The edges of the structure are transformed by using bending stiff elements.The connection with nature is obvious if we realize that a human body can be seen as a membrane (the skin)stretched over bones (wire-frame)and muscles (pneumatic structure). Fig.4. Fig.5. Nouvelle DestiNation Bundespavillon,Swiss Expo 02(Eckert Eckert Architekten) Fig.6.Rigidized inflatable structure (A.Pronk) 3 Form-Active/Surface Active In the open-air theatre in Soest a pneumatic structure was used as a mould.This mould was then rigidized,which resulted into a bent stiff beam that was combined with cloth.The result was a tensile structure.This technique was then studied.The purpose was to use this technique to realize complete buildings. Heinz Isler has already demonstrated that it is possible to rigidize a pneumatic mould to construct buildings.The same principle is used in aerospace engineering for realizing antennas and space habitats.(In Soest the same principle is used to construct architectural shapes.)The surface of the building was not the result of the mechanics but the result of an architectural design process.At the Technical University of Delft and Eindhoven a group has been formed that has taken on the challenge of finding a way to realize blobs by means of transforming and rigidizing
Making Blobs with a Textile Mould 307 is the tensile structure of the Swiss pavilion (Figs. 4,5) at the Expo 2002. The edges of the structure are transformed by using bending stiff elements. The connection with nature is obvious if we realize that a human body can be seen as a membrane (the skin) stretched over bones (wire-frame) and muscles (pneumatic structure). Fig. 4. Fig. 5. Nouvelle DestiNation Bundespavillon, Swiss Expo 02 (Eckert Eckert Architekten) Fig. 6. Rigidized inflatable structure (A. Pronk) 3 Form-Active/Surface Active In the open-air theatre in Soest a pneumatic structure was used as a mould. This mould was then rigidized, which resulted into a bent stiff beam that was combined with cloth. The result was a tensile structure. This technique was then studied. The purpose was to use this technique to realize complete buildings. Heinz Isler has already demonstrated that it is possible to rigidize a pneumatic mould to construct buildings. The same principle is used in aerospace engineering for realizing antennas and space habitats. (In Soest the same principle is used to construct architectural shapes.) The surface of the building was not the result of the mechanics but the result of an architectural design process. At the Technical University of Delft and Eindhoven a group has been formed that has taken on the challenge of finding a way to realize blobs by means of transforming and rigidizing
308 Arno C.D.Pronk and Rogier Houtman pneumatic structures.As a first study a model has been build that consists of bal- loons and a wire-frame that is placed in a nylon stocking (Fig.2).It is possible to make many different forms with this technique.After modeling the shape a polymer resin is applied(Fig.3).This physical model can be analyzed by means of a finite element computer program that looks at the active behavior of the surface of the structure.The input for the program is generated by a 3d scan(Fig.17). 4 Stage Covering for an Open-Air Theatre 4.1 Introduction This semi-permanent membrane structure covers the stage of the open-air theatre in Soest (the Netherlands)Fiber reinforced plastics are used for the production of a structural optimized and therefore lightweight and complex arch shaped struc- ture.By using an inflatable mould the arch could be produced more economically (30%cost reduction).In the production the vacuum injection method is utilized for stiffening flexible fibers. The owner of the Soest open-air theatre asked for a protection against bad weather for the stage.Therefore we suggested covering it with a lightweight mem- brane structure.A suspended membrane floats above the stage,so that visual rela- tions with the natural environment are still preserved(Fig.7).Outside the theatre- season the structure could partially be dismantled in this way the environment that is protected by national government is not visually disrupted.Two guyed columns are part of a dismantling system and could be used for hoisting the temporary membrane.The form of the spatial membrane is,beside the indirect support of the columns,the result of an arch.Because of this arch the protective area of the cov- ering is increased and additional curvature in the membrane is improved (Fig.8). In this way the membrane structure is a combination of two highpoint surfaces and an arched surface,the stage covering works like a tensegrity structure.The columns and arch transmit compressive loads.Both the Tensile loads and the stabilization of the whole structure are transmitted and organized by the prestressed membrane and cable structure. Fig.7.The stage covering for the Fig.8.An arched beam ensures an Soest open-air theatre in the Nether- increase of the protective area and the lands(H.Werkman) curvature of the membrane structure
308 Arno C.D. Pronk and Rogier Houtman pneumatic structures. As a first study a model has been build that consists of balloons and a wire-frame that is placed in a nylon stocking (Fig. 2). It is possible to make many different forms with this technique. After modeling the shape a polymer resin is applied (Fig. 3). This physical model can be analyzed by means of a finite element computer program that looks at the active behavior of the surface of the structure. The input for the program is generated by a 3d scan (Fig. 17). 4 Stage Covering for an Open-Air Theatre 4.1 Introduction This semi-permanent membrane structure covers the stage of the open-air theatre in Soest (the Netherlands) Fiber reinforced plastics are used for the production of a structural optimized and therefore lightweight and complex arch shaped structure. By using an inflatable mould the arch could be produced more economically (30% cost reduction). In the production the vacuum injection method is utilized for stiffening flexible fibers. The owner of the Soest open-air theatre asked for a protection against bad weather for the stage. Therefore we suggested covering it with a lightweight membrane structure. A suspended membrane floats above the stage, so that visual relations with the natural environment are still preserved (Fig. 7). Outside the theatreseason the structure could partially be dismantled in this way the environment that is protected by national government is not visually disrupted. Two guyed columns are part of a dismantling system and could be used for hoisting the temporary membrane. The form of the spatial membrane is, beside the indirect support of the columns, the result of an arch. Because of this arch the protective area of the covering is increased and additional curvature in the membrane is improved (Fig. 8). In this way the membrane structure is a combination of two highpoint surfaces and an arched surface, the stage covering works like a tensegrity structure. The columns and arch transmit compressive loads. Both the Tensile loads and the stabilization of the whole structure are transmitted and organized by the prestressed membrane and cable structure. Fig. 7. The stage covering for the Soest open-air theatre in the Netherlands (H. Werkman) Fig. 8. An arched beam ensures an increase of the protective area and the curvature of the membrane structure
Making Blobs with a Textile Mould 309 Due to its position in the audience's view and its proportions,the arch con- tributes in certain extent to the architecture of the structure.Therefore,special attention is given to the elaboration of the structural arch.The arch'dimensions exceed several times the thickness of the membrane and the cables.To avoid an abrupt change between the 'thick'arch and 'thin'membrane,a tapered arch sec- tion is desirable.The result is a conical arch.Because the mass of the arch would influence the membrane shape,a lightweight construction is necessary.This conical arch,which is characterized by geometrical complexity due to multiple curvature, and the necessity of a lightweight structure.asked for the use of an unconventional construction material and production technology. 4.2 Materialisation Conventional construction materials like steel and aluminium and accompanying production technologies are not suitable for making lightweight multiple curved arches.The material properties and production methods of fibre reinforced plastics (FRP)matches the arch requirements.Some advantages of fibre reinforced plastics are:rigid and lightweight construction possibilities,fatigue resistance,chemical and corrosion resistance,freedom in design and form and the possibility to integrate parts.Important disadvantages are the cost prices of material,mould,production (labour)and engineering.In the case of complex shapes,for example a conical arch, approximately 50%of the production costs consist out of model costs.Therefore an effective way of cost reduction is to decrease the mould price. 4.3 Geometrical Complexity and Production Technology Through the utilisation of a pneumatic mould the cost price of the arch is reduced with 30%(Fig.9).In the production of the mould the same computer applications (EASY,FEM-based software)and production technologies are used as those used for the development of the membrane structure.After modelling and formfinding in EASY cutting patterns are generated and used for the production of the mould. The internal over-pressure ensures the rigidity of the inflatable mould.The general dimensions,like the distance between the supports,are controlled by an auxiliary structure (Fig.10). 100 Fig.9.Pneumatic mould supported Fig.10.General dimensions of the by the auxiliary structure (Ten- mould tech/Buitink Zeilmakerij)
Making Blobs with a Textile Mould 309 Due to its position in the audience’s view and its proportions, the arch contributes in certain extent to the architecture of the structure. Therefore, special attention is given to the elaboration of the structural arch. The arch’ dimensions exceed several times the thickness of the membrane and the cables. To avoid an abrupt change between the ’thick’ arch and ’thin’ membrane, a tapered arch section is desirable. The result is a conical arch. Because the mass of the arch would influence the membrane shape, a lightweight construction is necessary. This conical arch, which is characterized by geometrical complexity due to multiple curvature, and the necessity of a lightweight structure, asked for the use of an unconventional construction material and production technology. 4.2 Materialisation Conventional construction materials like steel and aluminium and accompanying production technologies are not suitable for making lightweight multiple curved arches. The material properties and production methods of fibre reinforced plastics (FRP) matches the arch requirements. Some advantages of fibre reinforced plastics are: rigid and lightweight construction possibilities, fatigue resistance, chemical and corrosion resistance, freedom in design and form and the possibility to integrate parts. Important disadvantages are the cost prices of material, mould, production (labour) and engineering. In the case of complex shapes, for example a conical arch, approximately 50% of the production costs consist out of model costs. Therefore an effective way of cost reduction is to decrease the mould price. 4.3 Geometrical Complexity and Production Technology Through the utilisation of a pneumatic mould the cost price of the arch is reduced with 30% (Fig. 9). In the production of the mould the same computer applications (EASY, FEM-based software) and production technologies are used as those used for the development of the membrane structure. After modelling and formfinding in EASY cutting patterns are generated and used for the production of the mould. The internal over-pressure ensures the rigidity of the inflatable mould. The general dimensions, like the distance between the supports, are controlled by an auxiliary structure (Fig. 10). Fig. 9. Pneumatic mould supported by the auxiliary structure (Tentech/Buitink Zeilmakerij) Fig. 10. General dimensions of the mould
310 Arno C.D.Pronk and Rogier Houtman 4.4 Rigidizing Infatable Structures A rigidizable inflatable structure can be described as a structure that is flexible when inflated and becomes rigid after exposure to an external influence.Therefore it is not necessary o maintain the overpressure.There are several rigidizing techniques developed and more are still under development.They can be divided into three categories:thermosetting composite systems,thermoplastic composite systems and aluminum/polymer laminate system.Advanced rigidizing systems used for space applications are designed for specific structures and may be very expensive.In civil engineering,vacuum injection,which is a thermosetting composite system is a fea- sible way of rigidizing membranes. 4.5 Structural Optimisation The structural engineering of the membrane structure is done with the use of the software package EASY,which is based upon the finite element method (FEM).To examine the shape of the structure and its reaction to external forces.the structure is first modelled with an arch set up as a spatial truss with a defined stiffness.Then this model is used for the structural analysis of the complete structure,consisting of a membrane and supporting cables and columns.Also the deformations due to extreme loading (wind and snow loads)are examined. In order to be able to produce the synthetic arch the stiffness has to be de- termined.The pre-stress in the membrane and boundary cables causes an axial compression in the arch.Hence the curve of the arch will increase.The arch consists of synthetic fabrics rigidized by injecting resin into this fabric.By varying the use of material (e.g.thickness of the layers,layers of different materials)a range of E- moduli can be obtained.Also the moment of inertia is a variable.Therefore a variety in stiffness and bending resistance is possible.As said before,in order to find the desired shape the initial arch is designed having less curvature than ultimately was needed.an E-module of 210 GPa(210.000 N/mm2,comparable to steel)is used. The initial moment of inertia (Iy)was set at 855-10 mm4,resulting in stiffness 1.8-1012 Nmm2.First the deformations of the arch under pre-stress are calculated. The pre-stress in the membrane and the boundary cables cause the arch to deform and result in an increase of curvature. EASY-BEAM is used to determine this initial curve.Then the stiffness is used to calculate the composition of the synthetic arch,(a specific E-module with needed Iy)?? To be able to be more material-efficient a second step is taken.By adjusting the E-module from 210 GPa to 60 GPa a new stiffness is found(E/=5.14.1012 Nmm2). The initial curve of the arch is also adjusted to its new stiffness.Deformations of the curve under pre-stress are calculated,as are the deformations under extreme loading.These deformations turned out to be more than desired. A third step had to be taken.The stiffness had to be increased considerably.This is obtained by a change in the moment of inertia (I).In the first step of the design the diameter of the arch was determined at 200 mm.By enlarging this diameter to 360 mm a factor 20 of increase in ly is achieved (also a change in layer composition was introduced).Because of architectural consideration and in order to economize the use of material even more ly is varied within the arch.This is translated in a tapered cross-section,with a decrease in diameter towards the ends of the arch
310 Arno C.D. Pronk and Rogier Houtman 4.4 Rigidizing Inflatable Structures A rigidizable inflatable structure can be described as a structure that is flexible when inflated and becomes rigid after exposure to an external influence. Therefore it is not necessary o maintain the overpressure. There are several rigidizing techniques developed and more are still under development. They can be divided into three categories: thermosetting composite systems, thermoplastic composite systems and aluminum/polymer laminate system. Advanced rigidizing systems used for space applications are designed for specific structures and may be very expensive. In civil engineering, vacuum injection, which is a thermosetting composite system is a feasible way of rigidizing membranes. 4.5 Structural Optimisation The structural engineering of the membrane structure is done with the use of the software package EASY, which is based upon the finite element method (FEM). To examine the shape of the structure and its reaction to external forces, the structure is first modelled with an arch set up as a spatial truss with a defined stiffness. Then this model is used for the structural analysis of the complete structure, consisting of a membrane and supporting cables and columns. Also the deformations due to extreme loading (wind and snow loads) are examined. In order to be able to produce the synthetic arch the stiffness has to be determined. The pre-stress in the membrane and boundary cables causes an axial compression in the arch. Hence the curve of the arch will increase. The arch consists of synthetic fabrics rigidized by injecting resin into this fabric. By varying the use of material (e.g. thickness of the layers, layers of different materials) a range of Emoduli can be obtained. Also the moment of inertia is a variable. Therefore a variety in stiffness and bending resistance is possible. As said before, in order to find the desired shape the initial arch is designed having less curvature than ultimately was needed. - an E-module of 210 GPa (210.000 N/mm2, comparable to steel) is used. The initial moment of inertia (Iy) was set at 855·104 mm4, resulting in stiffness 1.8·1012 Nmm2. First the deformations of the arch under pre-stress are calculated. The pre-stress in the membrane and the boundary cables cause the arch to deform and result in an increase of curvature. EASY-BEAM is used to determine this initial curve. Then the stiffness is used to calculate the composition of the synthetic arch, (a specific E-module with needed Iy.)?? To be able to be more material-efficient a second step is taken. By adjusting the E-module from 210 GPa to 60 GPa a new stiffness is found (EIy = 5.14 ·1012 Nmm2). The initial curve of the arch is also adjusted to its new stiffness. Deformations of the curve under pre-stress are calculated, as are the deformations under extreme loading. These deformations turned out to be more than desired. A third step had to be taken. The stiffness had to be increased considerably. This is obtained by a change in the moment of inertia (Iy). In the first step of the design the diameter of the arch was determined at 200 mm. By enlarging this diameter to 360 mm a factor 20 of increase in Iy is achieved (also a change in layer composition was introduced). Because of architectural consideration and in order to economize the use of material even more Iy is varied within the arch. This is translated in a tapered cross-section, with a decrease in diameter towards the ends of the arch
Making Blobs with a Textile Mould 311 Fig.11.Bending for power,a pole Fig.12.Bending forces in beam- vaulter using a beam's bending stiff- elements of conical arch.calculated in ness and deformation EASY-BEAM In this third model Iy varies between 16170.104 mm4 in the middle section to 8170.104 mm at the ends.The deformations under pre-stress and extreme loading are checked and are within the design boundaries. These insights resulted in a tapered glass-and carbon fiber beam,with its di- ameter varying between 150 to 360 mm. 4.6 Vacuum Injection For the production of the arch the vacuum injection method is used to impregnate the resin in the woven fibres (Figs.13-15).Around the pneumatic mould alternately layers of fibres and resin are placed.To create a closed system the whole package is wrapped with some airthight and protective foils.In the closed system a pressure differential is applied that impregnates the fabric with resin.The pressure differential of the technique is obtained by means of a vacuum.The injection has to take place within the cure time of a resin.The following formula (1)expresses the filling time (tan)as a function of the porosity (and permeability (K)of the reinforcement, viscosity ()of the resin,flow distance (1),and applied pressure (AP). 品 The objective is to design a channel layout that ensures full wetting of the fabric at each location.Three distinctive injection strategies for a three-dimensional object can be followed,viz..edge injection:downward,upward and sideways.Downward injection is sometimes disadvantageous because bubbles will be entrapped more easily and there is the increased risk of dry spots due to race tracking by the runner channels.The choice between the other two injection strategies depends on the geometrical shape of the product.Factors that are of influence are the number of inlet ports and the total injection time that,when minimal,are both at an optimum. In this case upward injection is used
Making Blobs with a Textile Mould 311 Fig. 11. Bending for power, a pole vaulter using a beam’s bending stiff- ness and deformation Fig. 12. Bending forces in beamelements of conical arch, calculated in EASY-BEAM In this third model Iy varies between 16170 · 104 mm4 in the middle section to 8170 · 104 mm4 at the ends. The deformations under pre-stress and extreme loading are checked and are within the design boundaries. These insights resulted in a tapered glass- and carbon fiber beam, with its diameter varying between 150 to 360 mm. 4.6 Vacuum Injection For the production of the arch the vacuum injection method is used to impregnate the resin in the woven fibres (Figs. 13–15). Around the pneumatic mould alternately layers of fibres and resin are placed. To create a closed system the whole package is wrapped with some airthight and protective foils. In the closed system a pressure differential is applied that impregnates the fabric with resin. The pressure differential of the technique is obtained by means of a vacuum. The injection has to take place within the cure time of a resin. The following formula (1) expresses the filling time (tfill) as a function of the porosity (ϕ) and permeability (K) of the reinforcement, viscosity (ν) of the resin, flow distance (l), and applied pressure (∆P). tfill = ϕ · ν · l 2 2 · κ · ∆P The objective is to design a channel layout that ensures full wetting of the fabric at each location. Three distinctive injection strategies for a three-dimensional object can be followed, viz.. edge injection: downward, upward and sideways. Downward injection is sometimes disadvantageous because bubbles will be entrapped more easily and there is the increased risk of dry spots due to race tracking by the runner channels. The choice between the other two injection strategies depends on the geometrical shape of the product. Factors that are of influence are the number of inlet ports and the total injection time that, when minimal, are both at an optimum. In this case upward injection is used
312 Arno C.D.Pronk and Rogier Houtman Fig.13. Fig.14. Fig.15 Production of the conical arch,by using the vacuum injection method. Both glass and carbon fibres are applied (photos:Rep-air Composites) 5 Indoor Ski Run After the case of the open-air theatre students carried out several studies,Henno Hanselaar has carried out a very interesting one that shows the possibilities of the structures.He designed an indoor ski run with blob appearances and analyzed the mechanical behavior of this structure.The design has been made with the aid of the computer program Maya 4.0.This program is designed to make virtual animations, which are used for example in video games.It is also easy to design blobarchitecture and kinetic buildings.A three-dimensional site was drawn with the help of geodetic information from the local government. Two lines were drawn on the ground of the slope that acted as the edges of the shell structure.Profile lines were drawn between the ends of these lines (they will function as rails)and on arbitrary distances between the ends of these lines.With the "Birail 3+"-function Maya generates a surface between the drawn profile lines. The surface can easily be transformed by changing the profile lines.The "Rebuild". function generates an even smoother surface.When the final shape is obtained,the drawing can be exported as an Iges file type. 5.1 Surface-Active Analysis of the Mechanical Behavior This file type can be imported in the computer program DIANA.It is the FEM package that is used to make a structural analysis of the rigidized shell.For pre and postprocessing DIANA makes use of the FEMGVX program.In the main menu of FEMGVX there are two options.The first is Femgen.This can be used for generating a 3d model and modifying the properties.The second option is Femview.With Femview the calculation results can be viewed.The building of the model has been done,as described above,in Maya. 5.2 Conclusions from the Structural Calculations After all the results of the structural analysis have been processed the next phase was the evaluation and the possible material adjustments.If it appears that certain values are not satisfying a different solution has to be found Most striking is the
312 Arno C.D. Pronk and Rogier Houtman Fig. 13. Fig. 14. Fig. 15. Production of the conical arch, by using the vacuum injection method. Both glass and carbon fibres are applied (photos: Rep-air Composites) 5 Indoor Ski Run After the case of the open-air theatre students carried out several studies, Henno Hanselaar has carried out a very interesting one that shows the possibilities of the structures. He designed an indoor ski run with blob appearances and analyzed the mechanical behavior of this structure. The design has been made with the aid of the computer program Maya 4.0. This program is designed to make virtual animations, which are used for example in video games. It is also easy to design blobarchitecture and kinetic buildings. A three-dimensional site was drawn with the help of geodetic information from the local government. Two lines were drawn on the ground of the slope that acted as the edges of the shell structure. Profile lines were drawn between the ends of these lines (they will function as rails) and on arbitrary distances between the ends of these lines. With the “Birail 3+”-function Maya generates a surface between the drawn profile lines. The surface can easily be transformed by changing the profile lines. The “Rebuild”- function generates an even smoother surface. When the final shape is obtained, the drawing can be exported as an Iges file type. 5.1 Surface-Active Analysis of the Mechanical Behavior This file type can be imported in the computer program DIANA. It is the FEM package that is used to make a structural analysis of the rigidized shell. For pre and postprocessing DIANA makes use of the FEMGVX program. In the main menu of FEMGVX there are two options. The first is Femgen. This can be used for generating a 3d model and modifying the properties. The second option is Femview. With Femview the calculation results can be viewed. The building of the model has been done, as described above, in Maya. 5.2 Conclusions from the Structural Calculations After all the results of the structural analysis have been processed the next phase was the evaluation and the possible material adjustments. If it appears that certain values are not satisfying a different solution has to be found Most striking is the
Making Blobs with a Textile Mould 313 Fig.16.Model in DIANA Fig.17.3D scan of Blob oject large deflection of the system.But due to all the irregular bent surfaces there is no reference for the deflection.In this case a deflection of for example 400mm or 800mm cannot be seen.The structural system partly functions as a shell.At places where there is a transition from one curvature to another the outer forces are transferred by means of a bending moment.This is of course a bad situation for a thin walled structure.There are different solutions for this problem.From the solutions that were thought of the option of varying the wall thickness was chosen. Fig.18.Wall locally strengthened Fig.19.Wall locally strengthened in around problem area problem area 5.3 The Form-Active Analysis of the Structure The form of the indoor ski run was analyzed by means of describing the form by sections.To achieve the designed form there are a number of possibilities for the inflated structural elements that are put under the skin.At first the cross sections in width direction are shown.Next the different inflated structural elements are explained
Making Blobs with a Textile Mould 313 Fig. 16. Model in DIANA Fig. 17. 3D scan of Blob oject large deflection of the system. But due to all the irregular bent surfaces there is no reference for the deflection. In this case a deflection of for example 400mm or 800mm cannot be seen. The structural system partly functions as a shell. At places where there is a transition from one curvature to another the outer forces are transferred by means of a bending moment. This is of course a bad situation for a thin walled structure. There are different solutions for this problem. From the solutions that were thought of the option of varying the wall thickness was chosen. Fig. 18. Wall locally strengthened around problem area Fig. 19. Wall locally strengthened in problem area 5.3 The Form-Active Analysis of the Structure The form of the indoor ski run was analyzed by means of describing the form by sections. To achieve the designed form there are a number of possibilities for the inflated structural elements that are put under the skin. At first the cross sections in width direction are shown. Next the different inflated structural elements are explained
314 Arno C.D.Pronk and Rogier Houtman Fig.20.Support construction placed Fig.21.Support construction placed under the roof on top of the roof The width cross sections are more or less sinclastic.At several spots there is an anticlastic curvature.This indicates that there will be no structural inflated element underneath.The tension in the skin in longitudinal direction will have to apply the anticlastic curvature (Fig.23).The longitudinal sections also show a global sinclastic shape and locally anticlastic curvature.This has to alternate with the width anticlastic curvature (Fig.22). Fig.22.Longitudinal cross sections
314 Arno C.D. Pronk and Rogier Houtman Fig. 20. Support construction placed under the roof Fig. 21. Support construction placed on top of the roof The width cross sections are more or less sinclastic. At several spots there is an anticlastic curvature. This indicates that there will be no structural inflated element underneath. The tension in the skin in longitudinal direction will have to apply the anticlastic curvature (Fig. 23). The longitudinal sections also show a global sinclastic shape and locally anticlastic curvature. This has to alternate with the width anticlastic curvature (Fig. 22). Fig. 22. Longitudinal cross sections