Dissertation M.arch Technology 2014 University of Nottingham by Ar.Gaurav Goel India by Gaurav Goel

Department of Architecture and Built Environment

INVESTIGATING THE ROLE OF COMPUTER SOFTWARE FOR CONCEPT DESIGN OF TENSILE MEMBRANES IN ARCHITECTURE: A COMPARISON OF PHYSICAL AND DIGITAL MODELLING PROCESS.

Author:Gaurav Goel

Student number: 4186119. A dissertation submitted in partial fulfilment of the regulations for the Degree of March in Technology, in the University of Nottingham, September 2014.

ACKNOWLEDGEMENT I would like to acknowledge immense efforts of my dissertation supervisor Dr. Paolo Beccarelli for his constant support, motivation, and valuable feedback for this research. His keen interest and expertise in the field of tensile membranes has been appreciated. Moreover, valuable advice of Dr. John Chilton, who heads the Chair of Architecture & Tectonics at University of Nottingham in UK, was very helpful in shaping and development of this dissertation. I would also like to extend my gratitude to Dr. Robert Wehdorn, developer of Formfinder software, for helping me while carrying this research. Finally, I am grateful to my family and friends for their moral support during this dissertation. They provided me the strength and encouragement to carry this research.

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ABSTRACT Tensile membranes are allured for their flamboyant forms in the built environment. These forms were initially designed and visualized by architects through physical models of soap films and stretched fabrics, which were explored for the first time by the architect Frei Otto. These models involved intensive and tedious process for designing and were affected by intrinsic inaccuracies. Hence, computer software programs were specifically developed. These software programs are currently recognised for assisting the engineering tasks related to the design of tensile membranes, but they are underused and less acknowledged for their concept design. This aspect motivates this study to investigate the roles of software programs in concept development of tensile membrane shapes in architecture. In order to investigate these roles of software, processes of performing specific tasks related to concept design of tensile membranes were performed through physical and digital modelling tools. For physical modelling a stretched fabric model was chosen whereas Formfinder software was used to design in digital environment. Henceforth, these processes were compared based on time and convenience of designer. This comparison highlighted the advantages of both physical and digital methods, to identify unique features of Formfinder for demonstrating roles of software programs in concept design of tensile membranes. This study revealed that software programs like Formfinder can play a vital role in the concept development of these forms when compared to the traditional techniques of physical model making. Although physical models cannot be overlooked due to their real world interaction with designers, software programs could be credited for enhancing this design process through their unique digital tools. This study highlighted that an existing trend of using software to design a concept in architecture has started to permeate in the field of tensile membranes. KEYWORDS: - Tensile membranes, software programs, Formfinder, modelling

TABLE OF CONTENTS PAGE

ACKNOWLEDGEMENT ..................................................................................................... iii ABSTRACT ........................................................................................................................ iv LIST OF TABLES ............................................................................................................... vii LIST OF ILLUSTRATIONS .................................................................................................. vii INTRODUCTION ................................................................................................................ 1 Chapter 1

AIM AND METHODOLOGY ......................................................................................... 4 1.1 Aim..................................................................................................................... 4 1.2 Methodology ...................................................................................................... 4

LITERATURE REVIEW .................................................................................................. 6 2.1 Introduction........................................................................................................ 6 2.2 Tensile membrane structures............................................................................... 8 2.3 Concept design of tensile membrane structures.................................................... 8 2.4 Form-Finding of tensile membrane structures ....................................................... 8 2.5 Physical model making for tensile membrane structures ....................................... 8 2.6 Advent of computer tools in tensile membrane design for architecture ................ 11 2.7 Review of current software programs for tensile membrane design ..................... 11 2.8 Research Gap .................................................................................................... 13 2.9 Conclusion of literature review .......................................................................... 14

TENSILE MEMBRANE STRUCTURES AND FORM-FINDING TECHNIQUES ................. 15 3.1 Tensile Membrane structures............................................................................. 15 3.2 Characteristics of tensile membrane structures................................................... 15 3.3 Typologies of shapes for tensile membrane structures ........................................ 16 3.4 Components and connections: Anticlastic Membrane structures ......................... 17 3.5 Design Process for Tensile Fabric Structures........................................................ 18 3.6 Form-finding of tensile membranes .................................................................... 20 3.6.1 Physical Modelling for Form-Finding....................................................... 20 3.6.2 Digital Modelling for Form-Finding......................................................... 21 3.7 Formfinder Software program............................................................................ 22

PHYSICAL AND DIGITAL MODEL MAKING PROCESS ................................................ 24 4.1 Tasks performed to study the physical and digital modelling process.................... 24 4.2 Choosing tensile membrane form for modelling exercise ..................................... 25 v

4.3 Physical model for twin hypar ............................................................................ 26 4.3.1 Making initial concept model making ..................................................... 26 4.3.2 Process for changing parameters of tensile membrane form ................... 30 4.3.3 Process of getting information about concept form from physical model . 32 4.4 Digital model of twin hypar................................................................................ 36 4.4.1 Initial model making process in Formfinder ............................................ 36 4.4.2 Process for changing parameters of the tensile membrane form in Formfinder.................................................................................................... 41 4.4.3 Process of getting information or data from physical model of tensile membrane form in Formfinder....................................................................... 45

COMPARISON OF PHYSICAL AND DIGITAL MODELLING PROCESS AND RESULTS .. 50 5.1 Comparison: Process of initial concept model making.......................................... 51 5.2 Comparison: Process of changing height of anchor points.................................... 52 5.3 Comparison: Process for changing position of support poles ................................ 54 5.4 Comparison: Process for increasing force along boundary edge and adjusting curvature of edge boundary .................................................................................... 55 5.5 Comparison: Process for adding a ring profile to membrane surface .................... 57 5.6 Comparison: Process for obtaining shadows for concept model ........................... 58 5.7 comparison: Process for analysing flat areas for avoiding water and snow collection .............................................................................................................................. 60 5.8 Comparison: Processes of obtaining cutting pattern and surface area of membrane .............................................................................................................................. 61 5.9 Additional features of Formfinder software for concept design of tensile membranes ............................................................................................................ 62

DISCUSSION AND LIMITATIONS .............................................................................. 64 6.1 Discussion on Advantages of designing concept of tensile membranes through physical modelling process ...................................................................................... 64 6.2 Discussion on Advantages of designing conceptual forms of tensile membranes, through digital modelling Process used in Formfinder software ................................. 65 6.3 Limitations........................................................................................................ 67

CONCLUSIONS .......................................................................................................... 68 7.1 Conclusions....................................................................................................... 68 7.2 Future developments of the research ................................................................. 69

REFERENCES................................................................................................................... 70

LIST OF TABLES TABLE 1 Time spent on performing tasks with physical and digital modelling technique……………………………………………………………………………………………………………………………………….50

LIST OF ILLUSTRATIONS FIGURE 1 STEPS FOLLOWED FOR REVIEWING LITERATURE............................................................................. 7 FIGURE 2 TYPES OF TENSILE MEMBRANE STRUCTURES............................................................................... 17 FIGURE 3 DIFFERENT SHAPES OF ANTICLASTIC MEMBRANES ........................................................................ 17 FIGURE 4 COMPONENTS AND CONNECTIONS IN TENSILE HYPAR FORM ........................................................... 18 FIGURE 5 SOAP FILM MODELS ............................................................................................................ 20 FIGURE 6 IMAGE OF STRETCHED FABRIC MODEL ...................................................................................... 21 FIGURE 7 FORM-FINDING AFTER DESIGNER DRAW EDGES OF DESIRED SHAPE OF TENSILE MEMBRANE. .................... 22 FIGURE 8 GENERAL LAYOUT OF FORMFINDER PROGRAM ........................................................................... 23 FIGURE 9 CHOSEN TWIN HYPAR FORM FOR CONCEPT DESIGN TO COVER AN IMAGINARY SPACE ............................ 25 FIGURE 10 MATERIALS FOR MODEL PLYWOOD, ACRYLIC, WOODEN STICKS , FABRIC ........................................... 26 FIGURE 11 (1) PLAN OF AREA FOR IMAGINARY SPACE TO BE COVERED , (2) LASER CUTTING BASE, (3,4) FINAL BASES FOR PHYSICAL MODEL ............................................................................................................... 27

FIGURE 12 WOODEN SUPPORTS FOR ANCHORING FABRIC .......................................................................... 27 FIGURE 13 FABRIC CUTTING .............................................................................................................. 28 FIGURE 14 STRETCHING FABRIC .......................................................................................................... 28 FIGURE 15 ANCHORING FABRIC TO WOODEN STICKS WITH SLITS, ANCHORED GROUND POINT WITH FISHING WEIGHT . 29 FIGURE 16 INITIAL CONCEPT MODEL FOR TWIN HYPAR MODELLED THROUGH PHYSICAL TECHNIQUE (SCALE: - 1:20)... 29 FIGURE 17 PROCESS OF SLIDING BASE WITH GROUND ANCHOR POINTS TO CHANGE THEIR HEIGHT......................... 30 FIGURE 18 IMAGE SHOWING SHIFTING OF SUPPORT POLE IN PHYSI CAL MODEL ................................................ 31 FIGURE 19 PULLING ENDS OF BOUNDARY FOR CHANGING FORCE AND CURVATURE PROFILE OF EDGE ..................... 31 FIGURE 20 (1) RING PROFILE MOUNTED ON WOODEN SUPPORT AT HEIGHT OF RING . (2) TENSILE MEMBRANE FORM AFTER RING PROFILE I NDUCED IN TENSILE MEMBRANE....................................................................... 32

FIGURE 21 IMAGE OF HELIODON AND ITS ADJUSTMENT PARTS FOR SHADOW SETTINGS, DIAGRAM SHOWING POSITION OF THE LIGHT TO SIMULATE EACH MONTH ...................................................................................... 33

FIGURE 22 OBTAINED SHADOW OF PHYSI CAL MODEL AT 12 AND 1 PM RESPECTIVELY ....................................... 34 FIGURE 23 IMAGE SHOWING POSSIBLE FLAT AREAS ON TENSILE MEMBRANE SURFACE BASED ON VISUAL PREDICTION 34 FIGURE 24 PROCESS FOLLOWED TO GENERATE CONCEPTUAL CUTTING PATTERN FROM PHYSICAL MEMBRANE FORM .. 35

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FIGURE 25 DRAFTED PLAN FOR IMAGINARY SPACE TO BE COVERED .............................................................. 36 FIGURE 26 IMPORTING PLAN OF IMAGINARY SPACE FROM CAD TO FORMFINDER ............................................ 37 FIGURE 27 USING SKETCH TOOL AND SKETCHING INITIAL BOUNDARIES OF FORM WITH HELP OF BASE PLAN ............. 38 FIGURE 28 PLANAR NET ON XY PLANE OBTAINED AFTER CLOSING BOUNDARIES DRAWN FROM PEN TOOL ............... 38 FIGURE 29 PANEL FOR SETTING GRID DIMENSIONS FOR GROUND PLANE DISPLAYED IN SOFTWARE......................... 38 FIGURE 30 SETTING HEIGHT OF ANCHOR POINT TO ACHIEVE CONCEPTUAL ANTICLASTIC MEMBRANE ..................... 39 FIGURE 31 SKETCHING POLE SUPPORTS FOR TENSILE MEMBRANE TO GENERATE ANTICLASTIC MEMBRANE SHAPE ...... 40 FIGURE 32 INITIAL CONCEPT MODEL FOR TWIN HYPAR MODELLED THROUGH DIGITAL TECHNIQUE OF FORMFINDER SOFTWARE............................................................................................................................. 40

FIGURE 33 IMAGE SHOWING MOVE COMMAND , SETTINGS TAB FOR ENTERING EXACT HEIGHT FOR ANCHOR POINTS , AND BOTH ORIGINAL AND UPDATED MODEL OF TWIN HYPAR ...................................................................... 41

FIGURE 34 CHANGING THE PROFILE OF THE SUPPORT POLES IN FORMFINDER .................................................. 42 FIGURE 35 CHANGING FORCE IN BOUNDARY EDGE THROUGH FORMFINDER .................................................... 43 FIGURE 36 CHANGING CURVATURE OF BOUNDARY PROFILE THROUGH FORMFINDER ......................................... 44 FIGURE 37 ADDING A RING TO THE INITIAL TWIN HYPAR FORM THROUGH FORMFINDER ..................................... 45 FIGURE 38 GENERATING SHADOWS OF TENSILE FROM THROUGH FORMFINDER ............................................... 46 FIGURE 39 ANALYSING FLAT AREAS FOR INITIAL FORM AND FORM WITH AN INDUCED RING ................................. 47 FIGURE 40 PROCESS OF CUTTING PATTERN GENERATION THROUGH FORMFINDER SOFTWARE .............................. 48 FIGURE 41 VIEWING CALCULATED SURFACE AREA OF MEMBRANE SHAPE MODELLED IN FORMFINDER .................... 49 FIGURE 42 COMPARISON OF INITIAL CONCEPT MODELLING PROCESS............................................................. 52 FIGURE 43 COMPARISON OF PROCESS TO CHANGE HEIGHT OF ANCHOR POINTS ............................................... 53 FIGURE 44 COMPARISON OF PROCESS FOR CHANGING POSITION OF SUPPORT POLES ......................................... 55 FIGURE 45 COMPARISON OF PROCESS FOR INCREASING FORCE ALONG BOUNDARY EDGE AND ADJUSTING CURVATURE OF EDGE

PROFILE ...................................................................................................................... 56

FIGURE 46 COMPARISON OF PROCESS FOR ADDING A RING PROFILE TO MEMBRANE SURFACE .............................. 58 FIGURE 47 COMPARISON OF PROCESS FOR OBTAINING SHADOWS OF TENSILE FORM ......................................... 59 FIGURE 48 COMPARISON OF PROCESS FOR ANALYSING FLAT AREAS ON MEMBRANE SURFACE .............................. 60 FIGURE 49 COMPARISON OF PROCESSES FOR OBTAINI NG CUTTING PATTERN AND SURFACE AREA OF MEMBRANE...... 62

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INTRODUCTION Lightweight structures have existed for ages in world of architecture. These structures are widely used in architecture for their ability to cover large span spaces with optimum use of materials. This efficient use of materials makes them environmentally friendly and a sustainable alternative for low impact buildings. Besides this, they provide structures with less visual weight and allow architects to explore the architecture of curved forms. These eye-catching freeform structures can be achieved economically through these types of structures. An example of such lightweight structure is a tensile membrane structure. Tensile membrane structures offers intriguing shapes and forms for covering spaces in architecture. These structures provide membrane surfaces which form attractive shapes when put in tension. In addition, they provide permanent and temporary lightweight structures in architecture. Moreover, they offer an advantage of low embodied energy, shorter construction time and lesser running cost when compared to conventional framed structures. These structures also have an advantage for short term construction projects, therefore, these membrane structures have been employed widely in architecture through design of facades, temporary pavilions, exhibition structures, stadiums and amphitheatre roofs. An example of this is the Facade of the Olympic stadium in London which was constructed for 2012 Olympic Games. Furthermore, the use of tensile membranes within architecture was notably appreciated after a German architect and engineer Frei Otto introduced them to the world, through his research and experiments in second half of the 20th century. His experiments and design methodology gave a fundamental contribution to the development of tensile structures. Projects like the German pavilion for Montreal expo in 1967 and the roof for the Olympic stadium in Munich designed by Otto marked a milestone in the onset of tensile membrane structures in mainstream architecture. One of the notable contributions of Otto was in developing process of designing and visualizing these structures through model making. Tensile membranes shape themselves according to tension induced in them to acquire exciting forms, which were complicated to model. Beside s this, they cannot be modelled by rigid materials due to non-linear behaviour of membranes. Therefore, Otto developed models of soap film and stretched fabric to visualize and design these forms. Moreover, mathematical rules which describe the behaviour of soap film were similar to tensile membranes. In fact, these models allowed designers to experience real world interaction with these forms along with understanding their structural behaviour in actuality. Initially these models were documented and analysed through manual techniques for engineering and construction purposes. But this 1

process was intensive and required lengthy calculations for manual form finding of tensile membranes. On the other hand, this process became more tedious when iterations of th e same design had to be worked out during design process of complex structures. With this there was also a problem of accuracy and human errors in physical models. Therefore, computer software program was used in 1966 for the first time by Klaus Linkwitz to simulate these self-generated tensile forms. (Otto, Rasch et al. 1995) These software programs mostly helped in form finding and engineering analysis of these membranes. Due to this reason computer software programs entered into field of tensile membranes and many engineers started to use them for analysing complex structures of tensile membranes. Since then many software packages have been developed to assist specific tasks for their design and construction. Today these computer software programs are used for immense calculations and engineering analysis of tensile membranes. However, there are very few digital tools which provide opportunity for architects and designers to ease the process of initial concept design of tensile membrane forms. Therefore, despite the development of software programs customized for these forms, there is not much evidence of using software programs for their concept development. Contrary to this, software programs have been widely used at concept stage in contemporary architecture practice. CAD, Google Sketchup and rhino are some of the commonly used programs that help designers to visualize and develop their concept form efficiently. These software programs offer the capability to instantly visualize forms along with ability to play with their geometry in digital environment. This helps in speeding the design process by providing multiple iterations of the design with varying parameters. It is extremely intriguing to see that immense capabilities of software programs havenâ&#x20AC;&#x2122;t been sufficiently exploited in the field of concept designing for tensile membrane structures. This brings out an interesting topic for this dissertation research. Through the course of this study, an attempt has been made to establish the role of computer software programs in concept design of tensile membrane structures in architecture. In order to achieve this, a methodology mentioned below was followed. Firstly, a basic tensile form based on a twin hypar was assumed as a concept design solution for an imaginary space to be covered. Secondly, this form was modelled using physical modelling process of stretched fabric and digital modelling process of the computer software called Formfinder. During this modelling exercise, methods of performing specific tasks for conceptual design of tensile 2

membranes were derived for physical and digital modelling. Moreover, time was constantly recorded for each task when it was performed using both modelling techniques. These tasks included making initial concept models, performing parametric operations with their concept geometry and analysing them to obtain geometrical and technical information used in concept development. Eventually, methods of performing these tasks were compared based on time and convenience. Through this comparison, the benefits and distinctive features of software programs were obtained. Then, this information was used to define the role of computer software program in concept design of tensile membrane forms. The outcomes of this research can motivate architects and design professionals to use potentials of software programs during conceptual design of tensile membranes. These potentials would also encourage novice designers with limited engineering knowledge of these structures, to experiment with tensile forms without being completely dependent on physical models. This dissertation is organized into seven chapters. Chapter 1 provides information on aim of research and detailed methodology followed for this dissertation. Besides this, Chapter 2 contains literature review to explore previous literature and validate the aims of this dissertation. In addition to this, chapter 3 presents information about tensile membrane structures along with methods and tools used for their form finding. After this, in chapter 4 processes performed for modelling a concept model through physical and digital modelling are explained along with illustrations. Consequ ently, chapter 5 contains a comparison of these processes to obtain results whereas chapter 6 presents discussion of these results along with limitations. Finally, Chapter 7 states conclusions and future developments of this research.

CHAPTER 1 AIM AND METHODOLOGY

This chapter gives an introduction to aims and methodology of this re search. Aim of this research is mentioned in first section of this chapter and a detailed methodology is given in second section. 1.1 Aim The aim of this research is to investigate the role of computer software programs in concept designing of tensile membrane structures. In order to investigate these roles, this study will attempt to discover the potential of software programs by comparing the digital modelling process to the conventional technique of physical modelling in field of tensile membranes. 1.2 Methodology This research could be performed by using both qualitative and quantitative method of research through inductive approaches. Literature review on this topic was scanned through papers, peer reviewed articles, books and other academic sources. They demonstrated a strong inductive approach in their research methodology. Most of them used a case example to analyse facts and then induced a set of observations for final conclusions. Therefore , this approach would be suitable for my dissertation research. For achieving aim of this dissertation, the methodology written below was followed. 1

Initially a literature review was carried out to analyse the work done in this field already and to investigate the relevance of this research. After this, tensile membranes were explored for gaining knowledge as a novice designer, which was followed by understanding form finding of these membranes through physical and digital tools and techniques.

Then a technique based on stretched fabric model was selected for physical modelling whereas Formfinder software was chosen to model a concept in a digital environment.

Following this a tensile form of twin hypar was assumed to be a concept idea of an architect to cover an imaginary space. This space is assumed to be 10m x 6 m in plan with a hei ght of 3.5m.

Besides this, specific tasks for concept design were selected to be performed while modelling the twin hypar. These tasks involved initial modelling of concept form, performing parametric operations and analysing concept form to gather its geometrical and technical data.

Subsequently, the twin hypar form was modelled using stre tched fabric at a scale of 1:20 and tasks specified mentioned in step 4 were performed on this model along with recording of time taken to perform each task.

The same form with similar dimensions was modelled again using the digital tools provided by Formfinder software program (version 3.5 beta) and the time used for accomplishing each task was noted down.

Afterwards, process followed while performing each task was used to draw a flow chart along with making a table of time taken to perform each task through physical and digital methods.

These process flow charts were compared based on parameter of time and convenience of designers. Subsequently, they were used to obtain advantages of both digital and physical modelling at concept design stage of tensile membranes. These advantages were treated as results of comparison.

Finally, these results were discussed and a conclusion was written for this dissertation research .

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction Architectural design is a process of realizing architectural solutions and can be represented initially in form of sketches, physical or digital models. In this process physical models play an important role as they help to visualize 2 dimensional forms or drawings in 3 dimensions. (Porte and Neale 2000) Physical models are made on a smaller scale to give architects a tangible form which can be changed according to design needs. However, in recent time advancement in design software have opened new avenues for exploring forms and initial ideas virtually on computer screens. To point out this Oxman (Oxman 2008), mentions that new digital technologies are enhancing process of design as compared to conventional methods using paper. Moreover, computers help designers to visualize forms in similar ways as physical models in digital environment but with options to visualize the model with different view angles. This indicates the role of computer programs and physical models for concept design in field of architecture. In fact, the association of computers with concept design is not new in general architectural practice. Gropius (1964) mentioned that computers can help a designer to boost creativity. This suggests that computer tools have been related to concept design in archi tecture from past and their benefits were realised early in the practi ce. These tools included computer aided design (CAD) and computer aided Machining (CAM) software programs which utilizes technology of computers for design and production. A brief history of these software programs could be traced from 1963, when Ivan Sunde rland developed sketchpad with a graphical interface. This software allowed graphical interaction of a user through a light pen to draft a drawing along with use of buttons to input parameters of design. This was followed by development of CATIA software program whi ch enhanced capability of these tools from 2d drafting to 3d visualization in 1970. Eventually , AutoCAD was released in 1982 and e ra of using computer software in architectural design started. (Broquetas, 2010) Since then there has been a significant advancement in CAD and design programs like AutoCAD, Google Sketchup, architectural studio, Rhino 3d other commercial software packages. (Anderson, Esser et al. 2003) 6

These programs are known for their benefits during conceptual design stage in generic architecture practice. Pascucci (2012) recognized these programs for their ability to save time, increase work efficiency, provide precision and control over conceptual design. In addition to this Szalapaj (2013), praised CAD programs for their potential to handle parametric changes done during concept design. Feature of interoperability to export concept models directly into engineering software for better collaboration is also appreciated for these computer tools. Hence, use of software programs could be observed in concept design process of mainstream architecture, other than use of physical models. Likewise, this connection can be explored specifically for branch of tensile membranes in architecture design. While this literature review it has been demonstrated that the general advantage of software for designing membrane structures is mainly acknowledged for engineering tasks due to the clear advantages of being accurate and reliable. However, the role of computer software is not clear and potentially undervalued in design of tensile membranes. Therefore, this literature review aims to develop this argument along with highlighting relevance to investigate this issue. This literature review is performed by following steps show below. (Figure 1)

Figure 1 Steps followed for Reviewing literature

2.2 Tensile membrane structures The similarity with an umbrella is probably the most efficacious way to understand the basic principles of tensile membrane structures. When we open an umbrella, all metal members present in it change their profile and induce tension in the attached fabric to form a tight spherical skin on top. This stretched fabric can be referred to as tensile membrane and whole system can be seen as tensile membrane structure. In tensile membrane structures the membrane material and the boundary cables are exclusively working in tension. The level of pretension and double curvature prevents the fluttering and allows the creation of elegant shapes and forms. 2.3 Concept design of tensile membrane structures The concept can be seen as the initial idea of any architectural design. When this concept is translated into design through drawings and models, it becomes concept design. Similarly in tensile membranes concept design can be viewed as first ideas of design to decide form of membranes according to need of architectural program. This concept is generally designed by architects and designers. According to Rodrigues (2008), concept design for tensile membrane geometry and structure cannot be separated; therefore, the need for understanding forces to achieve desired form is important. Therefore, during concept design of these structures forms are self-generated when tension is induced in the membrane. This design process will be discussed further in chapter 3. 2.4 Form-Finding of tensile membrane structures Form-Finding can be defined as the process of determining a stable geometrical configuration of the fabric structure with specified design parameters. The aim of Form-Finding for tensile membrane forms is to find a form which physically stable under tension, so that all forces acting on it are in equilibrium. There are many methods of Form-Finding which are used and they will be discussed in chapter 3. 2.5 Physical model making for tensile membrane structures One of the first examples of physical models for showing load bearing structure was the model made for dome of Florence which was designed by Brunelleschi, as mentioned by architectural review magazine in 1968 (Otto and Gab 1990). Similarly, Antonio Gaudi expressed idea of load bearing structure through suspended 3D models (Otto, Rasch et al. 1995). Whereas, according to Otto (Otto and Gab 1990) Frei Otto was among one of the significant contributors for developing physical models to study tensile membranes. This shows how physical models have been important for load bearing structures throughout history during design process. 8

They were treated as tools to visualize forms that cannot be visualized efficiently with help of drawings and sketches only. In this sequence, literature related to use of physical model for designing tensile membranes is presented below and possibilities of using computer programs for performing same task are indicated. Tents were oldest membrane structures. These structures gained significant attention with work done by Frei Otto in 1954 when he established a link between their form and tension forces through his experiments at the Institute of lightweight Structures in Germany. He also contributed towards developing a method for generating physical models of tensile surfaces. These method included models of soap film and stretched fabrics or nets. Eventually, these models helped in realizing numerous projects dealing with tensile structures. A number of models were made for designing important structures like German pavilion and Olympic roofs in Germany. Besides this, many pre design models were made and several options were tested to achieve a design. (Otto, Rasch et al. 1995) This shows the lengthy process which was used to find initial concept form without aid of computer tools. Thus, a need of digital tools at that time could be established as they could have been used for initial form finding in substitution of physical models. However, physical models are widely appreciated by Otto in his book â&#x20AC;&#x153;IL25: experimentâ&#x20AC;? in 1990, where despite of the lengthy process of making physical models it has been highlighted that their role is important in design of tensile membranes. This book me ntioned that physical models allow simulation of physical reality to almost real time situations. This stresses importance of software at concept design again as it could simulate the real behaviour precisely with computing capabilities. Additionally, same book voiced that forms derived by Otto at concept stage through physical were self-forming and they were governed by natural laws. Due to this initial design of concept form had to be in conformity of these natural laws of forces. This problem of adjusti ng original shape of concept form due to natural self-forming shape of tensile membrane might have been solved by computers. According to Bechthold (2008), physical models are widely used to explore prestressed membranes. It has been highlighted that a logical equilibrium shape could only be found if prestress forces are included in a model and boundary conditions are carefully modelled according to reality. This can be seen critically as it would be difficult for architect to put real boundary conditions at concept level whereas computers could be of help in achieving this at early stages.

In this line of investigation it is essential to brief review soap film and stretched fabric models which are used to generate instant forms of tensile membranes at concept level. As they were often used for concept stages of design, problems related to these techniques can be investigated to highlight need of software tools. According to Otto (Otto, Rasch et al. 1995) soap films are referred as membranes which are formed from liquids when frame with closed boundaries are dipped inside these liquids. These soap film models by Otto linked behaviour of soap film and tensile membranes. When soap was added to water its negatively charged head oriented towards the liquid molecule whereas hydrocarbon tail oriented itself towards air. This phenomenon gave stress which was uniform throughout the soap surface to develop a minimal surface (Isenberg 1978). Therefore, this behaviour of soap film inspired Otto to use these models for mimicking physical model of prestressed tensile membranes. These models proved beneficial for conceptual design of membrane shapes but they were also criticized by Otto due their fragile nature and disability to produce pure minimal surfaces when modelled on lager scales. This again reveals need of software tools which could be of help at this task of determining minimal surface shapes. Furthermore, stretched fabric models were used to dosing tensile membrane forms. These models are made from stretching fabric between boundaries. These type of models exhibited similar properties as soap film models. Due to durability of these models, they are used more widely over soap film models. These models can be used to mimic minimal surfaces which are quite similar to real ones. However, shapes obtained from these models are based on stiffness, which differs according to placement of warp (thread in longitudinal direction of weaving) and weft threads (thread in traverse direction of weaving) in cloth. (Bechthold 2008) Therefore, a pure minimal surface that could be described mathematically is not obtained. This shows how this process can also be criticized for its accuracy at conceptual levels and computer software could be employed to fulfil this task at concept level. As a result of above literature, a constant need of software programs for tensile membrane design can be observed at concept design stage through review of problems in using physical models in tensile membrane design. Further literature will attempt to understand how and why computers entered field of tensile membrane design so that reason of acknowledgement of these software tools can be traced.

2.6 Advent of computer tools in tensile membrane design for architecture As mentioned by Guena (GuĂŠna and Untersteller 2007), Otto indicated in 1962 that designing a tensile structure is a complex task as the form of a structure under tension is difficult to predict. It was clear that there was a need of computers for this task as form-finding for tensile structures needed knowledge of engineering and time. Besides this, when shape of membrane structures got complex, form-finding became tedious. Therefore, computer simulation was experimented for first time by Klaus Linkwitz in 1966 on Frei Ottoâ&#x20AC;&#x2122;s advice (Otto, Rasch et al. 1995). He also highlighted the possibility of software programs in future which would be integrated with algorithms for finding a form with numerical methods and which can self-simulate forms. This shows how Otto was seeking computers for engineering and detailed analysis of tensile membrane forms only, whereas software tools could probably help in doing initial modelling by architects as similar to soap film and stretched fabric models. Furthermore, digital tools for tensile membranes are acknowledged for variety of tasks other than form-finding. Campbell (1991) appreciated these tools for generating cutting patterns for fabrication of these structures. This fact was supported by Sastre (2013), in his article on teaching tensile architecture. Moreover, Armijos (2009) acknowledged these software programs for assisting in fabrication and installation process. Besides this, Cotton (2009) appreciated these tools for shortening design time and reducing development costs of membrane structures. This exhibits that software programs for designing tensile membranes are continued to be acknowledged for their engineering capabilities only. Moreover, lack of usage of these software programs at concept stage could be observed clearly. In fact, these programs developed significantly in recent times and following this, a review of some software programs is presented below. 2.7 Review of current software programs for tensile membrane design According to information given by Postle (2011) and software reviews published online by Industrial Fabrics Association International (2014), a list of current software programs can be acknowledged. From this list some software programs which are often used by students and professionals are analysed and discussed briefly to reveal their potentials in design of tensile membranes. Some information for this review is studied and interpreted from websites of respective software programs. 1. Mpanel: - This software is developed by Meliar design, a firm based in UK. This software is used for form-finding along with static analysis of the structure. This software is an additional toolbar installed inside the AutoCAD software platform. It allows to model 11

meshes and then tensions them to induce anticlastic behaviour. According to Senagala (2008), this software is useful in the panelling process of structure. To be specific Senagala mentions that Mpanel can be beneficial to tackle compensation of prestress, adjusting seam allowances. Therefore, this software is observed to be advantageous in stress analysis and panelling process. 2. NDN: - As given on website aeronaut.org this software is developed for FEM analysis of tensile membranes for Engineers and has an ability to optimize the form of Membranes and structural systems of steel. It is divided into many sections which are known as environments. All these environments help in specific phase of designing. Though this software contains tools for model building it is highlighted by Schedlbauer (2008), for its used in engineering tasks such as static analysis, sizing of members, generating data for external loads and generating cutting patterns. 3. ForTen 3000:- This software is developed by Gerry Dâ&#x20AC;&#x2122;anza and it is used for form-finding, static analysis of structure, and patterning. According to Westre (2009), this software is equipped with better tools for Form-Finding as compared to drawing the form of tensile structure membrane. In this software the skeleton of tensile membrane is modelled in other software packages such as AutoCAD and Rhinoceros 3d and then this model is imported into this program for analysis of forces, optimization of form and patterning of panels. So it can be seen that this software seems to be equipped with tools which are used for more technical and engineering aspects of designing a tensile membrane structure. 4. Surface: - This is a program for creating a 3d tent shapes. A form can be developed and shapes of panel can be worked out to be joined to form the tensile shape. This software helps in altering forms for tensile membranes through parameters such as lengths, tension and position of anchor points. Therefore, this software is capable of Form-Finding and patterning applications in tensile membrane design. 5. Tensile draw: - This software is used for modelling of 3d membrane structures. It is used as a plug-in for AutoCAD or Rhino 3d software. As reviewed by Westre (2009), after an initial form for membrane shape is modelled in these software programs, a form is shaped according to calculations by this software. These calculations are based on parameters and stresses defined by the user. This software is useful for simulating forms for fabric structures that are complex in geometry. Overall it is appreciated for its engineering capabilities.

6. Rhino Membrane: - It is software plug-in for rhino 3d software package which is used for modelling NURBS (Non Uniform Rational B splines) surfaces. After a membrane shape is modelled it can be relaxed using rhino Membrane plug-in. It uses mathematical algorithm of Finite element Analysis to optimize membranes to equilibrium. It is capable of optimizing forms like hypar, minimal surfaces and even pneumatic cushions. This plug-in does not allow for concept modelling though it can accept and analyse concept models made in rhino 3d environment. 7. Formfinder: - it is a software package developed by the engineer and architect Robert Wehdorn. This software is developed with a view to sketch tensile membrane structures onto computer screen directly, so that software integrates need of early design process. After a form is sketched in this program with help of tools provided, it generates a sh ape with equilibrium to give a stable tensile membrane form. This shape can be exported later into other engineering software for structural optimizations. Moreover, this software places a significant importance to concept process and not appreciated for i ts potentials for engineering tasks. From review of software programs above it is observed that most programs today are mainly focused on the engineering analysis of tensile membranes. There are very few software programs that provide platform optimised for designers and architects to model concept for tensile membrane structure. In the list of software programs above, only Formfinder shows capability of providing tools for concept design of tensile membranes by architects and designers. 2.8 Research Gap After a review of software programs presented above in section 2.7, it can be clearly observed that there are very less digital tools for architects and designers to use at concept stage for designing tensile membranes. Moreover, section 2.5 of literature presented a dire need of digital tools at the concept design stage when compared to the physical models of tensile membranes. On the other hand, section 2.6 and 2.7 indicated that current software programs provide more capabilities for engineering tasks. Therefore, their potentials and benefits in concept design needs to be studied. An area of interest which should be investigated is how computer software programs can support an architect or designer in conceptual design of tensile membranes through its uni que capabilities. This investigation becomes significant when a gap in opinion of researchers can be observed for use of digital tools in concept design of tensile membrane structures.

Lansdown (1994) commented that computers have not evolved in terms of their involvement within creative and conceptual process of design. Moreover Dorsey (Dorsey, Xu et al. 2007), appreciated CAD systems for being successful in advance stages of design but critisized their application at conceptual level due to their requirement of inputing accurate geometry at early stage of design. In addition to this, Sierra (Sierra, serna et al. 2004) highlighted that there are no digital tools of computer to assist process of findind intial shape of membrane structures. This indicates that softaware programs for concept design of tensile membrane shapes are not present and they are generaly criticized for their role in this process. Contrary to this researchers have appreciated computer software for their efficacy in concept formation of tensile membrane shapes. Software programs for designing tensile membrane allows designer to modify form and shape of membrane more easily as compared to physical model (Armijos 2009). In fact, Heshmati (Heshmati and MeeĂ&#x;-Olsohn 2009) informed that Robert Wehdorn defined sketching of tensile membrane structures by hands as a complex process. Therefore, Robert Wehdorn developed Formfinder software and highlighted need of user friendly software for novice designers to design concept of tensile membranes. Hence, from the facts above a gap was highlighted in the literature which would be addressed by this research work. One part of literature critisizes computer software programs for concept design of tensile membranes, but conversely other part of literature appreciates software programs for conceptual design of tensile membrane structures. 2.9 Conclusion of literature review The literature review presented in this chapter and the gap highlighted above clearly established a need to investigate roles of computer software programs during concept design of tensile membrane structures. Furthermore, this review revealed that software programs have been used for concept design in mainstream architecture from early times but this has to be investigated especially for tensile membranes. Conventionally, Physical model making was the most popular tool for initial design of these structures. Thus, the role of software programs could be evaluated by comparing physical model making process with the process followed for computer software programs.

CHAPTER 3 TENSILE MEMBRANE STRUCTURES AND FORM-FINDING TECHNIQUES

This chapter presents basic understanding of tensile membranes along with tools and techniques used for their form-finding. Brief information of their characteristics, typologies, components and connections is presented in this chapter. In addition, design process used for tensile membranes is described. Henceforth, information on techniques and tools used for form-finding of membrane structures are discussed briefly for both physical and computational methods. Finally, a section describes the software Formfinder, which was mentioned in chapter 2 for designing concept of tensile membranes. This would help in identifying the physical and digital method for modelling a twin hypar form in this research for comparison. 3.1 Tensile Membrane structures Tension structures are type of structures which are composed of membranes and cables in tension with few structural elements under compression and bending. These tension structures are widely used for their role in thin shell and lightweight structures in architectural applications. Coated fabrics are one of the materials which have been used widely in architecture for these types of structures. Therefore, tensile membrane structures refer to another name given to tensioned fabric structures used in architecture. These are one of the typology of structural surfaces which are made of thin skins made from fabric or other materials. However, other typologies of surface structures include grid shells, folded plate structures, shell structures and combinations of these structures. Furthermore, membrane structures are often used as a roof, as they can economically and attractively span large distances. They have distinct characteristics for which they have been used in architecture. (Armijos 2008) 3.2 Characteristics of tensile membrane structures 1. Lightweight: These structures are very light weight in nature. For example, fabric such as polyester can weigh as low as 200gm/ m2 to 270 gm/ m2 which would be very lightweight for construction. However, with coating of materials like PVC on the fabric this weight can be 1kg/sqm, which is relatively low as compared to framed structures.

2. Thin edges: Fabric materials provide thin edges and help aesthetics. These membranes can be as thin as 1mm. 3. Cover large span: As mentioned above, lightweight and thin thickness of these structures allows them to cover large spans. Furthermore, these type of structures work in tension to cover a large area without support. 4. Curved shapes: These structures obtain curved shapes when stretched because of the low shear stiffness of the materials like fabric. 5. Transparent and Translucent: Ability to achieve transparency is unique in these structures due to material innovations. 6. Quick and easy to erect: These structures mostly comprises of prefabricated fabrics or nets according to shape and size of designed form of tensile membrane. So when anchor points are established on site this fabric is stretched with help of lifting equipment. This process is quick and easy to erect as compared to other thin shell structures. (Schock 1997) 3.3 Typologies of shapes for tensile membrane structures There two types shapes for tensile membrane structures based on stresses and curvature of the form. These are named as anticlastic and synclastic shapes. Anticlastic shapes are those shapes in which there is saddle like curved shape, which is achieved due to applying stress mechanically in membrane plane through its linear boundaries. However, synclastic shapes are pneumatic structures in which there are spherical shapes with double curvature. These shapes are achieved by applying tension through hydraulic or pneumatic pressure. One more way to understand anticlastic and synclastic shapes is that centre of radii for main curvatures are present on opposite sides to each other in anticlastic surfaces, for example saddle or hyperbolic shapes, whereas synclastic shapes have radii of double curvatures in same direction. For this dissertation we will focus on anticlastic membranes which are mechanically prestressed as w e will use them for performing modelling experiments later. (Bechthold 2008) General overview of classification for tensile membrane shapes can be seen at a glance in figure 2 presented on next page.

Figure 2 Types of Tensile Membrane structures

Three types of Anticlastic membrane shapes are commonly used in architecture. These are saddle shapes like hypar, point supported forms like cones and ridge and valley forms which are elongated versions of saddle shapes (Fig 3). In these forms saddle shapes are produced when alternate high and low anchor points of membrane edges.

Figure 3 Different shapes of anticlastic membranes (source: - Innovative Surface Structures: Technologies and Applications)

For this dissertation research we will focus on saddle shape of membranes as twin hypar form was selected in the methodology for performing modelling though physical and digital tools, because it is one of the common anticlastic form of tensile membrane. 3.4 Components and connections: Anticlastic Membrane structures

Anticlastic membranes which are mechanically prestressed consist of two main parts: Membrane which forms the surface of the shape and the cables or rigid structural elements which forms the boundary profiles of tensile form. Membrane in this form is generally connected at the edges to cables with high strengths or to structural elements which are rigid like frames, arches, beams or truss systems. A connection of membranes at the edges can be achieved by putting cables inside membrane sleeves present at boundary of membrane structure. These cables form catenary shapes when they are anchored to the rigid structure for transferring the loads to foundations. (ibid.) Moreover, it should be noted that when any of these component is tensioned in this structural composition it will affect the resulting shape of these membranes because shape of tensile membrane depends on tension forces induced in these components. Figure 4 shows a hypar form with different components and their possible connections with help of a marked diagram.

Figure 4 Components and connections in tensile hypar form

3.5 Design Process for Tensile Fabric Structures Designing Tensile Fabric structures Involves several steps and considerations. These steps according to Armijos (2009) are:-

1. Designing basic form One of the most important considerations to design a tensile fabric membrane is to make a form with a level of prestress which is enough to prevent swinging of fabric. This can achieved through designing shapes with double curvatures. 2. Deciding boundary connections The process of making form with sufficient tension is followed by determining boundaries of the fabric which will act as membrane for the structure. These Membranes are attached to the boundaries for their edge connections. Boundaries can be a part of wall or beams that are connected to edges of the membrane or these can be point connection s to columns, poles or other frame structure. These point connections for membranes are known as anchor points. These connections are established through plates that are attached to hardware which can be adjusted in length for varying tension. Generally a curved edge or catenary shape is formed between connection points of membrane. These edges are provided with sleeves that can contain cable for structural support. 3. Form-Finding When boundaries of fabric are determined and anchor points are identified, it is possible to progress towards form-finding. Form-finding is done to find a shape of membrane which has stable forces and equilibrium state. This exercise of form finding can be done using physical models or through computer software tools. Physical models for tensile membranes can be made through soap films and fabrics as mentioned in literature review before. These can help the designer to understand and visualize tensile structures. Whereas, computer software programs have embedded algorithms to automatically simulate form finding. 4. Analysis for structural aspects After a stable form is found for a tensile membrane shape it is ready for analysis for structure. This analysis is done to compensate and optimize form for bearing loads. These loads will consider formâ&#x20AC;&#x2122;s reaction to dead and live loads. These loads can be loads generated due to wind, snow, equipment or people. This structural investigation also identifies areas on surface with high stress and possible places where water can collect in case rain. Whole of this process enables engineers to determine size of structural elements associated with tensile fabric structure. 5. Material specification and pattern generation After the form of the membrane is optimized structurally a material is specified based on design requirements. This material is tested for expansion under loading conditions and then form is analysed for patterning. Patterning is a process in which the 3d form of a tensile

membrane can be subdivided and transformed into a set of 2d panels, which can be later joined together to achieve designed membrane form. 3.6 Form-finding of tensile membranes Form-finding is one of the major tasks of an architect in design of tensile membrane structures. It is a process of shape finding in which a suitable surface shape of tensile has to be found out. This surface shape should be suitable to withstand all applied loading on the structure, while fulfilling the constraints of a specific architectural design. This form-finding exercise is a vital step in designing of tensile membrane structures and can be performed using physical and digital methods. 3.6.1 Physical Modelling for Form-Finding For physical modelling process of form-finding two methods can be employed as mentioned in chapter 2 of literature review. These two methods include making soap film models or highly elastic membranes such as fabrics. (Froster and Mollaert 2004) Soap Film models In this type of model a surface of soap film is generated between threads or steel wires (Fig 5). This soap film is obtained when closed or linear profiles of wires or threads are immersed in a soap solution. This method was developed in detail by Frei Otto and his team, which recognised this method as suitable method of form-finding of real tensile membrane structure. Soap films provide minimal area of surface between two closed boundaries because they are type of minimum energy systems. These films provide a uniformly stressed surface between curved rigid edges or a set of linear edges.

Figure 5 Soap Film models

These models are less durable and fragile despite of adding hardening agents such as gelatine to soap solution. Therefore, these models demonstrate a disadvantage to be used as a design tool. However, these models are known to be very accurate for form-finding as they have immensely small amount of self-weight to produce deviations from minimal surfaces which are pure in nature. 20

Stretched Fabric Models Form-finding of tensile membranes can also be performed using model s of high elastic membranes. These models have same properties like soap film models. They can be made on a larger scale unlike soap films which show noticeable deviations if modelled on a large scale. These models are more durable as compared to soap films. Simple stretched fabric model can be made easily through materials like pantyhose or net fabric, base board, thump pins and dowels to support high points in the structure. (Bechthold 2008)

Figure 6 Image of stretched fabric model

3.6.2 Digital Modelling for Form-Finding Digital modelling is performed through computers for form-finding of tensile membranes today. These computational techniques can reproduce behaviour of physical models used for form finding. Many software programs are currently available for this task and some of them were mentioned in chapter 2 of literature review. A computer uses two widely accepted methods to simulate physical behaviour of tensile membranes: force density method and dynamic relaxation method. Moreover, finite element method is also used for tensile membranes under influence of load specifically. For this dissertation force density and dynamic relaxation methods are discussed briefly, as detailed explanation of these methods are beyond the scope of this dissertation. Force Density Method In this method an analytic technique is used to linearize the equations of form-finding for a tensile membrane. Due to linearization this method becomes independent of membraneâ&#x20AC;&#x2122;s material properties. The membrane in this method is considered as network of linear bar elements and nodes which are joined with pinned joints. Besides this, each element in tensile me mbrane is specified with force density ratio (force in cable / length of cable) to obtain different shapes in equilibrium for different ratios. This method is very efficient numerically and an equilibrium shape of a membrane can be found out easily through different iterations. (Sierra, serna et al. 2004) 21

Dynamic Relaxation In this method a problem of geometric non-linearity is resolved by associating it to a dynamic problem. Due to this association it uses principles related to dynamics for form-finding exercise. However, dynamic properties of a membrane like damping characteristics and mass needs to be defined during this process. Henceforth, forces are balanced at each node along with giving amount of residual forces from which movement of these nodes are produced in the direction of those forces. Modified positions of these nodes are continuously computed until a shape in equilibrium is achieved. The residual forces at this equilibrium stage are very small. (ibid.) 3.7 Formfinder Software program As mentioned briefly in chapter 2, Formfinder program is a software program tailored to assist architects and designers to design form-active structures like tensile membranes. This software can be operated like a sheet of paper and pencil to sketch a tensile form in digital environment. The main aim of this software is to perform form-finding automatically to generate a 3d geometry which is feasible. The resulting form is affected by the edge condition that a user can draw using its tools. This edge is drawn as blue line when edge points are placed. When a closed polygon is drawn using these edges, a net is formed between boundaries of polygon like a soap film. When edge points of this net are rose to a height, a new shape is calculated through â&#x20AC;&#x2DC;Force Densityâ&#x20AC;&#x2122; algorithm. This net matches the edges drawn by a designer approximately, relaxed to a position where all internal forces are nearly equal (Fig 7). This net obtained through software depicts suitable state of a tensile membrane. (Formfinder software Gmbh, 2014)

Figure 7 Form-finding after designer draw edges of desired shape of tensile membrane.

General Layout of software The general layout of Formfinder program consists of four main areas. (Fig 8) 1 Symbol bar (Toolbar): This bar has buttons to control all major actions and design tools.

2 Properties Panel: This panel allows designer to access to tools for parametric operations like changing height of anchor points, edge shapes, or geometrical proportions. 3 Dialogue Panel: It provides access to web browser inside software to compare design with existing built projects. 4 Viewport: It is a window in which user can work in 3d dimensions with help of mouse and keyboard to perform modelling of tensile membrane form. (ibid.)

Figure 8 General layout of Formfinder program

This chapter gave an understanding of tensile membranes and their form-finding techniques. Consequently, a stretched fabric model would be used for physical modelling, due to its durability as compared to soap film model. In addition, Formfinder software would be used for digital modelling due to its capability for conceptual form-finding. This model making exercise would be presented in the following chapter.

CHAPTER 4 PHYSICAL AND DIGITAL MODEL MAKING PROCESS

This chapter was written with the intention to demonstrate the process of concept model making for tensile membrane with physical and digital methods. Physical model making was carried out with the technique of a stretched fabric model whereas digital modelling was performed using Formfinder software. Information about fabric models and Formfinder software was discussed in chapter 3. This model making exercise with physical and digital technique would help in deriving the processes of both modelling techniques followed for concept design of tensile membrane form. 4.1 Tasks performed to study the physical and digital modelling process Processes of physical and digital modelling techniques were studied for performing specific tasks. These tasks are performed commonly by architects and designers during concept design of tensile membrane structures. Some of these tasks studied for this research are:

Making model for initial form chosen for tensile membrane structure



Altering basic parameters of geometry and forces in concept form



Obtaining geometric and technical information about concept form

Parameters of geometry for conceptual forms are commonly changed by archite cts or designers while designing. These changes could be referred as parametric operations here. Some of these parametric operations performed to study process of altering parameters are:

Changing of the boundary conditions by altering position of anchor points,



Changing position of support poles,



Changing pretstress or force values in edges of membrane shape



Changing radius of edge profiles

These parametric changes are generally altered to achieve a desired architectural form. Moreover, the addition of a new boundary to membrane surface and generating cutting patterns are some of the processes which are often performed during concept design stage. Hence, the process to perform these tasks was also studied. In addition, process of obtaining information like shadow patterns, flat areas on surface, and surface area of membrane were studied. 24

However, the process for obtaining cutting patterns was not performed in this exercise of model making due to absence of full version of the software used. Therefore, the process of performing this task was studied from secondary sources for both physical and digital modelling technique. Since the methodology of this research compares physical and digital modelling process based on time and convenience, a time value was also recorded for all the processes performed with physical and digital models. These time values were tabulated in chapter 5 for comparison purpose. However, while calculating time it was assumed that an architect was equipped with basic knowledge of using Formfinder software. This software has a simple interface and it took an hour to learn the software basics from tutorials provided on its website. In fact, process of obtaining cutting pattern was not performed with concept model in this research. Therefore, a time parameter is not recorded for this task. 4.2 Choosing tensile membrane form for modelling exercise For model making exercise a form for tensile membrane was chosen. Armijos (2008) suggested that there are three elementary forms related to tensile fabric structures. These include hypar, barrel vault and cone. Therefore, to study process of modelling, a variation of simple hypar form was chosen as an initial concept form. This chosen form is called twin hypar; it is a combination of two hypar forms. This form looks like a square or rectangle in plan with number of points which are high or low in elevation view. The form chosen was dimensioned to cover an imaginary space of 7.5 m wide and 12.5 m long with high points located at 3.5m. Fig (9) shows the form described above. For this form a physical model at 1:20 scale was made along with digital model using Formfinder software program.

Figure 9 Chosen Twin Hypar form for concept Design to cover an imaginary space

4.3 Physical model for twin hypar After choosing a form for tensile membrane a physical model of twin hypar was made on scale 1:20. This section mentions the steps followed to perform each task while physical modelling of a twin hypar. These tasks were mentioned in section 4.1.

4.3.1 Making initial concept model making Making initial model for tensile membrane form included the following steps. These steps are listed below with the process followed to complete each task for model making. 1. Choosing materials Materials for the base of model included 6mm ply board and 4 mm acrylic sheet, support poles were wooden sticks of 8.5 mm diameter, whereas a net fabric was chosen to construct surface for tensile membrane. These materials were chosen to produce a durable physical model which could be used to perform further changes to geometry of membrane later. (Fig 10)

Figure 10 Materials for Model Plywood, Acrylic, wooden sticks, Fabric

2. Preparing base After deciding the materials for model, the base for placing rigid supports of twin hypar was prepared. This base was cut using laser cutting machine placed at centre for 3D design in University of Nottingham (UK). Drawings and images of this base for tensile membrane model are shown below in fig 11. Two similar bases were cut for this model for moving one of them in order to change height parameters at a later stage. This designed base was also marked with a grid of 25 mm to keep a sense of scale during the physical model maki ng process. In addition, holes were cut on the base to the size of diameter of the wooden sticks. It allowed holding the sticks after changing position in the model.

Figure 11 (1) Plan of area for imaginary space to be covered, (2) laser cutting Base, (3, 4) final bases for physical model

3. Erecting supports for tensile membrane In this phase wooden sticks of 8.5 mm diameter were taken and they were placed inside the holes on the base. In these sticks a slit was made at the top to anchor fabric after stretching it. Fig 12 shows the wooden sticks placed in position before stretching net fabric for tensile membrane.

Figure 12 Wooden supports for anchoring fabric

4. Cutting fabric for stretching After erecting the support sticks, the net fabric to be stretched for tensile membrane form was cut. A rough amount of fabric was marked and cut to required dimensions. These rough 27

dimensions were taken from rectangular plan of chosen twin hypar and they were marked on the fabric. An approximate offset on fabric was marked from these dimensions to allow the extension of net fabric. Finally, a piece of net fabric was obtained for anchoring which would be used to model a twin hypar form.

Figure 13 Fabric cutting

5. Stretching and anchoring the edges on support sticks When fabric was cut, it was stretched between anchor points to generate a tensile form (Fig 14). Figure 9 displayed that twin hypar have 6 anchor points. From these, 3 points are high and 3 points are low. The higher points were achieved by anchoring the fabric into the slit, which was cut at the top of the wooden stick. Eventually, fishing weights were used to stop the fabric from sliding back. For lower points the fabric was anchored at the holes on the base (Fig 15).

Figure 14 Stretching fabric

Figure 15 Anchoring Fabric to wooden sticks with slits, anchored ground point with fishing weight

In this way a physical form of twin hypar was achieved, after anchoring the fabric ends at the top of the wooden supports (Fig 16). This process demonstrates the conceptual model making of tensile membrane form through the physical model of stretched fabric.

Furthermore, the processes for changing different parameters of this physical model are described in the following section. These parameters are often changed at concept design of tensile membranes by architects and designers.

Figure 16 Initial concept model for twin hypar modelled through physical technique (scale: 1:20)

4.3.2 Process for changing parameters of tensile membrane form This procedure was important to study because at the concept stage geometrical parameters of shape and form are often changed by designers and architects. For changing specific parameter different techniques were followed with the fabric model. These techniques are described below with respect to parameter changed. 1. Changing height of anchor points Changing position of anchor points while concept design of membranes is common. This task was performed by sliding one of the bases of physical model to a height of 0.6m. This adjusted the height of lower points on the ground. The distance for sliding the base upwards was measured using a metric scale. During this process the tensile fabric changed its shape after re-tensioning and a new shape was formed when lower points on the base of the model were lifted up. (Fig. 17)

Figure 17 Process of sliding base with ground anchor points to change their height

2. Changing position of support poles While designing architectural concept, sometimes the supports of membrane structure needs to be shifted in plan. This was accomplished in our physical model by placing the support pole from one hole to another on the base. The grid marked on the base provided desired position for new position of support pole. After this support pole was repositioned and the fabric was re-tensioned to achieve a new tensile membrane shape. (Fig 18)

Figure 18 Image showing shifting of Support pole in physical model

3. Changing force along boundary edge In order to achieve specific changes in the shape during concept design the level of tension in the membrane edge has to be changed. This parameter was changed in physical model by inducing more tension to the desired edge. This tension was induced by pulling the two ends of the membrane edge, until a desired shape of membrane was achieved. This process of changing force of membrane edge could be seen below in Fig 19.

Figure 19 Pulling ends of boundary for changing force and curvature profile of edge

4. Adjusting curvature(sag) of edge profile In order to achieve a specific form of tensile membrane, altering the radius of curvature of the edges could be required sometimes. In physical model this curvature was adjusted approximately when force along the boundary was changed. Edge curvature was affected when force was applied at both the ends of an edge of the fabric. When this force was increased the radius of the edge also increased.

5. Addition of new boundary to membrane surface 31

While designing tensile membranes, adding a boundary or inserting a new profile to membraneâ&#x20AC;&#x2122;s surface could be one of the possibilities to explore their form and geometry. This would generate a new surface shape for membrane as required by designer.

For this exercise a ring was chosen to be introduced into twin hypar surface. A wooden stick of 2.5m at 1:20 scale was taken and it was attached to the circular wooden disk of 0.4 m diameter and 4mm thickness, to make profile model of the ring. This sti ck was placed on the co-ordinate (8.5 m, 2 m) on the base grid and membrane was re-tensioned. This resulted in a new form with ring inserted into twin hypar shape. Fig 20 shows this process below.

Figure 20 (1) Ring profile mounted on wooden support at height of ring. (2) Tensile membrane form after ring profile induced in tensile membrane

4.3.3 Process of getting information about concept form from physical model In this part, process for obtaining information of concept shape required for designing a concept is presented. This process was studied to obtain the following information:-

1. Sun-Shadow study for shadow pattern It is important to analyse shadows of form while designing an architectural concept. For obtaining shadows of our physical model a heliodon was used, which is a device to simulate position of sun relative to a flat surface. This simulation was done using a horizontal surface and light source which was fixed. Image of heliodon used for this task is shown in fig 21 below. 32

For this study latitude of 52.9 degrees for Nottingham city was set and light beam was set for month of august. For setting latitude, month and time different dials were rotated and set as shown in fig 21.

After this model was clamped to the tilted surface of heliodon and two shadows were photographed for 1:30 pm and 3:00 pm respectively, by adjusting time scale ( Fig 22). Therefore, this process was followed for studying shadows of concept model, through physical technique.

Figure 21 Image of Heliodon and its adjustment parts for shadow settings, Diagram Showing position of the light to simulate each month

Figure 22 Obtained shadow of physical model at 12 and 1 PM respectively

2. Inspecting flat areas on the membrane surface While designing a tensile membrane structure, its conceptual form is also inspected for the areas which are flat and could become problematic due to water and snow collection. These areas are minimized during form finding at concept stage, in order to avoid any additional unexpected loads. In physical model used for this exercise flat areas were analysed approximately from visual inspection. An experienced designer could predict some areas which seem to be flat. Figure 23 below represents an example of these areas in our physical model of twin hypar based on visual prediction.

Figure 23 Image showing possible flat areas on Tensile Membrane surface based on Visual Prediction

3. Obtaining cutting pattern When 3d surface of membrane have to be manufactured using flat membranes, a 2d cutting pattern is required. This is a very sophisticated process and requires knowledge of geometry for the development of 3D surfaces. Due to the focus on concept design, this work is mainly based on the conceptual approach described by Onate (OĂąate and KrĂśplin 2006) for producing cutting pattern. The process for this task was not performed with physical model of twin hypar for this dissertation as mentioned earlier but it was studied and understood through secondary information to understand and describe a process. Hence, the process understood by examples available in literature was compared to the digital process. Firstly, the form of the twin Hypar would have been marked with dividing lines and then these can be cut. These strips of fabric after been cut would release tension and shrink. Therefore, an approximate offset could be taken from obtained geometry to get final cutting pattern for conceptual design stage. (Fig 24)

Figure 24 Process followed to generate conceptual cutting pattern from Physical Membrane form

4. Calculating surface area of the membrane This information is very important for concept design. Area of surface and volumes to be covered are basic parameters to be fulfilled by designer or an architect while designing. For tensile membranes this information could be extracted from a physical model by using mathematical formulas. For getting area of membrane surface, cutting pattern could help. Area of all panels in cutting pattern could be calculated and added to get an approximate surface area of the tensile membrane form.

Therefore, a description of process for each task carried out with physical model for concept design of tensile membrane was understood. Henceforth, these same tasks would be performed using digital tools of Formfinder software to understand the process of performing those tasks though digital modelling technique.

4.4 Digital model of twin hypar This section analyses the process of performing the same tasks by means of digital tools such as the Formfinder software. This program is customised for architects and designers of tensile membranes and it was discussed in chapter 3. It uses the Force Density Method to find a form in equilibrium state. For this modelling exercise, same tasks performed with physical model were performed again using tools of Formfinder software. These tasks and processes are described in detail in the following paragraph. 4.4.1 Initial model making process in Formfinder 1. Preparing drawing for plan of tensile membrane supports In this step a 2d drawing was prepared for the base plan of tensile structure. This was done on AutoCAD software program by using its 2d drafting tools. This cad drawing was drawn with precise dimensions according to the chosen size of the twin hypar.

Figure 25 Drafted plan for imaginary space to be covered

2. Importing drawing into Formfinder After making a 2d plan for placement of tensile structure in CAD drafting software, this drawing was exported to Formfinder software. A .dwg format of the drawing file was exported using the export command in AutoCAD. Eventually, this file was imported into Formfinder software by using import command in the file menu. This Process could be seen in images of the screenshots below. (Fig 26)

Figure 26 Importing Plan of Imaginary space from CAD to Formfinder

3. Sketching the perimeter or boundaries of tensile membrane shapes in XY plane For this step, tools of Formfinder program were used. To sketch the boundaries of perimeter, the edge controller command of sketch tool was used. After selecting this command a closed polygon was sketched on the base drawing which was imported in step 2. This polygon was made by selecting the support anchor points marked in the 2d drawing (Fig 27). Closing this polygon generated a planar net for the fabric structure within the enclosed boundaries on XY plane (Fig 28). After this a planar mesh was formed and the area to be enclosed by the membrane was obtained. Therefore, the original CAD plan was deleted from the software. Furthermore, measurements were checked using grid marked in the software which was set to 1m x 1m by default. However, the size of the default grid could be changed from the settings tab and then Grid options could be altered as shown in Fig 29.

Figure 27 Using Sketch tool and sketching initial boundaries of form with help of base plan

Figure 28 Planar net on XY plane obtained after closing boundaries drawn from pen tool

Figure 29 Panel for setting grid dimensions for ground plane displayed in software

4. Lifting anchor points above XY plane After obtaining a planar mesh surface from the step above, anchor points were shifted to the required heights. This was done by selecting the points to be moved and then using the move command shown in Fig 30. By selecting this tool the anchor points of the planar net were shifted to a required height by adjusting values in the properties panel as shown by the red box marked in Fig 30. By lifting these points to 3.5 m height an anticlastic form of twin hypar was generated. This geometry of tensile membrane in digital environment was in equilibrium. This was achieved with the help of an embedded algorithm of force density method within Formfinder. The force density method for form-finding was explained in chapter 3.

Figure 30 Setting height of anchor point to achieve conceptual Anticlastic Membrane

5. Sketching the support poles Support poles on which the fabric will be anchored were drawn after the form of the twin hypar was achieved, by shifting the anchor points to their required heights. This was done in Formfinder by selecting rigid elements command. When this command was selected a rigid support was drawn from the XY plane to the position of the anchor point. This process is shown below in Fig (31).

Figure 31 Sketching pole supports for tensile membrane to generate anticlastic membrane shape

Finally, an anticlastic membrane shape of the twin hypar was achieved by using digital tools of Formfinder. The final model of the twin hypar with specified measurements could be seen in fig 32 below. After obtaining the model of the twin hypar in digital environment, the process of altering the parameters related to its geometry inside Formfinder are described in the following text.

Figure 32 Initial concept model for twin hypar modelled through digital technique of Formfinder software

4.4.2 Process for changing parameters of the tensile membrane form in Formfinder 1. Changing height of anchor points For changing the height of a particular anchor point, first it was selected as in initial model (Fig 33). Afterwards, move command mentioned earlier in initial model making proce ss was used. This command could be used to move the points intuitively in X Y and Z directions inside 3d space of digital environment. In addition, this process was more accurate when height of the anchor point (Z value in our case 0.6 m) was directly typed into the properties panelâ&#x20AC;&#x2122;s settings tab for a specific location (Fig 33). After changing the position of anchor points, Formfinder updated the shape of membrane through its embedded force density algorithm. Eventually, a rigid boundary command was used to add new support poles by using the method employed for step 5 in section 5.4.1. Therefore, it allows the user to play with the geometry of the tensile membrane structures in the digital environment and keeps simulating real time physical form on the computerâ&#x20AC;&#x2122;s screen.

Figure 33 Image showing Move command, settings tab for entering exact height for anchor points, and both original and updated model of twin hypar

2. Changing position of the support poles and their curvature To reposition the support poles, the supports of initial digital model were deleted and new poles were drawn using the rigid boundary command. While drawing these support poles the default grid inside Formfinder was used to place them on the exact positions. These 41

support poles were drawn with the same process followed in step 5 of section 5.4.1. Moreover, Formfinder allowed changing the curvature of the support poles along with reporting the length of these support poles in the tensile form. This process could be seen in Fig (34) below.

Figure 34 changing the profile of the support poles in Formfinder

3. Changing force along the boundary edge In order to change the magnitude of force in boundary edges, some clicks were enough in Formfinder. Moreover, accurate value of required force could be induced at concept level to achieve a desired shape in this software. To change the force along a boundary for achieving a specific shape, the specific boundary edge was selected to change the magnitude of force. Then the amount of force (15kN) was entered in the properties panel under settings as shown in fig (35).

Figure 35 Changing force in boundary edge through Formfinder

4. Adjusting curvature(sag) of edge profile When force in the edge cable was changed through the process mentioned above, the curvature of the edge was also altered to generate a specific form. In this software this was achieved through entering the values under sag tab in properties panel as shown in fig (36). In Formfinder a sag could be specified either by altering the rise of the edge arc (in meter or percentage) or by inputting radius of sag in meters. Besides this, three dimensional orientation of sag for rotating the boundary edge could be altered by changing angle in elevation value tab.

Figure 36 Changing curvature of boundary profile through Formfinder

5. Addition of new boundary to membrane surface As mentioned in physical modelling section this could be a very crucial step for concept design of a tensile membrane structure. This allows designer to explore more options of design. In order to add a new boundary to membrane, a ring with a diameter of 0.4m was introduced into the membraneâ&#x20AC;&#x2122;s surface of the twin hypar. This addition was achieved by clicking and selecting the digital mesh of the initial form inside the software. This displayed the options of net type in the properties panel. Eventually, the net type was changed from regular net type to a radial one (Fig 37.1). After net type was changed to radial pattern a ring was introduced in the surface of the twin hypar form. This is shown below in fig (37.2).

This ring could be adjusted in terms of its location in space and its inner radius, by entering required values into the properties panel. These values could be changed repeatedly until a final shape is agreed for concept design. Moreover, from the properties panel parameters of the net can also be altered. 44

Figure 37 adding a ring to the initial twin hypar form through Formfinder

4.4.3 Process of getting information or data from physical model of tensile membrane form in Formfinder

1. Sun-Shadow study for shadow pattern Formfinder provided a tool for sun studying shadow patterns for the designed tensile membrane structure. To simulate these shadows Nottingham city was set as a geographical 45

location and the month of august was chosen. These same parameters were used for generating shadows through heliodon in physical model of tensile membrane also.

For obtaining the shadows in Formfinder, show options panel was accessed and then sun tab was selected. Eventually, â&#x20AC;&#x2DC;show shadowsâ&#x20AC;&#x2122; option was selected from the settings. In this tab a geographical location along with date and time was entered into the specified boxes by the user (Fig 38.1).

Finally, a shadow of the designed concept was achieved in the viewport window. For this model shadow at 1:30 and 3:00 pm were obtained respectively. However, the sliders highlighted in fig (38.2) were adjusted to vary the date and time, so that the shadows for different time and date of year could be obtained from the same model quickly.

Figure 38 Generating shadows of tensile from through Formfinder

2. Inspecting flat areas on the membrane surface through Formfinder Formfinder software provides an instant feedback for areas which are flat and prone to water and snow collection. These areas were recognised in physical model of the twin hypar with help of a visual analysis to identify the flat areas approximately. Initial model of twin hypar model along with the model achieved after the addition of a ring profile was used to recognize the flat areas with digital tools. Eventually, this helped in showing how more complex tensile forms could be checked for flat areas in this software. In order to investigate flat areas on the surface of tensile membrane form, show option tool bar was clicked. Henceforth, themes tab was selected in the properties panel. From this panel contours option was selected under the net options ( Fig 39). This generated the contours on the membrane surface and the area without contours represented the flat areas. These contours could be made more visible by changing thickness and colour of the lines representing them. This was achieved by changing option as highlighted in the fig (39).

Figure 39 Analysing flat areas for initial form and form with an induced ring

3. Cutting pattern The full version of Formfinder software provides the option to export the geometry of surfaces into other software programs for obtaining the cutting pattern of a tensile membrane form. The twin hypar geometry used for this exercise could be exported to rhino 47

3d software to obtain the cutting pattern. This process was not performed due to the nonavailability of the full version of Formfinder, which would have allowed exporting the tensile membrane geometry in .dxf format. However, this process was analysed by means of secondary sources, which explained this process for a simple hypar form. This process could have been followed with the twin hypar to obtain the cutting pattern. For this process initially digital model shall be exported to .dxf format using the export command available in the full version of Formfinder. Eventually, it could be inserted into rhino 3d software. In this software, imported geometry could be divided into strips and surface for each strip could be formed again using network surface command. Later, these surfaces could be selected and 2d pattern for each strip could be generated using the smash command. This whole process is depicted below in Fig (40).

Figure 40 process of cutting pattern generation through Formfinder software

4. Calculating surface area of membrane In order to determine the surface area of a membrane form, manual methods of measuring area could be avoided in Formfinder. This program automatically displays the area when the digital mesh of model is selected. Moreover, it determines the values for volume covered under membrane surface, which would have been tedious to calculate in physical model manually. (Fig 41)

Figure 41 Viewing calculated surface area of membrane shape modelled in Formfinder

Consequently, this chapter helped in understanding the processes followed in the physical and the digital modelling techniques to perform the tasks related to the concept design. Eventually, this information of processes obtained through model making exercise provided the primary data for comparison of both the processes followed in the physical and the digital modelling technique. This data are presented and compared in next chapter.

CHAPTER 5 COMPARISON OF PHYSICAL AND DIGITAL MODELLING PROCESS AND RESULTS

In this chapter an attempt has been made to compare process flows of physical and digital modelling techniques employed for tasks performed during concept design of tensile membranes by designers. Flow charts of these processes were derived with help of information obtained by model making exercise performed in chapter 4. Thus, a comparison of these processes was done on basis of time and convenience of designers, to obtain results. Advantages observed for performing those tasks from physical and digital modelling process were treated as results of comparison. Along with comparison process, Table 1 shown below was prepared on basis of time spent to perform specific tasks for concept design. This table helped to compare time efficiency of each process which was carried out to perform those tasks. The results of time comparison are mentioned along with result of process comparison in this chapter. This exercise helped in understanding advantages of the software, to perform a task during concept design stage of tensile membranes, when compared to the process followed for the same task using the physical modelling technique, based on a stretched fabri c model. The results obtained from these comparisons can be used for discussion, which will eventually help in forming conclusions for this dissertation. TABLE 1 - TIME SPENT ON PERFORMING TASKS WITH PHYSICAL AND DIGITAL MODELING TECHNIQUE SNO.

TASK PERFORMED WHILE CONCEPTUAL DESIGN

TIME

OF TENSILE MEMBRANE BY ARCHITECTS

PHYSICAL

PREPARATORY WORK

TAKEN

WITH

MODELIN G

TIME

TAKEN

WITH

MODELING TECHNIQUE IN

TECHNIQUE

FORMFINDER PROGRAM

BUYING MATERIAL:- 1

INSTALLING AND LEARNING

DAY

SOFTWARE :- 0.5 DAY

INITIAL CONCEPT MODEL MAKING

2 hrs.

5 min.

CHANGING HEIGHT OF ANCHOR POINTS

1.5 min.

6 sec.

CHANGING POSITION OF SUPPORT POLES

0.5 min.

10 sec.

INCREASING FORCE ALONG BOUNDARY EDGE

15 sec.

5 sec.

ADJUSTING CURVATURE/SAG

BOUNDARY

15 sec.

10 sec.

PROFILE

ADDITION OF RING TO MEMBRANE SURFACE

15 min.

10 sec.

OBTAINING SHADOWS FOR CONCEPT MODEL

FROM HELIODON:-

FROM SOFTWARE:-

10 min.

10 sec.

DEPENDS ON DESIGNERS

5 sec.

ANALYSING FLAT AREAS FOR PONDING

EXPERIENCE

AND SNOW COLLECTION

* Hrs â&#x20AC;&#x201C; hours, min â&#x20AC;&#x201C; minutes, sec. - seconds 5.1 Comparison: Process of initial concept model making It was noticed from figure 42, that fabric material handling was difficult in physical modelling technique as compared to software where physically no material was needed to be handled. Moreover, cutting the fabric was an approximate process in physical modelling where a rough amount of cloth was cut and an attempt was made to stretch it. Then this fabric piece if smaller had to be cut again for stretching. In addition, stretching fabric and anchoring it required more than one person due to controlling of different model parts in tension simultaneously. Contrary to this, the process of initial concept modelling in Formfinder software was performed by one individual with elementary knowledge of the software. Furthermore, it was not required to predict the amount of fabric before modelling surface membrane of concept model in Formfinder software. This software automatically generated the digital mesh and determined the three dimensional surface in equilibrium. Only the warp/fill pretension and the boundaries were needed to be specified. However, physical modelling process had its own advantages over digital ones. As it is clearly visible in figure 42, for making physical model no knowledge of software was needed. In addition, it was made with cheaper materials when compared to the cost of commercial software packages developed for membrane structures. Moreover, in digital modelling the sensory experience of modelling was missing as model of tensile membrane could not be experienced in real world environment. Besides this, in physical modelling structural behaviour was instantly predicted whereas the digital model needed another software for structural analysis, to predict this behaviour. In fact, comparing time from table 1 indicated that initial concept modelling through physical technique took 2hrs whereas in Formfinder this time was reduced to 5 minute only when basic software was known. 51

Figure 42 Comparison of initial concept modelling process

5.2 Comparison: Process of changing height of anchor points Through Formfinder software anchor points of tensile membrane can be shifted to exact height by entering exact height in properties of respective anchor points whereas in physical model it was done using an approximately by sliding base upwards with scaled measurement as shown in previous chapter.

Figure 43 Comparison of process to change height of anchor points

Moreover, Formfinder provided instant physical membrane form updated with new anchor points and readjusted tension, unlike physical model in which fabric was re -tensioned and re-anchored to visualize new membrane shape. Simultaneously, in computer software initial concept model was copied and new options of same form were visualized on same screen to generate multiple options. Although this could have been achieved with physical models by photographing them, digital models were more convenient and interactive. Moreover, making multiple physical models would involve more time and cost of material. Another advantage of physical modelling process for this task was an instant feedback of how materials behaved when height of anchor points was changed. This allowed an instant interaction with the forces acting in physical model. On the other hand, this prediction of material behaviour was absent in Formfinder software. Moreover, a comparison of time (table1) indicated that it took 1.5 minutes to perform this task with physical model (when it was designed especially for performing parametric changes), whereas with

Formfinder software it took only 6 seconds to do the same and generate the updated shape of tensile membrane.

5.3 Comparison: Process for changing position of support poles After changing height of anchor points a comparison between processes for changing position of support pole was made (Fig 44). Both processes followed with physical and digital model to perform this task depicted, that Formfinder provided an opportunity of changing its position to exact coordinates. This was achieved by redrawing it on new position through rigid boundary tool, after anchor points were shifted to a new position. Whereas in physical model this process was performed with help of marked grid on the base of physical model, but it required re-tensioning and re-anchoring of fabric ends again, to obtain new form of tensile membrane. Moreover, in Formfinder software there were more options to alter profile of support poles to outward and inward curves through specifying radius or curvature, unlike in physical model where curved poles would have to be modelled especially for visualizing if needed in concept design. Besides this, support poles could be rotated on their axis also, through a command called elevation along with obtaining their length value by software instantly. An advantage of using physical modelling process over digital process for this task was that support poles had thickness and they reacted to real world forces. On the other hand, support poles modelled digitally by rigid boundaries option were not affected by any force. These elements did not have thickness and they did not show real time behaviour in software, when they are subjected to force by stretched fabric. Therefore, changing position of support poles in Formfinder software is apt for visualization only. A comparison of time in table 1 indicated that performing this task in physical model takes half a minute whereas it was done in 10 seconds using digital tools in Formfinder software.

Figure 44 Comparison of process for changing position of support poles

5.4 Comparison: Process for increasing force along boundary edge and adjusting curvature of edge boundary Along with studying process for changing position of support pole in concept models, processes for changing force in boundary edge of tensile membrane and adjusting curvature of boundary in the physical and the digital model were observed through figure 45 respectively.

Figure 45 Comparison of process for increasing force along boundary edge and adjusting curvature of edge profile

It was observed that process for performing both tasks was same in physical modelling, as changing force in boundary edge affected the curvature of the boundary in physical model also. On the other 56

hand, while modelling through Formfinder these processes were different as a user could specify precise radius with particular magnitude of force for exact requirements for concept design. Formfinder software provided an option to input exact magnitude of force required in particular boundary along with options to set its curvature profile through specifying sag in percentage or meters. These tasks could be done in physical model approximately at concept design stage as shown in physical processes mentioned in figure 45, but it would require a long time and tedious technique to achieve tensile form for specific amount of force and curvature. Moreover, different options could be generated for different force and curvature values at same time, to generate more options for concept stage through software. At the same time, physical modelling allowed to experience tactility of materials, which would provide more interactivity while changing force in edges intuitively by pulling both ends through hands. Comparison of time depicted that performing the above tasks with physical model took 15 seconds where as both force and curvature of boundary were altered in 5 and 10 seconds respectively with digital modelling (table 1). 5.5 Comparison: Process for adding a ring profile to membrane surface Another important task often performed while concept design of tensile membranes included addition of new boundary to initial concept model. Therefore, process followed for addition of ring in both physical and digital model is shown in figure 46. The comparison between both processes depicted that a custom profile of desired ring was needed to be manually cut and mounted onto a wooden support in physical model whereas changing the net option to radial type, was sufficient for performing this task in Formfinder software. Moreover, as noticed in process performed above, re-tensioning and re-anchoring of fabric was needed in physical model after ring was placed in position on the marked grid. Conversely, this process could be skipped in digital model of tensile membrane in Formfinder. In fact, during physical modelling process a designer could place a ring profile freely within the physical model, which would have fostered more imagination during concept design stage. In addition, Formfinder also provided capability to adjust ringâ&#x20AC;&#x2122;s inner radius and its location in 3d space to generate multiple options from the digital model. This would have otherwise required cutting a new geometry of the ring in physical modelling. These ring parameters could be changed for obtaining an instant simulation of physical form in real time by using tools of Formfinder.

Time comparison for addition of ring in physical and digital model displayed that physical model took 15 minutes to add a ring profile to an existing model whereas this was achieved in only 10 seconds through digital tools of Formfinder.

Figure 46 Comparison of process for adding a ring profile to membrane surface

5.6 Comparison: Process for obtaining shadows for concept model From figure 47 below process of obtaining shadows was compared. It was seen that physical process involved many adjustments of dials in heliodon for getting shadows of membrane form for a specific date and time. Moreover, a latitude value was needed for getting shadows at specific location and

setting a light beam in a special room was required for getting shadows of physical model. Conversely, digital model used by Formfinder software generated shadows instantly by selecting sun options and at the same time, there was no need of latitude value for a specific location as software provided a world map for choosing the location.

Figure 47 Comparison of process for obtaining shadows of tensile form

Furthermore, adjustments for date and time were easily done through sliders and updated shadows were generated instantly in the viewport window, without any need of special equipment or place as in the case of using a heliodon. However, an advantage of physical method of obtaining shadows of materials having different surface textures in real world cannot be overlooked.

Table 1 displayed that these shadows took lesser time to generate through computer. Through software it took 10seconds to generate shadows along with adjusting all the parameters whereas it took 15 minutes to obtain shadows of the physical model. 5.7 comparison: Process for analysing flat areas for avoiding water and snow collection

Figure 48 Comparison of process for analysing flat areas on membrane surface

This comparison (Fig 48) depicted, that an instant visualization of flat areas was obtained through contours which were generated on membrane surface by Formfinder. Moreover, these contours were updated with changes in the shape to show flat areas again.

Conversely, this task could be performed for physical model by an experienced designer through a visual inspection. At the same time, a pressure from hand could have been applied for adjusting these flat areas in physical modelling process. In this process a comparison cannot be made exactly, as time taken to inspect flat areas visually depended on capability and experience of a designer whereas software did this job instantly after clicking an appropriate option.

5.8 Comparison: Processes of obtaining cutting pattern and surface area of membrane Both processes for this task were time consuming. They are depicted in figure 49 below. As noticed, physical process offered an opportunity for designers without prior knowledge of software to perform this task. However, digital process needed a prior knowledge of Formfinder software along with Rhino 3d. Currently functionality to generate cutting pattern is absent in this software, therefore rhino 3d has be used for this purpose along with it. At the same time, software depicted an advantage of providing 2d drawing of cutting pattern without a need to compensate for tension. Conversely, in physical process a fabric shrinks from originally tensioned shape after flattening due to release of tension force. Hence, to compensate this shrinking paper strip method would have to be used for obtaining cutting pattern, which is very intensive and time consuming and relatively inaccurate. Therefore, this task could be accomplished using Formfinder instantly and accurately as compared to physical process. In fact, sof tware would provide a correct 2d pattern through the unroll command only if the surface is deployable (single curvature). However, an approximate pattern is generally acceptable for concept design. Moreover, in physical process strips obtained from cutting pattern would have been used to calculate area of surface through mathematical formulas whereas Formfinder software could calculate surface area of membrane automatically. Therefore, the whole surface area for designed membrane shape could be calculated instantly with help of software as opposed to physical process.

Figure 49 Comparison of Processes for obtaining cutting pattern and surface area of membrane

All comparisons in this chapter presented advantages of the physical and the digital modelling process for concept design of tensile membranes. In fact, Formfinder program have some capabilities that could be beneficial for designing concept of these forms specifically. These capabilities could contribute in understanding how digital modelling could take an edge over physical modelling process of stretched fabric models. 5.9 Additional features of Formfinder software for concept design of tensile membranes Other than digital tools used for performing tasks in chapter 4, Formfinder provides more tools and options for conceptual design of tensile membranes. Moreover, these tools give better capabilities to Formfinder for designing these forms, when compared to physical modelling process. These tools and options are listed below:-



Formfinder provides a tool for comparing modelled tensile form with a real world project through the help of a database. This database is created by the developers of Formfinder program and it contains information of existing membrane structures in the world. Hence, this would provide an instant comparison of concept with an existing real world project similar to concept shape.



It has a specific tool to select the material from a data bank with latest materials available on the market, so that a designer could think of material on concept stage.



It provides the option to specify forces in warp and weft directions, so that a designer could obtain minimal surface which is not a case in physical model of stretched fabric.



There is a specific tool in Formfinder for inserting 3d models of corner connections to the digital model of concept form. Moreover, a tool to add textures on membrane surfaces provided opportunity to visualize concept more realistically.



A rain analysis tool displays marked area which would be dry under modelled concept form. This gives an instant idea of boundary for dry area under membrane’s surface in case of rain. Eventually, this could help to place appropriate architectural functions within that area. Conversely, recognizing these dry areas would be difficult in physical models of stretched fabric.



Merging two tensile membrane shapes to obtain new tensile form through a shared boundary is possible in Formfinder without any tedious process of material handling as in stretched fabric model.



Formfinder provides a tool for cost estimation also, this tool helps to estimate the costs of realizing your concept design through its embedded functionality. Furthermore, interoperability of digital models developed by using Formfinder allows them to be exported to other engineering software for their structural and environmental analysis. Conversely, both tasks of cost estimation and analysis of these forms would be time consuming on the basis of a physical model.

All the features of Formfinder software indicated in this section depicted the probability of software being beneficial for concept design of the membranes as compared to the physical modelling process of stretched fabric. To sum up, this chapter helped to compare the processes derived from primary model making exercises. This data was then used to obtain results of comparison in form of advantages offered by both physical and digital modelling process. Henceforth, these observed advantages for both processes are discussed in the following chapter.

CHAPTER 6 DISCUSSION AND LIMITATIONS This chapter provides a discussion of the results obtained from the comparisons made in previous chapter. This would assist in identifying unique capabilities of software programs in concept design when compared to benefits of physical modelling process. This will eventually help in achieving the conclusions for this dissertation. 6.1 Discussion on Advantages of designing concept of tensile membranes through physical modelling process From benefits of physical modelling process mentioned in chapter 5, it was observed that physical modelling supported process of design in a different way than software programs. From section 6.2, it could be observed that unlike software programs like Formfinder, physical modelling process allows designer to visualize and interact with tensile membrane models in real world to interact with them through their sensory experience. This would invite more imagination of an architect or designer at concept stage of design. This corresponds to findings of Cheng (1995), who claimed that physical model communicates with designerâ&#x20AC;&#x2122;s emotions to boost design imagination. In addition, it was also revealed that physical models are much more efficient in understandi ng various details of connections and assembly of various parts. These parts in case of twin hypar model used for this dissertation included support poles, fabric membrane, and anchoring devices. Moreover, in all the processes related to changing geometry parameters shown in chapter 4, a constant need of re-tensioning and re-anchoring fabric was seen. This implied that through physical modelling process, an instant understanding of structural behaviour of fabric materials under tension could be obtained unlike software programs like Formfinder, which needs a special computational analysis to provide equivalent feedback. For example, while physical model making, it was noticed that tension from fabric tilted support poles from their initial positions but this observation was absent while modelling in Formfinder. This observation coincides with opinion of Otto (Otto, Rasch et al. 1995), who explained that physical models of tensile membranes are good tools to simulate built reality in advance. Furthermore, these physical modelling processes followed for changing parameters of geometry, also suggest that this process offers designer with an opportunity to change parameters intuitively rather than inputting their specific values into software. For instance, changing force and curvature of boundary edge of tensile membrane shape was more intuitive and interactive as compared to

Formfinder due to need of feeding exact values. This shows how software programs can sometime limit designer's creativity to play with tensile membrane geometries at early design stage. Therefore, this discussion provided an insight into benefits of physical modelling process to design tensile membranes as compared to software programs. 6.2 Discussion on advantages of designing conceptual forms of tensile membranes, through digital modelling process used in Formfinder software In spite of the benefits offered by physical modelling processes, the results in chapter 5 also stated a number of advantages offered by Formfinder program to design and visualize these forms. These benefits of Formfinder can be discussed to evaluate the role of computer programs in design process of tensile membranes. Initially a comparison of time was done between physical and digital modelling process, to evaluate the parameter of time. The time spent to complete the specific tasks for concept design was recorded and their values were summarized in Table 1 (chapter 5). This table suggested that these tasks can be accomplished in exceptionally lesser time than physical modelling process, if designers are trained in software already. For instance physical modelling of initial model took 2 hrs. However, through software this time got reduced to 5 minutes only. A same pattern of time reduction was also observed for performing parametric changes during design of the selected twin hypar form. Moreover, it was also evident that using digital model of Formfinder program provided instant information of geometric parameters and technical aspects of membrane shape, as manual calculations were not required. This information included measurements of surface area, force in membrane edges, and cutting pattern of form and visual diagram of flat areas on membrane. Therefore, this time comparison indicates that software programs such as Formfinder can be used as quick digital tools for designing and visualizing tensile membranes when compared to physical design and modelling process. This confirms the opinions of Cotton (2009) and Pascucci (2012), which highlighted that software programs, not necessary for membrane structures, help in shortening time of design process. Furthermore, a significant advantage observed in chapter 5 was that Formfinder software required a single designer only to design and perform tasks related to concept design of tensile membranes. Whereas on the other hand, in physical modelling process more than one designer was needed during modelling process, due to simultaneous handling of multiple elements in physical model which were under influence of real world forces. Therefore, this depicts that using software

programs during design of these structures could reduce the number, and the costs, of designers working on a design project. Along with this Formfinder software showed a major benefit in performing parametric operations on initial design model. As seen in all digital processes such as changing height of anchor points, adjusting curvature of boundaries in membrane form or adjusting tension in edges, Formfinder provided an instant feedback of updated geometry with more rational values of parameters often needed for comparing multiple options. Moreover, when parameters were changed in software, original membrane form was intact and these operations were performed on a copied model to obtain multiple options. This allowed visualizing same concept form of tensile membrane with different parametric values simultaneously on screen unlike in physical modelling process, where it would require making copies of physical model manually. Therefore, it suggests that architects can explore complex tensile forms easily at early design stage now, due to parametric tools of Formfinder. This finding also corresponds to opinion of Harding ( Harding et al., 2012), who appreciated this advantage of parametric software tools for generic architectural design. In addition, the geometry obtained inside Formfinder mimicked real time behaviour of tensile fabrics due to its embedded algorithm of shape finding. So while performing parametric changes, a designer can play with model inside the digital environment as in real world, without tedious handling of fabric and other parts of physical model. This indicates that Formfinder software has an advantage of providing quick feedback of geometry for shape finding of tensile membranes through less tedious technique as compared to physical modelling process. This is in agreement to Armijos ( 2009), who supported this fact as mentioned in chapter 2 of literature review. Along with parametric capabilities, Formfinder was also helpful in achieving accuracy for the tasks performed in modelling processes. For instance, when a specific amount of force was required to be applied in membrane edges, Formfinder was used to calculate its related edge profile automatically. Therefore, this software can be seen as an ideal tool to apply measured changes in digital models of tensile membranes while early design process. This makes an agreement to opinion of Pascucci (2012), who stressed the importance of software tools to provide accuracy in architecture design. Eventually, this accuracy would help designers to obtain a rational tensile form, which probably would not show a drastic deviation from concept when subjected to engineering analysis. Consequently, an advantage of interoperability was also noticed in Formfinder when the digital model of tensile membrane was exported to rhino3d for generating cutting patterns (chapter 4). Hence, these models can be exported directly into other software programs for obtaining 2d

drawings of cutting pattern, structural analysis diagrams and other engineering information needed to test the rationality of concept form. As a result, this would help in better coordination between designers and engineers at early design stage to analyse design with engineering practicalities. In addition, the digital model of twin hypar in Formfinder was used to obtain geometrical information of modelled tensile form automatically without manual calculations. This gave an opportunity to know area of surface membranes, volume covered by it, and dimensions of shape directly from computer screen. Along with this it helped in analysing these forms for shadows and flat areas easily and quickly as compared to physical models. In chapter 4, Formfinder was used to obtain shadow of tensile form instantly for a specific location and time. It was also used to visualize twin hypar for flat areas. These areas were prone to water collection on membrane surface and they were judged by contour map generated on membrane surface by Formfinder program. This suggests how software modelling process can help in using the digital model to obtain their information instantly as compared to physical modelling process. In fact, some unique tools of this software provided benefits during concept design stage of tensile membranes. These tools provided capabilities of rain analysis, cost estimation, comparison of modelled concept with existing projects, setting warp and weft ratio, and inserting 3d model of end connections into digital model of structure. All these capabilities of software programs show a clear possibility to enhance design process and assist in achieving an economical and efficient design that can be built in reality. 6.3 Limitations The outcomes of this research can be subjected to some limitations due to constraints of time and available resources. One of the limitations of this study is that it was performed for an anticlastic type of tensile membrane only. This form was adopted due to limited availability of software programs to design concept for other tensile membrane forms, such as pneumatic structures. Moreover, only one basic form of twin hypar was modelled to compare the process of designing though the physical model and software. Besides this, all the tasks related to the initial design of these additional forms could not be performed for the comparison made in this research due to limited time. In addition, software program was evaluated for its benefit while assuming that a designer is equipped with elementary knowledge of computer software. These limitations and assumptions could possibly affect the conclusions for this research, but they could be overcome through future research on this topic.

CHAPTER 7 CONCLUSIONS

7.1 Conclusions This dissertation research was conducted to investigate the role of computer software programs during conceptual design stage of tensile membrane structures. In order to achieve this, Formfinder software was used to model a tensile membrane form. In this sequence, processes of performing specific tasks at initial design stage were studied through this software. Then, these processes were compared with similar processes of conventional physical modelling technique based on the parameters of time and convenience to designers. Eventually, this helped in recognising the distinct advantages of software programs like FormFinder to define their roles while developing an initial form of these structures. These roles were important to be defined because current software programs which are customised for designing tensile membranes are only acknowledged for their engineering tools. Whereas, today there are some software programs that indicate possibility of supporting designers to enhance concept design after making physical models of these structures. However, there is a lack of software programs especially designed for architects in this field. For these reasons, this research issue was important to be investigated. This research revealed that the significance of physical modelling technique for designing tensile membranes cannot be overlooked as they provide a sensory experience to designers while designing tensile shapes. However, software programs like Formfinder can provide unique tools for membrane structures, to extend and enhance the design ideas obtained from physical models. Moreover, these software programs can help to design and refine the concept of these forms in much lesser time as compare to physical modelling technique. Today these software programs provide an instant feedback and visualization of real time geometry for tensile membranes in an accurate way. Besides this, these forms are interoperable with engineering tools for collaborating with engineers since the initial designing phases. This allows to asses structural implications of these forms at early stage of design. Moreover, they are efficient tools for performing parametric changes instantly and allow obtaining multiple options with different parameters, to visualize them simultaneously. In addition, a major benefit of this software shows ability of digital tools to provide geometrical and engineering information related to tensile 68

form automatically, which can help to inform their initial design. This information can range from geometrical parameters such as surface area to technical information like amount of forces in the boundary of tensile membranes. Though software programs are already acknowledged for concept design in mainstream architecture, this acknowledgement can be established for the field of tensile membranes as well due to this research. Further, this study emphasized the need of computers in architectural designing of concept for form active structures like tensile membranes. Therefore, software developers can be encouraged to develop special software to aid in concept development of these structures. A wider impact of this study would motivate architectural practises and students to employ these structures frequently in their design without restraint. 7.2 Future developments of the research This research could be developed by investigating roles of digital tools in design of form active structures other than tensile membranes. It would create awareness of more software programs tailored for designing these specific types of tensile forms. Moreover, it would be enthralling to research how sensory experience of physical modelling technique can be integrated into software programs in field of membrane structures. To investigate this integration a possible link of virtual reality and digital models of these forms can be explored in future, to engage senses of designers within computer simulated environment while designing tensile membranes. Furthermore, this research can be evolved to overcome its current limitations. In order to achieve this, a similar study can be developed for other anticlastic membrane forms such as ridge-valley and point supported shapes. In addition, this research can be performed for synclastic forms such as pneumatic structures. Besides this, process of other tasks that are performed while designing the concept of tensile membranes can be investigated with physical and digital techniques to expand the scope of this dissertation.

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