APPLICATION OF TENSILE MEMBRANE STRUCTURES IN ARCHITECTURE Paula Pecina
Fig.1, Denver International Airport, Fentress Architects, Denver, Colorado, USA
VIA UNIVERSITY COLLEGE, DENMARK Bachelor of Architectural Technology and Construction Management May 2012
BATCoM Bachelor of Architectural Technology and Construction Management
DISSERTATION TITLE: APPLICATION OF TENSILE MEMBRANE STRUCTURES IN ARCHITECTURE CONSULTANT: Henrik Jansson
AUTHOR: Paula Pecina DATE/SIGNATURE: 14.05.2012. VIA Student number: 147225 Number of copies: 2 Number of pages: 31 Number of characters: 60 425
All rights reserved – no part of this publication may be reproduced without the prior permission of the author. This dissertation was completed as part of a Bachelor of Architectural Technology and Construction Management degree course – no responsibility is taken for any advice, instruction or conclusion given within!
1.1 Abstract Nowadays we search the results that are better and options that can sustain more. Combined with new materials and construction techniques, that are lighter, stronger and more flexible, we can achieve more in the field of construction and architecture. Tension structures can extend architects’ imagination due to construction lightness unlimited length and flexibility, those are innovative and comparatively new solutions, getting more and more popular. The tensile construction field has grown considerably in the last years and is predicted to grow further. Such structures are becoming bigger and more sophisticated, combining modern tensional construction systems and membrane structures in architecture can give great results thanks to their properties, buildability and physics principles. There is a need for professional to be better informed about the general behaviour, physical aspects, the advantages and disadvantages of using tensile structures in relation to big-scale constructions, as well as small canopies. This dissertation is dedicated for someone who is interested in innovative, solutions that could be used in practice, and with vital interests in building physics, static design and novel building materials. To take a practical approach to my research I decided to base on case studies of existing tensional and membrane structures used within architecture. A few examples of how such structures have been successfully applied in contemporary constructions. They will show the real-life aspect to the problem and tell more about its construction, lifespan performance, durability, maintenance and users response. Key words: Tensile Architecture; Membranes; Cable- Strut Systems; Grid Systems; Structural Domes; Fabrics;
1.2 Acknowledgement I would like to thank Henrik Jansson, for help and advice during my dissertation writing . His guidance throughout the process was really helpful and relevant. Then I would like to express my gratitude to my internship mentor, that planted my interest in the field of Tensile Architecture.
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I Introduction part ..................................................................................................... 1 1.1 Abstract ..................................................................................................... 1 1.2 Acknowledgement ..................................................................................... 1 1.3 List of Figures ............................................................................................. 3 1.4 Report overview ........................................................................................ 5 1.4.1 Problem Statement ........................................................................ 5 1.4.2 Research Questions ........................................................................ 5 1.4.3 Background to the report ............................................................... 5 1.4.4 Research Delimitations................................................................... 6 1.4.5 Research Methodology .................................................................. 6 2 Introduction toTensile Structures ........................................................................ 7 2.1 Introduction............................................................................................... 7 2.2 History ....................................................................................................... 8 3 Tensile Structures properties ............................................................................... 9 3.1 Design and properties ................................................................................ 9 3.2 Construction ............................................................................................ 11 3.3 Analysis of structural principles of Tensile Structures............................... 12 3.4 The benefits and disadvantages of tensile architecture sional systems .... 16 4 Material choice and sustainability solutions for Tensile Structures ................... 17 4.1 Membrane Materials ............................................................................... 17 4.1.1 PVC- Polyester Reinforced ............................................................ 18 4.1.2 PTFE-Woven Fibreglass ................................................................ 18 4.1.3 ETFE- Ethylene Tetra Fluoro Ethylene ........................................... 19 4.2 Membrane Material properties ............................................................... 20 4.3 Sustainability ........................................................................................... 21 5 Case studies for application of Tensional Structures in Architecture ................. 22 5.1 Case study Tensile Membrane Canopy structure, Horsens ...................... 23 5.2 Case study Millenium Dome, London, UK ................................................ 25 5.3 Case study Allianz Arena, Munich, Germany ........................................... 27 6 Conslusion .......................................................................................................... 30 7 Bibliography ....................................................................................................... 31
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Fig.1, Denver International Airport, Fentress Architects, Denver, Colorado, USA http://www.birdair.com/projectGallery/browse.aspx?id=stadiums Fig.2 Frei Otto, Olympic Stadium Munich, 1972 http://bioinspiredarchitecture.wordpress.com/ Fig.3 Herzog de Meuron, Allianz Arena M端nchen, 2005 http://www.checkonsite.com/wp-content/gallery/munich-allianz-arena/munich-allianz-arenachristian-scholz.jpg Fig.4 Sioux Tipi, Fort Yeates http://www.bisonquest.com/teepee.html Fig.5 The tent-like structures,of the nomads of Turkestan http://en.wikipedia.org/wiki/Yurt Fig.6 Vladimir Shukhov, First tensile steel structure, Nizhny Novgorod, 1895 http://upload.wikimedia.org/wikipedia/commons/2/27/Tensile_Steel_Lattice_Shell_of_Oval_Pavil ion_by_Vladimir_Shukhov_1895.jpg Fig.7 Vladimir Shukhov , Doublecurvature steel lattice Shell , 1897 http://www.skyscrapercity.com/showthread.php?t=678936 Fig.8 Buckminister Fuller, U.S. Pavillon, 1967 http://www.flickr.com/photos/artimageslibrary/3761543516/ Fig.9 SOM Architects, Fabric tensile roof at the Jeddah Airport, 1977 http://www.structuremag.org/article.aspx?articleID=553 Fig.10 Millennium Dome, structural details http://www.therunninghead.com/casestudies/pdf/space.pdf Fig.11 Millennium Dome, Section http://architecture.about.com/od/greatbuildings/ig/Richard-Rogers-Partnership-/MillenniumDome-Section.-0Ci.htm Fig.12 Double-curvature, system basis Fig13. Example of anticlastic form http://shadesofgreendesign.com.au/biomimicry-structural-efficiency-structural-artists/ Fig.14. The dome, hyperbolic paraboloi,d parallel valley, shaped membranes http://bldgsim.files.wordpress.com/2008/10/tensile.jpg?w=425&h=246 Fig.15 Allianz Arena structure design http://www.asce.org/uploadedImages/NewsNEW/CE_Magazine/2008_Issues/August_2008/0808feat5.jpg Fig.16 Gridshell structure http://www.carpenteroakandwoodland.com/timber-engineering/gallery/gridshell-chiddingstonecastle Fig.17 Tensegrity structure http://t3.gstatic.com/images?q=tbn:ANd9GcQTT_Kq5YHgDg7nYwO1YZa74ya3lMBvkgUZG2PkWKk2Baf19GmC2v-258V Fig.18 Textile membrane materials http://www.karinpatriquin.com/site/2012/04/18/tensile-structures/ Fig.19 ETFE membrane in Aquatic Center, Beijing http://www.robaid.com/wp-content/gallery/gadgets1/konarka-6.jpg Fig.20 PTFE membrane, Nelson Mandela Bay Stadium, South Africa http://2010stadiumwatch.blogspot.com/2009/02/now-were-into-twenties.html Fig.21;Sustainable solutions for membrane structure 3
http://www.southgatechamber.com/what-are-the-modern-revolutions-in-buildinginfrastructure.html Fig.22 Tensile Membrane Canopy Structure, Horsens Park Figure by author Fig.23 Mast base for tensional structure Figure by author Fig.24Anchor for tensional structure Figure by author Fig.25 Richard Rogers Architects ,Millennium Dome tensile structure, London http://www.aviewoncities.com/london/millenniumdome.htm Fig.26 Interior Stucture, Millenium Dome http://www.me-engineers.com/projects/?office=san-diego&category=professional_arena Fig.27 Roof Plan, Millenium Dome http://architecture.about.com/od/greatbuildings/ig/Richard-Rogers-Partnership-/MillenniumDome-Floor-Plan.htm Fig.28 Site &Roof Plan, Allianz Arena http://files.myopera.com/POM032002/albums/213618/Allianz%20Arena_plan.jpg Fig.29 Arena lit in different colours, depending on an event http://designinquiry.net/wp-content/uploads/2009/02/allianz-arena.jpg Fig.30 Section, Allianz Arena http://www.egodesign.ca/en/article.php?article_id=130&page=7 Fig.31 ETFE membrane, Allianz Arena http://www.egodesign.ca/en/article.php?article_id=130&page=7 Fig. 32 Construction of Allianz Arena http://i29.tinypic.com/9tjqyf.png
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/ REPORT OVERVIEW 1.4.1Problem statement The final subject selected for my dissertation research is “Application of Tensile Membrane Structures in Architecture�. I had decided on it due to my personal interest in this kind of constructions, as well as my desire to increase knowledge about them. This dissertation is both a theoretical introduction to Tensional Structures and research on how theory translates into practice. The urge to invent something new and unique always triggered architects and engineers to look for new and interesting ways to express their design ideas. The race for the invention of innovative methods often revolutionized the fields of architecture and construction. Taking a concept and then reaching a stage in which buildings are developed from a bold idea to an innovative solution. I believe that Tensional Structures fall in this category, being the edge-pushing concept in the construction field. I would like to analyse its construction properties and then base my research on the precedent case studies. Researching what is their life-span, performance and if they are environmentfriendly. I will concentrate on a static aspect, behavior of these structures on real life examples, investigating types of materials that can be used as tensile membranes, analysing their efficiency and parameters Finally answering the question, what is the future for Tensional and Membrane in architecture and construction?
1.4.2 Research questions What are the benefits of using Tensioned and Membrane Structures? Which kind of covering materials can give the best results and assure durability? What is the prognosis for future development in this field? 1.4.3 Background to the report This dissertation is a part of the final semester at the VIA University College, Bachelor of Architectural Technology and Construction Management programme. In this report I would like to concentrate on an unusual type construction-Tensile and Membrane Structures. It will provide information on materials and technology. The dissertation gives an overview of how this kind of structures can be used alternatively in contemporary architecture.
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1.4.4 Delimitations This dissertation provides information on tensile and membrane structures, range of choice for materials available in the building industry. A form-finding solution and structural principles are being analysed, but this research does not provide quality assurance, formulas, or methods of calculating such structures. All of this information has been complied to the best of my knowledge. It is based on the information provided in the literature and excludes any liability. All rights to the photographs are property of photographer; refer to the list of figures.
1.4.5 Methodology This dissertation is based on qualitative research and empirical quantitative methodologies. Most of the data in the report is provided by books and articles. Some of the information found in the dissertation is based on my own experience and analysis.
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/ INTRODUCTION TO TENSILE STRUCTURES 2.1 INTRODUCTION Present development in architecture is triggered by many factors, probably most important reason is how building industry is driven by construction and technical advancements, and vice versa. While new ambitious and forward-looking architectural designs are created, technology needs to catch up to meet the challenge, boundaries are being pushed. One of the most interesting and exciting part of recent architecture development are undoubtedly tensile structures. They go under few categories, which are membrane structures, pneumatic structures, grid shells and cable domes. Thanks to theirs unconventional design attract attention, and physical properties, have a very good performance, and new range of materials provide better and better properties. With increasing ecological awareness and the new technical possiblities, thanks to investment and research on technology, the use of Tensioned and Membrane Structures are greatly expanding in the field of Architecture nowadays. They have been mostly applied in the major event centres, airports, expos and stadiums built in recent years. Due to their ability of spanning long distances without it can be found in such groundbreaking structures as for example Fentress Bradburn Architects’ Denver International Airport, SOM Architects’ Jeddah International Airport, which is the largest roof structure in the world, or Norman Foster’s Khan Shatyr Entertainment Centre, which is the highest tensile structure in the world.
Fig.2 Frei Otto, Olympic Stadium Munich, 1972
Fig.3 Herzog de Meuron, Allianz Arena Munich, 2005
Today, textile structures are found in almost all climatic zones and serve a wide variety of functions. The materials used to fabricate these membranes have changed much since the beginning and now high-tech fabrics, with upgraded properties are being used. The materials commonly used in the preparation of membranes reflect sunlight well, which makes them very effective as covers in temperate, sultry and arid. But they also have good performance in windy and cold zones- while combined with other construction systems. The textile architecture is no longer used solely for the design of roofs, domes or canopies, but is also used to cover the facades of buildings with by pneumatic cushions, like ones in Munich new stadium- Allianz Arena. 7
I would base my research on a case studies of: Millennium Dome, The O2, London, UK, Allianz Arena, Munich, Germany as examples of structure application in large-span buildings. As well as a small-scale case study example of temporary, demountable canopy for amphitheater in Horsens.
2.2 HISTORY Simple tensile structures were used as shelters or tent-like structures for centuries, primarly by nomadic cultures, as Indian’s Tipis, or Mongolian’s Yurt taking advantage of their simplicity, relocation possibilitis and small footprint. As the cover materials they were using animal skins, primitive woven mats, or an intertwined plant fibers.
Fig.4 Sioux Tipi, Fort Yeates
Fig.5 The tent-like structures, of the nomads of Turkestan
Thruough the times their form and use was developing, depanding on region and times. They are still used in impoverished parts of the world, but in developed countries this kind of constructions were forgotten for a long time, pushed to a side as antiquated and inefficient. Gladly in XIX century they were re-invented and are used and developed ever since. The history shows that such types of structures have been built before their structural behaviour was fully understood and described. The early practitioners had to rely on intuition and courage rather than on written knowledge. Even though the idea of Tensile Architecture is basing on a long-known tent like structures, but methodologies needed for the design modern tensile structures were develop not so long ago. That is why we say that this is a relatively new kind of construction. In the modern era their attributes and structural elegance found appreciation and then the search for new forms started. Finally in XIX century, at the times of industrial revolution, many engineers and architects were looking for a new construction possibilities, something that will give height and strength, but at the same time could be light. Fig.6 Vladimir Shukhov, First tensile steel structure, Nizhny Novgorod, 1895
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Among the first ones to further develop the idea of tensile structures were American architect and systems theorist Richard Buckminster engineer, Russian architect Vladimir Shukhov and German architect and German engineer Frei Otto. Shukhov worked on light-weight hyperboloid towers and roof systems and also heir mathematical analysis. His research structured around the various construction forms as gridshell structures. He was the one to design the first steel tensile structure. Richard Buckminster contributed significantly to the development of tensegrity technology and was a precursor to applying a membrane structures in architecture. He was able to create his largest geodesic dome in the shape of the sphere the U.S. Pavillon for Expo in 1967. Frei Otto accomplished his pioneering work by using physical models, conducive to the precise determination of the membrane’s structural characteristics, he incorporated tensile structure idea in the architecture, for example in construction of German pavilion at Expo 67 in Montreal and later designed tensile membrane roof of the Olympic Stadium for the 1972 Summer Olympics in Munich.
Fig.7 Vladimir Shukhov , Double curvature steel lattice Shell , 1897
Fig.8 Buckminister Fuller, U.S. Pavillon, 1967
Once boundaries were pushed in the field of Tensile Architecture amazing results were created, and now can admire beautiful and futuristic architectural landmarks, which enraptured attention back in the times they were build, as they still do now.
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/TENSILE STRUCTURES PROPERTIES 3.1 DESIGN AND PROPERTIES Thanks to the unique characteristics and flexibility of architectural tensile structures virtually unlimited designs of distinctive elegant forms can be achived. Less support columns create more functional, aesthetically pleasing spaces. The majority of large-scale facilities require roofs of 1000 m2 or greater. For industrial facilities, such big cubic capacity space is not exceptional, but for facilities as stadiums, or sport halls, roofs require an individual approach and advanced design solutions. The specificity of such design requires development of structural systems that eliminate internal support in the form of columns or structural walls, that is where the application of tensile structures is the best solution. Proper materials should be chosen to correspond to the designs in order to obtain optimal architectural and technical effects. Such characteristics as reflection, absorption and scattering should be taken under consideration. Membrane diffuses the sound, with absorption and reflection working in a non-accumulative action. The absorption and transmission of light in each wave band change depending on type of material used, but most of the materials used in membrane architecture have relatively good light transmission. In daylight, the membrane's translucency offers soft diffused naturally lit spaces reducing interior lighting costs. At night, the artificial lighting creates an ambient exterior luminescence.
Fig.9 SOM Architects, Fabric tensile roof at the Jeddah Airport, 1977 For form finding, structural analysis and cutting pattern calculation, a computer modeling is often used, it can considerably upgrade the design time and quality. It is the procedure in which the shape of the surface is determined by the interaction between geometry and forces. Mechanically stressed contours and slopes of lines have to be determined, static analysis is based on a nonlinear system into which starting values are entered after form finding. It offers force-finding tools for optional pre-stress, flexibility and sensitivity integration. 10
It is important, during the design of tensile structures, many aspects such as weather resistance, optical, acoustic properties and the physical parameters should be looked into deeper than it is done in conventional type of construction design process. That is due to of limited number of precedent projects and limited choice of membrane materials. Appealing structures and detailed solutions, as well as new methods of thermal and acoustic separation contributed to the process . The installation process should be anticipated and planned during the design of the structure, especially if it is large project, that needs special construction solutions. An appropriate method should be developed, taking into account all the conditions, the stability of the structure, handling the material and the weather conditions. As well specific instructions should be provided to installers. Unlike traditional structures, membrane structures are primarily under tension and have characteristics that set them apart from other forms. With greater creative possibility inevitably comes greater technical competency. In the design the calculation of the magnitude of the forces, design details of the structural parts and connections, a form to be applied in predetermined sequences of assembly must determined. That is why when using membrane structures, it is often structural designer who manage the project.
3.2 CONSTRUCTION Once the structure is designed, the process of membrane manufacture and structure installation begins. First step is to adapt the chosen membrane material for application. For a simple free-standing canopy structure the preparation is easy and most adjustments can be made on site. If the design of a big scale project the special manufacture of tensile membranes is needed. Material is cut by plotters, following the designer-developed pattern. Once the patterns are prepared, they must be joined to form the membrane. There are different ways to attach the panels, depending on the type of work and the fabric chosen. The junctions is then sewn and welded by high frequency. After the manufacturing of the membrane is completed the packed and transported to the installation site. Transport is an important part of the process, as to protect each of the parts of the membrane from potential friction and shock, it should be folded to make the installation on site easier. Once that is done, then the membrane must be mounted of to the perimeter poles structure. The installment of the membrane depends on its type, if it is rigid or flexible. Flexible curved edges enable prestressing of the fabric as a result of the tensile force applied on the edge, allowing transfer the normal or tangential stresses on membrane edge system. The rigid edges maintain the fabric in a continuous way through a support structure, which has greater lateral stiffness. For both cases there is a great variety of solutions and finishes that affect the perimeter of material. A special attention should be paid to the dimensional accuracy of the positioning of the support system, as well as proper placement of the plates and anchorage connections. During the lifting of the membrane, it may be necessary to use a cross bar that prevents structure from damage. Very important aspect is to consider the weather conditions of the days in which the construction will take place. In the event of wind force above 25 km / h the assembly is not advised. 11
The construction of Tensile Structures depends on the project scale and techniques used. The above mentioned process is the most common one. 3.3 ANALYSIS OF STRUCTURAL PRINCIPLES OF TENSILE ARCHITECTURE Form and deflection are the most important aspects to analyze while designing Tensional Structure. Engineer has to choose a set of boundary conditions in the process of defining the shape of the membrane. To ensure the stability and withstanding forces a calculation of imposed, wind loads and snow loads have to be taken into account. In general a Tensile Structure is type of construction involving the use of elements on with tensional forces are implied, with no compressive forces action, or bending, giving it great construction advantages. That is the quality that offers possibilities of large spanning and utilizing a variety of free standing forms, innovative structural systems, primarily canopies or domes.
Fig.10 Millennium Dome, structural details
Fig.11 Millennium Dome, Section
Tensile structures fall into two main types, ones that transfer tensile loads into adjoining structures and ones that contain loads within their boundaries. The first type may generate large lateral loads, which can result in the need for additional reinforcement in existing structures, as masts and cable tied to ground will most of the time need a for anchors to resist the loads, as the structure must be securely fixed to the ground, or substructure. For wide span constructions, cables are required for anchoring and stabilization and additionally they need extra ballast. The ones that contain loads within their boundaries have better static performance, but still have to be fixed to the substructure. The characteristics of tensile structures is that there is no stiffness against loading perpendicular to the surface of the membrane, achieved by a cable-membrane structure. It can be increased in two ways, using geometry or using prestressing.
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“The structural behaviour of cable-membrane structures can be characterized by the following equation:
(1) where T1 and T2 are the internal forces in the membrane in the direction of the principal curvature, R1 and R2 are the radii of the principal curvature and F is the external load. In the case of cablemembrane structures only tension forces can develop in the structure which means that: (2) and if there is no external force the following formula can be obtained from Equation 1:
(3) Formula 3 suggests some very important information about the shape of the cable-membrane structure, as to satisfy this formula the only possibility is if the sign of the radii of the principal curvatures are different.� from Teaching the design of cable-membrane structures, by P. Ivanyi
As structures rely on double curvature to resist loads, an imposed download can only be resisted by tension in the horizontal direction, to prevent it from excessive loads, or structural failure. Curved geometric shape created from the rotation of only straight lines is generating a tensional twist of an otherwise flat plane. This shape is an very efficient, loadbearing structural shape when properly arranged. The warping of the shape reduces its tendency to buckle in compression. The duality of this form, its simple beauty and structural strength, blurry the lines between architecture and engineering,. During creation of buildings, and forge connections between the professions. Fig.12 Double-curvature, system basis A form in which the dominant curves both move in the same direction is called synclastic form, when the two dominant axes curve in opposite directions the result is an anticlastic form. So that the bowl-like shape is a synclastic form and a saddle is an anticlastic form. Most tensile structures are based on an anticlastic surface geometry.
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Fig13. Example of anticlastic form There are four generic types of commonly used anticlastic surfaces: the cone, saddle, the hyperbolic paraboloid and the parallel valleys. In essence, each of which is constituted by four elements warped, wherein the degree of twist depends on the choice of conditions perimeter. As the membranes for tensile structures can be formed of different geometrical shapes and are investigated focusing in their particular properties, as the fundamental frequency vary with the level of natural preload. It has no bending stiffness or compression by itself that is why it has to be compressed to act as a structural element. “Conical ‘‘tent’’ shape(...)is a prestressedanticlastic surface; • Ridge ‘‘tent’’ shape is an anticlastic form characterized by a catenary ridge line supporting the membranes between two point supports _masts_ nominally at the edge of the structure. The same concept can be developed in a circular configuration; • Pleated surface shape, where the membrane surface appears folded or pleated, to form an undulating surface of ridges and valleys. This differs from the previous category in that the surface is only slightly, if at all, anticlastic, and becomes synclastic when subjected to loads. Load is carried in one direction; • Saddle form is characterized by a single anticlastic surface;” From: Jurnal of structural engineering / June 2002 / 703 The tensile structures use fabrics to form flexible surfaces, then joining by rigid elements, edge conditions are the provisions of all elements in contact with the membrane and on ropes, masts, arches, beams. Therefore, each surface is the result of the choice of a specific boundary conditions. In order to cope with the varying loads, the structure must be adjusted accordingly.
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Fig.14. Different forms of tensile membranes
To function properly membrane must be pre-tensioned ,atherwise it would not be able to disperse external loads in various directions through tension forces, without forming folds. A few construction methods are distinguished: supported structure (ex.Millenium Dome case study) or pneumatically pre-stressed (ex.Allianz Arena case study), and machanically pre-stressed structures (ex.Tensile Canopy project in Horsens) ;more in the Case Studies chapter.
Fig.16 Gridshell structure
Fig.17 Tensegrity structure
The other important structure concept is tensegrity, it is a form in with the forces of tension and compression are in reciprocal balance, giving great stability results. Its name is created from connecting words- tension and integrity. The rigid elements as rods or beams used as three-dimensional elements, that cannot be in direct contact, but should connected with slender elements. The simple example of the concept could be the bicycle wheel consisting of stressed rods. Tensegrity is still not widely known and used. Based on geometrical shapes and its physical characteristics tensile structures can provide designers and end users with a variety of aesthetic free-form designs, as well a use of tensional 15
membranes that can be used in various projects.
“A space grid structure _SGS_ is a 3D system assembled of line agreements _Engel 1968_, so arranged that forces are transferred in a3D manner. A force applied on the space grid system, typically at a node, is distributed among the axial members. When SGSs have depth or thickness, they are commonly referred to as space frames, double-layer grids, or space trusses. Single layer semi-spherical space grids are commonly known as geodesic domes.� From: Jurnal of structural engineering / June 2002 / 703 For the rigid structure a grid ribs are often used. A steel grid is a special shell structure, most often used as a skeleton for big roofing, or dome-like construction. Basing on strength from its double curvature, in the same way as fabric structures does, but is constructed of a special ribs. Its lattice shells are made of a structural braids, in which many relatively weak, linear elements are linked by many compounds, where they lie on a surface that encloses a space its and its supporting structure consists mostly of steel.
Fig.15 Allianz Arena grid structure design 3.4 THE BENEFITS AND DISADVANTAGES OF TENSILE ARCHITECTURE Tensile fabric structures are an environmentally sensitive medium. They give the opportunity of creating, compliment to the natural environment, an interior-exterior connection, thanks to open spaces, its lighting characteristics and natural light penetrating the fabric. When the material used has a light-transmittance, a combination of a daytime translucency effects and night-time luminosity can give a feeling of being outdoors, together with the security and comfort of indoors. A decreased energy-consuming by reduce the need for artificial lighting during daytime, without any artificial lighting provided, it could completely satisfy the needs of users. Probably the biggest advantage of this type of structures is possibility to designing an architectural form, that can be aesthetically pleasing and allows a high degree of creative freedom. It is particularly suitable for organic shapes with complex geometry. This can be achieved by large spans connections creating results often not achievable with conventional materials and systems. The big performance advantage is its strength to weight ratio that offers savings in complexity and cost of the supporting structure, thanks to utilising a variety of geometrical, more efficient forms. 16
As lightweight tensile structures bear less building load than traditional construction systems and the membrane's elasticity offers better earthquake resistance. The other great advantage is mobility of such structures, if large shelters are required for finite periods of time, then they can be designed for quick relocation and re-erection. Membrane materials offer the benefit over traditional construction ones, the curvature of structure diffuses the sound, with absorption and reflection working in a non-accumulative action. Being lightweight and flexible, fabric interacts better with natural forces than a rigid material. Among the disadvantages of tensile architecture we could name, the conventional buildings in general have longer lifespan. When used as a big-scale building it has a considerably big construction cost and necessity to possibility of heating and cooling costs increase, as it cannot reach the insulation values of hard-walled structures. When it is a pneumatic structure needs to have continuous operation of fans to maintain pressure in the membranes, often requiring extra power supply. These types of structures are not advised to be used for facilities where access restrictions are applicable. In structures where airlocks are usually needed, like for example certain industrial sites. There is still a lot to be discovered in field of tensile architecture, a as relatively new construction not has not so many precedent projects and patents
/ MATERIAL CHOICE AND SUSTAINABILITY SOLUTIONS FOR TENSILE STRUCTURES 4.1 Membrane Materials One of the key components of a tensile structure is the material used. It determines the aesthetic appeal, durability and has a big influence on costing and maintenance. While deciding on the cover material, main aspects that should be taken under consideration are structure-design and location requirements for the building. Membrane cover types used in tensile architecture vary greatly. At the beginning mostly used fabrics were simple textiles, canvas, woven mats, or fibers. Tensile textile fabrics have a great advantage, are generally easy to make and to stretch. However, the properties, durability and selfcleaning properties of simple textile materials are poor. Its properties will change due to outward movement of the coating mould-increasing agent and ultraviolet effects so that its surface and colour will gradually change overtime.
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Fig.18 Different textile membrane materials
Later, as the demands have become more strict, this field started developing. That is why the search for materials more durable than fabric started. As a result now we have a vast choice of materials for membranes and this industry is growing rapidly, more and more new covering materials are created. 4.1.1 PVC- Polyester Reinforced, coated with PVDF Nowadays diverse types of membranes are used among them we have PVC, PVDF, Teflon-coated Fiberglas and silicon-coated Fiberglas. One of the newest architectural membrane materials that is proven to be most cost effective and the most prevalent in Tensile Architecture is PVC- Polyester Reinforced, coated with PVDF lacqueron on both sides. In general, the service year of a PVC membrane material with coated PVDF surface course is over 25 years, while the service year of PVC membrane material with coated PVDF surface course is 10 to 15 years. In order to improve the durability and self-cleaning of this type of membrane material, a PVF or PVDF surface course can be added to the surface of coating. PVC membrane material is cheap and is can come in various colours. PVC (polyvinyl chloride) and PVDF (polyvinylidene fluoride) coated polyester fabrics are the most common waterproof membranes. Depending on fabric weight and coating, warranties of up to 15 years are offered making these an extremely attractive long term solution for any waterproof covered area. Offering good light transmission, they allow diffused natural light to fill the area, eliminating the need of artificial lighting. 4.1.2 Woven fibreglass coated with polytetrafluoroethylene (PTFE) As further developments were made in technology, PTFE came to replace the PVC coated polyester fabric as the material of the membrane structures in Europe. PTFE if an abbreviation for Woven fibreglass coated with polytetrafluoroethylene (PTFE) is a very durable Architectural Fabric available presently in the field . PTFE is essentially inert to environmental contaminants, ultra-violet light, has fire resistant properties and a proven lifespan exceeding 30 years. PTFE membrane material has good durability and does not turn yellow or 18
mouldy in due to atmospheric environment. Additionally, rainwater will flow away after forming water drips on the surface as it has good self-cleaning properties. However, PTFE membrane material is more expensive and is stiffer that the substitutes. 4.1.3 Ethylene Tetra Fluoro Ethylene (ETFE) One of the most exciting membrane materials in the design industry Ethylene Tetra Fluoro Ethylene (ETFE) foil has set the construction world alight with the huge range of potential applications.It is the most comonny used membrane building material of the moment, ETFE foil is a high translucency fabric which isvery economically friendly, practical and show the best properties for big-scale projects. An ETFE roof can be formed either by stretching the ETFE into panels, or or alternatively by supported membrane by a cable net. If finds use in two different forms, as singleply ETFE and as an alternative, ETFE foil can be used to form ETFEcushions. Single ply ETFE provides minimal insulation but maximum lightness. Using inflation units the ETFE cushions provide a lightweight and insulated roof installation and can be manufactured to any shape or size. For glare reduction, alternatively, by adding additional layers of ETFE foil to a cushion, light transmission and solar gain can be controlled. Multi-layer ETFE cushions can also be constructed. The inflated cushions and single ply ETFE are approximately 1% the weight of glass – this means a significantly reduced amount of structural framework is required which in turn has a substantial cost benefit. Its light weight nature, and very similar appearance to glass, means that it is frequently chosen for new buildings, adopting this material in order to achieve large spans without intermediate steelwork. ETFE is often used as an effective replacement for glazing as it transmits up to 95 per cent of natural light and weighs a fraction of the mass and tends to be used to create inside-outside connection in a project. As well as being a low flammability material, the ETFEfoil is also self-extinguishing which means it is a good option when health and fire safety is a specific concern. The foil itself can also be engineered to help control and adapt to solar glare, the foil can be printed with a pattern to provide glare reduction, iincorporating movable layers and printing. A good example of ETFE material is the Allianz Arena football stadium in Munich, where the inflated cushions are lit internally with LED lighting. Other major projects around the globe include the 'Water Cube' Olympic swimming arena in Beijing and the Eden Project in Cornwall, which was the first structure to use ETFE cushions.
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Fig.19 ETFE membrane in Aquatic Center, Beijing
Fig.20 PTFE membrane, Nelson Mandela Bay Stadium, South Africa
With a lifespan of more than 30 years ETFE foil is unaffected by UV light, environmental weathering and pollution and does not become brittle or discoloured over time, ensuring it is a building material here for the long term. Exciting times lie ahead with ETFE foil as ETFE increasingly becomes a vital material in the construction industry. Even though PVC and PVDF are slightly more cost effective and better known. Teflon or PTFE coated materials are used in high value projects as they have better lifespan and resistance to corrosion and degradation. 4.2 Membrane Materials Properties The acoustic properties of membrane material are similar to its optical qualities and include reverberation and transmission loss properties for the various frequencies of sound waves. Furthermore the ceiling can collect the reflection of sound waves to impact upon the indoor acoustic environment. Reverberation and sound absorption properties determine the quality of acoustic properties of buildings with membrane structures. Unfortunately single-layer fabric materials have poor acoustic properties and can result in strong echoes and weak sound absorption. Corresponding architectural measures need be taken to improve the acoustic environment of buildings with membrane structure. There is an ongoing study in this field. There is a number of sound-absorption membrane on the market, the lining can lower reverberation and increase sound absorption but at the same time can degrade translucent qualities. The thermal insulation performance of buildings with membrane structures can be a challenge, single-layer membrane is unlikely to provide a realistic comparison to a traditional construction material. Depending on a type of structure it can be either rather poor, but could be used as a shelter for warm climate. On the other hand it can be really efficient if it is used as a void membrane with air captured inside, more suitabe for cold or mildenvironment. Multi-layer membrane systemcan be made to meet thermal insulation requirements for summer and winter, U-value of 2.7 to 0.8 W/m2K can be achived, depending on a type of form and structure.
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The first type would be a single layer membrane therefore, it is only applied to open buildings or in areas with milder climate and is mostl designed for a shelter,or shadow casting purpouses. The latter one it has a really good thermal parameters due to its air-filled pads. When the thermal insulation property of a building is required to be high, multi-layer membrane structure can be adopted, with air buffer between single membranes. At the same time it is important while designing such structures, to remember about possiblity of creating a glasshouse effect of overheating and that membrane materials are not very good with limiting the impact of external environment. The heat transfer coefficient of membrane material is high, as well cooling-power due to that a special air-conditioning, cooling system is necessary. The substrate of membranematerial is itself non-inflammable or flame retardant. Glass fiber isnon-combustible material, while polyester fiber is non-flammable material. When membrane material is applied in half-open buildings such as the grandstand tent of stadium, the awning of public facilities and architectural art sketches and in temporary structures fireproofing safety need not be taken into consideration. However, when membrane material is applied in a roof system of totally enclosed and permanent buildings, as the fireproofing of a membrane material in terms of fire-proofing, smoke volume, toxicity and structural collapse have to be considered. In enclosed buildings, utilization of PVC membrane or its modern substitutes should be should be taken into account. Another matter connected to the fireproofing of membranes is maintaining the stability of the framework in the case of damage. When the membrane material loses tension, the framework of membrane structure should not collapse. In materials are not adequately suited to the project, then it will be difficult to adequately protect it fire, but as well from damage by tearing, or weak insulation, heat and sound properties. Tensile materials as the covering system for construction are directly exposed to the external atmosphere. To determine the range of application quantifiable data on the following aspects will be necesseary resistance to chemical and biological substances like fungi, salt,acids, as well as mechanical abrasion: hail, vandalism. Being affected by natural environment, daylight, temperature variations, rain, erosion and dust, the look of the membrane material reflects its years of service. Present, weather aging tests are undertaken to evaluate the weather resistance of a new membrane materials and new solutions that can withstand more are created.
4.3 Sustainability Parallel to the development of new tensile membrane structures and materials, question of sustainability and recycling of it is arising. After researching their properties and buildability we can assume that they have many advantages, comparing to conventional construction systems, but what can we say about their their adaptation to the environment? Various energy-saving solutions can be incorporated into design of tensile structure. And this aspects have increasingly important role in the tensile architecture. This applies in paricular to the 21
choice of materials and execution of construction. A special approach is needed to determine the range of application ofthe aspects as cradle to cradle or recycling. Materials that tensile membranes are made from, mentioned in previous chapter, as PTFE, fiberglass membrane, or ETFE, are a non-toxic, flame-resistant fabrics that features unique properties, while actively neutralizing airborne pollutants and odors. The canopiees and membranes can be made from the recyclable architectural materials such as PVC and PVDF that allows to be recycled into different products at the end of their useful lives. That gives the reassurance of making a sustainable choice while designing.
Fig.21; Sustainable solutions for membrane structure Some sustainable solutions are beeing developed in connection with membrane structures, a good example is a canopy that that converts sunlight into electricity by the means of photovoltaics. The prototypesof such are now beeing tested and the further developement onto the big-scale projects is planned. Fitting covering areas of tensioned-membrane canopies with solar panels, has great sustainable potential . As grid shell structures are manufactured with steel, it can be demonted and re-used, recycled an infinite amount of times, saving energy and raw materials every time it is re-processed. The lightweight character of the membranes and the minimal support steelwork required mean that tensile structures are an excellent way to lower construction embodied energy. This makes them a good choice for project that calls for a sutainable approach and environmental responsibility in its design. The variety of sustainable fabric options, together with the re-using of membrane material and steel structure, allows to say that tensile structures work togetherwith the environment, not against it. 22
/ CASE STUDIES FOR APPLICATION OF TENSILE STRUCTURES IN ARCHITECTURE I would like to start analysisng case studies with a simple, small-scale tensile structure and then go further to the big span-constrtions. My purpouse is to investigate and show how application of tensile structures can vary depending on the use purpouse and size of the project and what are the differences in their various properties,materials and costs.
5.1 CASE STUDY TENSILE MEMBRANE CANOPZ STRUCTURE, CAROLINE AMALIE PARK ,HORSENS, DENMARK To look for a good exaple of a small-scale tensile structure, I didn’t have to look far, as there is one in the city of Horsens. A canopy for the amphitheater located in Caroline Amalie Park, the stage area benefits from a conical umbrella structure with a one piece skin, covered with a large sheet of rigid tarpaulin fabric, strong, flexible and resistant material.
Fig.22 Tensile Membrane Canopy Structure, Horsens Park Throughout the summer, it hosts several out-door concerts, monted in spring and disassembled for winter time. It shows advantage of this type of construction- its lightness, feasibility and mobility.It is easy and quick to set up, dismantle, and relocate. It is very light because of its structural stability derived from pre-stressed shape. It spread on a rods, tensioned and connected to the concrete stage by a fixed anchors. Stability in the direction perpendicular to the base support is provided by the angle of the application tool against the guide section or the base suppor,t to which the guide hook is fixed. The core of the construction are 2 masts, which are the main support the he structure. Its assembly includes a base support, guide hook, loop, and a tie. The guide hook has to be fixed to the base support and includes a guide section and hook section. 23
The guide section includes a length of substantially uniform width. The loop attaches to or forms part of the tie, then the guide hook retains the loop. The loop and the tie are in tension. In one embodiment; the tensile structure may be assembled by fixing the guide hook to the base support, temporarily locating the loop in an application tool recess of an application tool, and applying a force to the application tool, which moves the loop along the guide section imparting tension into the tie. Until the loop moves to the end of the hook section and snaps into the hook section, the loop and tie stay in tension.
Fig.23 Mast base for tensional structure
Fig.24Anchor for tensional structure
The canopy material tarpaulin is a waterproof piece of fabric, which is often used for outdoor protection against wind and weather in mild climats. It is made of reinforced plastics like polyethylene, coated with urethane. Used in this particular project mostly due to its low purchase and maintanance costs. Its looks might not be the biggest benefit, but thanks for its durability and parameters it is a good choice for wet climates such as Denmark. It proofs to be easy to maintance fabric, it can help reduce maintenance costs due to its self-cleaning properties. Lightweight structures, as this one can be a more effective solution than traditional ones, offering building owners reduced costs, with considerably lower initial cost than conventional buildings, lower operating expenses, simplicity of design, structural effectiveness, quality and unique style. That is why tensile membrane outdoor canopies, as above case study are a popular product widely used by many residential and entertainment organizations.
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5.2 CASE STUDY MILLENNIUM DOME, LONDON, UK The Millennium Dome was designed by Richard Rogers Architects, in coordination with Happold structural engineers. Built on a 180 acre site, on the 'Greenwich Peninsula' is one of the largest tensile constructions ever built, and the iconic symbol of modern architecture in London.
Fig.25 Richard Rogers Architects ,Millennium Dome tensile structure, London Millennium Dome, as well called The O2, at the time it was built had the world's largest roof, with diameter of 365 meters – symbolizing the number of days of the year. The height of the Millennium Dome is 50 meters, and if including the support towers 100 meters. Inside we can find 30 commercial halls, of which the largest is the O2 Arena, which is intended for up to 24 000 people, what makes it the largest Multi-Purpose Hall in Europe . The Millennium Dome was built to house a major exhibition celebrating the beginning of the millennium. It opened on January 1, 2000 and closed on December 31 of that same year. The original exhibition complex was demolished, but the shell of the dome remains, the costs of maintaining it are approximately £1 million per month. The Millennium Dome is now centrepiece of the The O2 entertainment district with an indoor arena, exhibition space, a music club, a cinema, bars, and restaurants. The facility will also be used to host the basketball and gymnastics competitions in the 2012 Olympic Games. The public monies expended in the Dome construction and maintenance will be recouped to a modest degree through this converted temporary use. Although it is called dome, in reality it is not. It is a cable-suspended membrane structure, due to its physical properties it cannot withhold its own weight and require structural support of a cable network and structural masts. In the plan view it resembles a large white tent with yellow masts, one for each month or for every hour of a clock face. 25
Fig.26 Stucture of interior, Millenium Dome
Fig.27 Roof Plan, Millenium Dome
The canopy is made of glass fiber cloth coated with PTFE, a durable and resistant to harsh and rainy weather plastic, which has an estimated minimum lifetime of 30 years. The entire roof structure weighs less than the presured air contained within the building . Roof symmetry is interrupted by a ventilation hole at shaft Blackwall Tunnel. The project was frequently discussed by the press, regarded as the failure- poorly planned, badly carried out and leaving the government with problem of what to do with it later. Numerous changes at management and leadership before and during the exhibition, had limited or no results. A total of 7 million people visited the exposition, compared to the original estimate of 12 million visitors. 628ÂŁ million was used to finance the project, making it one of the most expensive tensile membrane structures ever made. There was a widely discussed controversy and public energy expended in delving into the reasons why the Dome project failed to live up to expectations are the further hidden costs, that arise during implementation process, that are never to be recovered. The cost of Dome cannot be rationalised very readily and ultimate worth of the project should be measured by how well future mega projects will be handled. Unlike the press, reports from visitors were extremely positive, but still the building was not as big success as planned, now being only partly used.
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5.3 CASE STUDY ALLIANZ ARENA, MUNICH, GERMANY The Allianz Arena was designed by Herzog and de Meuron Architects with co-operation with Arep structural engineers. Its floor space is 171.000 m², it has a use of football stadium and is located at the northern end of the Munich. The constriction took place from autumn 2002 to spring 2005, its total costs amount 375 million €, included 11 million for the cover, excluding steelwork. With a surface of 65,000 square metres, it resulted in a price of 170 € per square metre. On the sides facade stretches with its elegant canopies made with eight-meter-long honey-combs, showing artistic approach towards architecture and engineering. It was the architects’ intention, to create a metaphorical ropes connected in the ring shape, to wrap around the stadium to bond the audience together. The nuance about the stadium is that in the evening the facade glow from a distance, the inflated cushions are lit internally with LED lighting to make them shine in varying shades, with the symbolic colour of currently paying team, red for FC Bayern Munich games, blue for those of TSV 1860 and white for neutral games.
Fig.29 Arena lit in different colours, depending on an event Pads with an area of 35 square meters each are made of a diamond metal panels covered with cushins made of ETFE (ethylene-tetrafluoroethylene copolymer) at a pressure of 35 hPa, and each one of them has a slightly different shape. Arena membrane skin consists of a 2874 such air bags with a total area of 64.000 square meters. It is the world's largest roof made of foil. This film has a thickness of only 0.2 mm and transports up to 98% of UV rays. The cushions consist of two single layers made of the thin foil. Both foils, the upper and lower, need a pre-stress to bear the external loads, like wind uplift, wind download and snow load without wrinkles. 27
“This was the first really large pressurized-cushion ETFE structure built. There were some design problems to resolve because of its scale, but it’s really a multiplication of design elements that were already proven. When we first saw Herzog & de Meuron’s design proposal, they wanted to use polycarbonate panels, but we recommended the use of pressurized ETFE cushions, due to the fact that this material won’t burn without a supporting heat source. Its transparency also allowed us to fulfill the lighting element of their design proposal. From a design perspective, it was fortunate that we were able to change from the initial concept of polycarbonate panels to the ETFE cushions,” adds Hupe “We were able to increase the size of the diamond-shaped elements to more closely match the architectural scale of the structure” Richard Fuchs, managing director of R+R Fuchs Ingenieurbüro für Fassadentechnik, the structural engineering firm responsible for the façade
Fig.31 ETFE membrane, Allianz Arena Fig. 32 Construction of Allianz Arena The choice for this material was made at an early design stage, at a time when ETFE was still quite unpopular and only sparse references of small surfaces could be shown to prove the feasibility of the concept. Every panel has a transparent inner. Those forming the facade have a translucent white outer, but the roof panels are completely transparent, allowing sunshine and light to fall onto the pitch. To provide sun- and noise protection during events, variable curtains are arranged below the roof structure and as a roof canopy is movable it can be slide to the side, as weather conditions allow. Big ventilators located under the stadium, have to pump up air into the structural membrane panels.
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Fig.28 Site &Roof Plan, Allianz Arena The construction of the stadium is a concrete bowl and steel truss roof construction, providing high load bearing capacity and low friction force. The structural system for the bowl is based on multi-storey reinforced concrete sway frames with some stability provided by the eight stair and lift cores. The frames are approximately 8m apart and placed concentrically on 96 gridlines around the pitch. Some variants and auxiliary gridlines were required in the corners.
The main beams are arranged radially with a diamond-shaped grid spans, structure loads are sustained on 48 main cantilever beams, made of parabolic steel truss girders, approximately 65 m long and weighing up to 106 t. A Secondary roof structure forms a rhomboidal ‘steel net’ within which the panels are supported.. Membranes are stretched in between, with connections made by clamping a line welded over the edge of the covering skin, required due to the spatial geometry of the connections. A special calculations and planning was necessary to calculate and implement such advances structure. Project was developed using Arup engineers specially developed parametric stadium design software. The installation was implemented without scaffolding, but by means of specially trained freeclimbers. Fig.30 Section, Allianz Arena Basing on the above researched case studies I can say that Tensional Structures can be successfully applied in various construction types and both big and small projects can advantage from its uncial properties. 29
/ CONCLUSIONS Before starting my research I had already a great interest in the topic of “Application of Tensile Membrane Structures in Architecture�, but now I appreciate the advantages of it even more. During this dissertation I have considered the subject from technical and pragmatic perspectives. I have learned a lot about researched kind of structures and new types of membrane materials available at the market and found much new for me information in this field. I believe that in this dissertation I was able to interest the reader into discovering more about the subject and hope that in the future membrane architecture and special structures will become more commonly used. Supported by precedent case studies I have researched that Tensional Structures can be successfully applied in various construction types.. Those examples could serve as an illustration to the feasibility of application of a lightweight structure to cover large spans buildings but as well taking advantage of these structures in small-scale projects. Its parameters can vary significantly depending on design type and materials used. Unfortunately the disadvantage showed in the bigscale projects is economical aspect. Using this kind of structure is expensive and due to limited number of previous examples of such buildings there are often unexpected hidden costs. To search for the kind of covering membrane materials that can give the good results and assure durability. In the material section I was able to look into fabrics available in the field now and compare them. As diverse types of membranes used in tensile structures, such as PVC, PVDF, Teflon-coated Fiberglas are commonly used. PVC and PVDF are more cost effective. Advancements in the technology of tensile and membrane structures are continually occurring and there is no doubt that as technology increases the quality of the materials used and their durability will also get better. That is why I believe the prognosis for future development in the Tensile Structures field is positive. The on-going innovation in computing techniques, material and digital fabrication technology is changing the field. It will revolutionize the design, analysis and construction of tensile membrane structures. A new analysis tools will enable the accurate prediction of structural behaviour and manufacturing processes. In order to improve cost-related aspects and sustainability it is important that new techniques are developed. It is hoped that new methods and modern materials will be developed to make membranes structures more durable and architecturally Society wants more functional and impressive buildings. If tensile structures are to meet their full potential, then they need to be well designed. The further research in his branch of construction is needed to make it not only more technologically developed but as well environmentally friendly. There are still many aspects that have to be advanced and more sustainable approach is needed. It will making the application of such structures more common, and economically efficient practice.
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/BIBLIOGRAPHY Berger H., 2005, Light Structures - Structures of Light: The Art and Engineering of Tensile Architecture, Bloomington, USA: Author House Bing W. B., 2004, Free-stading Tenson Structures From tensegrity systems to cable-strut systems,London UK: Spon Press Forster B., Mollaert M. 2009, Built environment in Europe through tensile structures, Grecco C. Carlo Santoro, 2008, Beijing- the new city, Milan: Skira Editore Jeska S. , 2009, Transparent plastics Design and technology, Berlin, Germany Kaltenbach F., 2004, Translucent Materials, Munich, Germany: Detail Praxis Sandaker B., 2010, On Span and Space, Exploring structures in architecture London, UK:Routledge Uffelen Ch. , 2008, Pure Plastic new materials for today’s architecture, Munich, Germany Publications available from the websites: Material studies Weber, Ireland. [online] Available at: <http://www.weber.ie/construction-mortarproducts/find-the-right-solution/case-studies.html> Millennium Dome Report. [online] Available at: <http://www.ukessays.com/essayexamples/marketing-essay-examples/millennium-dome-report.php> Shade to order. [online] Available at: <http://shadetoorder.com/> Tensinet. [online] Available at: <http://tensinet.com/> Unique Inflatables. [online] Available at: http://www.uniqueaesthetics.com Wikipedia. [online] Available at: <http://www.wikipedia.org/> Articles Baraona Pohl E, 2008 ,Watercube Bradshaw R. Special Structures: Past, Present, and Future Journal of structural engineering / June 2002 / 709 Garcia Ch. / El Pabellón de Venezuela en la Expo 2000, Hannover Hemmington, N., Bowen, D/Satisfying the basics: reflections from a consumer perspective of attractions management at the Millennium Dome, London/ International Journal of Tourism Research/ 2005
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