Betonarme kabuk yapılar tarihi gelişimi ve geleceği
Concrete shells, their historical developments and future
Yazar: KENAN KOÇYİĞİT
Danışman: PROF. DR. KAYA ÖZGEN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Mimarlık Ana Bilim Dalı / Yapı Bilgisi Bilim Dalı
Derece: Yüksek Lisans, 1997
Konu: Mimarlık = Architecture
Dizin: Betonarme = Reinforced concrete ; Kabuk yapılar = Shell structure ; Tarihsel gelişim = Historical development

Özet:
Kabuk yapılar sonsuz sayıda form üretme kabiliyetine sahip, malzeme kullanımında ve büyük açıklıkları geçmede son derece etkin sistemlerdir. Bu tezde, taşıyıcı sistemler içinde ayrı bir yeri ve önemi olan betonarme kabuk yapılar, tarihi gelişim süreci içinde tanıtılmaya çalışılmıştır. Çalışma dört bölümden oluşmaktadır. Giriş bölümünde kabuk yapıların tanımı yapıldıktan sonra kabuk çeşitleri belli bir sistematik içinde sınıflandırılmış, bu sınıflandırma içindeki farklı tiplerin strüktürel Özellikleri anlatılmıştır. İkinci bölümde ^betonarme kabuk- yapıların gelişimi tarihsel bir süreç altında değerlendirilerek, modern kabuk uygulamalarından örnekler verilmiştir. Üçüncü bölümde kullanılan çağdaş kabuk tejmikleri anlatılmış ve geleceğe ışık tutan günümüzün seçkin örnekleri ele alınmıştır. Son kısım olan değerlendirme ve sonuç bölümünde ise betonarme kabukların günümüzün geniş açıklık geçmede kullanılan diğer alternatif sistemlerle kısa bir karşılaştırılması yapılıp, gelecekle ilgili değerlendirilmesi yapılmıştır. IX

Abstract:
Shells are the systems which have a form of a surface or a combination of surfaces in space. They are three dimensional structural systems that carry the loads to the supports primarily through the action of membrane stresses and this makes possible to obtain an efficient use of material. Their thickness is considerably small compared with the other dimensions. Having rigidity from their geometry, they can cover large spaces without using interval supports. According to the surface curvature shape, shells can be classified under two headings: Single curvature and double curvature shells. Double curvature shells can be in the form of dome (curvature on the same direction), can have horse saddle form (curvature on the opposite direction) or can have combination of these forms. Except from geometrical shapes, there are structural behavior difference between single and double curvature shells. In the ideal way, all the loads are carried by the membrane stresses in the system without creating bending moments. Cylindrical shells are the most common single curvature shells that are used widely in buildings. The structural behavior of them can be described as a beam behavior in the longitudinal direction and a special arch behavior in the tranverse direction. Engineering therminology divides the long barrel and small barrel because of their different structural characteristics. If the ratio between the length and the width is more than two the cylindrical shell is called as long barrel. It is the ideal type that the loads form axial membrane forces. Small barrels have different structural behavior that necessitate special structural solutions because of the extra bending moments occurring in the shell section. The double curvature shells are very efficient structures compared with single curvature shells. The most common type of double curvature on same direction is the dome form. According to the membrane theory, on the ideal supporting condition, meridian forces consist of compression forces only and hoop forces over the neutral axes are compression, under the neutral axes are tension forces. If the ideal supportingcondition can not be applied, for example on a pointed support condition, by using pre-stressing or transition arch solution, ideal membrane stress distribution can be obtained. Hyperbolic paraboloid is the most important double curvature on the opposite direction form. Compression forces occurs on the upward parabolas direction and tension forces occurs on the downward parabolas direction. If any shape deformation occurs by the compression forces, the tension forces resist and avoid the deformation and by this way an extreme rigidity is obtained. For around 2000 years single and double curvature shell structures have been used to cover large span buildings. In the Roman period Pantheon, in the Byzantine period Hagia Sophia had the largest domes of their time. Middle age and Rönesans period produced many domed forms which can be accepted as pioneering examples of modern shells. Generally, these were constructed from masonry, brick or unreinforced concrete, materials strong in compression but relatively weak in tension and have a very big span-to-thickness ratio. However, with the advent of reinforced concrete which is a mouldable material strong in both compression and tension, it became possible to construct thin shells with span-to-thickness ratios commonly in the region of 500:1. Invention of the reinforced concrete gave large possibilities to builders and at the beginning of the 20ft century it led to the construction of reinforced concrete shells. One of he earliest domes in reinforced concrete is Constanza Mosque in Romania, built in 1905 by the Romanian engineer Gogu Constantinescu. The Centennial Hall, built in Germany in 1912-1912 by Max Berg also can be accepted as a representative of a new era. However the real golden age of shells began in 1920, when Carl Zeiss built a 15 mm. thick, small experimental shell in Jena and W. Bauersfeld and F. Dischinger settled the problems of the theory and erection of domes and cylinders and created the Zeiss-Dwidag patent. Thus, the first modern shell, designed and built with the knowledge of structural mechanics, was the experimental planetarium in Jena, completed in 1923. The first hyperbolic paraboloids were constructed in by Giargo Baroni from 1934 through 1937. Konrad Hroban who used this form his projects in XICzechoslovakia made some theoretical studies about this subject and after 1940's, his forms were used widely in industrial buildings. Two European engineers had important roles on the development of shell form. On of them is Eduardo Torroja whose productive years span to the period from the twenties to fifties. The other one is Pier Luigi Nervi who had used different technics in shell construction. The Market Hall, built in Algericas, Spain by Torroja is one of important buildings in the shell history because it is the first dome in polygonal boundary. His other projects are Hipodrome Grandstand (1935) and workshops of Torroja Institute near Madrid (1946). Torroja and Nervi both had an immense influence on the conceptual design of shells and the development of form, both through their own works and through their publications. The Cement Hall, erected in Swiss National Exhibition, Zurich in 1939 can be described as an exhibition structure demonstrating the potential of thin shells. The second world war interrupted for a time the building of reinforced concrete shell structures but in 1947 they won again their place, by the halls of the Brynmawr Rubber plant covered with elliptical paraboloids. In the United States of America two remarkable shell roofs were constructed in 1954-1955, the St. Louis air station by Yamasaki and the auditorium of the Massachusetts Institute of Technology by Saarinen. In France the noteworty structure of this kind is the exhibition hall of the National Center of Industry and Technology built in 1957. It is the so far is the largest span reinforced concrete structure. Two remarkable structures were built in Rome in 1958 and 1959 by Pier Luigi Nervi, the Small Sports Palace and the Sports Palace. They are important structures because they had a unified concept of design and construction that optimizes the various factors of structure, architecture and construction, based on prefabrication. Working in the tradition of such masters as Torroja and Nervi, and acting of as a designer and a builder at the same time, Candela demonstrated not only the basic economy of the hyperbolic paraboloid, but also its dramatic architectural possibilities. He used the true potential of the hyperbolic paraboloid in a series of projects like Los Martinez Restaurant, built in Xochimilco, Mexico in 1958, San Jose Obrera Church in 1960 and many other churches built in this form. xuTWA Terminal, built in New York Kennedy Airport is an interesting build that has to be mentioned about. Although this exciting curvilinear composition, designed by Eero Saarinen in 1962, is not a real shell in terms of its thickness, it has left an inspiring mark on the development of thin shells. The Sydney Opera House, built between 1957-1973, stands as a gigantic sculpture showing the impressive possibilities of the shell forms. The main characteristic of the shell structures is to span large spaces with a minimum section. They are economical in the consumption of materials. Structural efficiency and the lightness are the other positive points of the shell structures. But the high cost of the formwork and the labour intensive traditional construction, oriented the builders to find alternative construction technics. Special pneumatic forming, plastic foam forming are alternative formworks that have been used for several projects. Fiber-reinforced shells also give great expectations for the future. By prefabrication of the shell elements and assembling them on a re-usable form work with the post-tensioning method is another solution for the economy of the construction. Nervi had used this technic for his several successful projects. Shell structures were used widely for medium and long span roof structures from 1920's until the !970's that is the period when steel was often in short supply. Since the 1970's, one of the reasons of the decline in the use of reinforced concrete shells is the structural steel sections available at competative prices. Space frame structures and the tensile membranes which have enabled architects and engineers to cover large areas with lightweight, translucent structures, have taken much of the potential market for shells. On the other hand there are examples that prove the rationality of the shell structures where have been used appropriate design and construction methods. The most important criteria is the distance that the structure spans. Despite the capital cost savings of a steel frame, a steel structure can have huge thermal expansion problems and a lower thermal mass, compared with the higher density of concrete. King Dome, built in Seattle in 1975 proves the validity of using long, thin shell concrete comparable to the span of the Superdome, built in New Orleans in 1975. Norman Foster's torus shell structure is the only rational solution for American Air Musium project in Duxford, England. xiiiMany developing countries do not produce their own steel and can not import large quantities of structural sections for building construction. In these countries labour is often cheap and most construction materials are expensive. Therefore the shell construction can be economical in these countries. The Baha'i House of Worship, built in India in 1987 by Iranian architect, Fariburz Sahba, shows that high- tech concepts do not always demand high-tech solutions. Membrane structures may be inappropriate for some situations because they have a limited life span, depending on the material used, and they are difficult to insulate. On the other hand, modern concrete shells are very durable and they require minimal maintenance as they use good quality, well-compacted concrete which is maintained in compression to eliminate cracking. Sprayed insulation materials can be used to achieve the final shape of the shell formwork without having expensive timber lining. Improvements in concrete technology have also made the task of placing, compacting and finishing the shell easier. Norwich Spor Village, built in England in 1987-1991 demonstrate the advantages of current thin shell construction. All the ten shell roofs of the Spor Village were designed by Swiss engineer Heinz Isler who has more than 30 years experience of the design and construction of reinforced concrete shell structures. He has managed to overcome one of the main problems, the cost of the formwork in his projects by developing re-usable systems. Recently, there is a return to the shell construction for these reasons and with the leadership of the last period shell building master Heinz Isler, many other shell structures are observed to be designed and build especially in England and several other countries. XIVBÖLÜM 1 GİRİŞ 1.1 KABUKLARIN TANIMI Tanım olarak kabuk, 'uzay mekanında bir yüzey formu veya yüzeylerin birleşimi olan bir forma sahip sistemdir' denilebilir [1]. Kalınlıkları diğer iki boyutları yarımda çok küçük olan ve iç kuvvetleri, esas itibariyle, orta yüzeylerine paralel olarak etkiyen gerilmelerden oluşan, sürekli veya süreksiz üç boyutlu taşıyıcı sistemlerdir [23. Tasanmlarmdaki amaç ölü yükün en aza indirilmesi ve strüktürün büyük eğilme gerilmeleri olmaksızın bir membran gibi çalışması için mümkün olduğu kadar ince tutulmasıdır. Yükleri mesnetlere öncelikle yüzey gerilmeleri şeklinde taşırlar ve bu da çok etkili, verimli bir malzeme kullanımına izin verir. Minimum malzeme ile maksimum strüktürel avantaj elde edilmiş olur. Yüzey geometrilerinin sağladığı rijitlikle ara mesnetler olmadan çok büyük açıklıkları geçebilirler. Özellikle çift eğrilikli kabuklar bilinen en etkili strüktürel formlar arasında yer alır. Doğadaki doğal kabukların çoğu da çift eğriliklidir. Yumurta ve çekirdek kabuklan, insan kafatası en bilinen örneklerdendir. Doğal olarak meydana gelen bu kabukların çatlaması veya kırılması oldukça güçtür. Kabuk yapıların taşıyıcı sistemler içinde ayrı bir yeri ve önemi vardır. Mimarlar bu strüktürlerin dramatik mekanlar yaratma özelliklerine haiz formlarından çok hoşlanmışlar, mühendisler ise kullanılan malzemenin maksimum olan etkinliğinden büyük ölçüde etkilenmişlerdir. Aslında mimarlık tarihine bakıldığında anıtsal değerdeki yapıların çoğunun kabuk biçiminde olduğu, en azından bir kabuk elemanından yararlandığı görülür. O zamanki mevcut yapı malzemesi olan taş ve tuğlayla, kubbe ve tonoz yapıda anıtsal bir ifade bulmuş, daha sonraları yirminci yüzyılda betonarmenin bulunmasıyla günümüzün ince kabuk yapılan gelişmiştir. Mimarlık tarihi uzmanı ve eleştirmeni Siegfried Gideon betonarme ince kabuklan büyük sosyal binalan örten güncel tonozlar olarak tanımlar [1]. Kabukların sağladığı strüktürel etkinlik, malzemedeki kazanç, hafiflik, estetik zenginlik, donatı ve temellerdeki ihmal edilmeyecek mertebedeki ekonomi gibi