Giydirme cephe çift cam ünitelerinde rasyonel boyut seçimi
Selection of rational sizes for double glazing units in curtaion walls
- Tez No: 21900
- Danışmanlar: DOÇ. DR. OKTAY CANSUN
- Tez Türü: Doktora
- Konular: Mimarlık, Architecture
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 139
Özet
ÖZET Çok katlı binalarda yaygın olarak uygulanan giydirme cam cephelerin bileşenlerinden biri olan çift cam üniteleri bu çalışmada geometrik konfigürasyonu ve rüzgar basıncı karşısındaki mekanik davranışı yönünden incelenmiş tir. îlkin cam türleri, bunların fiziksel özellikleri ve ünitelerin oluşturulması açıklanarak cephelerin eğimli olması durumunda ortaya çıkan sorunlar ile geometrik özel.J- likler belirlenmiştir. Daha sonra rüzgar basıncının etkisi irdelenerek, plakların eğilme dayanımını belirleyen faktörler ve kırılma olasılığının saptanması açıklanmıştır. Dayanım verilerinin hesap değerine dönüşümü tanımlanarak rüzgar ve cam para - metreleri arasında ilişkiler kurulmuştur. Rüzgarın davranış şekli ve hızını belirleyen faktörlere yer verilerek binaların rüzgara karşı olan tepkisine değinilmiş ve bina ile cephe boyutlarının etkisi irdelen - mistir. Meteorolojik verilerin değerlendirilerek rüzgar hızının belirlenmesi bir ekstrem veri analizi yöntemiyle gerçekleştirilmiştir. Rüzgar hızına bağlı basınç ve cam boyutu bağıntılarına geçilerek daha önce yapılan çalışmaların sonuçları özetlenmiş ve ayrıca titreşim etkisi incelenmiştir. Eğime bağlı olarak ünitelerdeki dış ve iç cam plakların kalınlıklarını belirleyecek yöntemler açıklanmıştır. Plakların rüzgar basıncı ile olan ilişkilerinin ortaya konmasından sonra çift cam ünitesinin bir bütün olarak davranışı irdelenerek geometrik ve mekanik parametrelerin dış ve iç cam plakların karşıladığı basınç oranlarına etkisi belirlenmiştir. Yukarıdaki bölümlerden yararlanarak çift cam ünitelerine yönelik bir performans değerlendirme yöntemi geliştirilmiş ve etkin algoritmalar kullanılarak bilgisayar ortamına aktarılmıştır. Yöntemin uygulanması ile elde edilen sayısal sonuçlar ve yapılan çıkarımlara çalışmanın sonunda yer verilmiştir. xıı
Özet (Çeviri)
SUMMARY SELECTION OF RATIONAL SIZES FOR DOUBLE GLAZING UNITS IN CURTAIN WALLS High-rise buildings constitute a large part of current architecture. Gn these buildings the application of curtain walls have been significantly increased due to their attributes such as appearance, ease and speed of erection, high manufacture standard, acceptable thermal and weather resistance. The improvement of materials and manufacture processes by advanced technology has now enabled this type of cladding to become a satisfactory solution. Another advantage of curtain walls is the versatility they provide to form inclined plane arrangements. However in the design stage elevational alternatives are only evaluated in terms of aesthetics and cost. No method exists which enables these alternatives to be compared in terms of rational use of materials. The decision may be arbitrary“or made on an unreliable intuative basis. Consequently higher cladding and maintenance costs may be encountered together with reduced performance. On a larger scale these performance and economical losses will subsequently reflect on to the manufacture industry, adversely affecting its function and impeding development and progress. These consequences would be averted if selection of the elevation grid is made by an analytical method to achieve efficiency in elevation design. The curtain walls in question consist of 3 main components : 1. Carrier Frame: Anodized or electro-static polyester powder coated, extruded aluminium sections form storey- high mull ions and shorter length transoms. 2. Double Glazing Units: 2 Glass plates are assembled together by means of an aluminium spacer and elastomeric seals with an air space in between. These are then installed into the carrier frame and jointed with the frame by continuous gaskets. Effective dimensioning of these units has been the primary subject of this thesis. 3. Fixings: The mull ions are suspended from the edge of the floor slab above and connected to the one below by means of a sliding joint, where as well as at the mullion- transom junctions, spigots are mostly used. xiiiGlass can be.. defined as an inorganic material which retains its amorphic molecular structure also in the solid state. Considering the mechanical properties it is hard and brittle, has a high compressive-, but low tensile strength. Under tensile. stresses glass fails readily due to brittleness and the presence of structural irregularities in the form of microcracks in the glass surface. No plastic deformation occurs at the point of failure. The tensile strength can be improved by implementing a thermal process called tempering (Float Glass: 30 N/mm2, Tempered Float Glass: 50 N/mm2 ). on most curtain walls float glass is used which has more regular and parallel surfaces and is produced by floating molten glass mixture over a bed of molten tin. The tempering process involves rapid codling of heat softened glass plates. Hence both surfaces contract while the inside remains hot. When the plates cool down a residual compressive stress in induced on the surfaces and a tensile stress in the middle. Under an imposed external load such as wind load the resultant tensile stress on the surface which actually initiates fracture, will then be reduced. &ie constraint on the use of tempered glass is that it can not be cut or drilled after having being processed. For curtain wall applications the outer plate of the double glazing unit is chosen as reflective tempered glass and the inner plate as clear float glass, the reason being that the outer one will be subjected to large wind pressures or to impact by projectiles. If the inclination of the elevation plane is large, then laminated or wired glass is used on the outside. as a safety precaution. Also for solar control the outer plate usually has a reflective metallic film located as an interlayer or adhered to the inside surface of this plate. Double glazing units have a complex mechaniaal behaviour under the influence of wind pressure due to the interaction of both plates through the sealed air gap in between. As unit dimensions and wind pressure increase this interaction becomes more significant. Maximum unit dimensions are dictated by the manufacture processes. Various national standards give diverse values for maximum dimensions. In the case of a building having inclined glazed planes, these are exposed to more demanding structural and climatic conditions than vertical planes. Special problems that arise include. 1. Excessive deflection of mullions due to longer spans and the glazing self weight and snow components of the total load. 2. Increased risk of water penetration through the joints, receiving more rain. On a rational elevation grid the total joint length should be reduced and therefore the size of the double xxvglazing units increased, in effect reducing the number of mullions. and transoms. As a result less material will be used in the carrier frame and the risk of water penetration will also be reduced because there will be shorter lengths of joints per unit. The planar geometry of rectangular units can be expressed as a function of small and large dimensions (a,b) or alternatively of glass area (A) and ratio of large and small dimensions (n).. The combined parameter describing the geometrical property of the unit can be called as its' compactness ratio (c). As the unit area increases or circumference decreases the value of c increases. However having larger units has the drawback of requiring thicker glass plates. This fact jeopordizes effective use of glass as a constructional resource. Therefore an optimization of parameters A, C and n is required. In this thesis the optimal values of these have been found to bellying within the limits below: ' 1.0 < n « 2.15 and (0.23 /A)4 C < (0.25 /a) Due to the amorphic composition of. glass there will be variations on the bending strength of plates in every batch produced. When there is a choice to be made between different batches it would be advantageous to choose the batch with the smaller average strength and narrower strength distribution rather than the batch with a higher average and wider distribution. Factors which determine the strength of glass are as follows: Dimensions of the plate, wind, load duration and frequency, surface characteristics (location, size and direction of micro e- racks) moisture, heat and chemical environment. On a plate under stress the initial crack may not always occur at the point of maximum stress. Micro cracks also cause stress concentrations and lower the allowable maximum stress. If the direction of the cracks is not parallel to the direction of principal tensile stresses fracture is. more likely to occur. The probability of failure can be predicted by the 2 or 3 parameter Weibull distribution function based on statistical values for sample failure stresses. Since the failure stress (Pf ) is dependent on load duration, Pf values for different durations are transformed into a standard equivalent 60 s. value to represent the strength of a plate of a certain size. The wind pressure is related to the wind speed which is influenced by the following factors: Geographical location, Altitude, Orientation, Seasonal variations, Ground roughness, Building height and form, Topography. A linear regression method has been chosen for the analysis of extreme data to determine the probability of a given maximum wind speed not being exceeded in a given period. Large rigid buildings are considered to behave statically under the influence of wind. As the wind speed varies across the building surface advantage can be taken of the average wind speed. The gust wind pressure is determined mainly by the building height and diagonal length. A. relationship has been derived for determining the response xvby a multiplication factor according to preferences. The weighting would then be reflected in the global results. The method has been transferred to computer environment in Pascal 5.0 high level language using. efficient programming algorithms. To operate the program the user is requested to specify the following data t 1. Relevant maximum wind pressure 2. Inclination angle of the glazed elevation 3. Acceptable minimum small -dimension and maximum large dimension of the double glazing unit 4. Dimension increment The calculated performance values are displayed in descending order of magnitude with the corresponding unit dimensions and both plate thicknesses. The following general conclusiona may be drawn from the numerical results obtained by this method: 1. The largest size of unit has the maximum Geo.P.V. at all wind pressures. 2. The size of the unit with- the maximum Mec.P.V. varies, non-1 inearly at different pressures. 3. Considering maximum Glo.P.V., as pressure increases both dimensions, decrease,, but the small dimension decreases at a higher rate than the large dimension. 4. As pressure rises Geo.P.V. falls, but Mec.P.V. and Glo. P.V. rise. 5. At low pressures Geo. P.V. is higher than Mec.P.V. and at high pressures lower. 6. As the inclination angle falls Geo.P.V. falls as well while Mec. and Glo. P.V. rise. Also as the pressure rises the variation in performance values falls. XVlllThe influences of these parameters as they vary, have been summed up below: 1. Small (a/t]_) results in small deflections due to rigidity and a larger part of wind pressure is then carried by the windward plate* 2. Also at small (a/t-j_), P3 increases non-linearly with (s/t^. 3. As (t2/t, ) increases P, decreases. 4. In the case of pressure bfeing applied from the opposite direction, as (t2/t, ) increases P, again decreases. 5. As (b/a) increases, rigidity and consequently P, increases. For constant plate area the increase is more on rigid units than on flexible units. In the final part of this thesis a comparative analysis method has been proposed for evaluating at any given wind - pressure and inclination angle, the geometrical and mechanical performance of double glazing units of different sizes. In order to be able to conduct the comparison the 2 dimensions constituting the size of a unit have been represented in a triangular matrix which is then transformed into a vector. To assess the performance of units 3 criteria have been. established in the light of the previous parts: 1. Geometrical Performance Value (Geo.P”V.): The ratio of the compactness ratio and the^sum of the windward and leeward plate thicknesses (C/(t-, -+ t2J) is required to be, as high as possible implying a "high compactness ratio and a low plate thickness. Hence a unit with a relatively large size and thin plates will have a- high Geo. P. V. 2. Mechanical Performance Value (Mec.p.V. ): The. percentage of wind pressure carried by the. windward plate (Pd.) is required to be as near to 50 % as possible. Ideally when both plates carry the same amount of pressure (50 %) then maximum performance would be obtained from that unit. If however P^ approaches 100 % then this would mean that the leeward plate would be making a very small contribution mechanically. 3. Global Performance Value (Glo.P.V.): This has been defined as the arithmetic mean of Glo.P.V. and Mec. P.V. expressing the overall performance of that unit. Absolute performance values are then converted into relative values between 1 and 100 by linear interpolation. The upper and lower limits are initially established by maximum and minimum sizes and wind pressures. Depending on the circumstances in which this evaluation is to be applied/ any one or more of these criteria may be selected by the user. If the global performance is selected then the geometrical or mechanical performances may also be weighted xviiby a multiplication factor according to preferences. The weighting would then be reflected in the global results. The method has been transferred to computer environment in Pascal 5.0 high level language using. efficient programming algorithms. To operate the program the user is requested to specify the following data t 1. Relevant maximum wind pressure 2. Inclination angle of the glazed elevation 3. Acceptable minimum small -dimension and maximum large dimension of the double glazing unit 4. Dimension increment The calculated performance values are displayed in descending order of magnitude with the corresponding unit dimensions and both plate thicknesses. The following general conclusiona may be drawn from the numerical results obtained by this method: 1. The largest size of unit has the maximum Geo.P.V. at all wind pressures. 2. The size of the unit with- the maximum Mec.P.V. varies, non-1 inearly at different pressures. 3. Considering maximum Glo.P.V., as pressure increases both dimensions, decrease,, but the small dimension decreases at a higher rate than the large dimension. 4. As pressure rises Geo.P.V. falls, but Mec.P.V. and Glo. P.V. rise. 5. At low pressures Geo. P.V. is higher than Mec.P.V. and at high pressures lower. 6. As the inclination angle falls Geo.P.V. falls as well while Mec. and Glo. P.V. rise. Also as the pressure rises the variation in performance values falls. XVlll
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