Boru enkesitli çekme çubuklarında delik çevresi takviyelerinin deneysel incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 55708
- Danışmanlar: PROF.DR. TEVFİK SENA ARDA
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 31
Özet
ÖZET Uzay kafes sistemler, 1950'li yıllardan beri özellikle hareketli yükleri az olan çatı ve benzeri bina bölümlerinde, büyük açıklıkları aşmak için yaygın olarak kullanılmaktadır. Türkiye'de de, özellikle 1985 'ten itibaren, uzay kafes sistemler yaygın olarak kullanılmaya başlanmıştır. Türkiye'de bu konuda imalat yapan şirketlerin, düğüm noktası taşkilinde büyük oranda, Mero tipi benzeri düğüm noktası detayı tercih ettikleri görülmektedir. Bu tip düğüm noktalan, eksenleri birbirine dik, üç doğrultuda ve bunların uzay açı ortaylarında olan diş açılmış deliklere sahip masif kürelerden oluşmaktadır. Boru kesitli çubukların uçlarında hareketli bir bulon ve bunun üzerine bağlı bir somun-manşon bulunmaktadır. Çubukların esasım teşkil eden borularda, boruların genelde her iki ucunda, hem galvanizleme işlemi için, hem de herhangibir anda bulon boru içine kaçarsa onu yeniden yerine takabilmek amacıyla, galvanizleme veya bulon deliği denilen bir delik bırakılmaktadır. Boruda açılan bu delik, hem kesitte bir azalma meydana getirmekte, hem de bulunduğu enkesitte gerilme yığılmalarına neden olmaktadır. Bu nedenlerle, çubuğun çekme kuvveti taşıma kapasitesi azalmaktadır. Bu yüksek lisans tezi çalışmasında, boruların her iki ucunda bulunan galvanizleme veya bulon deliklerinin gerilme yayılışına olan etkisi ve eksenel çekme yüküne maruz boruların taşıma gücü deneysel olarak incelenmiştir. Ayrıca, galvanizleme deliğinin sakıncalarını gidermek amacıyla, deliğin iç yüzüne, dışardan görülmeyecek şekilde,bir takviye levhası kaynaklanarak deneysel gözlemler yapılmıştır. Bu amaçla, Î.T.Ü. İnşaat Fakültesi Yapı Laboratuarlarında üçü takviyeli, üçü takviyesiz altı deney yapılmıştır. Yapılan bu deneyler sonucunda eksenel çekme yükü altodaki galvanizleme deliğinin taşıma gücüne olan etkisi teorik enkesit, teorik brüt enkesit ve deneysel enkesitte, takviyeli ve takviyesiz durumlar için ayrı ayrı incelenmiş ve karşılaştırmalar yapılmıştır. Bu karşılaştırmaların sonucunda, büyük çaplı boru çubuklarda, delikte yırtılma sonucu kesitin kopmasına yol açan galvanizleme deliklerinin içerden levha kaynaklanarak takviye edilmesiyle olumlu sonuçlar elde edilmiştir. vii
Özet (Çeviri)
THE EXPERIMENTAL STUDY OF STBFFNERS AROUND THE HOLES AT TUBE CROSS-SECTION TENSILE MEMBERS SUMMARY Since 1950, space trass structures have been used widely, especially at roofs or similar parts of constructions on which there is no effective live loads. The cause of this choice, using space truss structures, can be defined as: -lightness of weight, -stifhess, -high degree of indeterminancy, -almost no bending element therefore using minimum quantity of materials, -freedom of drawing and forming, -great facility in erection, in disassemble and in changing the truss members. Also in Turkey, space truss members have been used widely since 1985. The using ratio of space truss structures in Turkey, has increased continuously, every year. At Table 1 and Figure 1, the condition of usage of the capacity of space truss structures in Turkey is given. Tablel.The Capacity and Capacity Usage of Steel Space Truss Construction in Turkey Approximately, fifteen cnstruction companies,manufacture products on this subject in Turkey, 85 % of these companies prefer to choose a joint type similar to Mero joint type, in their manufactures. This kind of joint type is made up of a sphere in which there are screwed holes at three directions perpendicular to each other and at their bisectors. Members of space truss structures are connected to this sphere with high- strength bolts at the joints. viu40 -. 30 ?. 20 -. 10 The Production of Steel Construction in Turkey (t04kN) 45.7 36.4 34.4 ' Total Production 32.1 30.3 26.1 \ 19.5 \ V\15.2 I4.T“ 16.1 14.S 19.7 Private Sector 18.3 -”(except Space Truss) 16.3 \ \ 12.4' State Sector 0.1 0.2,, Space Truss 1.9 r:i,, ^ Years 1988 1989 1990 1991 1992 Figure 1 Development of Steel Construction Production In Figure 2, a member of a space truss structures with its joint detail is given. Generally, a hole called bolt hole or galvanisation hole is constituted at each extremity of a tube cross-section, space truss member. This bolt hole is used not only for galvanization process but also to replace a bolt at any time it falls in the tube member, during the montage. bolt or galvanization hole shank brad hole bolt conical extremity Figure 2. A Member of Space Truss Structure With its Joint Detail IXIn this study, the stress distribution on the bolt holes and their reinforcement with welded stiflhers under tensile load are examined. At laboratories of Civil Engineering Faculty of Istanbul Technical University, experiments on six samples had been done to determine the ultimate load carrying capacity. Three of these experiments were done on testing elements reinforced by stiflhers and the other three were without stiffiiers at all. First of all, it can be suitable to be interested in stress, stress distribution and stress concentration concepts. The actual magnitude of the normal stress at any point of cross-section can not be calculated until some assumption has been made about the nature of the stress distribution. The formulas for determining stresses in simple structural elements are based on the assumption that, the distribution of stress on any section of a member can be expressed by a mathematical law or equation of relatively simple form. For example, in a tension member subjected to a axial tensile load, the stress is assumed to be distributed uniformly over each cross section and, is obtained by dividing the load by the corresponding area of transverse cross section. The equation which is used to calculate the uniform stress is: P in which, a = uniform normal stress (N / mm2) P = axial tensile load ( kN ) F = cross sectional area (mm2) The distribution of elastic stress across the section of a member may be nominally uniform or may be vary in some regular manner. When the variation is abrupt within a very short distance, the intensity of stress increases greatly and the condition is described as stress concentration. It is usually due to local irregularities of form such as small holes, screw threads, scratches and similar stress raisers. The assumption that the distribution of stress on a section of a simple member may be expressed by simple laws, may be in error in many caes. The effects such as : - abrupt changes in section which can occur at the roots of threads of a bolt at the bottom of a tooth on a gear, at a section of a plate or beam containing a hole, at the corner of a keyway in a shaft, - pressure at the points of application of the external forces, for example at bearing blocks near the ends of a beam, at the points of contact of the wheels of a locomotive and the rail, at points of contact of gear teeth or a ball bearing on the races,- discontinuities in the material itself, such as, nonmetallic inclusions in steel air holes in concrete, pitch pockets and knots in timber, or variations in the strength and stiffness of the component elements of which the member is made, such as, crystalline grains in steel, fibers in wood, ingredients in concrete, - initial stresses in a member that result, for example, from over-straining and cold working of metals during erection or fabrication, to heat treatment of metals, to shrinkage in castings and in concrete, or to residual stress resulting from welding operations, - cracks that exist in the member, which may be the result of fabrication, such as, welding, cold working, grinding or of other causes, may cause the stress at a point in a simple member, such as a bar, to be radically different from the value calculated by ordinary formulas. The conditions that cause the stresses to be greater than those given by the ordinary stress equations of mechanics of materials are called discontinuities and stress raisers. These conditions destroy the assumed regularity of stress distribution by sudden increases in the stress, called stress peaks, at points near the stress raisers. Often, large stresses due to stress concentrations are developed in only a small portion of a member. These stresses are called localized stresses or simply, stress concentrations. Whether the significant stress in a metal member under a given type of loading is the localized stress at a point, or a smaller value representing the average stress over a small area including the point, depends on the internal state of the metal such as, grain type and size, state of stress, temperature and rate of straining. All of these factors may influence the ability of the material to make local adjustments in reducing the damaging effect of the stress concentration at the point. The maximum intensity of elastic stress produced by many kinds of stress raisers can be ascertained by mathematical analysis or direct strain measurement and is usually expressed by the factor of stress concentration. The stress concentration factor can be defined as: a in which, k : stress concentration factor, cw : maximum stress, o : average stress at minimum section XIIn an element, as in the case of force lines, stress trajectories which have to pass through the material, pass by concentrating around a geometric hole or discontinuity. Meanwhile, average spacing between force lines decreases. This situation causes a formation of stress concentration or a local stress increase because of the frequency of many force lines squeezed at the same area (Figure3). Opening a hole at the tube causes not only a dimunition but also an accumulation of stress at its cross-section. For this reason, the carrying capacity of the member decreases under tensile force. t t t t T t t t TTTTTTTT Figure 3. Force Lines at a Tensile Element In this master thesis, the influence of bolt holes to the stress distribution and carrying capacity of tube members under tensile force are studied. In addition, to get rid of the undesirable effects caused by this hole, a stiffher is welded as a reinforcement, inside the tube unless it can be seen from outside. After that process, experimental observations are realised. As a result of six experiments, the influence of bolt hole under axial tensile force is examined and compared by theoritical, theoritical gross and experimental cross-section for each of the reinforced and unreinforced cases. With the help of these comparisons, the inside reinforcement of the bolt holes by welded plates is found suitable and useful. By this manner, it is seen that one can improve the carrying capacity under axial tensile force unless the member fails by the rupture of the bolt hole at the cross-section and almost reach the carrying capacity expected at gross cross-section. xu
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