Korige boruların tasarımı

Abstract

Boru iletim hatları sanayinin gelişmesiyle birçok alanda kullanılmaya başlamıştır. Enerji iletim hatları, kanalizasyon, içme ve sulama suyu hatları, elektrik, vb. birçok mühendislik yapılarında gömülü boru hatları kullanılmaktadır. Gömülü boruların çeşitli alanlarda kullanılması araştırmacıların dikkatini çekmiştir. Dolayısıyla bu konuda yüzlerce araştırma yapılmıştır. Gömülü boruların yük altında davranışları incelenip, daha mukavim borular elde edilmeye çalışılmıştır. Böylece daha ekonomik ve daha dayanıklı borular üretilebilmektedir. Akışkanların düşük seviyeli basınçlarda nakli için çeşitli plastik malzemelerden, o cümleden HDPE (Yüksek Yoğunluklu Polietilen)?den yapılmış farklı profilli (eksenel kesitli) korige borular yaygın olarak kullanılmaktadırlar. Korige borular genel olarak silindirik kabukların dış yüzeylerine farklı profilli ince duvarlı(cidar kalınlıklı) bantların sarılması, birkaç silindirik kabuğun içiçe konsentrik yerleştirilmesi ve pozisyonlarının uygun ara elemanları ile sabitlendirilmesi yöntemleri ile yapılabilirler. Değişik şekillerde yapılan ara elemanları ilgili kabukların pozisyonlarının sabitlendirilmesi dışında borunun mukavemetinin artmasını da sağlar.Korige borular tasarımları bakımından önemli faklılıklar gösterdiklerinden gerilme şekil değiştirme durumlarının hassas olarak incelenmesi için genel bir analitik yöntemin geliştirilmesi yönündeki çalışmalar kabul edilebilir bir zaman aralığında efektif sonuçlar vermeyebilir. Bazı yapılarda sayısal yöntemlerle alınmış sonuçlar mevcuttur fakat onların genelleştirilmesinin özel karakterli olduklarından verimsiz olacağı muhtemeldir. Problemin etkin çözüm yöntemlerinden biri incelemelerin rijitliği ilgili korige borunun rijitliğine eşit seçilmiş sürekli ve sabit enkesitli (düz) borular üzerinde yapılması olabilir. Korige borular gömülü durumda, ağırlıklı olarak, düşey yöndeki yüklerin etkisindedir. Bu bakımdan söz konusu boruların şekil değiştirme durumları genel olarak düşey diametral düzlem üzere ters yönlü eşit şiddette yüklerin etkisinde yapılan testlerle değerlendirilirler. Dolayısıyla, ince cidar kalınlıklı sonlu silindirik kabuğun diametral düzlem üzere ters yönlü eşit intensivli yayılı yüklerin etkisinde oluşan gerilme-şekil değiştirme durumunun incelenmesi faydalı olabilir. Bu çalışmada ise boru toprak etkileşimi incenerek yeni farklı bir korige tasarımı yapılmıştır. Boru toprak etkileşimi fotoelastik yöntem kullanılarak deneysel olarak detaylı olarak incelenmiştir. Fotoelastik deneyde boru malzemesi olarak epoksi reçine özlü optik hassas malzeme kullanılırken toprak malzemesi olarak kayın ağacı kullanılmıştır. Ayrıca bilgisayar programı ABAQUS yardımıyla sayısal analiz yapılarak deney sonuçları ile karşılaştırılmıştır. Deney sonuçları ile modelleme sonuçları büyük benzerlik göstermektedir.

Pipeline transmission lines began to be used in many areas by development of industry. Buried pipelines are used in many engineering structures such as power transmission lines, wasteway, drinking and irrigation water lines, electricity, etc. Embedded pipes used in various fields has attracted the attention of researchers. On this account, research has been done about it hundreds. Examined the behavior of buried pipes under the load, tried to be more resistant pipes. In this way, pipes can be manufactured more economically and more resistant.Corrugated pipes made from different plastic materials with a various types of axially sectioned profiles are widely used for fluid transportation at lower pressures, for inctance from this group high density polyethylene. Corrugated pipes, in general, are produced wrapping thin-walled tapes having different types of profile over outer surfaces of cylindrical shells, concentrically placing a number of cylindrical shells and fixing their positions with appropriate connection elements. Produced these connection elements in a different types not only allow to fix the related cylindrical shells but also to increase the strength of pipes.The high-density polyethylene pipe has good potential for economic use for marine oil and gas pipelines, underdrains, storm sewers, culverts, and other subsurface drainage structures. In view of its inherent chemical and corrosion resistance, light weight, toughness, flexibility, easy splicing, and consequent easy handling and installation, HDPE piping is used extensively for gas pipelines. In the transportationindustry, over forty states in the US use HDPE pipes as part of a 40% annual growth in the use of thermoplastic, HDPE and polyvinyl chloride (PVC) pipes in transportation construction projects.The efforts in order to develop a general analytical method for the precise examination of state of strain-stress of corrugated pipes may not give effective results in an acceptable period of time since pipes significantly display differences in terms of design. Some results obtained using numerical methods exist, but the generalization is likely to be inefficient due to their special characters. One of the effective solution methods of the problem can be that taking the stiffness of cross section of the related corrugated pipe is equal to another continuous and constant (flat) one.As it known, corrugated pipes in embedded cases mainly are subjected to vertical loads. In this respect, state of strain of pipelines traditionally, in general are evaluated with the tests carried out under the influence of vertical loads, equal intensity but in the opposite directions in the diametrical plane. Therefore, the examination of state of strain-stress of thin-walled finite cylindrical shells under the equal distributed loads in the opposite directions in the diametrical plane may be useful.High density polyethylene has an increasingly important role for the pipe industry. These materials offer many advantages such as lower density, resistance to corrosion and chemicals, relatively low cost and ease of processing that they have been permanently replacing conventional materials.There are some studies about the plastic pipes and pipe-soil interaction in the technical literature. Reddy et al. defined the maximum tangential stress locations as the shoulder which was above 45° springline. It was stated by Moore that highest circumferential stresses were located at the springline. Moser and Folkman stated that dimpling occurs generally at 3 and 9 o'clock positions in the field performance tests of profile-wall HDPE pipes and beginning of wall crushing observed at the 9:30 and 2:30 o'clock positions. Experimental study of Dhar and Moore showed that maximum circumferential strain occurred at springline. McGrat and Schafer stated that maximum compressive circumferential strain occurred at crown and maximum tensile circumferential strain occurred at the springline as a result of their parallel plate simulation. Burgon and Keatley showed that maximum stress locations were at the springline. There is a need for the detailed investigation of state of stress for the buried pipe problems experimentally.In this study, buried HDPE pipes were investigated using photoelasticity which allows analyzing in details state of stress on the buried pipe model. Investigations are carried out for the photoelastic plane models taking into account the analogy between plane state of stress and strain and independency of state of stress from Poisson?s ratio in plane stress. Different type of corrugated profile pipes were compared. Also, covered corrugated profile pipes were investigated in terms of the local buckling and different types of strip geometries were analyzed numerically. Buried condition of the pipes is also an important issue and buried pipe was modeled by using photoelasticity in the final part of this study. As a result of the experiment, maximum stress locations in the pipe model were close to crown and about ±20° away from springline in terms of the differences between principal stress values.New and different corrugated pipe is designed by examined the interaction of soil and pipe. Pipe-soil interaction experimentally investigated in detail using photoelastic method. In photoelastic experiment, epoxy resin which the optical sensitive material is used as pipe material. The beech tree is used as soil material. In addition, numerical analysis done with the help of a computer program ABAQUS are compared with the experimental results. The experimental results show great resemblance with the modeling results.The part of the model which imitates the pipe is made of the optical-sensitive material based on epoxy resin (araldite). Material of the model has following optical-mechanical properties: modulus of elasticity, E=3500MPa and the fringe value of optical sensitive material ?_0^1.0 =9.57 N/mm?fringe. The soil was modeled using wood having porous structure (beech). Parts of the model are prepared using tooling machines with the required specific tools and cooling taking care of no additional optical effect. Specifically, external diameter of the pipe and internal diameter of the wood part of the model are close fit. The part of the model imitating the pipe was placed below the loading surface with a dimension of its inner diameter A set-up consists of a frame was designed and then prepared for loading the model. Base of the model was placed on the horizontal smooth surface. Model was supported from right and left sides with plates which are designed do not prevent from its displacements. The set-up creates uniform axial compressive loading onto the models. Loading of the model was created by a prismatic lever. The load is transferred to the model with a ball.