Prefabrike yuvalı temelin dış yükler altındaki davranışının incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 75335
- Danışmanlar: PROF. DR. METİN AYDOĞAN
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: İnşaat Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 101
Özet
ÖZET Yüksek lisans tezi olarak sunulan bu çalışma üç ana bölümden oluşmaktadır. Çalışmada, Prefabrike kolonların ankastreliğini sağlamakta kullanılan yuvalı ( çanak ) temelin, kolondan gelen kesit tesirleri altında davranışı incelenmiştir. Çalışmanın ilk bölümünde Prefabrikasyon Teknolojisi tanıtılarak, avantajları, kullanım alanları sıralanmış ve kısaca Prefabrike Betonarme sistemlerden bahsedilmiştir. Daha önce bu konuda yapılmış bazı çalışmalara yer verilerek, yuvalı temelin kolon yükleri altındaki genel davranışından bahsedilmiştir. İkinci bölümde, çalışmada örnek alman yuvalı temelin davranışı incelenmiştir. Yuvalı temelin idealleştirilmesinde üç boyutlu solid ve çubuk eleman kullanılmıştır. Yuvalı temelin zemin ile bağlantısı, çökmeye karşı elastik yaylarla sağlanmıştır. Hesap kabuleri, idealleştime ve yardımcı bilgisayar programı hakkında kısaca bilgi verilmiştir. Üçüncü bölümde ise, ikinci bölümde açıklanan literatür ve çeşitli kaynaklarda belirtilen hesap ve yük kabulleri, çalışmada elde edilen sonuçlarla karşılaştırılmış ve yuvalı temelin davranışı gözönüne alınarak donatı yerleşim durumu hakkında önerilerde bulunulmuştur. xı
Özet (Çeviri)
SUMMARY EVALUATION OF THE MECHANISM OF A SOCKET BASE UNDER THE COLUMN LOADINGS In this study, socket base connection which can be designed to provide substantial moment resistance at the column base is considered. The subject is enlarged under three main attempts. In the first attempt, the state-of-the-art of precast technology with advantageous and backdraws as well as its applicability are introduced. A comprehensive review of the precast concrete structures is also given. Detailed literature survey on the mechanism of the socket base connections formed into the foundations under column internal forces is discussed. By a simple meaning, precast technology is a solution technique for a quick construction with pre-designed, standardized and, as a consequence, precast elements and their components, intending for the use of these with a through understanding of engineering fundamentals and structural design. With this study, only precast concrete structures are considered. By the years up to 19th century, industrial structures were constructed mainly with wooden structural frames or steel frames with riveted joint. But, later, concrete frame structures started to be used extensively in practice. However, precast technology appears, later on, providing individual application for some regions in where the currently applied construction technology is not applicable due to bad climatic conditions through the year. Following years to date, all over the world as well as in Turkey, it found extensive applicability with developments in the transportation along with lifts and fitting tools which are improved qualitatively and increased in number. This technology gives a sharper focus to qualitative production reflecting the use of a rational system performance design methodology, mass production and feasibility from economical point of view. In precast industrial concrete structures, design criteria including design concept and procedure is formed based on following points; number of spans and span length, essentials for structural functionality, therefore, industrial productivity ( i.e. number of cranes, etc.), soil condition, precast members, their components as well as their connection details. XllFor the industrial concrete structures, shear or portal frames are used. Of these beam-column frames, column to foundation connections are formed to supply a rigid joint for moment resistance at the column base, hinge or rigid joints are utilized for girder to column connections. The purpose of a connection is to transfer load from one precast member to another. Although, rigid connections are always more preferable in particular for the column to foundation connections with respect to the hinge connections. In practice, application is not easy to form the base fixity conditions of the columns. To provide substantial moment resistance at the precast column base, socket base connections formed into the foundations are used extensively in precast concrete structures. Force transfer in between elements is provided with cast-in-place concrete. This is done filling spaces between the column and the base socket with structural grout. The procedure is same for both multispan or single span structures. But, at the design step, the most important factors to which enough attention should be given are soil condition and unwilling affects due to the general mechanism of foundation, therefore possible failure phenomena, during fixation and service life. In socket base systems, the subject which is still open to the discussion is the load distribution pattern on the walls of the socket base due to the column end forces. Suggested reinforcement detail between the column and the foundation is achieved by clarifying the paths of the transformation of the end forces into the socket base, visualizing connection behavior and ensuring the compatibility of connection behavior with behavior of the overall structural system. In the first attempt, therefore, a comprehensive review from literature survey on a general mechanism of the socket base-foundation systems under column end forces is discussed in detail. In references, this type of base connection is analyzed based on two different schemes, assuming that column and walls of the socket base act together as a single unit or each element acts independently in order to draw the limit conditions. Smooth-faced socket walls and column end surface generate independent behavior of each member at the joint whereas rough-faced socket walls and column surface cause to act as a single unit in an analytical solution limits. In practice, after filling spaces between the column and the base socket with highly strengthened structural grout in order to act as a single unit, following conditions should be satisfied; a) Both, socket base walls and part of the column end surface to be cast in the socket should be tooth-faced. For this purpose, corrugated plate, sheet or hard plastics like PVC can be used. Mould of the column end can be arranged ensuring the compatibility of connection behavior, b) Grout should be at least at the structure's strength quality and also oppressed gently with a help of vibrator, c) Flesh thickness of the socket base should not be less than l/3th of the socket base dimension or 10 cm. XlllIf surfaces at the connection joint are not rough-faced. Erected grout between socket walls and column surface does not transfer any tension forces, therefore the continuity is not completed. As a consequence of this, each element acts independently. Under the column end forces, load distribution over the walls of the socket base, design assumptions and corresponding values of the design loads show differences. Therefore, reinforcement detail on the socket walls also display similar differences. In addition, influences of the soil condition on loading is not considered for this part. As a result, in the first attempt, general behavior and mechanism of the socket base connection formed in the foundation under the column end forces are drawn. Quantitative and qualitative information is given. Other types of the socket base connections, stalk and mass concrete is not considered in this study. But the effects of the soil condition is taken into account, general idea on the behavior of the stalk type base is drawn. Stalk type socket base are used in case of the application difficulties due to the elevation differences in the field or it is preferred by the owner to provide functionality depending on space use. Reinforced concrete retaining wall behind the stalk type socket base is usually constructed to reduce earth pressure due to surcharge. In the second attempt, a case study is conducted for a socket base connection formed in the foundation to reflect the general behavior. Foundation is modeled by three dimensional solid and bar elements. Elastic springs are utilized in the socket base connection in the foundation not to fall down in vertical direction. Assumptions done in the analysis, idealizations and brief information about software is introduced. Socket base is analyzed for two different soil conditions and results are presented by the help of figures and plots. Construction joint between column end surface and the socket walls is filled by concrete BS-30 and it is assumed that there no exist any pores in the filling thanks to vibration. Precast column is made of concrete BS-25 and concrete of the socket base foundation is BS-16. Fixation of the precast column is done first by wooden wedges and later it is finalized with grout. However, in mathematical analysis, for the sake of simplification, it is assumed that bolt connection underneath the column does not exist during the fixation process and wooden wedges do not exit during service life. Foot of the foundation has five rows with a 12.5 cm height solid finite elements. Socket model is consisted of the 10 cm height solid elements at the first row and with a 20 cm length for next 6 rows, it is whole modeled from 7 rows of the solid elements. All is connected to each other from nodal points. XIVSpace as an construction joint between the socket walls and the precast column surface chosen to be 10 cm and filled with grout is modeled by fictive bar elements which have hinge type nodal points at both ends. The reason for using the fictive bar element for the construction joint is to evaluate the interactive behavior between the column end at the joint and the socket base wall surfaces within the construction joint. Construction joint is assumed not to be deformed till column end forces are completely applied. There are 16 fictive bar elements used to model the column end, 28 bars in the front wall of the socket perpendicular to the loading direction, and similar to front mesh, 28 bar elements in the back wall. In the loading direction, two walls faced each other, each one is consisted of the same 28 bar elements. Whole construction joint is made of 128 fictive bar elements. Geometrical properties of the bars are designed based on the possible loading conditions depending up on the mesh sensitivity, therefore, equivalent representative area. After all loading, condition is satisfied depending on the transferred forces from precast column end to the internal faces of the socket base. Fictive bar elements which is tensile force resistant with hinge ends are removed step by step to reach the final equilibrium. The connection between the socket base and the base ground on which it rests is formed to resist vertical settlement by elastic springs. Coefficients of the elastic springs for vertical settlement resistance is defined based on the dimensions of the area which is subjected to the loading. With this approach, behavior of the foundation is evaluated as a thick plate on an elastic soil. This yields close solution to the real behavior as expected. Forces in the precast column are not assigned to the nodes as nodal forces but distributed over the surface as a face load. So, internal forces transferred from column to the base are considered as much as close to the real pattern. Because of the features of a solid element, rotational degrees of freedom about x, y and z axes are restrained but displacements in each axis are realized. Displacements in both x and y axes of the four corner nodes in the foundation are restrained not to be unstable. A pad foundation rested on a compressible soil can be assumed that it has an elastic fixed end at the base and it has a resistance for settlement and rocking. These capabilities can be introduced by the help of the cofactors Rv and Re. Cofactor means the value of the force ( Moment ) which can make a unit displacement ( or relative displacement differences can be assumed to be rotation. ) in an elastic medium. These cofactors are functions of the soil elasticity modulus Es ( or base modulus ks ). As well known from the theory of the strength, calculated internal forces R and M, which are in fact distributed over the cross-section, are the values assumed acting on the mass center line through the cross-section of the structural element. XVIn light of this, stresses distributed over the cross-section should be integrated to get an idea about the internal force values on the mass center. Results obtained from the software package are given for node calculation points and central calculation points of the elements. Therefore, nodal outputs ( Stresses ) should be integrated over the surface. Likewise, stresses calculated at the element center should be multiplied by the cross-sectional area to obtain the acting force at the element center. In the third attempt, comparative study is done to see the differences between results obtained from conducted studies and algorithms as well as loading assumptions given in papers and references. Considering behavior of the socket base foundation, nodal and element center stresses are reevaluated to point out the whole behavior of the socket under the precast column loads and then suggestions are made. Over-stressing is observed in the top region to a depth of 20 cm over the socket walls. It is the most critical part of the base in any case of loading. As a result of this study, the outputs match with those of the previous studies. This load distribution depicts a trend decreasing gently from highly concentrated part at the center of the face of the socket in y direction through both walls in x direction. In z direction, around the support region, it increases as moving down, in contrast to this observation, on the spans, it decreases. Critical cross-section can be evaluated to a depth of 20 cm over the socket wall. However, in many references, for the same foundation model, it is suggested to be 40 cm. Another important point seems worthy to be mentioned here, under the compression forces condition, internal forces are formed in a limited value in the bottom region of the socket walls ( beginning from bottom edge in the lower region to a depth of 30 cm ). In this region, load distribution in y direction, in contrast to the upper part, increases from supports to the mid span. Intensity of the internal forces at the end of the precast column decreases gently as moving up and in the middle region tensile forces are seen. Transferred compression forces from the column end face to the adjacent socket wall is found to be around 53.8 tons. Of 53.8 tons, only 46.6 tons is seen in the top region to a depth of 20 cm. On the back wall surface, the compressional area beginning from bottom to a depth of 50 cm and the average value of this region is 21.18 tons. In this region with 50 cm depth, the pattern of the load distribution in z direction matches with the accepted common pattern as pointed out in reference papers. But, in y direction, this distribution increases gradually from supports to the mid span. On the other hand, as expected, the back wall surface of the socket within the region to a depth of 60 cm holds the tensional forces. XVIIn the top region of the socket walls parallel to the loading direction, local load condensation is observed. Also, as observed from the pattern of the load distribution in x direction, in the lower region where the precast column end face meets with the foot, values of the compression forces over the span are calculated higher than those of the supports. In general, when internal forces over the socket walls are considered, front wall of the socket under compression with top 20 cm and back wall with a region to 50 cm behave as an plate fixed through the tree edges. Also, it is clarified that the force distribution is not seen in the top region. One reason for the formation of the compression forces in the lower region of the front wall is that the height of the socket walls is high and as a result of this, moments become dominant with respect to the axial forces. For this type of the socket walls in which higher geometric features exist, reinforcement can be increased in the top region in between 20 cm and 40 cm and in the region where socket and the foot meet. As a whole, influence of the soil condition on the region on where the socket base rests is assumed to be negligible. As an further step in this study, it may need to be finely meshed model of the socket base under the consideration results in an acceptable range of convergence when compared to the exact behavior. This will reduce the differences between the analysis based on the finite element algorithm and the real behavior as expected. XVU
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