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Tabakalı zeminlerde yatay yüklü kazıklar

Lateral loaded piles in layered soils

  1. Tez No: 39556
  2. Yazar: DURMUŞ DELEN
  3. Danışmanlar: DOÇ.DR. OĞUZ TAN
  4. Tez Türü: Yüksek Lisans
  5. Konular: İnşaat Mühendisliği, Civil Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1994
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 129

Özet

ÖZET İnşaat mühendisliği uygulamalarında pek çok yapı kazıklı temel üzerinde oturmaktadırlar. Viyadük, köprü, baca, kule, askeri ve sivil havacılık radarları, nükleer santraller, derin su rıhtımları, limanlar ve deniz içersinde inşa edilen deniz fenerleri, petrol arama platformları gibi sayılan gittikçe artan yapılar yatay yüklere maruz kalmaktadırlar. Eksenel düşey yükler yer çekimi etkisine bağlı iken, yanal yükler genellikle, rüzgar, dalgalar ve deprem gibi kuvvetler nedeni ile ortaya çıkmaktadırlar. Özellikle deniz yapılarının geoteknik tasarımında en önemli unsur rüzgar ve dalganın oluşturduğu tekrarlı yanal kuvvetlerdir. Ayrıca tankerlerin platforma yanaşmasından dolayı kısa süreli statik yüklemeler de söz konusu olmaktadır. Bu çalışmada, problemin tanımı yapıldıktan sonra yatay kuvvet etkisindeki kazıkların hesap yöntemleri verilmiştir. Bölüm (3)'de, yatak katsayısı kavramı üzerinde ağırlıklı olarak durulmuş ve bu kavramın tanımı, elde edilmesi ve yatak katsayısına etki eden faktörlerden söz edilmiştir. Bölüm (4)'de ise, p-y eğrilerinin tanımı ve teorik olarak elde edilmeleri anlatılmıştır. 5. Bölümde,“Tabakalı zeminlerde yanal yüklü kazık hesabı”başlığı altında ise iki tabakalı zemin şartlarında yanal yüklenmiş bir kazığın, zemin yüzeyinde yaptığı maksimum yatay yerdeğiştirme (deplasman) ile kazıkta oluşan maksimum momentin hesap yöntemi anlatılmıştır. Çalışmanın son bölümünde Bowlestarafından verilmiş olan bilgisayar programı çok tabakalı zemin şartlarına uyarlanmıştır. Bu programda yatak katsayısı sabit veya doğrusal olarak tanımlanabilmektedir. Davisson - Gilltarafindan verilen, boyutsuz katsayılar ve bu katsayıların kazık, zemin parametrelerine göre değişimi, geliştirilen program yardımı ile yeniden elde edilmiş ve sonuçların mukayesesi yapılmıştır. V

Özet (Çeviri)

LATERAL LOADED PILES in LAYERED SOILS SUMMARY Piles are frequently subjected to lateral forces and moments. Lateral loads, upward loads, and moments are generally due to forces such as wind, waves and earthquake whereas axial downward loads are due to gravity effects. For example, in quay and harbor structures, where horizontal forces are caused by the impact of ships during berthing and wave action ; in offshore structures subjected to wind and wave action; in lock structures; in pile-supported earth-retaining structures; in transmission -tower foundations, where high wind forces may act; and in structures constructed in earthquake areas, where some building codes specify that piles supporting such structures should have the ability to resist a lateral force of 10% of the appiled axial load. In the desing of such pile foundations, two criteria must be satisfied: First, an adequate factor of safety against ultimate failure; and second, an acceptable deflection at working loads. As in other fields of soil mechanics, these two criteria are generally treated separately and the desing is arranged to provide the required safety margins independently. Early engineers did not desing vertical piles to carry lateraly loads. Batter piles were provided for this purpose. In fact the Culmann graphical solution widely used up through the early 1950s as a means of analyzing pile groups carrying both vertical and horizontal loads. Later Hrennikoff proposed an analysis of pile groups using the lateral capacity of the piles as a parameter. In the early 1950s others (Palmer and Thompson, Mason and Bishop, Brown, Reese and Matlock) measured and used the finite-difference method of analyzing the lateral pile. Reese and Matlock provided curves as aids since it appeared many people were wary of this analytical method. Bowles included the finite-difference method along with a computer program in a textbook. In spite of certain advantages of the finite-difference method over many analysis procedures, some writers (Broms ) preferred alternative methods of analysis. In 1972 Bowles has developed a method which has the advantage of including almost any lateral-pile loading scheme and accounting for any type of soil, holes, changes in pile section. VIThe problem of a pile subjected to lateral loading is one of a class of problems conserned with the interaction of soils and structures. The solition of such problems usually involves the use of iterative techniques because the soil response is a nonlinear function of the deflection of the structure. An anchor pile subjected to a horizontal load from a cable attached at the ground surface; a pile that supports an overhead structure such as an advertising sing; a pile that is fixed against rotation at the groundline such as a pile supporting a reinforced concrete retaining wall; a pile that extends upwards and becomes a part of a flexible structure such as a pile supporting an offshore drilling platform are present examples of the kinds of loading that are frequently encountered in practice. Other loadings can also be analyzed. In all the cases illustrated the pile could also be subjected to an axial load. However, the presently available methods of analysis do not allow for a torque on the pile. Furthermore, the applied shear and moments and the resulting deflection must be in the same plane. It is assumed that the pile was straight before and after installation. The design of offshore structures should take into account the three types of lateral loadings that are given below: * Short-term static loading, * Cyclic loading, * Cyclic loading followed by static or cyclic loading. Laterally loaded piles are generally classified as below considering the pile head condition: * Free-head piles, * Fixed head piles. They may also be classified according to the pile penetration: * Rigid or short piles, * Flexible or long piles, * Semi-rigid or intermediate piles. The behavior of a pile under cyclic- lateral loading has been studied by many investigators and the results of these studies have been reported in the literature. Such techniques include linear subgrade reaction analysis, non-linear subgrade reaction analysis or p-y analysis, elastic analysis and finite element analysis. For the analysis of VIIpile behavior under cyclic loading, p-y method has certain advantages. Because the method used in this thesis includes constant ör linear subgrade reaction, cyclic loads are not considered. Of most practical interest to the engineer is a knowledge of the deflection of the pile and the bending moment in the pile, both as fünctions of depth. The bending moment is required in sizing the pile, and the deflection would be important with regard to the serviceability of the supported structure. The problem of laterally loaded piles is closely related to the familiar problem of a beam on an elastic foundation; however, in öne respect, it represents a more specialized case. Ali external forces and moments applied to the pile -soil system are introduced through boundary conditions existing at öne point, the top of the pile, while loading may be applied at many points along a beam. On the other hand, rational solitions of pile-soil interaction problems require generalization of the beam- on- elastic- foundation theory to account for the non-linear characteristics of real soils. The following differential equation for the problem of the laterally loaded pile is well known, and its solution has been discussed by a number of authors: EId!y_+Pxdi j 4^ ı '^ dxdx~ where Px = axialload y = deflection x = length along pile El = flexural stiffhess of pile Es=soil modülüs A number of methods proposed for the solution of the differential equation were discussed in this thesis. it is important to employ appropriate boundary conditions and the appropriate representation of the soil response through the selection of appropriate values of soil modulus. A comprehensive solution to the problem of the laterally loaded pile has two majör parts: 1-it is necessary to obtain complete information describing the behavior of the surrounding soil, 2-it is necessary to solve the differential equation. vıııIf the soil resistance - pile deflection relationship is not linear line then in the solution the elasto-plastic behavior of the soil must be considered. in this case, either the iterative applications of öne of the elastic methods, ör the behavior of the laterally loaded pile is examined by considering the physical model of the pile-soil system. The allowable lateral loads on piles is determined from the following two criteria: 1.Allovvable lateral load is obtained by dividing the ultimate (failure) load by an adequate factor of safety. 2.Allowable lateral load is corresponding to an acceptable lateral deflection. The sınailer of the two above values is the öne actually adopted as the desing lateral load. Methods of calculating lateral resistance of vertical piles can be divided into two categories: 1.Methods of calculating ultimate lateral resistance: Brinch Hansen's Method (1961) is öne of these methods. This method is based on earth pressure theory and has the advantage that it is applicable for c- soils and layered system. However, this method sufTers from disadvantages. it is applicable only for short piles and requires trial-and-error solution to locate point of rotation. Broms' Method (1964) also is based on earth pressure theory, but simplifying assumptions are made for distribution of ultimate soil resistance along the pile length. This method has the advantage that it is applicable for short and long piles, considers both purely cohesive and cohensionless soils and considers both free-head and fixed- head piles that can be analyzed separately. However, this method also has disadvantages. it is not applicable to layered system and it does not consider c- soils. 2.Methods of calculating acceptable deflection at working load: in modulus of subgrade reaction approach used in this thesis it is assumed that soils act as a series of independent linearly elastic springs. This method has the advantage that it is relatively simple, it can incorporate factors such as nonlinearity, variation of subgrade reaction with depth, and layered system and it has been used in the practice for a long time. However, this method has disadvantages that it ignores continuity of the soil and modulus of subgrade reaction is not a unique soil property but depens on the foundation size and deflections. in elastic approach, the soil is assumed as an ideal elastic continuum. The method has the advantage that it is based on a theoretically more realistic approach IXand it can give solutions for varying modulus with depth and layered system. However, it is difficult to determine appropriate strains in a field problem and the corresponding soil modulus. When piles are loaded laterally, they can be analyzed as infinite beams embedded in an elastic medium. For this type of analysis a modulus of subgrade reaction must be established. The modulus of subgrade reaction is a conceptual relationship between soil pressure and deflection that is widely used in the structural analysis of foundation members. Determination of the modulus of subgrade reaction is generally carried out by öne of the following methods: 1.Full-scale lateral -loading test on a pile: This method is time -consuming, requires çare and relatively expensive. 2.Plate- loading test: The main problem with this approach is the extrapolation of the results for a plate to a pile. it is difficult to make a plate-load test, except for very small plates because of the reaction load required. 3.Empirical correlations with other soil properties: A number of empirical correlations for the modulus of the subgrade reaction are available. For clays it is assummed that modulus of subgrade reaction is a constant with depth. For softer cohesive soils, for normally loaded clays and silts, and for granular materials, raodulus of subgrade reaction varies nearly linearly with depth near the ground surface in the zone that controls the pile behavior. For preliminary estimate, it may be taken from tables but for a more realistic determination of the modulus of subgrade reaction, a lateral pile load test is recommended. Engineers have long recognized the beneficial effect that the stifFering of the surficial soil has in reducing the lateral deflection of a laterally loaded pile. it is also known that a uniform soil deposit provides less resistance to a laterally pile near the ground surface than at greater depths. The effect of a two-layer soil system on the engineering behavior of a laterally loaded pile is investigated analytically in nondimensional terms by Davisson and Gül in 1963. A modulus of subgrade reaction is used to define the soil stiffhess; the stiffhess of the surface layer is defined in terms of that of the underlying layer. The complete range of relative stiffhess and relative thickness of the two layers is investigated. The surface layer is shown to have very important influence on the behavior of a soil-pile system. The nondimensional solutions presented by Davisson and Gill permit a quantitative estimate of the effects that soil layering ör seasonal variations in the properties of surficial soils can have on the engineering behavior of laterally loaded pile foundations. Furthermore the depth to which a soil deposit should be throughly Xinvestigated with respect to determining the subgrade modulus is defined, and is shown to be quite shallow. In 1974 Bowles made a computer program that uses matrix or finite-element method for laterally loaded pile. In this thesis, this computer program was improved for lateral loaded pile in layered-soil system. This program uses modulus of subgrade reaction as constant or linear. In 1963 Davisson and Gill presented the nondimensional solutions for lateral loaded free-head pile in nonlayered and layered soil system. In this thesis, the graphics which have been presented by Davisson and Gill, have been obtained with 10% difference and the graphical results have been compared. First, nonlayered system has been considered and the solutions are given for embedded lengths (z^J of 2,3,4, and 5. The common results of the studies in 1963 and in this thesis are those: Little curvature can be observed for the pile with length z^ =2. If the pile length less than 2R (R :Relative stiffness.), it behaves like a rigid (EI assumed infinite) pile. On the other hand, the deflection curve for zma^4 are close to that for 2^=5. So, it can be said that if the pile length greater than 4 or 5R, it behaves like infinite long pile. For layered system, the surface layer was considered to have thicknesses of 0.2R, 0.4R, 0.6R, 0.8R, and 1.6R. From a graphical comparison of the curves for the ratio (C) of stiffness of the layers, it can be observed that when C-values less than unity, the deflections are increasingly magnified as the thickness of the surface layer increases. On the other hand, the deflections are progressively reduced for C-values exceeding unity as the thickness of the surface layer increases. XI

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