• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.2
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• pp.187-193
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• 2023

This paper presents the buckling behavior of a pile considering its self-weight. The differential equation and boundary conditions governing the buckling of partially embedded piles in nonhomogeneous soils are derived. The buckling load and mode shape of the pile are numerically computed by the Runge-Kutta method combined with the Regula-Falsi algorithm. The obtained numerical solutions for bucking loads agree well with the results available from the literature. Numerical examples are given to analyze the buckling load and mode shape of the piles as affected by the self-weight, embedment ratio, slenderness ratio and boundary condition of the pile as well as the aspect ratio and rigidity ratio of the subgrade reaction. It is found that the self-weight of the pile leads to the reduction of the buckling load, indicating that neglecting the effect of self-weight may overestimate the buckling load of partially embedded piles.

• Journal of the Korean Geotechnical Society
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• v.39 no.3
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• pp.5-16
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• 2023

The effect of raft flexibility on piled raft foundations in sandy soil was investigated using a numerical analysis and an analytical study. The investigation's emphasis was the load sharing between piles and raft following the raft rigidity (K_R), end-bearing conditions. The case of individual piles and subsequently the response of groups of piles was analyzed using a 3D FEM. This study shows that the α_pr, load-sharing ratio of piled raft foundations, decreases as the vertical loading increases and as the K_R decreases. This tendency is more obvious when using friction piles compared to using end-bearing piles. The effect of raft rigidity is found to be more significant for the axial force distribution - each pile within the foundations has almost similar axial forces of the pile head with a flexible raft; however, each pile has different values with rigid rafts, especially with the end-bearing piles. The axial force of the pile base with floating piles shows similar point-bearing resistance for all the piles; however, it shows different values with end-bearing piles. The differential settlement ratio of rafts showed a larger value with lower K_R.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.6
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• pp.1271-1276
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• 2006

Vertical loads acting on corrugated metal culverts under negative arching condition were investigated through numerical analyses. Four kinds of corrugated metal culverts with span of 3m were considered in numerical analyses. Also, depths of cover were varied from 1m to 6m with increment of 1m. According to numerical analyses, magnitudes of vertical loads acting on culverts under the condition of negative arching were similar as overburden load on culvert. Furthermore, magnitudes of vertical loads acting on culverts supported by pile foundation were similar as those without pile foundation when depths of cover were less than about 2m. For larger depths of cover which are greater than about two times of span of culvert, magnitudes of vertical loads were slightly larger than those without pile foundation and its tendency becomes more clear as flexural rigidity of corrugated metal increases.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.977-988
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• 1994

In this paper, the comparisons between field measurments and numerical results ware performed for the settlements, lateral displacement in Jinwol interchange works on the Honam express way whose site was improved by sand drain for the constructions of over bridges, piers and abutments. The computer program was developed by coupling Biot's equation with Sekiguchi's elasto-viscoplastic model under plane strain conditions. Steel pipe piles for piers were replaced into the equivalent steel sheet pile wall. The characteristics of behavior for both the soil foundations and the sheet piles wall were investigated with the variation of axial force on the wall, rigidity of the wall, supported condition of sheet pile into hard strata and the location of anchored point.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.629-637
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• 2010

In this study, we analyzed lateral behavior of connected foundation for transmission tower in clay. For this study, we performed model lateral load test, measured load-displacement curve of connected foundation. For the tests, we manufactured connected foundation model that consider a change of rigidity, installed various measuring sensors for understanding of elements and general foundation behavior. From the test results, we measured load capacities using various methods, compared and analyzed these capacities.

• Structural Engineering and Mechanics
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• v.28 no.2
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• pp.221-238
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• 2008

Numerical solution to buckling analysis of beams and columns are obtained by the method of differential quadrature (DQ) and harmonic differential quadrature (HDQ) for various support conditions considering the variation of flexural rigidity. The solution technique is applied to find the buckling load of fully or partially embedded columns such as piles. A simple semi- inverse method of DQ or HDQ is proposed for determining the flexural rigidities at various sections of non-prismatic column ( pile) partially and fully embedded given the buckling load, buckled shape and sub-grade reaction of the soil. The obtained results are compared with the existing solutions available from other numerical methods and analytical results. In addition, this paper also uses a recently developed technique, known as the differential transformation (DT) to determine the critical buckling load of fully or partially supported heavy prismatic piles as well as fully supported non-prismatic piles. In solving the problem, governing differential equation is converted to algebraic equations using differential transformation methods (DT) which must be solved together with applied boundary conditions. The symbolic programming package, Mathematica is ideally suitable to solve such recursive equations by considering fairly large number of terms.

• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.759-767
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• 2003

This paper presents the simplified but more rational analysis method for the prediction of additional internal forces induced in integral abutment bridges. These internal forces depend upon the degree of restraint provided tc the deck by the backfill soil adjacent to the abutments and piles. In addition, effect of the relative flexural stiffness ratio among pile foundations, abutment, and superstructure on the structural behavior is also an important factor. The first part of the paper develops the stiffness matrices, written in terms of the soil stiffness, for the lateral and rotational restraints provided by the backfill soil adjacent to the abutment. The finite difference analysis is conducted and it is confirmed that the results are agreed well with the predictions obtained by the proposed method. The simplified spring model is used in the parametric study on the behavior of simple span and multi-span continuous integral abutment PSC beam bridges in which the abutment height and the flexural rigidity of piles are varied. These results are compared with those obtained by loading Rankine passive earth pressure according to the conventional method. From the results of parametric study, it was shown that the abutment height, the relative flexural rigidity of superstructure and piles, and the earth pressure induced by temperature change greatly affect the overall structural response of the bridge system. It may be possible to obtain more rational and economical designs for integral abutment bridges by the proposed method.

• Journal of the Korean GEO-environmental Society
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• v.5 no.3
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• pp.51-60
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• 2004

In Korea there are recently many attempts to expand a temporary soil nailing system into a permanent soil nailing system since the first construction in 1993. In the soil nailing system, the rigid facing walls act on restraining the deformation of the ground. These are purposed to minimize the damage of adjacent buildings or underground structures. In Korea, to minimize the relaxation of the ground, the soil nailing system in the downtown area is often used experientially together with braced cuts, sheet pile walls, soil cement walls (SCW), or jet grouting walls. However, for the conservative design, the confining effects by the stiff facing have been ignored because the proper design approach of considering the facing stiffness has not been proposed. In this study, various laboratory model tests are carried out to examining the influence the rigidity of facings on the global safety of soil nailing system. Also, the parametric studies using the numerical technique as shear-strength reduction technique are carried out. In the parametric study, the thickness of concrete facing walls is changed to identify the effects of the facing wall stiffness.

• Journal of the Korean Geotechnical Society
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• v.17 no.2
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• pp.85-93
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• 2001

본 논문에서는 연약지반에 시공된 교대말뚝기초에 인접하여 성토하중이 재하될 때 발생하는 측방유동의 발생메커니즘을 규명하기 위해 3차원 유한요소해석을 수행하였다. 본 수치해석에서는 점성토 지반과 점성토-사질토 지반 그리고 사질토-점성토 지반에 선단지지된 강관말뚝에 대하여 성토하중 크기(q=20, 75, 100kPa)와 말뚝두부조건(변위구송, 회전구속) 그리고 말뚝중심간격(s=2.5d, 5.0d, 7.0d, 단독말뚝)에 따라 측방유동압의 분포형태와 크기를 분석하였다. 그 결과 측방유동압의 분포형태는 교대말뚝기초의 수평변위와 유사한 형태로 나타났으며 측방유동압의 크기는 배면 성토하중의 크기에 대한 비로써 결정할 수 있었다. 그리고 점성토 지반과 점성토-사질토 지반의 경우, 측방유동압의 분포형태와 크기는 말뚝두부조건에 가장 큰 영향을 받는 반면 사질토-점성토 지반의 경우에는 말뚝두부조건보다는 토층조건에 가장 큰 영향을 받는 것으로 분석되었다. 본 연구결과를 토대로 연약지반에 시공된 교대말뚝기초의 측방유동에 대한 설계 및 해석시 지침자료로서 측방유동압의 분포형태와 크기를 추천.제안한다.

• Earthquakes and Structures
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• v.10 no.5
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• pp.1143-1179
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• 2016

Offshore wind turbines are considered as a fundamental part to develop substantial, alternative energy sources. In this highly flexible structures, monopiles are usually used as support foundations. Since the monopiles are large diameter (3.5 to 7 m) deep foundations, they result in extremely stiff short monopiles where the slenderness (length to diameter) may range between 5 and 10. Consequently, their elastic deformation patterns under lateral loading differ from those of small diameter monopiles usually employed for supporting structures in offshore oil and gas industry. For this reason, design recommendations (API and DNV) are not appropriate for designing foundations for offshore wind turbine structures as they have been established on the basis of full-scale load tests on long, slender and flexible piles. Furthermore, as these facilities are very sensitive to rotations and dynamic changes in the soil-pile system, the accurate prediction of monopile head displacement and rotation constitutes a design criterion of paramount importance. In this paper, the Fourier Series Aided Finite Element Method (FSAFEM) is employed for the determination of static impedance functions of monopiles for OWT subjected to horizontal force and/or to an overturning moment, where a non-homogeneous soil profile has been considered. On the basis of an extensive parametric study, and in order to address the problem of head stiffness of short monopiles, approximate analytical formulae are obtained for lateral stiffness $K_L$, rotational stiffness $K_R$ and cross coupling stiffness $K_{LR}$ for both rough and smooth interfaces. Theses expressions which depend only on the values of the monopile slenderness $L/D_p$ rather than the relative soil/monopile rigidity $E_p/E_s$ usually found in the offshore platforms designing codes (DNV code for example) have been incorporated in the expressions of the OWT natural frequency of four wind farm sites. Excellent agreement has been found between the computed and the measured natural frequencies.