• Coupled systems mechanics
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• 제3권3호
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• pp.305-318
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• 2014

The study deals with the physical modeling of a typical building frame resting on pile foundation and embedded in cohesive soil mass using complete three-dimensional finite element analysis. Two different pile groups comprising four piles ($2{\times}2$) and nine piles ($3{\times}3$) are considered. Further, three different pile diameters along with the various pile spacings are considered. The elements of the superstructure frame and those of the pile foundation are descretized using twenty-node isoparametric continuum elements. The interface between the pile and pile and soil is idealized using sixteen-node isoparametric surface elements. The current study is an improved version of finite element modeling for the soil elements compared to the one reported in the literature (Chore and Ingle 2008). The soil elements are discretized using eight-, nine- and twelve-node continuum elements. Both the elements of superstructure and substructure (i.e., foundation) including soil are assumed to remain in the elastic state at all the time. The interaction analysis is carried out using sub-structure approach in the parametric study. The total stress analysis is carried out considering the immediate behaviour of the soil. The effect of various parameters of the pile foundation such as spacing in a group and number piles in a group, along with pile diameter, is evaluated on the response of superstructure. The response includes the displacement at the top of the frame and bending moment in columns. The soil-structure interaction effect is found to increase displacement in the range of 58 -152% and increase the absolute maximum positive and negative moments in the column in the range of 14-15% and 26-28%, respectively. The effect of the soil- structure interaction is observed to be significant for the configuration of the pile groups and the soil considered in the present study.

• Coupled systems mechanics
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• 제7권4호
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• pp.455-483
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• 2018

The study deals with physical modeling of a typical three storeyed building frame supported by a pile group of four piles ($2{\times}2$) embedded in cohesive soil mass using three dimensional finite element analysis. For the purpose of modeling, the elements such as beams, slabs and columns, of the superstructure frame; and that of the pile foundation such as pile and pile cap are descretized using twenty noded isoparametric continuum elements. The interface between the pile and the soil is idealized using sixteen node isoparametric surface element. The soil elements are modeled using eight nodes, nine nodes and twelve node continuum elements. The present study considers the linear elastic behaviour of the elements of superstructure and substructure (i.e., foundation). The soil is assumed to behave non-linear. The parametric study is carried out for studying the effect of soil- structure interaction on response of the frame on the premise of sub-structure approach. The frame is analyzed initially without considering the effect of the foundation (non-interaction analysis) and then, the pile foundation is evaluated independently to obtain the equivalent stiffness; and these values are used in the interaction analysis. The spacing between the piles in a group is varied to evaluate its effect on the interactive behaviour of frame in the context of two embedment depth ratios. The response of the frame included the horizontal displacement at the level of each storey, shear force in beams, axial force in columns along with the bending moments in beams and columns. The effect of the soil- structure interaction is observed to be significant for the configuration of the pile groups and in the context of non-linear behaviour of soil.

• 한국지반공학회논문집
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• 제34권5호
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• pp.53-63
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• 2018

무리말뚝의 내진설계를 수행할 때 지반-말뚝 동적상호작용을 고려하는 것이 중요하다. 특히, 동적하중을 받는 무리말뚝의 횡방향 저항력은 무리말뚝 효과에 의하여 단일말뚝과 비교하여 감소한다. 그러나, 지금까지 지진하중을 받는 무리말뚝의 동적 무리말뚝 효과를 제안한 연구는 매우 부족한 실정이다. 그러므로, 본 연구에서는 건조 모래지반에 설치된 $3{\times}3$ 무리말뚝에 대한 동적 원심모형실험을 수행하여 무리말뚝 효과를 산정하였다. 이 무리말뚝 효과는 동적 p-y 곡선에서 극한 횡방향 지반반력과 지반반력계수에 대한 보정계수(multiplier)를 적용하여 고려하였다. 그리고, 본 연구에서 얻어진 동적 p-y 곡선을 Beam on Nonlinear Winkler Foundation 모델을 이용한 비선형 동해석에 적용하여 그 적용성을 검증하였다. 그 결과, 본 연구에서 제안한 무리말뚝의 보정계수가 원심모형실험 결과를 잘 모사할 수 있는 것으로 나타났다.

• Interaction and multiscale mechanics
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• 제2권4호
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• pp.397-411
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• 2009

The effect of soil-structure interaction on a simple single storeyed and two bay space frame resting on a pile group embedded in the cohesive soil (clay) with flexible cap is examined in this paper. For this purpose, a more rational approach is resorted to using the three dimensional finite element analysis with realistic assumptions. The members of the superstructure and substructure are descretized using 20 node isoparametric continuum elements while the interface between the soil and pile is modeled using 16 node isoparametric interface elements. Owing to viability in terms of computational resources and memory requirement, the approach of uncoupled analysis is generally preferred to coupled analysis of the system. However, an interactive analysis of the system is presented in this paper where the building frame and pile foundation are considered as a single compatible unit. This study is focused on the interaction between the pile cap and underlying soil. In the parametric study conducted using the coupled analysis, the effect of pile spacing in a pile group and configuration of the pile group is evaluated on the response of superstructure. The responses of the superstructure considered include the displacement at top of the frame and moments in the superstructure columns. The effect of soil-structure interaction is found to be quite significant for the type of foundation used in the study. The percentage variation in the values of displacement obtained using the coupled and uncoupled analysis is found in the range of 4-17 and that for the moment in the range of 3-10. A reasonable agreement is observed in the results obtained using either approach.

• Structural Engineering and Mechanics
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• 제49권1호
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• pp.95-110
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• 2014

The study deals with physical modeling of space frame-pile foundation and soil system using finite element models. The superstructure frame is analyzed using complete three-dimensional finite element method where the component of the frame such as slab, beam and columns are descretized using 20 node isoparametric continuum elements. Initially, the frame is analyzed assuming the fixed column bases. Later the pile foundation is worked out separately wherein the simplified models of finite elements such as beam and plate element are used for pile and pile cap, respectively. The non-linear behaviour of soil mass is incorporated by idealizing the soil as non-linear springs using p-y curve along the lines similar to that by Georgiadis et al. (1992). For analysis of pile foundation, the non-linearity of soil via p-y curve approach is incorporated using the incremental approach. The interaction analysis is conducted for the parametric study. The non-linearity of soil is further incorporated using iterative approach, i.e., secant modulus approach, in the interaction analysis. The effect the various parameters of the pile foundation such as spacing in a group and configuration of the pile group is evaluated on the response of superstructure owing to non-linearity of the soil. The response included the displacement at the top of the frame and bending moment in columns. The non-linearity of soil increases the top displacement in the range of 7.8%-16.7%. However, its effect is found very marginal on the absolute maximum moment in columns. The hogging moment decreases by 0.005% while sagging moment increases by 0.02%.

• 한국지반환경공학회 논문집
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• 제19권7호
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• pp.5-11
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• 2018

Instead of a single pile, group piles are usually used for the pile foundation. If the earthquake occurs in the ground where group piles are installed, dynamic behavior of group piles are affected not only by interaction of piles and the ground movement but also by the pile cap. However, in Korea, the pile cap influence is not taken account into the design of group piles. Research on dynamic behavior of group piles has been performed only to verify interaction of piles and the ground and has not considered the pile cap as a factor. In this research, 1g shaking table model tests were performed to verify the thickness of the pile cap affects dynamic behavior of group piles that were installed in the ground where the earthquake would occur. The test results show that, as thickness of the pile cap increased, acceleration and horizontal displacement of the pile cap decreasd while vertical displacement of the pile cap increased. The results also showed that, among the group files tested, acceleration, horizontal displacement, and vertical displacement of the bearing pile are smaller than those of the friction pile.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 봄 학술발표회 논문집
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• pp.259-266
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• 1999

In case that pile cap is in direct contact with underlying soil, the bearing mechanism for pile groups, including direct bearing effect of cap and its induced influence on pile-soil-cap interaction, should be properly considered. In this paper, the effects of pile caps on behaviors of pile groups in sandy soils were investigated by model tests, which consist of tests on 3 by 3 pile groups with/without contact on subsoil, single pile with/without contact and cap as a shallow foundation. Also, the influences of pile spacing in group piles on contact effects were investigated. The test results showed that the load carrying capacity of pile cap was large enough not to be ignored. However, the interaction effects due to contact between cap and subsoils were not revealed obviously in working load range. And in the design of pile groups, the bearing effect of pile cap when contacted with subsoils, can be reflected by simply summing up load settlement behaviors of each cap and group piles without contact.

• Geomechanics and Engineering
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• 제24권4호
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• pp.389-397
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• 2021

Pile foundation is a typical form of bridge foundation and viaduct, and large-diameter rock-socketed piles are typically adopted in bridges with long span or high piers. To investigate the effect of a mountain slope with a deep overburden layer on the bearing characteristics of large-diameter rock-socketed piles, four centrifuge model tests of single piles on different slopes (0°, 15°, 30° and 45°) were carried out to investigate the effect of slope on the bearing characteristics of piles. In addition, three pile group tests with different slope (0°, 30° and 45°) were also performed to explore the effect of slope on the bearing characteristics of the pile group. The results of the single pile tests indicate that the slope with a deep overburden layer not only accelerates the drag force of the pile with the increasing slope, but also causes the bending moment to move down owing to the increase in the unsymmetrical pressure around the pile. As the slope increases from 0° to 45°, the drag force of the pile is significantly enlarged and the axial force of the pile reduces to beyond 12%. The position of the maximum bending moment of the pile shifts downward, while the magnitude becomes larger. Meanwhile, the slope results in the reduction in the shaft resistance of the pile, and the maximum value at the front side of the pile is 3.98% less than at its rear side at a 45° slope. The load-sharing ratio of the tip resistance of the pile is increased from 5.49% to 12.02%. The results of the pile group tests show that the increase in the slope enhances the uneven distribution of the pile top reaction and yields a larger bending moment and different settlements on the pile cap, which might cause safety issues to bridge structures.

• 한국지반환경공학회 논문집
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• 제24권10호
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• pp.51-58
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• 2023

지진 시 상부구조물을 지지하는 무리말뚝의 동적거동은 상부구조물의 관성력과 지반의 운동력에 의해 서로 다른 복잡한 동적 메커니즘에 영향을 받는다. 지진 시 상부구조물의 관성력과 지반의 운동력에 의한 지반, 말뚝기초, 상부구조물의 상호작용을 고려하여 말뚝기초의 동적거동을 분석하는 방법으로 동적 p-y 곡선이 사용되고 있다. 말뚝기초의 동적 p-y 곡선을 확인하기 위한 대부분의 연구는 사질토 및 점성토로 이루어진 단일지반에 설치된 말뚝기초를 대상으로 확인되었을 뿐 다층지반에 설치된 말뚝기초의 동적 p-y 곡선을 확인하기 위한 연구는 미비한 실정이다. 이에 본 연구에서는 서로 다른 상대밀도를 갖는 이층지반의 상·하지반의 지층비가 상부구조물을 지지하는 무리말뚝의 동적거동에 미치는 영향을 확인하기 위해 1g 진동대 모형실험을 수행하였다. 그 결과 지층비가 증가할수록 지반, 말뚝캡, 상부구조물에서의 최대가속도는 증가하고, 말뚝기초의 최대휨모멘트의 발생 위치는 변화하는 것으로 나타났다. 그리고 말뚝기초의 동적 p-y 곡선의 기울기는 지층비에 따라 감소 및 증가하는 것으로 확인되었다.

• 대한토목학회논문집
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• 제44권2호
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• pp.191-201
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• 2024

본 연구에서는 3차원 유한요소 해석을 이용하여 기존 건축물의 수직증축 리모델링을 위한 말뚝지지 조건에 따른 기존 및 보강말뚝의 거동에 대해 분석하였다. 수치해석에서 기존 및 보강말뚝 거동의 영향인자로는 캡지지 조건(군말뚝 기초, 말뚝지지 전면기초)과 기존말뚝의 선단근입조건(암반근입, 토사근입)을 고려하였다. 기존말뚝과 보강말뚝의 정량적 거동 분석을 위해 침하량, 하중분담률, 해석 단계에 따른 심도별 축력을 결과로 도출하였다. 분석 결과, 선재하공법 적용에 기인하여 보강말뚝에서 가장 큰 침하량이 발생한 것을 확인하였다. 특히 선단근입조건에 관계없이 군말뚝에서 큰 침하량이 발생하였다. 말뚝지지 전면기초에서는 기초판(Raft)의 영향으로 인해 침하량 및 기존말뚝과 보강말뚝의 하중분담률이 작아지는 것을 확인하였다. 심도별 축력 분포도에서는 군말뚝과 말뚝지지 전면기초 간의 축력 분포에 차이가 나타났으며, 이는 침하량과 하중분담률에 영향을 미치는 주요 요소로 작용하는 것으로 보인다. 수치해석 결과를 바탕으로 수직증축 리모델링을 위한 말뚝기초 설계에 있어서 캡지지 조건과 선단근입 조건을 고려해야 함을 확인하였다.