• 대한기계학회논문집
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• 제18권1호
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• pp.101-112
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• 1994

The measurement of residual stress distribution of $Si_3N_4/SUS304$ joint was performed on 23 specimens with the same joint condition using PSPC type X-ray stress measurement system and the two-dimensional elastoplastic analysis using finite element method was also attempted. As results, residual stress distribution near the interface on the ceramic side of the joint was revealed quantitatively. Residual stress on the ceramic side of the joint was turned out to be tensional near the interface, maximum along the edge, varying in accordance with the condition of the joint and variance to be most conspicuous for the residual stress normal to the interface characterized by the stress singularities. In the vicinity of the interface, the high stress concentration occurs and residual stress distributes three-dimensionally. Therefore, the measured stress distribution differed remarkably from the result of the two-dimensional finite-element analysis. Especially at the center of the specimen near the interface, the residual stress, $\sigma_{x}$ obtained from the finite element analysis was compressive, whereas measurement using X-ray yielded tensile $\sigma_{x}$. Here we discuss two dimensional superposition model the discrepancy between the results from the two dimensional finite element analysis and X-ray measurement.

• 비파괴검사학회지
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• 제14권1호
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• pp.7-15
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• 1994

동을 중간재로 하는 $Si_3N_4/SUS304$ 접합재의 접합계면 근방의 잔류응력 분포를 유한요소법과 X선 응력측정법을 이용하여 해석을 하였다. 그 결과, 접합재의 세라믹부 계면 근방의 잔류응력 분포를 정량적으로 밝혀낼 수 있었다. 세라믹부에 발생되는 접합 잔류응력은 접합계면 근방에서 대단히 크게 나타났으며, 특히 최대인장 잔류응력 ${\sigma}_x$는 단부에서 발생하였다. 한편, ${\sigma}_x$는 접합계면 근방에서 3차원분포를 하고 있기 때문에 2차원 유한요소 해석결과와는 대단히 다른 값을 나타내고 있으며, 특히 시험편 중앙부의 계면 근방에서는 X선 실측결과가 인장 잔류응력임에 반하여 2차원 유한요소 해석결과는 압축 잔류응력으로 계산되어짐을 알았다. 따라서, 이와같은 3차원 분포를 하고 있는 접합계면 근방의 잔류응력 ${\sigma}_x$보다 간편하고 정확하게 예측할 수 있는 유한요소 해석모델에 대하여 서로 검토하였다.

• Structural Engineering and Mechanics
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• 제83권3호
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• pp.377-386
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• 2022

This paper considers dynamic impedance functions and presents a detailed analysis of the soil plasticity influence on the pile-group foundation dynamic response. A three-dimensional finite element model is proposed, and a calculation method considering the time domain is detailed for the nonlinear dynamic impedance functions. The soil mass is modeled as continuum elastoplastic solid using the Mohr-Coulomb shear failure criterion. The piles are modeled as continuum solids and the slab as a structural plate-type element. Quiet boundaries are implemented to avoid wave reflection on the boundaries. The model and method of analysis are validated by comparison with those published on literature. Numerical results are presented in terms of horizontal and vertical nonlinear dynamic impedances as a function of the shear soil parameters (cohesion and internal friction angle), pile spacing ratio and frequencies of the dynamic signal.

• Computers and Concrete
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• 제4권3호
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• pp.187-206
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• 2007

A rational three-dimensional nonlinear finite element model is described and implemented for evaluating the behavior of high strength concrete slabs under transverse load. The concrete was idealized by using twenty-nodded isoparametric brick elements with embedded reinforcements. The concrete material modeling allows for normal (NSC) and high strength concrete (HSC), which was calibrated based on experimental data. The behavior of concrete in compression is simulated by an elastoplastic work-hardening model, and in tension a suitable post-cracking model based on tension stiffening and shear retention models are employed. The nonlinear equations have been solved using the incremental iterative technique based on the modified Newton-Raphson method. The FE formulation and material modeling is implemented into a finite element code in order to carry out the numerical study and to predict the behavior up to ultimate conditions of various slabs under transverse loads. The validity of the theoretical formulations and the program used was verified through comparison with available experimental data, and the agreement has proven to be very good. A parametric study has been also carried out to investigate the influence of different material and geometric properties on the behavior of HSC slabs. Influencing factors, such as concrete strength, steel ratio, aspect ratio, and support conditions on the load-deflection characteristics, concrete and steel stresses and strains were investigated.

• Structural Engineering and Mechanics
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• 제49권1호
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• pp.1-22
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• 2014

A seismic evaluation is made of the response to horizontal ground shaking of cantilever retaining walls using the finite element model in three dimensional space whose verification is provided analytically through the modal analysis technique in case of the assumptions of fixed base, complete bonding behavior at the wall-soil interface, and elastic behavior of soil. Thanks to the versatility of the finite element model, the retained medium is then idealized as a uniform, elastoplastic stratum of constant thickness and semi-infinite extent in the horizontal direction considering debonding behavior at the interface in order to perform comprehensive soil-structure interaction (SSI) analyses. The parameters varied include the flexibility of the wall, the properties of the soil medium, and the characteristics of the ground motion. Two different finite element models corresponding with flexible and rigid wall configurations are studied for six different soil types under the effects of two different ground motions. The response quantities examined incorporate the lateral displacements of the wall relative to the moving base and the stresses in the wall in all directions. The results show that the wall flexibility and soil properties have a major effect on seismic behavior of cantilever retaining walls and should be considered in design criteria of cantilever walls. Furthermore, the results of the numerical investigations are expected to be useful for the better understanding and the optimization of seismic design of this particular type of retaining structure.

• 한국지반공학회논문집
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• 제19권6호
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• pp.245-259
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• 2003

본 논문은 강관 다단 그라우팅 터널 보강에 대한 메카니즘 규명에 대한 연구이다. 본 보강공법을 구성하고 있는 보강요소들의 복잡한 기하학적 특성과 각 보강요소들이 전체 보강 메카니즘에 기여하는 정도의 불명확성에 기인하여 본 공법으로 보강된 터널을 합리적으로 해석하기란 무척 어려운 문제로 여겨지고 있다. 따라서 본 연구에서는 균질화 기법을 도입하여 본 공법으로 보강된 지반매질을 하나의 복합체로써 정의하고 수치 모델화하여, 이를 기반으로 3차원 탄소성 유한요소코드를 개발하였다. 이때 균질화 기법과 연계된 굴착단계별 해석 등과 같은 터널해석을 위해 요구되는 다양한 실용적인 알고리즘들 또한 제안되었다. 이러한 과정으로 개발된 3차원 탄소성 유한요소코드를 이용하여 본 보강공법의 이방성 보강 메카니즘에 관하여 고찰되었으며, 이를 위해 다양한 주요 설계인자들에 대한 매개변수 연구가 수행되었다. 이를 통해 유도된 복합 보강 지반체의 역학적 거동특성은 각 구성 매질들의 기하학적 특성과 기여도 등을 잘 모사하고 있는 것으로 판단되었다.

• Earthquakes and Structures
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• 제23권1호
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• pp.101-113
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• 2022

A new type of fabricated subway station construction technology can effectively solve these problems. For a new type of metro structure form, it is necessary to clarify its mechanical properties, especially the seismic performance. A soil-structure elastoplastic finite element model is established to perform three-dimensional nonlinear dynamic time-history analysis based on the first fabricated station structure-Yuanjiadian station of Changchun Metro Line 2, China. Firstly, the nonlinear seismic response characteristics of the fabricated and cast-in-place subway stations under different seismic wave excitations are compared and analyzed. Then, a comprehensive analysis of several important parameters that may affect the seismic response of fabricated subway stations is given. The results show that the maximum plastic strain, the interlayer deformation, and the internal force of fabricated station structures are smaller than that of cast-in-place structure, which indicates that the fabricated station structure has good deformation coordination capability and mechanical properties. The seismic responses of fabricated stations were mainly affected by the soil-structure stiffness ratio, the soil inertia effect, and earthquake load conditions rarely mentioned in cast-in-place stations. The critical parameters have little effect on the interlayer deformation but significantly affect the joints' opening distance and contact stress, which can be used as the evaluation index of the seismic performance of fabricated station structures. The presented results can better understand the seismic responses and guide the seismic design of the fabricated station.

• Geomechanics and Engineering
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• 제25권2호
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• pp.99-109
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• 2021

Tunnel provide faster, safer and convenient way of transportation for different objects. The region where it is construction and surrounding medium has significant influence on the overall stability and performance of tunnel. The present simulation has been carried out in order to understand the behaviour of rock tunnel under static loading condition. The present numerical model has been validated with the laboratory scaled model and field data of underground tunnels. Both lined and unlined tunnels have been considered in this paper. Finite element technique has been considered for the simulation of static loading effect on tunnel through Abaqus/Standard. The Mohr-Coulomb material model has been considered to simulate elastoplastic nonlinear behaviour of different rock types, i.e., Basalt, Granite and Quartzite. The four different stages of rock weathering are classified as fresh, slightly, moderately, and highly weathered in case of each rock type. Moreover, extremely weathered stage has been considered in case of Quartzite rock. It has been concluded that weathering of rock and overburden depth has great influence on the tunnel stability. However, by considering a particular weathering stage of rock for each rock type shows varying patterns of deformations in tunnel.

• Geomechanics and Engineering
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• 제10권5호
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• pp.599-615
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• 2016

The present research presents experimental and finite element studies to investigate the behavior of piled raft-tunnel system in a sandy soil. In the experimental work, a small scale model was tested in a sand box with load applied vertically to the raft through a hydraulic jack. Five configurations of piles were tested in the laboratory. The effects of pile length (L), number of piles in the group and the clearance distance between pile tip and top of tunnel surface (H) on the load carrying capacity of the piled raft-tunnel system are investigated. The load sharing percent between piles and rafts are included in the load-settlement presentation. The experimental work on piled raft-tunnel system yielded that all piles in the group carry the same fraction of load. The load carrying capacity of the piled raft-tunnel model was increased with increasing (L) for variable (H) distances and decreased with increasing (H) for constant pile lengths. The total load carrying capacity of the piled raft-tunnel model decreases with decreasing number of piles in the group. The total load carrying capacity of the piles relative to the total applied load (piles share) increases with increasing (L) and the number of piles in the group. The increase in (L/H) ratio for variable (H) distance and number of piles leads to an increase in piles share. ANSYS finite element program is used to model and analyze the piled raft-tunnel system. A three dimensional analysis with elastoplastic soil model is carried out. The obtained results revealed that the finite element method and the experimental modeling are rationally agreed.