• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 연약지반처리위원회 학술세미나
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• pp.32-41
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• 2000

Sand drain as a vertical drainage is widely used in soft ground improvement Recently, sand, the principal source of sand drain, is running out. The laboratory model tests were carried out to utilize gravel as a substitute for sand. Though which the characteristics of gravel are compared to those of sand for engineering purpose. Two cylindrical containers for the model test were filled with marine clayey soil from the west coast of Korea with a column in the center, one with sand, the other with gravel. Vibrating wire type piezometers were installed at the distance of 1.0D, 1.5D and 2.0D from the center of the column. The characteristics of consolidation were studied with data obtained from the measuring instrument place on the surface of the container. The parameter study was performed on the marine clayey soil before and after the test in order to verify the effectiveness of the improvement. The clogging effect was checked at various depth in gravel column after the test. In-situ tests area was divided into two areas by material used. One is Sand Drain(SD) and Sand Compaction Pile(SCP) area, the other is Gravel Drain(GD) and Gravel Compaction Pile(GCP) area. Both areas were monitored to obtain the information on settlement, pore water pressure and bearing capacity by measuring instruments for stage loading caused by embankment. The results of measurements were analyzed. According to the test results, the settlement was found to be smaller in gravel drain than in sand drain. The increase in bearing capacity by gravel pile explains the result. The clogging effect was not found in gravel column. It is assumed that gravel is relatively acceptable as a drainage material. Gravel is considered to be a better material than sand for bearing capacity, and it is found that bearing capacity is larger when gravel is used as a gravel compaction pile than as a gravel drain.

• Geomechanics and Engineering
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• 제23권3호
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• pp.245-259
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• 2020

Tunnels have become an indispensable part of metro cities. Blast resistance design of tunnel has attracted the attention of researchers due to numerous implosion event. Present paper deals with the non-linear finite element analysis of rock tunnel having shear zone subjected to internal blast loading. Abaqus Explicit schemes in finite element has been used for the simulation of internal blast event. Structural discontinuity i.e., shear zone has been assumed passing the tunnel cross-section in the vertical direction and consist of Highly Weathered Granite medium surrounding the tunnel. Mohr-Coulomb constitutive material model has been considered for modelling the Highly Weathered Granite and the shear zone material. Concrete Damage Plasticity (CDP), Johnson-Cook (J-C), Jones-Wilkins-Lee (JWL) equation of state models are used for concrete, steel reinforcement and Trinitrotoluene (TNT) simulation respectively. The Coupled-Eulerian-Lagrangian (CEL) method of modelling for TNT explosive and air inside the tunnel has been adopted in this study. The CEL method incorporates the large deformations for which the traditional finite element analysis cannot be used. Shear zone orientations of 0°, 15°, 30°, 45°, 60°, 75° and 90°, with respect to the tunnel axis are considered to see their effect. It has been concluded that 60° orientation of shear zone presents the most critical situation.

• 전산구조공학
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• 제5권4호
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• pp.93-102
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• 1992

원자로내부구조물의 설계시 필요한 동적응답해석을 위하여 각 구조물의 정확한 진동특성을 파악할 필요가 있다. 한국표준형 원자력발전소를 위하여 설계된 제어봉집합체 보호구조물은 기존의 설계로 부터 많은 설계변경이 있었고, 또 이 구조물은 튜우브와 얇은 판이 사각격자형태로 이루어져 있고 연결봉에 의해 고정되는 등 매우 복잡한 형태로 구성되어 있어서 해석과 시험을 위한 진동측정프로그램을 수행할 필요성이 대두되었다. 따라서 본 논문에서는 보호구조물의 진동시험을 수행하여 동적특성을 구하였고 또한 유한요소모델을 이용하여 해석에 의해 시험조건하에서의 고유진동수와 모우드형상을 구하였다. 시험과 해석에 의한 모우드특성을 비교한 결과 매우 잘 일치함으로써 구조물의 동적응답을 구하기 위한 해석모델의 타당성을 보였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.397-401
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• 2008

Knowledge of dynamic characteristics of structural elements often can make difference between success and failure in the design of structure due to resonance effect. In this paper an analytical model of a cantilever beam having midpoint load is considered for structural optimization. This involves creating the geometry which allows parametric study of all design variables. For that purpose optimization of cantilever beam is elaborated in order to find the optimum geometry which minimizes its volume eventually for minimum weight using ANSYS. But such geometry could be obtained by different combinations of width and height, so that it may have the same cross sectional area yet different dynamic behavior. So for optimum safe design, besides minimum volume it should have minimum vibration as well. In order to predict vibration different dynamic analyses are performed simultaneously to solve the eigenvalues problem assuming no damping initially through MATLAB simulations using state space form for modal analysis, which identifies the resonant frequencies and mode shapes belonging to the lowest three modes of vibration. And next by introducing damping effects tip displacement, bending stress and the vertical reaction force at the fixed end is evaluated under some dynamic load of varying frequency, and finally it is discussed how resonance can be avoided for particular design. Investigation of results clearly shows that only structural analysis is not enough to predict the optimum values of dimension for safe design. Potentially this technique will meet maintenance and cost goals of many organizations particularly for the application where dynamic loading is invertible and helps a lot ensuring that the proposed design will be safe for both static and dynamic conditions.

• 대한치과보철학회지
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• 제54권3호
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• pp.246-252
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• 2016

이중관 가철성 국소의치는 지대치 간의 이차고정(secondary splinting), 응력의 수직 방향, 지대치 지렛점(fulcrum)의 내 외관 margin 부위 위치로 인한 지렛대 길이(the length of lever arm)의 감소로 소수 잔존치이거나 지대치의 상태가 좋지 않은 경우에도 성공적으로 사용될 수 있다. 또한 이중관(double crown)을 이용한 의치는 치아가 얼마 남지 않은 부분 무치악 환자 뿐만 아니라, 소수의 임플란트를 식립한 임플란트 오버덴처에 있어서 성공적인 치료결과를 보여주고 있다. 본 증례에서는 상악은 소수 치아가 잔존했고, 하악은 치조골 흡수 및 수축이 심하고 임플란트가 실패한 상태였다. 상악의 소수 잔존치는 치주적으로 불량하였고, 하악에는 2개의 임플란트만을 다시 식립하였다. 이러한 불리한 조건에서 이중관 가철성 국소의치를 이용한 치료를 계획하였다. 1년여 정도의 관찰 기간 동안 기능적, 심미적으로 만족스러운 결과를 얻을 수 있었으며, 이중관 가철성 국소의치의 효용성을 증명하였기에 본 증례를 보고하고자 한다.

• Structural Engineering and Mechanics
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• 제53권4호
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• pp.791-818
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• 2015

RC buildings constitute the prevailing type of construction in earthquake-prone region like Kathmandu Valley. Most of these building constructions were based on conventional methods. In this context, the present paper studied the seismic behaviour of existing RC buildings in Kathmandu Valley. For this, four representative building structures with different design and construction, namely a building: (a) representing the non-engineered construction (RC1 and RC2) and (b) engineered construction (RC3 and RC4) has been selected for analysis. The dynamic properties of the case study building models are analyzed and the corresponding interaction with seismic action is studied by means of non-linear analyses. The structural response measures such as capacity curve, inter-storey drift and the effect of geometric non-linearities are evaluated for the two orthogonal directions. The effect of plan and vertical irregularity on the performance of the structures was studied by comparing the results of two engineered buildings. This was achieved through non-linear dynamic analysis with a synthetic earthquake subjected to X, Y and $45^{\circ}$ loading directions. The nature of the capacity curve represents the strong impact of the P-delta effect, leading to a reduction of the global lateral stiffness and reducing the strength of the structure. The non-engineered structures experience inter-storey drift demands higher than the engineered building models. Moreover, these buildings have very low lateral resistant, lesser the stiffness and limited ductility. Finally, a seismic safety assessment is performed based on the proposed drift limits. Result indicates that most of the existing buildings in Nepal exhibit inadequate seismic performance.

• Journal of Periodontal and Implant Science
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• 제40권1호
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• pp.25-32
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• 2010

Purpose: The performance of implant surgery in the posterior maxilla often poses a challenge due to insufficient available bone. Sinus floor elevation was developed to increase the needed vertical height to overcome this problem. However, grafting materials used for the sinus lift technique eventually show resorption. The present study radiographically compared and evaluated the changes in height of the grafting materials after carrying out maxillary sinus elevation with a window opening procedure. This study also evaluated the difference between two xenogenic bone materials when being used for the sinus lifting procedure. Methods: Twenty-one patients were recruited for this study and underwent a sinus lift procedure. All sites were treated with either bovine bone (Bio-$Oss^{(R)}$) with platelet-rich plasma (PRP) or bovine bone (OCS-$B^{(R)}$)/PRP. A total of 69 implants were placed equally 6-8 months after the sinus lift. All sites were clinically and radiographically evaluated right after the implant surgery, 7-12 months, 13-24 months, and 25-48 months after their prosthetic loading. Results: Changes of implant length/bone length with time showed a statistically significant decreasing tendency (P<0.05). There was no significant change in the Bio-$Oss^{(R)}$ group (P>0.05). In contrast, the OCS-$B^{(R)}$ group showed a significant decrease with time (P<0.05). However, no significant difference was observed between the two groups (P>0.05). Conclusions: The results showed that there was significant reduction in comparison with data right after placement, after 7 to 12 months, 13 to 24 months, and over 25 months; however, reduction rates between each period have shown to be without significance. No significant difference in height change was observed between the Bio-$Oss^{(R)}$ and the OCS-$B^{(R)}$ groups.

• 콘크리트학회논문집
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• 제27권4호
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• pp.387-397
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• 2015

본 연구에서는 시공성 향상을 위해 데크플레이트와 비정질강섬유 콘크리트를 적용하여 현장 무배근 슬래브 시스템을 연구하였다. 제안한 슬래브에서는 온도철근을 강섬유로 대체하였다. 본 연구는 연속슬래브에서 상부 철근이 연속되지 않는 경우 슬래브의 상부 균열 제어를 주로 고려하였다. 실험변수로 비정질강섬유 혼입량, 강섬유 종류, 데크플레이트 종류, 연속구간의 철근 이음을 고려하였으며, 수직하중을 받는 2경간 슬래브를 실험하였다. 슬래브의 균열저항성능을 평가하기 위하여 연속슬래브의 하중에 따른 균열폭을 계측하였다. 실험결과, 상부 이음철근을 사용하지 않더라도 합성슬래브의 높은 휨강성으로 인하여 균열을 억제할 수 있는 것으로 나타났다.

• 한국지반환경공학회 논문집
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• 제17권10호
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• pp.13-22
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• 2016

본 연구에서는 가이드라인에 제시된 스퍼드캔의 설계 프로세스에 따라 서남해 연약지반 조건에 최적화된 스퍼드캔의 형상 및 크기를 도출하고, 안정성 평가를 위한 복합하중 작용 시의 항복면을 정의하였다. 이를 위해 일정한 수직하중 작용 시 수평하중과 모멘트 하중을 가하여 수평하중-수평변위, 모멘트-회전변위간의 상관관계를 통해 항복면을 산출하는 프로브 방법을 적용하였다. 분석 결과, 복합하중을 고려한 서남해 지반에서 요구되는 스퍼드캔의 직경은 8m로 나타났으며, 가이드라인에 제시된 지지력 산출경험식을 통해 지지력을 계산할 경우 얕은 심도에서는 비교적 정확한 지지력의 예측이 가능한 것으로 나타났다. 제시된 항복면은 Mohr Coulomb 모델과 Hardening soil 모델을 각각 적용하였을 시 서로 다른 형상을 보였으나, 스퍼드캔의 직경이 증가함에 따라 점차 확장되는 경향을 보였다. 본 연구를 통해 제시된 항복면은 실제 스퍼드캔이 설치될 지역의 지반조사 결과, 가이드라인과 더불어 추후 해상풍력단지 조성 시 스퍼드캔의 안정성 평가에 유용한 참고자료로 활용될 수 있을 것으로 판단된다.

• 한국지반공학회논문집
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• 제18권4호
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• pp.147-157
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• 2002

본 연구에서는 방사방향의 배수조건을 갖는 점성토의 압밀특성을 짧은 시간에 정확하게 평가할 수 있는 방사배수 일정변형률 압밀시험을 위한 시험기와 해석이론을 개발하였다. 개발된 시험기 및 해석이론에 대한 적용성을 검토하기 위하여 성형시료 및 불교란 시료에 대하여 방사배수 일정변형률 압밀시험과 단계하중 압밀시험을 실시하였다. 압밀곡선으로부터 평가되는 압밀정수 및 압밀계수에 대한 비교, 분석을 통하여 제안된 시험기 및 이론의 신뢰성과 적용성을 평가하였고, 방사배수 시험과 더불어 수행된 연직배수 일정변형률 압밀시험과 단계하중 압밀시험을 통하여 배수방향에 따른 영향과 시험기 및 해석이론의 적용성을 분석하였다. 또한, 일정변형률 압밀시험시 발생하는 과잉간극수압에 대한 분석을 통하여 간극수압의 발생 양상 및 실험결과에 미치는 영향을 확인하였다.