• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.2
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• pp.271-278
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• 2000

In this study the effect and applicability of viscoelastic dampers on the seismic reinforcement of steel framed structures are investigated in the context of the performance based design approach. The effect of the damper on dissipating the input seismic energy was investigated with a single degree of freedom system. For analysis models a five-story steel frame subjected to gravity load, a ten-story and twenty-story structure subjected to gravity and wind load were designed. The code-specified design spectrums were constructed for each soil type and performance objective, and artificial ground excitation records to be used in the nonlinear time history analysis were generated based on the design spectrums. Inter-story drift was adopted as the primary performance criterion. According to the analysis results, all model structures turned out to satisfy the performance level for most of the soil conditions except for the soft soil(operational level). It was also found that the seismic performance could be greatly enhanced, and the structures were led to behave elastically by installing viscoelastic dampers on appropriate locations.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.77-86
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• 2020

In this study, the importance of implied strength correction for shallow depths at a region of moderate to low seismicity with primary focus on its effect upon site natural period and mean period of the ground motion is investigated. In addition to the most commonly used Modified Kondner-Zelasko (MKZ) model, this paper uses a quadratic/hyperbolic (GQ/H) model that can capture the stress - strain response at large strains as well as small strain stiffness dependence. A total of six site profiles by downhole tests are used and 1D site response analyses are performed using three input motions with contrasting mean periods. The difference between non-corrected and corrected analyses is conditional on the site period as well as mean ground motion period. The effect of periods is analyzed by correlating them with the effective peak ground acceleration, maximum shear strains and amplification factors. The comparative study reveals that the difference is more prominent in soft sites with long site periods. Insignificant differences are observed when soil profiles are subjected to ground motion with very short mean period.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.157-160
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• 2011

본 연구에서는 광섬유 센서 기반 스마트 모니터링 시스템이 지중 열전도도 측정에도 효율적으로 적용될 수 있는지를 분석하였다. 이를 위해 광섬유 온도센서를 이용하여 지반의 열전도도를 측정할 수 있는 열응답 시험기가 개발되었다. 개발된 열응답 시험기는 기존의 RTD(Resistance Temperature Detector) 온도 센서 외에 광섬유 센서의 한 종류인 FBG(Fiber Bragg Grating) 센서도 실시간적으로 측정할 수 있는 시스템으로 구성되어 있다. 개발된 장비의 적용성 검증을 위하여 주문진 표준사를 이용하여 모형토조 내에 일정한 간극비에 맞추어 시료가 조성되었으며 지중열교환기는 U자형 파이프가 사용되었다. 20시간동안 열응답 시험을 통하여 광섬유 센서와 RTD 센서를 동시에 이용하여 온도값을 측정하여 표준사의 열전도도 값을 산출하였다. 그 결과 모형실험을 통한 열전도도 값은 탐침법을 통해 얻어진 열전도도 값과 선형 열원 모델(line source model) 해석해와 거의 유사하게 나타났으며 광섬유 센서와 RTD 센서와의 온도차는 0.1~0.3$^{\circ}$로써 유사한 값을 나타내었다. 따라서 본 연구에서 개발된 광섬유 기반 열응답 시험기는 지반의 열전도도를 측정하는데 효과적으로 사용될 수 있음을 알 수 있었으며 향후 지열시스템 가동에 따른 지중열 교환기의 손상도 평가 및 경보시스템 개발을 위해 지중열교환기의 거동을 실시간으로 모니터링 하는데 있어서도 효과적으로 사용될 수 있을 것으로 생각된다.

• Journal of the Korean Geotechnical Society
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• v.40 no.2
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• pp.95-103
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• 2024

The global increase in population and subsequent scarcity of terrestrial living spaces necessitates exploration of alternative habitats. Research into the development of underwater living areas provides promising avenues for the expansion of human living spaces and the use of marine environments. This study focuses on the failure envelope of suction caisson foundations subjected to combined loads in a marine setting, utilizing finite element analysis. The foundation is assumed to be embedded in clay characterized by a linear increase in undrained shear strength with depth, employing the von Mises constitutive model for the clay. The resulting failure envelope is represented as a tilted ellipse which expands as the undrained shear strength increases, maintaining a constant ratio between the major and minor axes. A comparative analysis of two suction caisson foundations with varying length-to-diameter ratios revealed that this ratio influences the dimensions of the failure envelope, with a tendency for the major-to-minor axis ratio to increase as the length-to-diameter ratio increases. These findings are critical for the design of suction caisson foundations in offshore environments.

• Geotechnical Engineering
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• v.8 no.2
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• pp.5-20
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• 1992

The physical-based and lumped-parameter hydrologic groundwater flow model for predicting the rainfall-triggered rise of groundwater levels in hillside slopes is developed in this paper to assess the risk of landslides. The developed model consists of a vertical infiltration model for unsaturated zone linked to a linear storage reservoir model(LSRM) for saturated zone. The groundwater flow model has uncertain constants like soil depttL slope angle, saturated permeability, and potential evapotranspiration and four free model parameters like a, b, c, and K. The free model parameters could be estimated from known input-output records. The BARD algorithm is uses as the parameter estimation technique which is based on a linearization of the proposed model by Gauss -Newton method and Taylor series expansion. The application to examine the capacity of prediction shows that the developed model has a potential of use in forecast systems of predicting landslides and that the optimal estimate of potential 'a' in infiltration model is the most important in the global optimum analysis because small variation of it results in the large change of the objective function, the sum of squares of deviations of the observed and computed groundwater levels. 본 논문에서는 가파른 산사면에서 산사태의 발생을 예측하기 위한 수문학적 인 지하수 흐름 모델을 개발하였다. 이 모델은 물리적인 개념에 기본하였으며, Lumped-parameter를 이용하였다. 개발된 지하수 흐름 모델은 두 모델을 조합하여 구성되어 있으며, 비포화대 흐름을 위해서는 수정된 abcd 모델을, 포화대 흐름에 대해서는 시간 지체 효과를 고려할 수 있는 선형 저수지 모델을 이용하였다. 지하수 흐름 모델은 토층의 두께, 산사면의 경사각, 포화투수계수, 잠재 증발산 량과 같은 불확실한 상수들과 a, b, c, 그리고 K와 같은 자유모델변수들을 가진다. 자유모델변수들은 유입-유출 자료들로부터 평가할 수 있으며, 이를 위해서 본 논문에서는 Gauss-Newton 방법을 이용한 Bard 알고리즘을 사용하였다. 서울 구로구 시흥동 산사태 발생 지역의 산사면에 대하여 개발된 모델을 적용하여 예제 해석을 수행함으로써, 지하수 흐름 모델이 산사태 발생 예측을 위하여 이용할 수 있음을 입증하였다. 또한, 매개변수분석 연구를 통하여, 변수 a값은 작은 변화에 대하여 목적함수값에 큰 변화를 일으키므로 a의 값에 대한 최적값을 구하는 것이 가장 중요한 요소라는 결론을 얻었다.

• Journal of the Korean GEO-environmental Society
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• v.7 no.1
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• pp.67-80
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• 2006

This paper presented an application of the geotechnical hybrid-online simulation to the consolidation settlement problem of soft clay. Conventional numerical analyses have used idealized soil constitutive models obtained from the laboratory soil tests. On the other hand, in the hybrid-online simulation, soil response was directly introduced to numerical analyses from the soil element test, and, therefore, the complicated parameter estimation was not required in this method. Fundamentals of the hybrid-online simulation method and the development of the algorithm and corresponding hardware and software for the system were presented in this study. Furthermore, an incremental loading consolidation and the hydraulic conductivity test and a comparative study using the Terzagh's conventional consolidation theory were carried out for the system verification including the performance of the experimental device and source coding of software components, and the data reliability obtained from the system. In conclusion, we found that the hybrid-online consolidation simulation system could reproduce the consolidation behavior of the remolded Kaolinite specimen withoutany discrepancies.

• Journal of the Korean Geosynthetics Society
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• v.19 no.1
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• pp.93-101
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• 2020

In order to predict the nonlinear behaviour of the soil, the elasto-plastic hyperbolic model was selected, which was considered to be relatively simple and highly predictable. The soil parameter determination and the behavior analysis program were developed by formalizing the functions related to the constitutive model. Each soil parameter was determined from the results of the drained triaxial compression tests of Baekma river sand with the change of relative density. The stress-strain behavior was predicted using the soil parameters determined under each condition. As a result, the deviator stress for the axial strain is verified to have a good match between the measured value and predicted value at each relative density. In the relationship between the volumetric stain and the axial strain, when the relative density is loose, the measured value and predicted value tend to match, and when relative density is dense, the predicted value of the volumetric strain appears somewhat smaller than the measured value due to the limitation of the constitutive model.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.2
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• pp.93-106
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• 2021

In general, segment lining tunnel refers to a tunnel formed by connecting precast concrete segments as a ring and connecting such rings to each other in the longitudinal direction of the tunnel. As the structural properties of the segment lining is highly dependent on the behavior of the segment joints, thus correct modelling of joint behavior is crucial to understand and design the segment tunnel lining. When the tunnel is subjected to ground loads, the segment joint behaves like a hinge that resists rotation, and when the induced moment exceeds a certain limit of the rotation then it may enter into non-linear field. In understanding the effect of the segment joint on the lining behavior, a moment-rotation relationship of the segment joint was explored based on the Japanese practice and Janssen's approach commonly used in the actual design. This study also presents a method to determine the rotational stiffness of joint refer to the bearing strength. The rotation of the segment joint was estimated in virtual design conditions based on the existing models and the proposed method. And the sectional force of the segment lining and joint were calculated along with the estimated rotation. As the rotation at the segment joint increases, the joint contact area decreases, so the designer have to verify the segment joint for bearing strength as well. This paper suggests a consistent method to determine the rotational stiffness and bearing strength of joints.

• Tunnel and Underground Space
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• v.30 no.4
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• pp.271-305
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• 2020

An effect of coupled thermo-hydro-mechanical and chemical (THMC) behavior is an essential part of the performance and safety assessment of geological disposal systems for high-level radioactive waste and spent nuclear fuel. Furthermore, numerical models and modeling techniques are necessary to analyze and predict the coupled THMC behavior in the disposal systems. However, phenomena associated with the coupled THMC behavior are nonlinear, and the constitutive relationships between them are not well known. Therefore, it is challenging to develop numerical models and modeling techniques to analyze and predict the coupled THMC behavior in the geological disposal systems. It is also difficult to verify and validate the development of the models and techniques because it requires expensive laboratory tests and in-situ experiments that need to be performed for a long time. DECOVALEX was initiated in 1992 to efficiently develop numerical models and modeling techniques and validate the developed models and techniques against the lab and in-situ experiments. In Korea, Korea Atomic Energy Research Institute has participated in DECOVALEX-2011, DECOVALEX-2015, and DECOVALEX-2019 since 2008. In this study, all tasks in the three DECOVALEX projects were introduced to the researcher in the field of rock mechanics and geotechnical engineering in Korea.