• Journal of the Korean Geotechnical Society
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• v.20 no.1
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• pp.121-129
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• 2004

In this study, a slope stability chart for assessing stability of homogeneous simple soil slopes is proposed. Most existing slope stability charts are based on limit equilibrium method, which is not rigorous in mechanical standpoint. Meanwhile, limit analysis based on the principle of virtual work and the bound theorems of plasticity is suitable for evaluating the stability of geotechnical structures such as slope due to its simplicity in computation and mechanical rigor. Numerical limit analysis taking advantage of finite elements and linear programming can consider various slope conditions and, in addition, find the optimum stability solution with effeciency. In this study, a numerical limit analysis program in terms of effective stress is developed and a mechanically rigorous slope stability chart is proposed by performing stability analyses for various slope conditions. Pore pressure ratio, commonly used in stability charts, is applied to consider the effects of pore pressure for effective stress analysis. As a result of comparison between proposed stability chart and Spencer's stability chart, it was found that Spencer's chart solutions are biased to lower bound which means conservative in design.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.232-232
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• 2022

1차원 관망해석모형과 2차원 지표면범람 해석모형을 이용한 도시지역의 실시간 홍수예·경보시스템 구축은 모형의 모의에 많은 시간이 소요되므로 한계가 있다. 또한, 연구유역에서 시나리오 강우에 대해 침수를 유발시키는 한계강우량을 1-2차원 모형의 시행착오법을 적용한 반복적인 수행을 통해 산정하는 것은 비효율적인 방법이다. 따라서, 본 연구에서는 이에 대한 해결책으로 로지스틱 회귀를 이용하여 배수분구별 침수 발생기준 강우량을 산정하고자 한다. 침수 발생 한계강우량 산정을 배수분구 단위로 제시하기 위하여 로지스틱 회귀분석을 이용하였다. 풍수해저감종합계획(2015)과 침수흔적도를 이용하여 배수분구 별 침수이력에 대한 데이터베이스를 구축하고, 이를 1-2차원 수리해석을 통한 침수심과 함께 로지스틱 회귀모형에 학습하였다. 지속시간 1시간, 10mm 강우부터 500년 빈도의 Huff 3분위 시나리오 17개를 사용하여 확률강우량을 산정하였고, 이를 1-2차원 수리해석을 위한 입력자료로 사용하였다. EPA-SWMM을 통한 1차원 도시유출해석과 FLO-2D를 통한 2차원 침수해석에서 20cm 이상의 침수심이 발생하거나 지상관측자료, 침수흔적도 및 풍수해저감종합계획에서 실제 침수가 발생했을 경우를 1, 그렇지 않은 경우를 0으로 하여 데이터베이스를 구축하여 로지스틱 회귀모형에 학습시켜 침수 발생 한계강우량을 산정하였다. 로지스틱 회귀분석을 통해 서울시 지역의 배수분구별 한계강우량을 산정할 수 있으며, 지속적으로 관측되는 강우 및 침수 발생 유무 자료를 추가함으로써 산정된 침수 한계강우량을 상회하는 강우 사상이 나타났을 시에 침수 발생 유무를 확인하여 본 연구에서 제안한 방법에 대해 검증이 가능할 것으로 보인다.

• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.7-22
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• 2023

In this study, the limit range of input acceleration was investigated based on time domain and response spectrum analyses by considering the relative density, groundwater depth, and soil type. Special attention was paid to the input acceleration and shear modulus of soil, which affect pile behavior. The surrounding soil was identified as an elastoplastic material and subjected to FLAC3D analysis using the Mohr-Coulomb and Finn models as well as FB-Multiplier analysis using a nonlinear p-y curve for soil spring. Based on the analyses, the limit range of acceleration on the pile is much higher for SP soil than for SM soil, and the groundwater level tends to reduce the limit range of input acceleration, irrespective of soil conditions. The limit range of acceleration was mainly affected by the shear modulus. The limit range of acceleration with nonlinear soil behavior is proportional to the relative density of the surrounding soil.

• Journal of the Korean Geotechnical Society
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• v.26 no.3
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• pp.47-57
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• 2010

Yield seismic coefficient plays an important role in the estimation of permanent displacement of a soil slope subjected to earthquake using Newmark's sliding block theory. However, yield seismic coefficients currently used in practices are not mechanically rigorous since most of them are estimated using limit equilibrium methods considering equilibrium condition only. Therefore, estimation of permanent displacement of a soil slope based on existing yield seismic coefficient may cause problems. Limit analysis estimating the range of mechanically rigorous solution is thought to be effective in evaluating the validity of existing yield seismic coefficient. In this study, a simple stability chart for yield seismic coefficient useful in practices is proposed by considering various slope conditions including stability number, slope inclination, strength parameters, etc.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.475-484
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• 1999

압력절점은 요소의 균등한 압력증분을 1개의 자유도로 갖는 절점이며, 유한요소의 하중-변위 평형방정식에 체적과 압력의 관계를 추가하여 한계압력 이후에서도 체적변화에 따른 압력증분을 직접적으로 제저할 수 있는 절점이다. 본 연구에서는 철근콘크리트의 평면 구성 방정식과 적층정식화에 적용한 쉘 요소에 압력절점을 추가하고 해석시 체적을 제어함으로써 철근콘크리트 원통형 구조에 대해 파괴까지의 극한내압 능력을 해석할 수 있는 체적제어 비선형 해석기법을 개발하였다. 본 논문에서 제안한 해석기법을 이용하여 철근콘크리트 원통형 구조물에 대하여 비선형 해석을 수행하여 한계압력과 한계압력 이후의 구조물의 거동을 예측하였으며 실험결과와 비교 검증하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.33-33
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• 2016

산사태 발생 예측은 재해를 예방하고 대처하기 위한 가장 근본적이며 효과적인 방법이나, 과학기술의 발전과 많은 노력에도 불구하고 아직 산사태의 발생 장소와 시기를 예측하는 것은 매우 어려운 일이다. 산사태 발생 예측 기법은 크게 경험론적 지수기법, 통계적 해석기법, 물리적 해석 기법으로 나뉠 수 있다. 이 세 방법은 각기 장단점이 있으나 일반적으로 후자로 갈수록 많은 데이터가 요구되고, 해석에 시간이 필요하며, 보다 신뢰할만한 결과를 도출할 수 있다. 경험론적 지수 기법은 국내에서 실무적으로 널리 활용되고 있으며, 통계적 해석기법에 관한 연구도 수행된 바 있다. 하지만 이 두 방법론은 일정량 또는 일정강도 이상의 강우 발생 시 산사태의 발생 위험도를 공간적으로 예측할 수 있으나, 산사태의 발생 시점과 연속적인 강우량 또는 강우강도의 관계를 정량적으로 분석하기 힘든 한계가 있어 최근에는 이러한 한계를 극복하기 위해 최근 무한사면안정 모형과 토양수분침투 모형을 결합한 시변 사면안정모형들이 활용되기 시작하고 있다. 대표적으로는 TRIGRS가 있으며, 이 모형에서는 선형화한 1차원 Richards 방정식의 해석해를 활용하여 토양수분량을 계산한 후 이 정보를 무한사면안정모형에 반영하여 시변적인 사면안정도를 구하고 있다. 하지만 Richards 방정식을 선형화하기 위해서 제한된 토양수분-압력 관계식이 사용되며, GUI가 제공되지 않아 전처리 및 후처리가 번거로운 한계가 있다. 본 연구에서는 이러한 한계를 개선하기 위해 3차원 Richards방정식을 수치적으로 계산하여 보다 다양한 토양수분-압력 모형과 초기조건을 반영할 수 있게 하였다. 또한 GUI를 지원하여 사용자가 보다 손쉽게 해석모형을 사용할 수 있도록 하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.2
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• pp.135-140
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• 2010

A new treatment is proposed to handle a deflection limit in the open-loop-onset-point (OLOP), which is commonly used in the prediction of pilot in-the-loop oscillation (PIO) due to a rate saturation. The new approach is motivated by the frequency response of a stand-alone actuator in that, unlike the suggestion by the original OLOP procedure, the rate limit onset is not delayed to a higher frequency by a deflection limit. Indeed, if a feedback control loop is closed, the rate limit onset can be shifted to a lower frequency since the controller tends to react with larger commands when deflection limited. The amplitude of the command at this onset frequency is combined with the deflection limit to estimate the associated gain reduction in the open-loop-onset-point in the final step of the OLOP process. The comparison of the new approach with the previous method reveals that an inaccurate optimism which can occur in the previous method is corrected by the proposed treatment.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.777-787
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• 1985

The study is concerned with the analysis of flanging as a sheet metal working process. In terms of mechanics, the flanging process can be divided into two groups, i.e, shrink flanging and stretch flanging. In this study, the shrink flanging process is analyzed by using the proposed energy criterion and the forming limit is found for the process. The forming limit for stretch flanging is also found by employing the neckind theory. Experiments are carried out for both processes. Approximate forming limits are obtained from the experiments. An approximate method to calculate the punch force is proposed and the computed results are compared with the experimental results. It is shown that there are good agreements in forming limits and punch forces between theory and experiments.

• Journal of the Korean Geotechnical Society
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• v.20 no.3
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• pp.85-96
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• 2004

The ultimate bearing capacity of surface foundations on a sand layer overlying clay has been theoretically investigated. First, a review of previous studies on the bearing capacity problems for this type of foundation was performed and a discussion was presented concerning the practical application. Second, the kinematic approach of limit analysis was used to calculate the upper bound of the true ultimate bearing capacity. The kinematic solutions are upper bounds and their accuracy depends primarily on the nature of the assumed failure mechanism. This approach makes it convenient to create design charts, and it is possible to trace the influence of parameters. Third, the commercial finite element program ABAQUS was applied to obtain the ultimate bearing capacity based on the elasto-plastic theory. Results obtained from the kinematic approach were compared with those from the program ABAQUS and the limit equilibrium equations proposed by Yamaguchi, Meyerhof and Okamura et al. Finally, the validities of the results from the kinematic approach, the results from the program ABAQUS and the limit equilibrium equations were examined.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.43-52
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• 2003

The present study is to investigate the ultimate behavior and limit state design of 2-I) R/C structures, with the changing of crack direction, and the yielding of the reinforcing steel bars, and Is to introduce an algorithm for the limit state design and analysis of 2-D R/C structures, directly from the finite element model. For the design of reinforcement in concrete the limit state design equation is incorporated into finite element algorithm to be based on the pointwise elemental ultimate behavior. It is also introduced a simplified nonlinear analysis algorithm for stress-strain relationship of R/C plane stress problem considering the cracking and its rotation in concrete and the yielding of the reinforcing steel bar. The algorithm is incorporated into the nonlinear finite element analysis. The analysis model is compared with the experimental model of R/C shear wall. In a simple design example for a shear wall, the required reinforcement ratios in each finite element is obtained from the limit state design equations.