• Journal of the Korean Society for Railway
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• v.17 no.1
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• pp.52-58
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• 2014

Plastic deformation of roadbed influences the stability and maintenance of concrete slab track. Long-term plastic deformation in a railway roadbed is generated primarily due to accumulated inelastic strains caused by repeated passing of trains. Prediction of cumulative plastic deformation is important in cost-effective maintenance of railway tracks as well as for the safe operation of trains. In this study, the vertical displacements in railway roadbeds with different thicknesses of reinforced roadbed were computed. Parameters of the power model for cumulative plastic strain were calibrated by using the data from triaxial tests and full-scale loading tests. Results of three-dimensional finite element analyses of standard roadbed sections provide us with design guidelines for the selection of the thickness of reinforced roadbed.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.3
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• pp.33-44
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• 1999

An energy balance procedure is developed to incorporate the effects of earthquake duration which involves the effect of cyclic loading and the corresponding cumulative plastic deformation. Particular emphasis is given to the flexural failure of non-seismically designed columns of reinforced concrete frames. For this, conceptual strength deterioration models for columns, governed by concrete, anchorage failure and longitudinal steel fracture due to low-cycle fatigue, are proposed. It is evident that the energy-based method has good agreement with the experimental data and is able to predict the failure mode.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.251-258
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• 2000

Based on the numerical investigations using steel bridge pier subjected to strong seismic excitations a new approach to seismic damage assessment for steel structures and their members has been proposed in conjunction with the suggested definition of failure state. The relevant failure form of the steel pier is evaluated. It is revealed that when a seismic load has a short period, the failure of global buckling beyond the allowable displacement is more dominant than that by that of the local buckling caused by the accumulation of plastic strain. When a seismic load is not beyond this certain part, but repeats within the range of where a plastic deformation occurs, the plastic strain is accumulated on the partial element of bottom edge of steel pier and the failure occurs by the local buckling from the accumulated plastic local strain.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.37-43
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• 2001

The energy concept has been extended to compare the hysteretic performance between various structural systems. As a result, the energy absorption efficiency is defined as the cumulative energy absorption capacity of a structural system normalized by that of the elasto-perfectly plastic system as a benchmark for comparisons. For this, the construction of energy curves from the experimental results obtained by cyclic loading tests is required. Using the proposed procedure, structures differing from each other in geometry, material and construction can be relatively and objectively compared for seismic performance. Also the beauty of this method is in its irrelevance to the structural failure mode. The proposed procedure was validated by application to the experimental results of two different specimens.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.4
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• pp.63-69
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• 2003

In this study seismic design procedure for buckling-restrained braced frame systems was proposed using hysteretic energy spectrum and accumulated ductility spectrum constructed from single degree of freedom systems. The hysteretic energy spectra and accumulated ductility spectra corresponding to target ductility ratio were constructed first. The cross-sectional area of braces required to meet a given target displacement was obtained by equating the hysteretic energy demand to the accumulated plastic energy dissipated by braces. Twenty earthquake records were utilized to construct the spectra and to verify the validity of the design procedure. According to analysis results of three- and eight-story buckling-restrained braced frame structures designed using the proposed method, the mean values for the top story displacement correspond well with the given performance target displacements. Also, the inter-story drifts turned out to be relatively uniform over the structure height, which is desirable because uniform inter-story drifts indicate uniform damage distribution. Therefore if was concluded that the proposed energy-based method could be a reliable alternative to conventional strength-based design procedure for structures with buckling-restrained braces.

• Journal of Korean Society of Transportation
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• v.6 no.2
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• pp.21-33
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• 1988

부적정한 도로포장 구조물의 설정 및 유지보수의 적정관리 미흡으로 표면의 피해와 소성변형이 장기간 발생된다. 이로 인한 가요성 통제 구조물의 파괴 원인은 일반적으로 포 장재료의 동질성, 선형탄성 상태의 가정 하에서 분석되었다. 그러나 아스팔트 재료의 특성은 엄밀히 분석해서 완전한 선형탄성이라고는 볼 수 없음은 잘 알려져 있다. 따라서 근본적으 로 포장체의 수명과 파양 예측에 오류 발생가능성이 높다 하겠다. 금번 연구는 이와 같은 종전의 경험적인 선형탄성 방법이 아닌 탄성일소성 상태하의 격자(mechano-lattice) 이론이란 새로운 기법을 도입하였다. 특히 마이너(Miner's Law) 이론의 누적손실과 확률을 적용하여 포장체의 피노수명과 손실을 예측할 수 있다. 금번 이론은 실제로 호주 빅토리아주의 멜보른(Melbourne)시 일부 지역구간을 모형으 로 선정되었다. 분석결과 가장 최적화된 도로포장 각층의 두께와 재료 선정을 하기 위하여 일정기간의 교통량, 상대적 손실지수와 잔여응력 및 표면 변위, 대기온도 그리고 습도의 영 향을 종합적으로 고려하여야 한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.2
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• pp.197-207
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• 2002

Energy dissipation capacity and earthquake responses of steel structures installed with unbonded braces(UB) were investigated. Parametric studies were performed for a single-degree-of-freedom structure under harmonic loads, and optimum yield strength of unbonded braces were derived. Nonlinear dynamic time history analyses were carried out to investigate the seismic response of multi-story model structures with UB having various size and strength. Various techniques were applied to determine proper story-wise distribution of UB in multi-story structures. The analysis results show that the maximum displacements of structures generally decrease as the stiffness of UB increases. However for some natural frequencies and seismic loads the maximum displacement and accumulated damage increases as the stiffness of UB increases.

• Journal of Korean Society of Steel Construction
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• v.23 no.2
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• pp.147-158
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• 2011

The purpose of this research was to analyze the connections of the seismic-performance values for domestic-performance-based designs. Basic research on the performance design method has been increasing of late, along with performance-based organization investigations. These investigations concern the performance level state of steel structure buildings. According to the performance limit state, seismic-performance values should be presented as appropriate steel structure engineering amounts. The first step, based on the full-scale steel structure experiments, involves researching on the making of a basic document. The moment-rotation angle relationship results of the experiment on the moment-frame connection were used to assort the functional and undamaged limits, which were assumed to be less than the yield moment. Moreover, the repairable and safety limits, which were assumed to exist between the yield and maximum moments, were assorted by investigating the accumulated plastic deformation ratio.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.15-22
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• 2003

The fatigue crack growth model is derived and the retardation model is proposed. The fatigue crack growth model considers the residual plastic stretch on the crack surface which results from the plastic deformation at the tip of fatigue crack. The fatigue crack growth rate is calculated by using the cumulative fatigue damage and plastic strain energy in the material elements at the crack tip. This model gives the crack growth rate in reasonable agreement with test data for aluminum alloy AL6061-T651 and 17-4PH casting steel. The fatigue crack growth retardation model is based on the residual plastic stretch produced from a tensile overload which reduced the plastic strain range of the following load cycles. A strip-yield model of a crack tip plasticity is used for the calculation of a plastic zone size. The proposed retardation model characterized the observed features and delayed retardation of the fatigue crack growth under tensile overload.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.317-329
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• 2001

서울지하철 터널의 상당 구간이 막장면이 풍화토에서 풍화암까지 변화하는 복합화강토지반에 건설되어 왔다. 화강암풍화지반은 심도에 따라 강도의 변화가 크며, 수위가 높고 투수성 지반인 특징을 갖는다. 터널은 주로 비원형 배수터널로 설계되고 NATM 공법으로 시공되었다. 이와 같은 여건의 터널현장에서 발생하였던 붕괴사례를 조사한 결과, 대부분의 붕괴가 터널 어깨 부근으로부터 시작되었고, 구조적으로 완전하지 않은 라이닝, 그리고 지하수와의 연관성 등의 공통적 특징이 확인되었다. 이러한 터널문제는 지반조건, 시공조건, 터널형상 등 경계조건이 복잡하여 한계평형 해석과 같은 종래의 해석적 방법으로 터널안정을 검토하기가 용이하지 않다. 그 가장 큰 이유중의 하나는 터널의 파괴메카니즘에 대한 분명한 정보를 알 수 없는데 있다. 파괴메카니즘의 조사에는 전통적으로 원심모형시험법이 많이 사용되어 왔다. 그러나 화강토지반내의 터널처럼 복잡한 경계조건을 갖는 터널문제에는 적용하기 어렵다. 따라서 이에 대한 하나의 대안으로서 본 논문에서는 지반거동의 비선형성을 고려하는 Coupled 수치해석법을 이용하여 파괴메카니즘을 조사하였다. 수치해석결과의 증분변위벡터, 누적소성편차변형률 그리고 속도특성치(velocity characteristics)의 분석을 통해 실제 붕괴사례와 잘 일치하는 명확한 파괴메카니즘을 파악할 수 있었다. 이로부터 복잡한 경계조건을 갖는 터널 문제의 안정해석을 위한 파괴메카니즘을 조사하는 수치해석적 접근방법을 제시하였다.