• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.124-124
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• 2017

Fe-Ni-Co 합금 박막(<$100{\mu}m$)을 황화물계 용액에서 전주공정으로 제조하였다. XRF로 측정한 박판의 평균 조성은 Fe-34 wt.% Ni-3 wt.% Co 이다. AFM으로 측정한 표면 조도는 35.2 nm 이다. 표면의 나노 경도는 평균 5.4 GPa 이었다. Oliver 모델을 적용한 구리 박막의 탄성하강강성도는 약 75 이었다. Alekhin 모델을 적용한 구리 박막의 마찰계수, 피로한계는 각각 0.134, 0.027 이었다. 유한요소법으로 평가한 Berkovich 형 나노압침선단의 하중분포를 이차원 선형 및 비선형 해석하면 1 [mN]의 정적하중을 가한 Fe-Ni-Co 박막은 약 576 [mN]로 예측되었다. 압침선단의 하중집중정도는 표면탐침현미경으로 관찰한 압흔의 변형정도와 유사한 경향을 보였다.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.1
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• pp.55-62
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• 1996

The dynamic photoelastic technique has been utilized to investigate the possibility of relieving the large local singular stresses which are induce in the corner of a right angled indenter. The indenter compresses a semi-infinite body dynamically with an impact load applied on the top of the indenter. The effect of geometric changes to the indenter in terms of the diameter (d) and the location (ℓ) of the notch on the relieving of the dynamic contact stresses are investigated. A multi-spark-high speed camera with twelve sparks was used to take dynamic photographs. The contact singular stresses were found to be released by introducing the relief notch along the indenter. The optimal location and geometry of the relief notch need further experimental investigation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.1
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• pp.27-41
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• 2023

Submerged floating tunnels must be connected to the ground to connect continents. The displacement imbalance at the shore connection between the underground bored tunnel and submerged floating tunnel can cause stress concentration, accompanying a fracture at the shore connection. The elastic joint has been proposed as a method to relive the stress concentration, however, the effect of the elastic joints on the dynamic behavior should be evaluated. In this study, the submerged floating tunnel and shore connection under dynamic load conditions were simulated through numerical analysis using a numerical model verified through a small-scaled physical model test. The resonant frequency was considered as a dynamic behavioral characteristic of the tunnel under the impact load, and it was confirmed that the stiffness of the elastic joint and the resonant frequency exhibit a power function relationship. When the shore connection is designed with a soft joint, the resonant frequency of the tunnel is reduced, which not only increases the risk of resonance in the marine environment where a dynamic load of low frequency is applied, but also greatly increases the maximum velocity of tunnel when resonance occurs.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.3
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• pp.185-192
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• 2023

In this study, fluctuating wind velocity for time history analysis is simulated by a single variate, single-dimensional random process using the KBC2022 spectrum about across-wind direction. This study analyzed and obtained the inelastic dynamic response for structures modeled as a single-degree-of-freedom system. It is assumed that the wind response is excellent in the primary mode, the change in vibration owing to plasticization is minor, along-wind vibration and across-wind vibration are independent, and the effect of torsional vibration is small. The numerical results, obtained by the Newmark-𝛽 method, shows the time-history responses and trends of maximum displacements. As a result of analyzing the inelastic dynamic response of the structure with the second stiffness ratio(𝛼) and yield displacement ratio (𝛽) as variables, it is identified that as the yield displacement ratio (𝛽) increases when the second stiffness ratio is constant, the maximum displacement ratio decreases, then reaches a minimum value, and then increases. When the stiffness ratio is greater than 0.5, there is a yield point ratio at which the maximum displacement ratio is less than 1, indicating that the maximum deformation is reduced compared to the elastically designed building even if the inelastic behavior is permitted in the inelastic wind design.

• The Journal of the Convergence on Culture Technology
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• v.6 no.3
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• pp.347-352
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• 2020

In this study, the variation of track impact factor according to the spring stiffness change rate of sleeper resilience pad was analyzed based on field measurements. In addition, the correlation between field measurement results and 7 million fatigue test results was verified. The fatigue effect diagram of the sleeper resilience pads was presented considering the nonlinear deterioration characteristics of the sleeper resilience pads used for the STEDEF track. Based on the field measurement results, the nonlinear characteristics of the track impact factor for the spring stiffness change rate over 30% of sleeper resilience pad on the track impact factor-track support stiffness diagram were analyzed to be consistent with the fatigue test results.

• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.79-91
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• 2016

Geosynthetic-reinforced and Pile-supported (GRPS) embankment method is widely used to construct structures on soft ground due to restraining residual settlement and their rapid construction. However, effect of cyclic loading has not been established although some countries suggest design methods through many studies. In this paper, cyclic loading tests were conducted to analyze dynamic load transfer characteristics of pile-supported embankment reinforced with geosynthetics. A series of 3 case full scale model tests which were non-reinforced, one-layer-reinforced, two-layer reinforced with geosynthetics were performed on piled embankments. In these series of tests, the height of embankment and pile spacing were selected according to EBGEO (2010) standard in Germany. As a result of the vertical load parts on the pile and on the geosynthetic reinforcement measured separately, cyclic loads transferred by only arching effect decreased with strength geosynthetic-reinforced case. However, final loads on the pile showed no differences among the cases. These results conflict with previous studies that reinforcement with geosynthetics increases transfer load concentrated on piles. In addition, it is observed that the load transferred to pile decreases at the beginning of cycle number due to reduction of arching effected by cyclic loading. Based on these results, transferred mechanism for cyclic load on GRPS system has been presented.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.2
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• pp.92-100
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• 2016

Reliability analysis of tripod support structure for offshore wind turbine was performed. Extreme distribution function of peak response due to wind and wave loads was estimated by applying peak over threshold(POT) method. Then, stress based limit state function was defined by using maximum stress of support structure which was obtained by multiplying beam stress and concentration factor. The reliability analysis result was compared when maximum stress was calculated from shell element. Reliability index was evaluated using first order reliability method(FORM).

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.255-265
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• 2003

A series of laboratory tests were performed to evaluate engineering properties of geobag system which is used for urgent restoration of the collapsed roadbed. In this study, the suitable geobag size was proposed as 44cm wide and 66cm long, and the suitable filling ratio of geobag was also proposed as 80% through the static loading tests. Also a series of model tests were carried out to investigate the characteristics of the engineering behavior and the distribution of earth pressure of the geobag roadbed under static and dynamic loading.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.5
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• pp.45-51
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• 2002

The characteristics of nonlinear seismic behavior and failure mechanism of RC space frame in railroad viaducts have been studied by the numerical analysis in time domain. The structure concerned is modeled in 3 dimensional extent and the RC frame elements consisting of fibers are employed for the columns. The fibers are characterized as RC zone and PC one to distinguish the different energy release after cracking resulted from the bond characteristic between concrete and re-bar. Due to the deviation of the mass center and the stiffness center of the entire structure the complex behavior is shown under seismic actions. The excessive shear force is concentrated on the column beside flexible one relatively, which leads to the failure of bridge concerned.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.69-82
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• 1991

The dynamic stability of the long vertical beam subjected to the periodic axial load is investigated. As a solution method, the Galerkin's method is used to obtain a set of coupled Mathieu type equations. To obtain the stability chart, both the perturbation method and numerical method are used, and the results of the both methods are compared with each other. The stability regions for the various boundary conditions are obtained, Also the effects of the viscous damping, the mean tension and the multi-frequency parametric excitation are studied in detail.