• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.457-464
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• 2003

최근 교량의 건설에 있어서 내진설계가 주요문제로 부각되면서, 구조물의 진동응답을 제어 하는 갖가지 형태의 진동제어 기법이 적용되고 있다. LRB(Lead Rebbe. Bearing), LUD(Lock Up Device)등 다양한 지진격리장치가 설계에 적용되고 있으며 특히, 설계변경 .내진보수보강과 같이 제약 조건이 있는 상황에서 유용한 면진방법으로 사용되고 있다. 이러한 지진격리장치는 기본적인 설계특성인 수평강성, 감쇠성능에 대한 검증을 필요로 한다. 특히, 지진과 같은 동적하중에 대하여 하중속도, 수직력, 변형률 등에 대한 의존성과 내구성의 검토가 필요하며 유사장치에 대하여 검증실험기준의 정립이 진행 중에 있다. 강재이력댐퍼인 E-Shape 댐퍼는 지진격리장치로서 교각의 고정단에 교좌장치로 설치되어 상시에는 탄성영역 내에서 거동하는 고정단의 역할을 하다가, 지진발생시에는 E-Shape형태의 강재댐퍼가 소성변형을 통한 이력거동으로 에너지 소산기능을 가진 교좌장치이다. 최근 LRB에 대하여는 다양한 특성실험이 수행되고 있으나 상대적으로 강재이력댐퍼에 대하여는 이러한 검증실험이 수반되지 않고 사용되고 있다. 본 실험연구에서는 E-Shape 강재이력댐퍼에 대하여 연직하중, 수평변형률, 수평속도에 패한 동적특성을 평가함으로서 강재이력댐퍼를 이용한 지진격리설계의 타당성과 면진성능을 평가해 보았다.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.5 s.39
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• pp.35-43
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• 2004

Small-scale models have been frequently used for seismic performance tests because of limited testing facilities and economic reasons. However, there are not enough studies on similitude law for analogizing prototype structures accurately with small-scale models, although conventional similitude law based on geometry is not well consistent in the inelastic seismic behavior. When fabricating prototype and small-scale model of reinforced concrete structures by using the same material, added mass is demanded from a volumetric change and scale factor could be limited due to aggregate size. Therefore, it is desirable that different material is used for small-scale models. Thus, a modified similitude law could be derived depending on geometric scale factor, equivalent modulus ratio and ultimate strain ratio. In this study, compressive strength tests are conducted to analyze the equivalent modulus ratio of micro-concrete to normal-concrete. Then, equivalent modulus ratios are divided into multi-phase damage levels, which are basically dependent on ultimate strain level. Therefore, an algorithm adaptable to the pseudodynamic test, considering equivalent multi-phase similitude law based on seismic damage levels, is developed. Test specimens, consisted of prototype structures and 1/5 scaled models as a reinforced concrete column, were designed and fabricated based on the equivalent modulus ratios already defined. Finally quasistatic and pseudodynamic tests on the specimens are carried out using constant and variable modulus ratios, and correlation between prototype and small-scale model is investigated based on their test results. It is confirmed that the equivalent multi-phase similitude law proposed in this study could be suitable for seismic performance tests on small-scale models.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2C
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• pp.71-79
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• 2009

This study is to develope the resilient modulus prediction model, which is the function of mean effective principal stress and axial strain, for three types of railroad trackbed materials such as crushed stone, weathered granite soil, and crushed-rock soil mixture. The model consists of the maximum Young's modulus and nonlinear values for higher strain, analogous to dynamic shear modulus. The maximum value is modeled by model parameters, $A_E$ and the power of mean effective principal stress, $n_E$. The nonlinear portion is represented by modified hyperbolic model, with the model parameters of reference strain, ${\varepsilon}_r$ and curvature coefficient, a. To assess the performance of the prediction models proposed herein, the elastic response of a test trackbed near PyeongTaek, Korea, was evaluated using a 3-D elastic multilayer computer program (GEOTRACK). The results were compared with measured elastic vertical displacement during the passages of freight and passenger trains at two locations, whose sub-ballasts were crushed stone and weathered granite soil, respectively. The calculated vertical displacements of the sub-ballasts are within the order of 0.6mm, and agree well with measured values. The prediction models are thus concluded to work properly in the preliminary investigation.

• Composites Research
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• v.20 no.3
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• pp.43-49
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• 2007

Dynamic instability of rotating disks is the most significant factor to limit its rotating speed. Application of composite materials to rotating disks may enhance the dynamic stability leading to a possible design of rotating disks with lightweight and high speed. Whereas much work has been done on the effect of transverse shear and rotary inertia, called Timoshenko effect, on the dynamic behavior of plates, there is little work on the correlation between the effect and the rotation of disk, especially nothing in case of composite disks. The dynamic equations of a rotating composite disk are formulated with the Timoshenko effect and the vibrational analysis is performed by using a commercial package MSC/NASTRAN. According to the results, the Timoshenko effect goes seesaw in some modes, unlike the well-known fact that the effect decreases as the rotating speed increases. And it can be concluded, based only on the present results, that decrement of the Timoshenko effect by disk rotation grows larger as the thickness ratio decreases, the diameter ratio increases, the modulus ratio increases, and the mode number increases.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.339-343
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• 2001

Shield tunnel having circular section located in the soil or soft rock layer is liable to deform in such a way that its two diagonal diameters crossing each other expand and contract alternately during earthquakes. Based on this knowledge, the ground-tunnel interaction effect for this particular vibration mode is investigated. The ground surrounding a tunnel is assumed to be a homogeneous elastic medium. The bonded boundary condition on the ground-tunnel interface is considered. This suggests a firm bond between the ground and the tunnel lining. As Poisson's ratio and stiffness of the ground increases, the strain induced within the tunnel lining increases.

• Journal of the Korean Geotechnical Society
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• v.16 no.5
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• pp.193-201
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• 2000

교란상태개념(Disturbed State Concept;DSA)모델릉 이용하여 포화사질토의 동역학적 거동을 모사하는 예측기법을 개발하였다. 실내진동전단시험 자료로부터 DSC모델 매개변수를 찾고, DSC 모델을 이용하여 전개한 응력중분과 변형률중분의 관계를 표현하는 탄소성구성방정식으로부터 진동하중을 받는 지반재료의 간극수압 및 유효응력 변화, 그리고 축자응력-축방향변형률 거동을 예측하였다. 압축 및 인장 재하시에는 DSC모델을 사용하여 변형률 경화(strain-hardening)및 진동하중에 의한 변형률 연화(cyclic-softening)현상을 모사하고, 제하(unloading)시에는 선형탄성모델을 사용하여 근사화하였다. 예측 결과를 실내전단시럼 결과와 비교하여 예측기법을 검증하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1994.04a
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• pp.45-50
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• 1994

최근의 로봇 매니퓰레이터는 고정밀, 고생산성, 유연성 자동화를 추구한다. 이에 따라 매니퓰레이터는 운동 정확성, 고속성, 안정성이 더욱 향상되어야 한다. 특히 매니퓰레이터 관절부의 탄성은 동적 변형 및 진동을 유발함으로써 운동 정확성과 안정성을 현저히 저하시킨다. 이러한 복잡하고 불확실한 구조를 갖는 로봇 시스템의 고속, 정확한 운동 제어를 위해서는 보다 효과적인 고급 제어 기법 및 제어 장치의 개발이 요구된다. 본 연구에서는 이러한 문제에 대한 하나의 대응 방법으로 인간의 지식 처리 방법을 모방한 퍼지제어를 적용하여 그 가능성을 본다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.5
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• pp.553-561
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• 2015

The exponential and power law functionally graded material(FGM) theory is reformulated considering the refined shear and normal deformation theory. This theory has ability to capture the both normal deformation effect and exponential and power law function in terms of the volume fraction of the constituents for material properties through the plate thickness. Navier's method has been used to solve the governing equations for all edges simply supported plates on Pasternak elastic foundation. Numerical solutions of vibration analysis of FGM plates are presented using this theory to illustrate the effects of power law index and 3-D theory of exponential and power law function on natural frequency. The relations between 3-D and 2-D higher-order shear deformation theory are discussed by numerical results. Further, effects of (i) power law index, (ii) side-to-thickness ratio, and (iii) elastic foundation parameter on nondimensional natural frequency are studied. To validate the present solutions, the reference solutions are discussed.

• Journal of KIISE:Databases
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• v.31 no.4
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• pp.362-372
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• 2004

One of the most difficult problems in building a distributed GIS lies in the heterogeneity of spatial databases. In particular, positional mismatches between spatial databases, which arise due to several reasons, may incur incorrect query results. They result in unreliable outputs of query processing. One simple solution is to correct positional data in spatial databases at each site, according to the most accurate one. This solution is however not practical in cases where the autonomy of each database should be respected. In this paper, we propose a spatial query processing method without correcting positional data in each spatial database. Instead of correcting positional data, we dynamically transform a given query region or position onto each space where spatial objects of each site are located. Our proposed method is based on an elastic transformation method by using delaunay triangulation. Accuracy of this method is proved mathematically, and is confirmed by an experiment. Moreover, we implemented using common use database system for usefulness verification of this method.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.189-197
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• 2003

In this paper, deformation characteristics of fiber-mixed-soils were studied at small strain range(0.0001%～1%) using resonant column test and triaxial test, and reinforcement effect was evaluated by the measure of maximum shear moduli. The effects of the major parameters such as fiber content, aspect ratio and fiber type on reinforcement were comparatively assessed. The specimens were remolded from Jumunjin Sand randomly mixed with discrete polypropylene staple fibers. Maximum shear moduli of fiber-mixed-soils increased by up to 30% and modulus reduction was also restrained in nonlinear range. Shear moduli increased as the aspect ratio increases. The reinforcement was more effective with fibrillated fiber than with monofilament fiber. The most effective reinforcement was achieved with the specimen of 0.3 % fiber content.