• Earthquakes and Structures
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• v.3 no.6
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• pp.805-820
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• 2012

An enhanced and efficient methodology is proposed for evaluating the robustness of an uncertain structure with passive dampers. Although the structural performance for seismic loads is an important design criterion in earthquake-prone countries, the structural parameters such as storey stiffnesses and damping coefficients of passive dampers are uncertain due to various factors or sources, e.g. initial manufacturing errors, material deterioration, temperature dependence. The concept of robust building design under such uncertain structural-parameter environment may be one of the most challenging issues to be tackled recently. By applying the proposed method of interval analysis and robustness evaluation for predicting the response variability accurately, the robustness of a passively controlled structure can be evaluated efficiently in terms of the so-called robustness function. An application is presented of the robustness function to the design and evaluation of passive damper systems.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1991.04a
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• pp.84-90
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• 1991

Underground structures usually consist of rock masses or concretes which can be cracked or have cracks. This study aims to develop an analysis program which can deal with the effect of discontinuous behavior due to those cracks using the block theory. It is assumed that rock masses form blocks along the discontinuity lines, and deformation within the block is relatively small. The behavior of discontinuity plane of the structures is divided into sliding along the discontinuity plane. separation of discontinuity by tensile force, and degradation of asperity angle of discontinuity plane by external force with sliding of rock Basses. These behaviors are implemented using constitutive relation and relevent load-displacement relation defined through normal and shear stiffnesses. Time varying displacements and block velocities are calculated by explicit time stepping algorithm. The effect of rock supports including rockbolts is also considered, and the tending effects which occurs in relatively thin lining is also considered.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.3
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• pp.55-65
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• 2000

구조물 지진해석을 위한 구조물 -지반 상호작용 해석에서도 비선형 지반 특성을 고려한 비선형해석이 요구되고 있어 구조물 비선형 지진 해석을 위해 기초 지반에 대한 수평방향 비선형 해석을 수행하였다. 기초지반은 UBC 분류에서 규정한 보통지반인 Sn 지반과 연약지반인 SE 지반을 고려하였고, 지반의 비선형 특성은 Ramberg-Osgood 모델을 이용하였다. 비선형 지반이 기초지반 수평 및 회전 동적 강성 및 감쇠비에 미치는 영향을 조사하기 위하여 얕은 기초와 묻힌기초에 대해 기초 크기, 지반깊이 및 말뚝유무에 따른 동적 강성 및 감쇠비 변화를 조사하였는데, 지반의 비선형 특성이 기초지반의 선형 수평 및 회전 강성과 감쇠비를 크게 감소 또는 증가시키는 것으로 나타났으며, 기초크기, 지반깊이 및 말뚝유무의 영향도 큰 것으로 나타나 구조물 지진해석시 기초크기, 지반깊이 및 말뚝유무와 함께 지반의 비선형성도 고려하는 것이 필요한 것으로 판단되었다.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.137-144
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• 2005

Seismic responses of a building are affected due to the site soil conditions. In this study, linear time history seismic analysis and nonlinear pushover static seismic analysis were performed to estimate the base shear forces of the 3, 5 and 7-story steel structure buildings considering the rigid and soft soil conditions. According to the study results, the steel structure buildings designed for the gravity loads and wind load showed the elastic responses with the moderate earthquake of 0.11g, and the soft soil layer increased the displacement and the base shear force of a building. Therefore it is more resonable to perform an elastic seismic analysis of a building structure with the moderate earthquakes considering the characteristics of the soft soil layer.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.7
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• pp.711-717
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• 2008

A modeling method for the modal and the transient vibration analysis of a multi-packet blade system excited by nozzle jet forces is presented in this paper. Blades are idealized as cantilever beams and the elastic structures like disc and shroud connecting blades are modeled as coupling stiffnesses. A modified Campbell diagram is proposed to identify true resonance frequencies of the multi-packet blade system. Different from the SAFE diagram that employs three dimensional space, the modified Campbell diagram Proposed in this study employs a plane to find the true resonance frequencies. To verify the existence of true resonance frequencies, nozzle jet forces are modeled as periodic forces and transient vibration analysis were performed with the modeling method.

• Structural Monitoring and Maintenance
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• v.4 no.3
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• pp.269-299
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• 2017

This paper presents a Level III damage evaluation methodology, which simultaneously, identifies the location, the extent, and the severity of stiffness damage in deep beams. Deep beams are structural elements with relatively high aspect (depth-to-length) ratios whose response are no longer based on the simplified Euler-Bernoulli theory. The proposed methodology is developed on the bases of the force-displacement relations of the Timoshenko beam theory and the concept of invariant stress resultants, which states that the net internal force existing at any cross-section of the beam is not affected by the inflicted damage, provided that the external loadings in the undamaged and damaged beams are identical. Irrespective of the aspect ratios, local changes in both the flexural and the shear stiffnesses of beam-type structures may be detected using the approach presented in this paper.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.176-179
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• 2003

This paper deals with the optimum design of thick-walled multi-layered composite tubes by minimizing the process-induced residual stresses under some constraints of structural stiffnesses. An analytic model based on quasi-static thermoelasticity is adopted for the calculation of the residual stresses in the multi-layered composite tubes. The numerical results of optimization show that, in the case of cross-ply CFRP tubes, the residual stresses can be reduced to a certain level by controlling ply thicknesses. However, the optimized tubes may be susceptible to cracking because the transverse residual stress is still large in a strength-based sense. To further suppress the residual stresses, the effects of stacking sequence, wall thickness and axial pretension on the optimum solutions are examined.

• Journal of the Korean Society for Advanced Composite Structures
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• v.5 no.4
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• pp.18-23
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• 2014

In this paper. the effects of the aspect ratio on the natural frequency of the advanced composite road structures is studied. The advanced composite structures are too difficult for such design engineers for construction and some simple but accurate enough methods are necessary. Some laminate orientations have decreasing values of $D_{16}$, $B_{16}$, $D_{26}$ and $B_{26}$ stiffnesses as the ply number increases. The plate aspect ratio considered is from 1 to 5. Most of the road structures have large aspect ratios, for such cases further simplification is possible by neglecting the effect of the longitudinal moment terms.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.191-195
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• 2011

The airframe ground vibration tests were conducted on the KC-100 aircraft according to the regulation requirement, KAS 23.629(a)(2) and the modal characteristics for the target modes were measured. To make FE model tuning, a design sensitivity approach with engineering judgment was implemented using MSC/Nastran and Attune, a genetic algorithm based parameter optimization software. Based on the comparison between initial prediction and test results, design variables such as beam cross-sectional properties and spring stiffnesses were devised. As the results, the correlation of the FE model to the GVT results was made appropriately, meeting the goal of matching the target frequencies within 5%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.772-777
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• 2013

This article presents the reduction of vibration generated by an automobile fuel pump. In order to analysis the vibration of the fuel pump, a simplified dynamic model is established, which is composed of a rigid rotor and a equivalent springs. The equivalent stiffnesses of the upper and lower assemblies are evaluated by the comparison of modal testing results and the finite element analysis. the stiffness for the oil film of the journal bearing is extracted by using Reynold's equation. In addition, the time responses for the vibration of the fuel pump are computed by using a commercial multi-body dynamics software, RecurDyn. Based on these results, some design suggestions are proposed to reduce the vibration of an automobile fuel pump.