• Computers and Concrete
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• 제22권2호
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• pp.221-225
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• 2018

In this paper, vibration analysis of concrete foundations resting on soil medium is studied. The soil medium is simulated by Winkler model considering spring element. The concrete foundation is modeled by thick plate elements based on classical plate theory (CPT). Utilizing energy method consists of potential energy, kinetic energy and external works in conjunction with Hamilton's principle, the motion equations are derived. Assuming the simply supported boundary condition for the concrete foundation, the Navier method is used for calculating the frequency of the structure. The effect of different parameters such as soil medium, mode numbers, length to width ratio and length to thickness ratio of the concrete foundation are shown on the frequency of the structure. At the first, the results are validated with other published works in order to show the accuracy of the obtained results. The results show that considering the soil medium, the frequency of the structure increases significantly.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.221-230
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• 2003

Employing classical beam theory for the design of RBS seismic steel moment connections was brought into question in this study, Both the experimental strain data and analytical results from the calibrated finite element analysis confirmed that the shear transfer mechanism in the RBS connection is completely different from that as predicted by classical beam theory Plausible explanations of a higher incidence of brittle fractures observed in the specimens with bolted-webs were presented. It was pointed out that the practice of providing web bolts uniformly along the beam depth is not consistent with the load path identified by both experimental and analytical results. More rational bolted-web details were proposed based on the identified principal load path,.

• Structural Engineering and Mechanics
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• 제70권6호
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• pp.661-669
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• 2019

Buckling analysis of shape memory alloy (SMA) rectangular plates subjected to uniform and linearly distributed inplane loads is the main objective in the present paper. Brinson's model is developed to express the constitutive characteristics of SMA plate. Using the classical plate theory and variational approach, stability equations are derived. In addition to external inplane mechanical loads, the plate is subjected to the pre-stresses caused by the recovery stresses that are generated during martensitic phase transformation. Ritz method is used for solving the governing stability equations. Finally, the effects of conditions on the edges, thickness, aspect ratio, temperature and pre-strains on the critical buckling loads of SMA plate are investigated in details.

• Steel and Composite Structures
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• 제31권3호
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• pp.243-259
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• 2019

This study deals with the nonlinear static analysis of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) truncated conical shells subjected to axial load based on the classical shell theory. Detailed studies for both nonlinear buckling and post-buckling behavior of truncated conical shells. The truncated conical shells are reinforced by single-walled carbon nanotubes which alter according to linear functions of the shell thickness. The nonlinear equations are solved by both the Airy stress function and Galerkin method based on the classical shell theory. In numerical results, the influences of various types of distribution and volume fractions of carbon nanotubes, geometrical parameters, elastic foundations on the nonlinear buckling and post-buckling behavior of FG-CNTRC truncated conical shells are presented. The proposed results are validated by comparing with other authors.

• 대한본초학회지
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• 제37권2호
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• pp.13-21
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• 2022

Objectives : The evaluation of academic achievement is pivotal for establishing accurate direction and adequate level of medical education. The purpose of this study was to firstly establish innovative item analysis technique of Item Response Theory (IRT) for analyzing multiple-choice test of herbology in the traditional Korean medicine education which has not been available for the difficulty of test theory and statistical calculation. Methods : The answers of 390 students (2012-2018) to the 14 item herbology test in college of Korean medicine were used for the item analysis. As for the multidimensional analysis of item characteristics, difficulty, discrimination, and guessing parameters along with item-total correlation and percentage of correct answer were calculated using Classical Test Theory (CTT) and IRT. Results : The validity parameters of strong and weak items were illustrated in multiple perspectives. There were 4 items with six acceptable index scores, and 5 items with only one acceptable index score. The item discrimination of IRT was found to have no significant correlation with difficulty and discrimination indices of CTT emphasizing attention of professionals of medical education as for the test credibility. Conclusion : The critical suggestions for the development, utilization and revision of test items in the e-learning and evidence-based Teaching era were made based on the results of item analysis using IRT. The current study would firstly provide foundation for upgrading the quality of Korean medicine education using test theory.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2009년도 Korea Superconductivity Society Meeting 2009
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• pp.12-12
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• 2009

• Structural Engineering and Mechanics
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• 제73권1호
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• pp.37-52
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• 2020

This paper investigates the free and forced longitudinal vibration of a double nanorod system using doublet mechanics theory. The doublet mechanics theory is a multiscale theory spanning between lattice dynamics and continuum mechanics. Equations of motion and boundary conditions for the double nanorod system are obtained using Hamilton's principle. Clamped-clamped and clamped-free boundary conditions are considered. Frequencies and dynamic displacements are determined to demonstrate the effects of length scale parameter of considered material and geometry of the nanorods. It is shown that frequencies obtained by the doublet mechanics theory are bounded from above (van Hove singularity) and unlike classical elasticity theory doublet mechanics theory predicts finite number of modes depending on the length of the nanotube. The present doublet mechanics results have been compared to molecular dynamics, experimental and nonlocal theory results and good agreement is observed between the present and other mentioned results. The difference between wave frequencies of graphite is less than 10% between doublet mechanics and experimental results near to the end of the first Brillouin zone.

• 한국지진공학회논문집
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• 제9권2호통권42호
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• pp.59-69
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• 2005

용접 철골 모멘트접합부는 일반적으로 평면유지의 가정을 전제한 초등휨이론에 의해 설계되어 왔다. 그러나 1994년 노스리지 지진 이후 보-기둥 접합부의 설계에 초등휨이론을 적용하는 것은 타당치 않음이 몇몇 연구자에 의해 제기된 바가 있다. 본 연구에서는 필자의 최근 해석 및 실험연구를 주 근거로 하여 다양한 형식의 접합부의 응력전달 메커니즘을 재평가하고, 거의 모든 용접 모멘트접합부의 설계에 초등휨이론을 적용하는 것이 부적절함을 보이고자 하였다. 보의 웨브, 수평헌치의 웨브, 리브 등과 같은 수직 플레이트 접합요소는 모두 스트럿 작용에 의해 응력을 전달하는 유사성이 있음을 해석적, 실험적으로 확인하였다. 또한 최근 가장 큰 주목을 받고 있는 고연성 RBS 접합부의 전단력 응력전달 메커니즘은 PN형식 접합부의 그것과 크게 다르지 않음을 확인하였다. 아울러 접합부 설계에 유용하게 활용될 수 있는 단순화된 해석적 응력전달 모형을 소개하였다.

• Smart Structures and Systems
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• 제21권3호
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• pp.279-286
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• 2018

The free longitudinal vibration of a circular truncated nanocone is investigated based on the nonlocal elasticity theory. Exact analytical formulations for tapered nanostructures are derived and the nonlinear differential governing equation of motion is developed. The nonlocal small scale effect unavailable in classical continuum theory is addressed to reveal the long-range interaction of atoms implicated in nonlocal constitutive relation. Unlike most previous studies applying the truncation method to the infinite higher-order differential equation, this paper aims to consider all higher-order terms to show the overall nonlocality. The explicit solution of nonlocal stress for longitudinal deformation is determined and it is an infinite series incorporating the classical stress derived in classical mechanics of materials and the infinite higher-order derivative of longitudinal displacement. Subsequently, the first three modes natural frequencies are calculated numerically and the significant effects of nonlocal small scale and vertex angle on natural frequencies are examined. The coupling phenomenon of natural frequency is observed and it is induced by the combined effects of nonlocal small scale and vertex angle. The critical value of nonlocal small scale is defined, and after that a new proposal for determining the range of nonlocal small scale is put forward since the principle of choosing the nonlocal small scale is still unclear at present. Additionally, two different types of nonlocal effects, namely the nonlocal stiffness weakening and strengthening, reversed phenomena existing in nanostructures are observed and verified. Hence the opposite nonlocal effects are resolved again clearly. The nano-engineers dealing with a circular truncated nanocone-based sensors and oscillators may benefit from the present work.

• Composites Research
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• 제32권1호
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• pp.13-20
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• 2019

본 연구에서는 전기 자동차의 주요 부품 중 하나인, Battery Module의 품질 Issue 및 부품특성 개선을 위해 복합재료를 사용하여 구조보강 하였으며, 단일소재의 단점을 극복할 수 있는 Hybrid 개념의 기구 구조 최적화를 수행하고 성능을 비교하였다. 이를 위해 고전 적층 판 이론(Classical Laminated Plate Theory, CLPT)에 따른 복합재료 주요 설계 변수 도출 및 복합재료 물성 예측 알고리즘에 대해 연구하였으며, 설계된 복합재료의 기계적 물성을 바탕으로 유한요소해석(FEM)을 통해 Battery Module의 성능을 검증하였다. 이를 통해 자동차 Battery 부품의 안정성 및 경량화 등의 부품 특성 개선 여부를 확인할 수 있었다. 최종적으로 검증결과에 따르면 Selective Composite Patch로 보강된 Hybrid Battery Module은 기존 Al Battery Module에 비해 30%의 중량 감소 및 제품 두께 32.5%를 줄일 수 있고, 충격 성능 유지 등 Hybrid 구조의 장점을 입증하였다.