• 한국철도학회:학술대회논문집
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• 한국철도학회 1999년도 추계학술대회 논문집
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• pp.471-478
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• 1999

In this study, we have Quantitatively estimated the mechanical properties of SM steels widely used in steel structures after correcting and analyzing the millsheets of the steels. From this result, in present, the mechanical properties of the steels produced in domestics have satisfied the prescribed values in Korean Standards on the whole. The mechanical properties of the steels were dependent of plate thickness and class of the steels. Also, there have been linear relations between the plate thickness and the mechanical properties of the steels. And the results of this study have shown the similar tendencies with the existing results. Because the upper limit value of yield strength are not prescribed in Korean Standards at present, it is necessary to prescribe the upper limit value of yielding ratio(or yield strength) in order to assure the deformation performance of the steels.

• Structural Engineering and Mechanics
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• 제86권2호
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• pp.157-165
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• 2023

In the present work, the vibration characteristics of sandwich nanocomposite shells, fortified with graphene platelets (GPLs) have been researched. The shell has been considered as the stadium roof shape with double curvatures under vibration due to earthquake. The nanocomposite has the matrix of concrete which is fortified with uniform or linear dispersions of GPLs. Also, the core possesses cellular type square architecture for which the effective elastic modulus has been defined in the context of relative density based relations. Based upon the classic shell strains containing two identical curvatures, the governing equations have been established and solved through differential quadrature approach. It will be seen that the vibrational frequencies rely on the core relative density, height of layers, the amount and dispersions of GPLs and even shell geometric parameters.

• Current Optics and Photonics
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• 제7권5호
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• pp.562-568
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• 2023

We designed a combined nanostructure of inverted pyramidal pits and nanoparticles, which can obtain much stronger field enhancement than traditional periodic pits or nanoparticles. The field enhancement |E|/|E₀| is greater than 10 in a large area at 750-820 nm in incident wavelength. |E_max|/|E₀| is greater than 60. Moreover, the hot spot is obtained outside the pits instead of localized inside them, which is beneficial for experiments such as surface-enhanced Raman scattering. The relations between resonant wavelength and structural parameters are investigated. The resonant wavelength shows a linear dependence on the structure's period, which provides a direct way to tune the resonant wavelength. The excitation of a propagating surface plasmon on the periodic structure's surface, a localized surface plasmon of nanoparticles, and a standing-wave effect contribute to the enhancement.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.314-318
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• 2000

For one-dimensional structures, a vibration response consists of direct and reflected waves from boundaries. Based on this concept of separable wave components, a modified travelling wave method (MTWM) is proposed in this paper: while all allowable waves are assumed and the boundary conditions are applied on by the conventional travealling wave method (TWM), in the proposed MTWM direct and reflected waves are assumed within the beam element, and the governing relations between direct and reflected waves are described in terms of the reflection or transmission coefficients. It is shown that the vibration response with considerable accuracy can be obtained compared to TWM for single and coupled beams. It is also shown that the band analysis to obtain quadratic response, or power flow response can be carried out by a slight change of the governing equations for one-dimensional structural systems. It is thought that the suggested MTWM can be used as a unified approach for predicting linear spectral response and/or quadratic band response involved in the one-dimensional structural vibration.

• Structural Engineering and Mechanics
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• 제43권5호
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• pp.561-582
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• 2012

Despite popularity of FEM in analysis of static and dynamic structural problems and the routine applicability of FE softwares, analytical methods based on simple mathematical relations is still largely sought by many researchers and practicing engineers around the world. Development of such analytical methods for analysis of free vibration of non-prismatic beams is also of primary concern. In this paper a new and simple method is proposed for determination of vibration frequencies of non-prismatic beams under variable axial forces. The governing differential equation is first obtained and, according to a harmonic vibration, is converted into a single variable equation in terms of location. Through repetitive integrations, integral equation for the weak form of governing equation is derived. The integration constants are determined using the boundary conditions applied to the problem. The mode shape functions are approximated by a power series. Substitution of the power series into the integral equation transforms it into a system of linear algebraic equations. Natural frequencies are determined using a non-trivial solution for system of equations. Presented method is formulated for beams having various end conditions and is extended for determination of the buckling load of non-prismatic beams. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained to those obtained using available finite element software.

• Steel and Composite Structures
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• 제7권2호
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• pp.87-103
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• 2007

This paper presents some of the results from an experimental research project on the behavior of extended end-plate connections subjected to moment conducted at the Structural Laboratory of Jordan University of Science and Technology. Since the connection behavior affects the structural frame response, it must be included in the global analysis and design. In this study, the behavior of six full-scale stiffened and unstiffened cantilever connections of HEA- and IPE-sections has been investigated. Eight high strength bolts were used to connect the extended end-plate to the column flange in each case. Strain gauges were installed inside each of the top six bolts in order to obtain experimentally the actual tension force induced within each bolt. Then the connection behavior is characterized by the tension force in the bolt, extended end-plate behavior, moment-rotation relation, and beam and column strains. Some or all of these characteristics are used by many Standards; therefore, it is essential to predict the global behavior of column-beam connections by their geometrical and mechanical properties. The experimental test results are compared with two theoretical (equal distribution and linear distribution) approaches in order to assess the capabilities and accuracy of the theoretical models. A simple model of the joint is established and the essential parameters to predict its strength and deformational behavior are determined. The equal distribution method reasonably determined the tension forces in the upper two bolts while the linear distribution method underestimated them. The deformation behavior of the tested connections was characterized by separation of the column-flange from the extended end-plate almost down to the level of the upper two bolts of the lower group and below this level the two parts remained in full contact. The neutral axis of the deformed joint is reasonably assumed to pass very close to the line joining the upper two bolts of the lower group. Smooth monotonic moment-rotation relations for the all tested frames were observed.

• 보건행정학회지
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• 제26권3호
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• pp.155-171
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• 2016

Background: In this study, state-owned medical institutes, industrial accident hospitals, veteran hospitals, and private medical clinics including 16 university medical institutes in the Seoul metropolitan area were selected to examine the causality of ethical management, positive psychological capital, and organizational effectiveness. Methods: The study analyzed 1,056 valid questionnaires to which a total of 1,325 nurses, medical technicians, doctors, and administrative staff in 34 healthcare organizations answered over two months from June to August 2015. The study also utilized a 'structural equation model,' and a 'hierarchical linear model' to conduct the analysis. Results: It was first found that ethical leadership, ethical management systems, and organizational ethics values, which are the three factors of ethical management, had significant influence on organizational commitment, and behavior. These are the three factors of employee organizational effectiveness. Second, ethical management, ethical leadership, ethical management systems, and organizational ethics values had significant influence on positive psychological capital. Third, positive psychological capital had significant influence on organizational commitment, turnover intention, and organizational citizenship behavior. Positive psychological capital presented an indirect effect on the relationship between the ethical management and organizational effectiveness of employees. The effect of positive psychological capital consisting of self-efficacy, hope, resilience, and optimism was confirmed in the healthcare organizations. Fourth, in relations among ethical management variables, ethical leadership showed a significant impact on ethical management systems, which had significant impacts on organizational ethics values, which had significant impacts on ethical leadership.

• 한국전산구조공학회논문집
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• 제29권4호
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• pp.309-315
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• 2016

최근 치의학 분야에서도 인체에 대한 구조적이고 역학적인 이해를 위하여 유한요소해석 기법이 널리 사용되고 있다. 따라서 본 연구에서는 CT 이미지를 기반으로 하는 유한요소모델링 기법을 제안하고, 실험결과와 비교하여 검증하였다. 또한 제안된 해석기법을 통해 교합 시뮬레이션을 구현하여 정상 I급 교합과 Full-CUSP II급 교합상태의 두개골 모델에 대하여 기하비선형구조해석을 수행하였다. 그 결과, 하악골이 같은 거리만큼 이동할 때 사람의 실제 교합력 범위에서는 두 모델의 교합력에 큰 차이가 없는 것으로 나타났다. 그러나 응력분포를 비교했을 때 정상 I급 교합모델은 치아 및 치조골 전반에 응력이 균등하게 발생하는 반면, Full-CUSP II급 교합모델의 경우 일부 구역에 응력집중 현상이 나타났다. 이는 치아의 부재 및 재배열로 인하여 교합면이 달라지면서 생긴 결과라고 분석된다.

• Structural Engineering and Mechanics
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• 제48권4호
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• pp.547-567
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• 2013

Nonlinear behavior of functionally graded material (FGM) plates under thermal loads is investigated here using an efficient sinusoidal shear deformation theory. The displacement field is chosen based on assumptions that the in-plane and transverse displacements consist of bending and shear components, and the shear components of in-plane displacements give rise to the sinusoidal distribution of transverse shear stress through the thickness in such a way that shear stresses vanish on the plate surfaces. Therefore, there is no need to use shear correction factor. Unlike the conventional sinusoidal shear deformation theory, the proposed efficient sinusoidal shear deformation theory contains only four unknowns. The material is graded in the thickness direction and a simple power law based on the rule of mixture is used to estimate the effective material properties. The neutral surface position for such FGM plates is determined and the sinusoidal shear deformation theory based on exact neutral surface position is employed here. There is no stretching-bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations and boundary conditions of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. The non-linear strain-displacement relations are also taken into consideration. The thermal loads are assumed as uniform, linear and non-linear temperature rises across the thickness direction. Closed-form solutions are presented to calculate the critical buckling temperature, which are useful for engineers in design. Numerical results are presented for the present efficient sinusoidal shear deformation theory, demonstrating its importance and accuracy in comparison to other theories.

• 한국강구조학회 논문집
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• 제12권3호통권46호
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• pp.281-290
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• 2000

본 연구에서는 강구조물에 자주 사용되고 있는 용접구조용강재를 대상으로 강재검사성적증명서를 수집하고 이를 통계적으로 분석, 정리해서 기계적 성질의 특성을 정량적으로 평가하였다. 본 연구결과 현재 국내에서 생산되는 용접구조용강재의 기계적 성질은 현행 KS에서 규정하고 있는 기준값을 만족하였으며, 판두께 및 강도등급과 일정한 상관관계가 있음을 알 수 있었다. 강종별 판두께 및 강도등급과 기계적 성질 사이에는 선형적인 비례관계가 성립, 본 연구결과는 기존 연구결과와 유사한 경향이 있음을 알 수 있었다. 현행 KS에서는 강재의 기계적 성질 중 항복점 응력에 대한 상한값이 규정되어 있지 않는데, 강재의 변형성능을 충분하게 확보하기 위해서는 항복비 (또는 항복강도)의 상한값을 규정 할 필요가 있을 것으로 생각된다.