• Structural Engineering and Mechanics
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• 제15권6호
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• pp.629-651
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• 2003

Current design specifications prescribe that the upper and lower reinforcement mat is required in the same amount to resist negative and positive moment in bridge decks. This design concept is primarily based on the unrealistic assumption that the girder plays a role of rigid support against deck deflection. In reality, however, girders are flexible and the deflection of girders affect the behavior of deck slabs. In the present study, an analytical method was developed to take the effect of the girder flexibility on the deck behavior into account. The method was formulated based on the slope-deflection equations of plates and harmonic analysis. Unlike the conventional finite element analysis, the input and output schemes are simple and convenient. The validity of the presented study was verified by a series of comparative studies with finite element analyses and experimental tests. It was shown from the analyses that the negative transverse moments of decks were significantly reduced in many cases when the girder flexibility were appropriately taken into consideration whereas the positive moments tend to increase. This poses a strong need to improve the conventional design concept of decks on rigid girders to those on flexible girders.

• International Journal of Railway
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• 제7권1호
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• pp.16-23
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• 2014

Reduction in railway-induced vibrations in urban areas is a very challenging task in railway transportation. Many mitigation measures can be considered and applied. Among these, a little attention has been paid to trenches. In this study, a numerical investigation on the effectiveness of in-filled trenches with pipes in reducing railway vibrations due to passing trains is presented. Particularly, a series of two-dimensional dynamic analysis was performed to model the behavior of ballasted railway track under harmonic load with ABAQUS software as a Finite Element method. In so doing, two types of in-filled trenches with pipes with steel and concrete materials have been investigated in this paper. In addition, effectiveness of pipes made of steel and concrete, filled with loose sand and clay in railway-induced vibration reduction has been assessed. The results point out that using in-filled trench with pipes does not effective a lot on railway-induced vibration reduction in comparison to other railway-induced vibration reduction methods. However, in-filled trenches with steel pipes are much more effective than in-filled trenches with concrete pipes. Moreover, filling pipes with loose sand and clay does not have any effect on vibration reduction efficiency of these in-filled trenches.

• 대한조선학회논문집
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• 제47권2호
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• pp.210-224
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• 2010

The aim of the present study is to investigate the buckling strength of plates and stiffened panels with opening under transverse thrust and shear actions. It is observed that the existing design formulation for critical-buckling strength of plates are not valid for perforated plates, because the current design formulation trends can significantly overestimate or underestimate the load-carrying capacity of plates when plates have large opening and/or are thick. A series of eigen value and elastic.plastic large deflection finite element analyses are carried out with varying the aspect ratio of plate, the opening size and location on plate until and after the ultimate strength is reached. Based on the results obtained from the present study, closed-form design formulations for the elastic buckling strength of plates and stiffened panels with opening are derived. The derived design formulations are considered plasticity correction of the material and verified by experimental tests and results of nonlinear finite element computations.

• Journal of Advanced Marine Engineering and Technology
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• 제23권4호
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• pp.504-513
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• 1999

Usually bellows are designed for the purpose of absorbing axial movement. To find out axial stiffness of bellows the axisymmetric shell theory using the finite element method is adopted in this paper. Bellows can be idealised by series of conical frustum-shaped elements because it is axisymmetric shell structure. The force required to deflect bellows axilly is a function of the dimensions of the bellows and the materials from which they are made. The displancements of nodal points due to small increment of force are calculated by the finite element method and the calculated nodal displacements are added to r-z cylinderical coordinates of nodal points. The new stiffness matrix of the system using the new coordinates of nodal points is adopted to calculate the another increments of nodal dis-placements that is the step by method is used in this paper. spring constant is analyzed according to the changing geometric factors of u-shaped bellows. The FEM results were agreed with experiment. Using developed FORTRAN PROGRAM spring constant can be predicted by input of a few factors.

• Journal of Advanced Marine Engineering and Technology
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• 제23권5호
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• pp.702-710
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• 1999

U-shaped bellows are usually used to piping system pressure sensor and controller for refriger-ator. Bellows subjected to internal pressure are designed for the purpose of absorbing deformation. Internal pressure on the convolution sidewall and end collar will be applied to an axial load tend-ing to push the collar away from the convolutions. To find out deformation behavior of bellow sub-jected to internal pressure the axisymmetric shell theory using the finite element method is adopted in this paper. U-shaped bellows can be idealized by series of conical frustum-shaped ele-ments because it is axisymmetric shell structure. The displacements of nodal points due to small increment of force are calculated by the finite element method and the calculated nodal displace-ments are added to r-z cylindrical coordinates of nodal points. The new stiffness matrix of the sys-tem using the new coordinates of nodal points is adopted to calculate the another increments of nodal displacement that is the step by step method is used in this paper. The force required to deflect bellows axially is a function of the dimensions of the bellows and the materials from which they are made. Spring constant is analyzed according to the changing geometric factors of U-shaped bellows. The FEM results were agreed with experiment. Using developed FORTRAN PROGRAM the internal pressure vs. deflection characteristics of a particu-lar bellows can be predicted by input of a few factors.

• Composites Research
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• 제29권1호
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• pp.33-39
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• 2016

본 논문에서는 3차원 평직 복합재료의 3-방향 섬유다발의 굴곡각에 따른 다양한 모델링을 구축하고, 제시한 모델에 대하여 등가 물성치를 예측하였다. 3차원 평직복합재료의 단위셀을 정의하고 미시역학 계산결과인 섬유다발 물성치를 사용하여 섬유다발에 굴곡각에 따라 물성치가 변화하도록 요소 물성축을 설정 후 3차원 평직 복합재료의 중시해석을 수행하였다. 계산결과 등가물성치는 참고문헌에 제시된 해석 및 실험값을 비교하여 타당성을 확보하였으며 계산결과 3-방향 섬유다발 굴곡각이 미치는 영향에 대하여 고찰하였다. 또한 초기파손 강도와 파손순서에 대해서도 조사하였다.

• Earthquakes and Structures
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• 제7권5호
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• pp.891-906
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• 2014

The purpose of this study is to propose a modification factor to reflect the lateral stiffness modification when a step is located in flat plates. Reinforced concrete slabs with steps have different structural characteristics that are demonstrated by a series of structural experiment and nonlinear analyses. The corner at the step is weak and flexible, and the associated rotational stiffness degradation at the corner of the step is identified through analyses of 6 types of models using a nonlinear finite element program. Then a systematic analysis of stiffness changes is performed using a linear finite element procedure along with rotational springs. The lateral stiffness of reinforced concrete flat plates with steps is mainly affected by the step length, location, thickness and height. Therefore, a single modification factor for each of these variables is obtained, while other variables are constrained. When multiple variables are considered, each single modification factor is multiplied by the other. Such a method is verified by a comparative analysis. Finally, a complex modification factor can be applied to the existing effective slab width.

• 한국공작기계학회논문집
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• 제18권1호
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• pp.36-41
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• 2009

This paper presents the development of a micro punching system with modified cymbal mechanism. To realize the micro punching, we introduced the hybrid system with a macro moving part and micro punching part. The macro moving part consists of a ball screw, a linear guide and the micro step motor and micro punching part includes the PZT actuators and displacement amplification device with modified cymbal mechanism. The PZT actuator is capable of producing very large force, but they provide only limited displacements which are several micro meters. Thus the displacement amplification device is necessary to make those actuators more efficient and useful. For this purpose, a cymbal mechanism in series is proposed. The finite element method was used to design the cymbal mechanism and to analyze the mode shape of the one. The displacement and mode shape error between the FEM results and experiments are within 10%. A considerable design effort has been focused on optimizing the flexure hinge to increase the output displacement and punching force.

• Steel and Composite Structures
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• 제2권1호
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• pp.35-50
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• 2002

A series of tests on simple-welded plate specimens (SWPS) and T-stub tension specimens simulating some of the joint details in moment frame connections were conducted in this investigation. The effects of weld strength mismatch and weld metal toughness on structural behavior of these specimens were considered under both static and dynamic loading conditions. Finite element analyses were performed by taking into account typical weld residual stress distributions and weld metal strength mismatch conditions to facilitate the interpretation of the test results. The major findings are as follows: (a) Sufficient specimen size requirements are essential in simulating both load transfer and constraint conditions that are relevant to moment frame connections, (b) Weld residual stresses can significantly elevate stress triaxiality in addition to structural constraint effects, both of which can significantly reduce the plastic deformation capacity in moment frame connections, (c) Based on the test results, dynamic loading within a loading rate of 0.02 in/in/sec, as used in this study, premature brittle fractures were not seen, although a significant elevation of the yield strength can be clearly observed. However, brittle fracture features can be clearly identified in T-stub specimens in which severe constraint effects (stress triaxiality) are considered as the primary cause, (d) Based on both the test and FEA results, T-stub specimens provide a reasonable representation of the joint conditions in moment frame connections in simulating both complex load transfer mode and constraint conditions.

• Geomechanics and Engineering
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• 제5권1호
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• pp.37-55
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• 2013

An important issue in the design of soil-nailing systems, as long-term retaining walls, is to assess their stability during seismic events. As such, this study is aimed at simulating the dynamic behavior and failure pattern of nailed structures using two series of numerical analyses, namely dynamic time history and pseudo-static. These numerical simulations are performed using the Finite Difference Method (FDM). In order to consider the actual response of a soil-nailed structure, nonlinear soil behaviour, soil-structure interaction effects, bending resistance of structural elements and construction sequences have been considered in the analyses. The obtained results revealed the efficiency of both analysis methods in simulating the seismic failure mechanism. The predicted failure pattern consists of two sliding blocks enclosed by three slip surfaces, whereby the bottom nails act as anchors and the other nails hold a semi-rigid soil mass. Moreover, it was realized that an increase in the length of the lowest nails is the most effective method to improve seismic stability of soil-nailed structures. Therefore, it is recommended to first estimate the nails pattern for static condition with the minimum required static safety factor. Then, the required seismic stability can be obtained through an increase in the length of the lowest nails. Moreover, placement of additional long nails among lowest nails in existing nailed structures can be considered as a simple retrofitting technique in seismic prone areas.