• Structural Engineering and Mechanics
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• v.28 no.4
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• pp.357-372
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• 2008

This study investigates effect of uncertainty in natural vibration period on the seismic demand. It is shown that since this uncertainty affects the acceleration and displacement responses differently, two ratios, one relating peak acceleration responses and the other relating the peak displacement responses, are not equal and both must be employed in evaluating and defining the critical seismic demand. The evaluation of the ratios is carried out using more than 200 strong ground motion records. The results suggest that the uncertainty in the natural vibration period impacts significantly the statistics of the ratios relating the peak responses. By using the statistics of the ratios, a procedure and sets of empirical equations are developed for estimating the probability consistent seismic demand for both linear and nonlinear systems.

• Steel and Composite Structures
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• v.37 no.1
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• pp.37-49
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• 2020

In this paper, free vibration finite element analysis of axially moving laminated composite beams subjected to axial tension is studied. It is assumed that the beam has a constant axial velocity and is subject to uniform axial tension. The analysis is based on higher-order theories that have been presented by Carrera Unified Formulation (CUF). In the CUF technique, the three dimensional (3D) displacement fields are expressed as the approximation of the arbitrary order of the displacement unknowns over the cross-section. This higher-order expansion is considered in equivalent single layer (ESL) model. The governing equations of motion are obtained via Hamilton's principle. Finally, several numerical examples are presented and the effect of the ply-angle, travelling speed and axial tension on the natural frequencies and beam stability are demonstrated.

• Advances in materials Research
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• v.4 no.1
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• pp.31-44
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• 2015

This paper presents a simple n-order four variable refined theory for buckling analysis of functionally graded plates. By dividing the transverse displacement into bending and shear parts, the number of unknowns and governing equations of the present theory is reduced, and hence, makes it simple to use. The present theory is variationally consistent, uses the n-order polynomial term to represent the displacement field, does not require shear correction factor, and eliminates the shear stresses at the top and bottom surfaces. A power law distribution is used to describe the variation of volume fraction of material compositions. Equilibrium and stability equations are derived based on the present n-order refined theory. The non-linear governing equations are solved for plates subjected to simply supported boundary conditions. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. The effects of aspect and thickness ratios, gradient index, on the critical buckling are all discussed.

• Steel and Composite Structures
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• v.6 no.4
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• pp.319-333
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• 2006

A rectangular plate made of a porous material is the subject of the work. Its mechanical properties vary continuously on the thickness of a plate. A mathematical model of this plate, which bases on nonlinear displacement functions taking into account shearing deformations, is presented. The assumed displacement field, linear geometrical and physical relationships permit to describe the total potential energy of a plate. Using the principle of stationarity of the total potential energy the set of five equilibrium equations for transversely and in-plane loaded plates is obtained. The derived equations are used for solving a problem of a bending simply supported plate loaded with transverse pressure. Moreover, the critical load of a bi-axially in-plane compressed plate is found. In both cases influence of parameters on obtained solutions such as a porosity coefficient or thickness ratio is analysed. In order to compare analytical results a finite element model of a porous plate is built using system ANSYS. Obtained numerical results are in agreement with analytical ones.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.95-103
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• 2001

The buckling of an orthotropic layer bonded to an orthotropic half-space with an interface crack subjected to compressive load under plane strain is analyzed. General solution to the stability equations describing the buckling behavior of both the layer and the half-space is expressed in terms of displacement functions. The displacement functions are represented by the solution of Cauchy-type singular integral equations, which are numerically solved. Numerical results of the critical buckling loads are presented fur various geometric parameters and material properties of both the layer and half-space.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.6 s.111
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• pp.634-642
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• 2006

For the analysis of dynamic contact between a catenary and a pantograph of high-speed electrical train, the numerical solution of the equations of motion of the vehicle pantograph and the catenary system subjected to the contact condition is obtained. The whole equations of motion of the catenary and the pantograph are simultaneously time integrated with the strict application of the contact condition. For the stability of the numerical solution, with the cubic spline interpolation of the catenary displacement, the velocity and acceleration constraints as well as the displacement constraint are imposed on the contact point. Especially it is shown that the Coriolis and centripetal accelerations are critical for the accuracy and stability of the computation.

• Earthquakes and Structures
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• v.17 no.5
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• pp.501-510
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• 2019

In the study, an experimental and numerical study is performed to investigate the efficiency of diagonal shear reinforcement (DSR) on reinforced concrete (RC) short beams. For this purpose, 7 RC short beam specimens were tested under a 4-point loading, and a numerical study is conducted by using finite element method. Additionally, the efficiency of addition of DSR to specimens is observed in the experimental study together with the increase in stirrup spacing. Analysis results are compared in terms of load-displacement behavior and failure modes. As a result of the study, a significant improvement both in shear and displacement capacities of the RC short beams are achieved along with addition of DSR in short beams. Moreover, it is deduced from the numerical results that increasing both the diameter and yield strength of DSR makes a significant contribution to the shear capacity and ductility of shear critical RC members.

• Journal of English Language & Literature
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• v.64 no.1
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• pp.135-150
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• 2018

Focusing on the hermeneutic instability of a key word of Paradise Lost, "wander," this study attempts to situate John Milton's early modern epic in the longue $dur{\acute{e}}e$ historical transition from seignorial to capitalist mode of production, especially the displacement and reorganization of producer population, a corollary of early phase of modernization. The historic experience of vagrancy and its normalization, and the concomitant shift of the primary human sociability from given to voluntary bonds, I suggest, shape and inform Milton's early modern rewriting of the Biblical story of the fall and his revising of the heroic epic romance into a plebeian romance of a wandering, companionate couple. While building on the critical consensus on this poem's deliberate distancing from the tradition of classical epic and chivalric romance, this essay argues that Milton re-appropriates and re-channels the aspirational aspect of chivalric wandering, or mobility, for his plebeian heroes, a companionate conjugal couple. The hermeneutic instability of the word wander, this essay suggests, captures the duality of the historic experience of vagrancy, both the tragic experience of displacement and the liberational and uplifting dimension of that experience.

• Wind and Structures
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• v.10 no.4
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• pp.367-382
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• 2007

A nonlinear numerical method was developed to assess the stability of suspension bridge catwalks under a wind load. A section model wind tunnel test was used to obtain a catwalk's aerostatic coefficients, from which the displacement-dependent wind loads were subsequently derived. The stability of a suspension bridge catwalk was analyzed on the basis of the geometric nonlinear behavior of the structure. In addition, a full model test was conducted on the catwalk, which spanned 960 m. A comparison of the displacement values between the test and the numerical simulation shows that a numerical method based on a section model test can be used to effectively and accurately evaluate the stability of a catwalk. A case study features the stability of the catwalk of the Runyang Yangtze suspension bridge, the main span of which is 1490 m. Wind can generally attack the structure from any direction. Whenever the wind comes at a yaw angle, there are six wind load components that act on the catwalk. If the yaw angle is equal to zero, the wind is normal to the catwalk (called normal wind) and the six load components are reduced to three components. Three aerostatic coefficients of the catwalk can be obtained through a section model test with traditional test equipment. However, six aerostatic coefficients of the catwalk must be acquired with the aid of special section model test equipment. A nonlinear numerical method was used study the stability of a catwalk under a yaw wind, while taking into account the six components of the displacement-dependent wind load and the geometric nonlinearity of the catwalk. The results show that when wind attacks with a slight yaw angle, the critical velocity that induces static instability of the catwalk may be lower than the critical velocity of normal wind. However, as the yaw angle of the wind becomes larger, the critical velocity increases. In the atmospheric boundary layer, the wind is turbulent and the velocity history is a random time history. The effects of turbulent wind on the stability of a catwalk are also assessed. The wind velocity fields are regarded as stationary Gaussian stochastic processes, which can be simulated by a spectral representation method. A nonlinear finite-element model set forepart and the Newmark integration method was used to calculate the wind-induced buffeting responses. The results confirm that the turbulent character of wind has little influence on the stability of the catwalk.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.29-41
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• 2007

An assesment technique for the quantitative evaluation of tunnel safety during tunnel excavation was newly proposed in this study using displacement measurements. First of all, field measurement guidelines used at tunnel construction sites in Korea and other countries were investigated. It was found out that the criteria of the guidelines were not clear and varied depending on the construction sites. The practical use of field measurement data for the evaluation of tunnel safety was very limited due to uncertainties of the guidelines related to the interpretation of measured data during the excavation. Critical strain concept is introduced in this study for the assesment of tunnel safety during the tunnel excavation. Moreover, the characteristics of tunnel displacements caused by the tunnel excavation were investigated in detail in order to investigate the practical application of the critical strain concept. The total tunnel displacements can be subdivided into three parts: displacements occurring ahead of tunnel face, displacements occurring prior to measurements, and displacements occurring after the installation of instruments. The characteristic of each portion of displacements is analysed in this study. Finally, a general method on the use of the displacement measurement data for the critical strain concept was suggested in the concrete manner, considering the field measurement practice in Korea.