• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.396-401
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• 2006

Dynamic behaviors of the impact damper are studied experimentally and numerically. In order to investigate wide range of excitation frequencies and amplitudes, a simple but high amplifying and bias-free experimental setup is designed. Experiments focused on the harsh operation condition demonstrate Accelerated mass loading which not only deteriorates the performance of the impact damper but also involves the structural resonance which should be avoided for the stability of the system. In the previous studies, instability or deterioration of the performance was reported for the off resonance frequency region. But this paper shows that the performance deterioration and structural resonances can be predicted. Using finite element modeling and analysis, accurate system parameters were derived and used for the numerical modeling employing the conservation of the momentum. Numerical study of the transient responses using 4th-order Runge-Kutta method demonstrates general performance of the system, and shows that accelerated mass loading phenomenon is deeply related with the vibration amplitudes and the mass of the auxiliary system.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.133-140
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• 1998

Material nonlinear analyses of RC(Reinforced Concrete) beams considering the tension stiffening effect and plastic hinge length have been conducted. Instead of taking the sophisticated layer approach which has some limitations in application to the large structures with many degrees of freedom. the moment-curvature relationships of RC sections previously constructed through the section analysis have been used. To reduce the numerical instability in nonlinear analysis and to remove the imprecision in calculation of ultimate resisting capacity, according to the used finite element mesh size, the tension stiffening effect and plastic hinge length have been taken into consideration. Finally, correlation studies between analytical and experimental results have been conducted with the objective to establish the validity of the proposed algorithms.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.135-140
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• 2007

In this paper, an Improved Dimension Reduction(IDR) method is proposed for uncertainty quantification that employes Kriging interpolation technic. It has been acknowledged that the DR method is accurate and efficient for assessing statistical moments and reliability due to the sensitivity free feature. However, the DR method has a number of drawbacks such as instability and inaccuracy for problems with increased nonlineality. In this paper, improved DR is implanted by three steps. First, the Kriging interpolation method is used to accurately approximate the responses. Second, 2N+1 and 4N+1 ADOEs are proposed to maintain high accuracy of the method for UQ analysis. Third, numerical integration scheme is used with accurate but free response values at any set of integration points of the surrogated model.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.567-568
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• 2006

We investigate the structures and the formation energy of inversion domain boundaries (IDBs) using the Tersoff empirical potential. Four kinds of IDBs ( A and B types for IDB* and Holt ) are considered. The IDBs with A type are energetically favorable compared to B type with the structural instability. The IDB* is also more stable than the Holt type in spite of fourfold and eightfold rings of bonds. We calculate the atomic configurations of the Holt IDBs induced by the interactions of the IDB* with the stacking faults $I_1$ and $I_2$. The stacking fault $I_2$ interacted with $I_1$ on the IDB induces the structural transformation from IDB* to Holt type.

• Structural Engineering and Mechanics
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• v.54 no.3
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• pp.579-595
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• 2015

A general geometrically non-linear model for lateral-torsional buckling of thick and thin-walled FGM box beams is presented. In this model primary and secondary torsional warping and shear effects are taken into account. The coupled equilibrium equations obtained from Galerkin's method are derived and the corresponding tangent matrix is used to compute the critical moments. General expression is derived for the lateral-torsional buckling load of unshearable FGM beams. The results are validated by comparison with a 3D finite element simulation using the code ABAQUS. The influences of the geometrical characteristics and the shear effects on the buckling loads are demonstrated through several case studies.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.04a
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• pp.240-247
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• 1997

Single-layer latticed domes, which ore consisted of slender linear elements, are able to transmit external loads to the structure by in-plane forces, therefore spatial structures can be constructed with the merit of its own lightweight. But, as external load reaches to any critical level at which each member has not material nonlinearity, the single-layer latticed dome shows unstable phenomenon. In particular, pin-connected single-layer latticed domes have much complicate unstable phenomena that are combined with nodal buckling and member buckling. Furthermore, single-layer latticed domes are very sensible to the initial imperfection which occurred inevitably in construction. In this study, we are going to grasp the characteristics of instability for the latticed dome by finite element method considering geometrical nonlinearity.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2004.05a
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• pp.59-62
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• 2004

The defect formation energy of boron nitride (BN) nanotubes is investigated using molecular-dynamics simulation. Although the defect with tetragon-octagon pairs (4-88-4) is favored in the flat cap of BN nanotubes, BN clusters, and the growth of BN nanotubes, the formation energy of the 4-88-4 defect is significantly higher than that of the pentagon-heptagon pairs (5-77-5) defect in BN nanotubes. The 5-77-5 defect reduces the effect of the structural distortion caused by the 4-88-4 defect, in spite of homoelemental bonds. The instability of the 4-88-4 defect generates the structural transformation into BNNTs with no defect at about 1500 K.

• Steel and Composite Structures
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• v.29 no.4
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• pp.509-526
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• 2018

The direct strength method adopted by the AISI Standard and AS/NZS 4600 is an advanced design method meant to substitute the effective width method for the design of cold-formed steel structural members accounting for local instability of thin plate elements. It was proven that the design strength formula for the direct strength method could predict the ultimate strength of medium strength steel welded section compressive and flexural members with local buckling reasonably. This paper focuses on the modification of the direct strength formula for the application to high strength and high performance steel welded section columns which have the nominal yield stress higher than 460 MPa and undergo local buckling, overall buckling or their interaction. The resistance of high strength steel welded H and Box section columns calculated by the proposed direct strength formulae were validated by comparison with various compression test results, FE results, and predictions by existing specifications.

• Wind and Structures
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• v.1 no.1
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• pp.59-66
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• 1998

The vibrations of bodies subjected to fluid flow can cause modifications in the flow conditions, giving rise to interaction forces that depend primarily on displacements and velocities of the body in question. In this paper the linearized equations of motion for bodies of arbitrary prismatic or cylindrical cross-section in two-dimensional cross-flow are presented, considering the three degrees of freedom of the body cross-section. By restraining the rotational motion, equations applicable to circular tubes, pipes or cables are obtained. These equations can be used to determine stability limits for such structural systems when subjected to non uniform cross-flow, or to evaluate, under the quasi static assumption, their response to vortex or turbulent excitation. As a simple illustration, the stability of a pipe subjected to a bidimensional flow in the direction normal to the pipe axis is examined. It is shown that the approach is extremely powerful, allowing the evaluation of fluid-structure interaction in unidimensional structural systems, such as straight or curved pipes, cables, etc, by means of either a combined experimental-numerical scheme or through purely numerical methods.

• Structural Engineering and Mechanics
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• v.19 no.2
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• pp.153-172
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• 2005

A new load/displacement parameter method is proposed for the simultaneous control of applied loads and structural displacements at one or more points. The procedure is based on a generalized Riks' method, which utilizes load/displacement parameters as scaling factors to analyze post-buckling phenomena including snap-through or snap-back. The convergence characteristics are improved by employing new relaxation factors through an incremental displacement parameter, particularly in a region that exhibits severe numerical instability. The improved performance is illustrated by means of a numerical example.