• Advances in nano research
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• v.9 no.2
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• pp.69-82
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• 2020

In this paper, a new explicit analytical formula is derived for the critical buckling load of Double Walled Carbon Nanotubes (DWCNTs) embedded in Winkler elastic medium without taking into account the effects of the nonlocal parameter, which indicates the effects of the surrounding elastic matrix combined with the intertube Van der Waals (VdW) forces. Furthermore, we present a model which predicts that the critical axial buckling load embedded in Winkler, Pasternak or Kerr elastic medium under axial compression using the nonlocal Donnell shell theory, this model takes into account the effects of internal small length scale and the VdW interactions between the inner and outer nanotubes. The present model predicts that the critical axial buckling load of embedded DWCNTs is greater than that without medium under identical conditions and parameters. We can conclude that the embedded DWCNTs are less susceptible to axial buckling than those without medium.

• Advances in nano research
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• v.9 no.2
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• pp.91-104
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• 2020

The bending, stability (buckling) and vibration response of nano sized beams is presented in this study based on the Eringen's nonlocal elasticity theory in conjunction with the Euler-Bernoulli beam theory. For this purpose, the bending, buckling and vibration problem of Euler-Bernoulli nanobeams are developed and solved on the basis of nonlocal elasticity theory. The effects of various parameters such as nonlocal parameter e₀a, length of beam L, mode number n, distributed load q and cross-section on the bending, buckling and vibration behaviors of carbon nanotubes idealized as Euler-Bernoulli nanobeam is investigated. The transverse deflections, maximum transverse deflections, vibrational frequency and buckling load values of carbon nanotubes are given in tables and graphs.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.92-95
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• 2002

A nonlinear finite element method is presented to evaluate the torsional buckling moment and failure of composite laminated cylinders. For the progressive failure analysis, the complete unloading method is used based on the maximum stress failure criteria. An arc-length method is incorporated to trace the postbuckling equilibrium path. Present finite element method is verified by the existing experimental and analytical results. The results of the parametric study show that the torsional buckling moments are sensitive to the geometric change, but are not much affected by the lay-up angle. All cylinders tested numerically show the unstable torsional buckling, and therefore the torsional buckling always leads to the catastrophic failure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.790-793
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• 2001

The characteristics of smart skin for wireless LAN system under compression load are investigated. The smart skin structure is composed of 3 layers of face material and 2 layers of core material. Theoretical formula for determining buckling load is derived by Rayleigh-Ritz method and compared with experimental result. The maximum length of specimen that buckling does not occur is determined by assuming that the compression load is sustained by only face material. In the experiment, if buckling occurs obviously then it follows the theoretical result well. In the process of buckling, the load supporting capability and the antenna property such as radiation pattern and reflection coefficient were examined.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.935-940
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• 2006

Numerical methods are developed for solving the elastica and buckling load of cantilever column with constant volume, subjected to a compressive end load. The linear, parabolic and sinusoidal tapers with the regular polygon cross-sections are considered, whose material volume and span length are always held constant. The differential equations governing the elastica of buckled column are derived. The Runge-Kutta method is used to integrate the differential equations, and the Regula-Falsi method is used to determine the horizontal deflection at free end and the buckling load, respectively. The numerical methods developed herein for computing the elastica and the buckling loads of the columns are found to be efficient and reliable.

• Journal of Korean Association for Spatial Structures
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• v.13 no.4
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• pp.49-56
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• 2013

Beam string structures(BSS) are one kind of efficient structure system because the bending moment in the beams is reduced greatly through the struts and the strings. As the struts in BSS are used as middle supports to the beam and always in compression, the buckling of the struts should be avoided. This paper investigates the lateral buckling of the struts in BSS. Firstly, the strut of a one-strut BSS is simplified into an analytical model by considering load is formulated and some special cases of the model are analyzed. Finally, the lateral buckling load of the strut is numerically examined by means of parameter studies. It is known that, because on end of the struts is jointed to the beam while the other end is connected to the strings, the buckling of the struts not only depends on the length of the struts and the stiffness of the joints, but also depends on the rise and the lateral stiffness of the beam, the layout of the strings and the number of the struts.

• Structural Engineering and Mechanics
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• v.54 no.4
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• pp.725-740
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• 2015

This study presents critical buckling load optimization of the axially graded layered uniform columns. In the first place, characteristic equations for the critical buckling loads for all boundary conditions are obtained using the transfer matrix method. Then, for each case, square of this equation is taken as a fitness function together with constraints. Due to explicitly unavailable objective function for the critical buckling loads as a function of segment length and volume fraction of the materials, especially for the column structures with higher segment numbers, initially, prescribed value is assumed for it and then the design variables satisfying constraints are searched using Differential Evolution (DE) optimization method coupled with eigen-value routine. For constraint handling, Exterior Penalty Function formulation is adapted to the optimization cycle. Different boundary conditions are considered. The results reveal that maximum increments in the critical buckling loads are attained about 20% for cantilevered and pinned-pinned end conditions and 18% for clamped-clamped case. Finally, the strongest column structure configurations will be determined. The scientific and statistical results confirmed efficiency, reliability and robustness of the Differential Evolution optimization method and it can be used in the similar problems which especially include transcendental functions.

• Structural Engineering and Mechanics
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• v.90 no.2
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• pp.117-125
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• 2024

This article presents the behaviour and design of cold-formed steel (CFS) web-stiffened lipped channel beams that primarily fail owing to the buckling interaction of distortional and global buckling modes. The incorporation of an intermediate stiffener in the web of the lipped channel improved the buckling performance leads to distortional buckling at intermediate length beams. The prediction of the strength of members that fail in individual buckling modes can be easily determined using the current DSM equations. However, it is difficult to estimate the strength of members undergoing buckling interactions. Special attention is required to predict the strength of the members undergoing strong buckling interactions. In the present study, the geometric dimensions of the web stiffened lipped channel beam sections were chosen such that they have almost equal distortional and global buckling stresses to have strong interactions. A validated numerical model was used to perform a parametric study and obtain design strength data for CFS web-stiffened lipped channel beams. Based on the obtained numerical data, an assessment of the current DSM equations and the equations proposed in the literature (for lipped channel CFS sections) is performed. Suitable modifications were also proposed in this work, which resulted in a higher level of design accuracy to predict the flexural strength of CFS web stiffened lipped channel beams undergoing distortional and global mode interaction. Furthermore, reliability analysis was performed to confirm the reliability of the proposed modification.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.4A
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• pp.207-215
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• 2012

Structural behavior of built-up compression members with unsymmetric connectors under buckling status has been studied through these experiments. When the distance between adjacent H-300 beams of built-up compression member is 2 m in length, and the H-300 beams are lengthened up to 30 m in length with three-10 m-H-beams by bolts and double arrayed, three specimen having each connector interval 4 m, 5 m, 6 m are experimented for evaluating buckling loads. The buckling loads from the experiments are compared with buckling loads of structural analysis using FEM and buckling loads of Timoshenko Eq. loads in order to figure out how the connectors' interval affects on longitudinal and lateral displacements, also strain of the built-up compression members as well. The result shows that the buckling loads tend to sharply decrease non-linearly according to connectors' interval increases. As well as that, the differences between experimental buckling loads and theoretical buckling loads and between experimental buckling loads and structural analyses buckling loads also have a tendency to be increased as the connector interval increases.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.1-4
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• 2000

This paper addresses a modified arc-length method for the nonlinear finite element analysis of a structure which is loaded in incremental and fixed forces, simultaneously. The main idea of the method is to separate the displacement term by the constant force from that by the incremental force. As the illustrative examples of the applicability of the present algorithm, a parametric study is performed on the nonlinear buckling behavior of composite cylindrical panels under the combined load of the incremented compression and the constant lateral pressure.