• Geomechanics and Engineering
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• v.21 no.5
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• pp.471-487
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• 2020

In this work, the buckling analysis of material sandwich plates based on a two-parameter elastic foundation under various boundary conditions is investigated on the basis of a new theory of refined trigonometric shear deformation. This theory includes indeterminate integral variables and contains only four unknowns in which any shear correction factor not used, with even less than the conventional theory of first shear strain (FSDT). Applying the principle of virtual displacements, the governing equations and boundary conditions are obtained. To solve the buckling problem for different boundary conditions, Galerkin's approach is utilized for symmetric EGM sandwich plates with six different boundary conditions. A detailed numerical study is carried out to examine the influence of plate aspect ratio, elastic foundation coefficients, ratio, side-to-thickness ratio and boundary conditions on the buckling response of FGM sandwich plates. A good agreement between the results obtained and the available solutions of existing shear deformation theories that have a greater number of unknowns proves to demonstrate the precision of the proposed theory.

• Computers and Concrete
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• v.32 no.1
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• pp.61-74
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• 2023

This article investigates the wave propagation analysis of the imperfect functionally graded (FG) sandwich plates based on a novel simple four-variable integral quasi-3D higher-order shear deformation theory (HSDT). The thickness stretching effect is considered in the transverse displacement component. The presented formulation ensures a parabolic variation of the transverse shear stresses with zero-stresses at the top and the bottom surfaces without requiring any shear correction factors. The studied sandwich plates can be used in several sectors as areas of aircraft, construction, naval/marine, aerospace and wind energy systems, the sandwich structure is composed from three layers (two FG face sheets and isotropic core). The material properties in the FG faces sheet are computed according to a modified power law function with considering the porosity which may appear during the manufacturing process in the form of micro-voids in the layer body. The Hamilton principle is utilized to determine the four governing differential equations for wave propagation in FG plates which is reduced in terms of computation time and cost compared to the other conventional quasi-3D models. An eigenvalue equation is formulated for the analytical solution using a generalized displacements' solution form for wave propagation. The effects of porosity, temperature, moisture concentration, core thickness, and the material exponent on the plates' dispersion relations are examined by considering the thickness stretching influence.

• Structural Engineering and Mechanics
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• v.64 no.3
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• pp.361-379
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• 2017

In this article, the vibration behavior of double-bonded sandwich microplates with homogeneous core and nanocomposite facesheets reinforced by carbon nanotube and boron nitride nanotube under multi physical fields such as 2D magnetic and electric fields is investigated. Symmetric and un-symmetric distributions of nanotubes are considered for facesheets of sandwich microplates such as uniform distribution and various functionally graded distributions. The double-bonded sandwich microplates rest on visco-Pasternak foundation. Material properties of sandwich microplates are obtained by the extended rule of mixture. The sinusoidal shear deformation theory (SSDT) is employed to describe displacement fields of sandwich microplates. Also, the dimensionless natural frequency is obtained by classical plate theory (CPT) and compared with the obtained results by SSDT. It can be seen that the obtained dimensionless natural frequencies by CPT are higher than SSDT. In order to study the material length scale parameters, modified strain gradient theory at micro scale is utilized and then, the equations of motion are derived using Hamilton's principle. The effects of different parameters such as foundation parameters including Winkler, shear layer and damping coefficients, various distributions and volume fraction of nanotubes, core to facesheet thickness ratio, aspect and side ratios on the dimensionless natural frequencies are discussed in details. The results of present work can be used to optimum design and control of similar systems such as micro-electro-mechanical and nano-electro-mechanical devices.

• Steel and Composite Structures
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• v.42 no.4
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• pp.501-511
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• 2022

Earthquake Resistant Design Philosophy seeks (a) no damage, (b) no significant structural damage, and (c) significant structural damage but no collapse of normal buildings, under minor, moderate and severe levels of earthquake shaking, respectively. A procedure is proposed for seismic design of low-rise reinforced concrete special moment frame buildings, which is consistent with this philosophy; buildings are designed to be ductile through appropriate sizing and reinforcement detailing, such that they resist severe level of earthquake shaking without collapse. Nonlinear analyses of study buildings are used to determine quantitatively (a) ranges of design parameters required to assure the required deformability in normal buildings to resist the severe level of earthquake shaking, (b) four specific limit states that represent the start of different structural damage states, and (c) levels of minor and moderate earthquake shakings stated in the philosophy along with an extreme level of earthquake shaking associated with the structural damage state of no collapse. The four limits of structural damage states and the three levels of earthquake shaking identified are shown to be consistent with the performance-based design guidelines available in literature. Finally, nonlinear analyses results are used to confirm the efficacy of the proposed procedure.