Sharif Digital Repository

In the present research, results of buckling analysis of 384 finite element models, verified using three different test results obtained from three separate experimental investigations, were used to study the effects of five parameters such as D/t, L/D, imperfection, mesh size and mesh size ratio. Moreover, proposed equations by offshore structural standards concerning global and local buckling capacity of tubular members including former API RP 2A WSD and recent API RP 2A LRFD, ISO 19902, and NORSOK N-004 have been compared to FE and experimental results. One of the most crucial parts in the estimation of the capacity curve of offshore jacket structures is the correct modeling of... 

Stored solids loads on silo vertical walls are composed of two orthogonal components: the horizontal component that internally pressurizes the silo and the vertical wall frictional component that causes axial compression. For an imperfect cylinder, the elastic axial buckling resistance may be considerably raised by a uniform internal pressure as it alleviates the detrimental effect of the geometrical imperfections. However, at high internal pressures, the combination of axial compression and circumferential tension may result into a plastic instability that is commonly termed elephant's foot buckling. Both stabilizing and destabilizing effects of internal pressure are taken into account by... 

Probabilistic thermal buckling analysis of composite plates with temperature-dependent properties under stochastic thermal fields is performed by developing a new temperature increment-based algorithm for solving the stochastic nonlinear equation. The temperature distribution is assumed to be a stochastic Gaussian field which leads to spatially varying stochastic mechanical properties. The stochastic thermal field is decomposed by applying the Karhunen–Loeve theorem. The combination of stochastic assumed mode method and polynomial chaos is proposed as an alternative solution for the time-consuming stochastic finite element method. The uncertainty of the critical temperature is studied by... 

In the present study, based on 12-unknown higher order shear deformation theory (HSDT), buckling and vibration analysis of FG-CNTRC rectangular plate are investigated for various types of temperature distribution and boundary conditions. Implementing Hamilton’s principle, the equations of motion are derived and solved by adopting the Navier solution for the simply supported boundary conditions and DQM method for other boundary conditions. Validation is carried out by comparing the numerical results with those obtained in the open literature. Also, a detailed parametric analysis is carried out to illuminate the influence of different system parameters such as CNT distributions, CNT volume... 

Due to the remarkable progress in the field of the manufacturing process, smart composites have become the desired target for high-tech engineering applications. Accordingly, for the first time, thermal buckling, critical voltage and vibration response of a thermally affected graphene nanoplatelet reinforced composite (GPLRC) microdisk in the thermal environment are explored with the aid of generalized differential quadrature method (GDQM). Also, the current microstructure is coupled with a piezoelectric actuator (PIAC). The extended form of Halpin-Tsai micromechanics is used to acquire the elasticity of the structure, whereas, the variation of thermal expansion, Poisson’s ratio, and density... 

This paper presents a nonlocal strain gradient theory for capturing size effects in buckling analysis of Euler-Bernoulli nanobeams made of threedimensional functionally graded materials. The material properties vary according to any function. These models can degenerate to the classical models if the material length-scale parameters is assumed to be zero. The Hamilton's principle applied to drive the governing equation and boundary conditions. Generalized differential quadrature method used to solve the governing equation. The effects of some parameters, such as small-scale parameters and constant material parameters are studied. © 2022 PAGEPress Publications. All rights reserved  

In this paper, the nonlinear three-dimensional (3D) stress analysis of shell structures in buckling and snapping problems is presented. The exact geometry or geometrically exact (GeX) hybrid-mixed four-node solid-shell element is developed using a sampling surfaces (SaS) method. The SaS formulation is based on the choice of N SaS parallel to the middle surface to introduce the displacements of these surfaces as basic shell unknowns. The SaS are located at the Chebyshev polynomial nodes (roots of the Chebyshev polynomial of degree N), that is, the outer surfaces are not included into a set of SaS. Such choice of unknowns with the consequent use of Lagrange polynomials of degree N–1 in the... 

Steel silos are one of the main structures for bulk solids handling and storage in many industries and agricultural sectors. A growing body of research suggests the importance of including the vertical component of earthquake ground motion in seismic analysis and design of certain structures. In the case of steel silos, this may induce additional meridional compression to exacerbate buckling failures in such thin shells. Accordingly, this paper investigates the buckling behavior of three cylindrical steel silos (i.e., a squat, an intermediate slender and a slender silo) with stepped walls subjected to horizontal only (H) and horizontal and vertical (HV) ground accelerations to address this... 

In this paper, a new analytical approach is proposed for free vibration and buckling analysis of a rectangular Mindlin plate resting on the Winkler–Pasternak foundation of varying stiffness. According to Mindlin theory, there are three independent governing differential equations. Thus, three Fourier series expansions along with auxiliary polynomial functions are employed to represent the plate's deflection and rotation angle functions. The process of making a set of equations is then completed satisfying the corresponding equilibrium equations and boundary conditions. The proposed method incorporates general elastic supports for all plate's edges, and subsequently can deal with all possible... 

In order to reduce the possibility of buckling problems related to the railway ballasted tracks, necessary measurements should be applied to improve the lateral resistance of tracks. There are different procedures for increasing the lateral force resistance of railway tracks that can be implemented using different materials to change the size, geometry, and dimensions of track components, especially sleepers. Although several studies have been conducted on winged sleepers, the present study investigates the application of mid-winged sleepers with a modified geometry and a dimension in the form of a novel approach. In this regard, several experimental tests and numerical modeling were... 

Due to rapid development of manufacturing process, composite materials with porosity have attracted commercially notices in advanced engineering applications. For this regard, buckling and vibrational characteristics of a porous composite cylindrical nanoshell reinforced with GPLs is investigated in this paper. The material properties of piece-wise graphene-reinforced composites (GPLRC) are assumed to be graded in the thickness direction of a cylindrical nanoshell and are estimated using a nanomechanical model. The novelty of our work is including the effects of porosity and GPLRC on natural frequency, critical axial load and critical temperature of the GPLRC cylindrical nanoshell. The... 

Buckling-restrained braces (BRBs) have been spread widely, especially in high seismic hazard zones due to their excellent energy absorption capacity. BRBs are composed of a main load-carrying steel core restrained with other elements mostly made of concrete and steel casing to preserve it from buckling. Although BRBs provide excellent cyclic behavior, a problem is with their heaviness, which leads to difficulties such as installation and transportation. This study presents a numerical and experimental investigation on a BRB with a new proposed restraining system composed of concrete panels confined with partially carbon fiber reinforced polymer (CFRP) strips to reduce the weight of the... 

Increasing the lifetime and improving the performance of structures through redesign and optimization are important, especially in marine structures. In general, there are two main groups of marine structures: onshore and offshore structures. Most marine structures are offshore, and these are divided into two categories: floating or sunken. One of the important parameters in the design of sunken structures is the critical load resulting from the buckling of walls, which can cause damage to the structure. In the present paper, three rectangular aluminum and steel compartments of different conditions and sizes were modeled using design analysis methods. Then, different finite element analyses... 

Dynamical instability characteristics of sandwich truncated conical shell are investigated. The three-layered shell is composed of advanced grid stiffened core and laminated composite skins. The core maybe made of three different fiber paths. The conical shell with simply-supported ends is subjected to two different types of time-dependent axial compressions. The equations of motion and compatibility are derived by considering Kirchhoff-Love assumptions and von Karman relations. The solution procedure is divided to two steps. First, the terms consisting of spatial derivatives are eliminated by applying a stress function and following the Galerkin method. Second, the terms with temporal... 

In this paper, the three-dimensional (3D) stress analysis of plate-type structures in instability conditions is presented. The displacement-based and hybrid-mixed four-node quadrilateral elements are developed taking the advantages of the sampling surfaces (SaS) method. The SaS formulation is based on considering inside the plate N not equally spaced SaS parallel to the middle surface to specify the displacements of these surfaces as primary plate unknowns. The displacements, strains and stresses are assumed to be distributed through the thickness using Lagrange polynomials of degree N–1 that lead to a well-set higher-order plate theory. The locations of SaS are based on the use of Chebyshev... 

A theoretical approach is presented to derive an explicit formula for buckling load and postbuckling path of advanced grid stiffened conical shells (stiffeners with laminated composite skins). Different types of fiber paths of grids including stringer, ring, and helical are considered. The simply supported truncated conical shell with imperfection is subjected to axial compression. Basic formulations are constructed using the classical theory of shells and von Karman type of nonlinear strain-displacement relationships. The equilibrium and compatibility equations are solved by Galerkin procedure, and an explicit relation is obtained to predict the equilibrium paths. Results for different... 

In the present study, based on 12-unknown higher order shear deformation theory (HSDT), buckling and vibration analysis of FG-CNTRC rectangular plate are investigated for various types of temperature distribution and boundary conditions. Implementing Hamilton’s principle, the equations of motion are derived and solved by adopting the Navier solution for the simply supported boundary conditions and DQM method for other boundary conditions. Validation is carried out by comparing the numerical results with those obtained in the open literature. Also, a detailed parametric analysis is carried out to illuminate the influence of different system parameters such as CNT distributions, CNT volume... 

In this research, thermal buckling and forced vibration characteristics of the imperfect composite cylindrical nanoshell reinforced with graphene nanoplatelets (GNP) in thermal environments are presented. Halpin–Tsai nanomechanical model is used to determine the material properties of each layer. The size-dependent effects of GNPRC nanoshell is analyzed using modified couple stress theory. For the first time, in the present study, porous functionally graded multilayer couple stress (FMCS) parameter which changes along the thickness is considered. The novelty of the current study is to consider the effects of porosity, GNPRC, FMCS and thermal environment on the resonance frequencies, thermal... 

Due to the remarkable progress in the field of the manufacturing process, smart composites have become the desired target for high-tech engineering applications. Accordingly, for the first time, thermal buckling, critical voltage and vibration response of a thermally affected graphene nanoplatelet reinforced composite (GPLRC) microdisk in the thermal environment are explored with the aid of generalized differential quadrature method (GDQM). Also, the current microstructure is coupled with a piezoelectric actuator (PIAC). The extended form of Halpin-Tsai micromechanics is used to acquire the elasticity of the structure, whereas, the variation of thermal expansion, Poisson’s ratio, and density... 

The buckling of generally laminated conical shells having thickness variations under axial compression is investigated. This problem usually arises in the filament wound conical shells where the thickness changes through the length of the cone. The thickness may be assumed to change linearly through the length of the cone. The fundamental relations for a conical shell with variable thickness applying thin-walled shallow shell theory of Donnell-type and theorem of minimum potential energy have been derived. Nonlinear terms of Donnell equations are linearized by the use of adjacent-equilibrium criterion. Governing equations are solved using power series method. This procedure enables us to...