Search

Buckling and sound radiation characteristics of curved sandwich panels subjected to combined thermo-mechanical loads are presented in the paper. The panel comprises a 3-D functionally graded graphene porous core sandwiched between FG-V Λ CNT reinforced composite face sheets (3DGrF-CF). The governing differential equations of 3DGrF-CF sandwich panels are derived using the parabolic shear deformation theory (PSDT), and the vibration responses are predicted using Navier's approach. The vibration response thus obtained is fed into the Rayleigh integral to capture the acoustic pressure. The buckling and sound radiation characteristics were found to vary significantly with the core's porosity coefficient and porosity grading pattern. However, the impact of this influence also depends on the magnitude of thermal & mechanical loading. This implies that selecting a core for acoustic comfort depends on the dominance of loading conditions and is illustrated using octave band analysis. • Buckling & vibro-acoustic analysis of 3DGrF-CF panels under thermo-mechanical loads. • Analytical prediction using Navier's & Rayleigh's approach considering PSDT. • Optimum porosity coefficient & grading pattern for different loading conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Repair of a composite laminate with delamination using micro-bolts is studied parametrically. The effects on compressive buckling load of delamination crack length, bolt material, bolt diameter and arrangement, and bolt–laminate clearance are considered. For 45- and 65-mm crack lengths, buckling load recovery rates using brass bolts are 90% and 73%, respectively. Using steel increases the rate by 6.6% compared to the intact specimen. Tests are performed fixing the number of steel bolts for bolt diameters of 0.6, 1.0, and 1.2 mm. The buckling load recovery rate using 1.2- versus 0.6-mm bolts increases by 6.8%. Finite element analysis confirms the effect of the bolt–laminate gap: 27% larger buckling load for no clearance than for a 0.1-mm gap. 18% higher buckling load, which is 97% of intact-specimen buckling load, is obtained for a 1.2-mm-diameter bolt repair by gluing bolts and holes and then tightening them compared with using bolts alone. [ABSTRACT FROM AUTHOR]

Abstract The study investigates the effect of eccentric load on the stability and postcritical states of thin-walled CFRP channel section columns under compression. Test specimens are subjected to compression on a testing machine provided with a fixture for applying eccentric compressive loads. Loading forces, deflection and strains of the column walls and web are measured. The experiments also involve examination of the operating performance of a structure undergoing buckling and determination of its postcritical equilibrium paths describing the relationship between load and deflection. Based on experimental results, numerical models of composite structures are designed and verified by the FEM. The scope of the numerical analysis involves performing a linear analysis of stability, which allows for determining the buckling mode depending on the amplitude of compressive load eccentricity and corresponding critical loads. The next stage of the analysis involves performing a nonlinear analysis of the structures with implemented geometric imperfections reflecting the lowest buckling modes. Based on obtained results, postcritical equilibrium paths of the developed FEM models are determined. Obtained equilibrium paths are then compared with experimental characteristics of real structures. The numerical results and experimental findings show a satisfactory agreement. [ABSTRACT FROM AUTHOR]

Abstract The paper investigates the possibility of bifurcation buckling from axisymmetrical equilibrium states of a heated circular plate with immovable edge. The plate is composed of a functionally graded material whose mechanical and physical properties are varied in the thickness direction according to the power law. Because of high compressive circumferential stresses that develop near the edge, the symmetrically deformed plate can buckle into asymmetric equilibrium configurations characterized by local circumferential waves (wrinkles). The problem of determining wrinkling thermal loads is formulated using the von Karman nonlinear plate theory based on the concept of physically neutral surface and solved by the power series method. The existence of wrinkling loads is examined for various pressure levels and boundary conditions. The calculation results are compared to the finite-element solution obtained by a general-purpose shell element. Highlights • Existence of wrinkling phenomenon of pressurized and heated circular FGM plates is examined. • The critical thermal loads that causes the plate to wrinkle are determined by the power series method. • Clamped plates exhibit wrinkling upon heating, whereas simply supported plates do not. • Findings on the wrinkling loads and modes agree with the finite-element simulations. [ABSTRACT FROM AUTHOR]

Highlights • Bistable metallic disks are manufactured by nanostructuring disks in a localized region. • Refined analytical models characterizing bistable behaviors are proposed. • Six transition types are found for bistable disks with different nanostructured regions. • Bistable metallic disks have good stabilities indicated by snapping forces. Abstract In contrast to conventional bistable disks manufactured using soft materials in spherical or domelike configurations, new bistable disks with designable configurations and high load-bearing capacities are proposed and developed based on the nanotechnology of surface mechanical attrition treatment (SMAT). A simple analytical model with explicit results, refined analytical models and numerical models are formulated to predict two stable configurations and study their transition processes. A simple algorithm that includes a confined equation for the formulated Ritz models is developed via a displacement control strategy to capture the full snapping processes of the bistable disks, which are actuated by a point force. The analytical models for the bistable disks identify various stable configurations and six transition strategies, and these are discussed systematically with respect to the design parameters. The ratio of the nanostructured region in the disks is found to have a critical influence on the stable configurations and the transition processes. The results from the experimentally manufactured bistable disks validate the obtained theoretical results. [ABSTRACT FROM AUTHOR]

Highlights • The differential system is solved with low computational cost. • The numerical results indicate a very good performance of the 6DE model proposed. • The 6DE model allows to obtain the equivalent properties for the beam-column model. • Practical expressions for the buckling loads exhibit an excellent agreement. Abstract Lattice towers and guyed masts are frequently used in the telecommunication industry, particularly to support antennas. These structural systems comprise a large number of elements (mainly, legs and diagonals) and for this reason, their representation by equivalent models is quite common and convenient. In a previous study, the authors derived a continuous model of a spatial lattice governed by nine differential equations (9DE). The legs trace forms a triangle and the diagonals with a zig-zag pattern are contained in three planes that join each two legs, defined as Pattern 1. Here and starting from an energy statement, the structural behavior of a 1D continuous model governed by six differential equations (6DE) which leads to a simpler representation of the lattice structure, is stated. This formulation considers the shear flexibility and the second order effect due to axial loads. Also, the inertial forces due to the legs and diagonals masses are taken into account. Numerical examples dealing with deflections, critical buckling loads and natural frequencies are solved with this 1D model. The results are compared with the outcomes found with finite element methods. A very good performance is attained with the proposed model. Finally, the equivalent properties for other patterns of diagonalization (Patterns 2, 3 and 4) different to the studied as well as the formulas to find the critical loads are included in Appendices. [ABSTRACT FROM AUTHOR]

Abstract This paper was dealt with buckling and post-buckling behavior of short thin-walled Z-columns made of a carbon-epoxy laminate, subjected to eccentric compressive load. The buckling mode and the buckling load of real structures versus load eccentricity were discussed. The study involved both experimental tests were carried out on real laminated structures and numerical simulations by the finite element method. The buckling load of real structures was determined by approximation methods on the basis of experimental and numerical post-buckling equilibrium paths of the structure. Additionally, in numerical simulations, the bifurcation load value was determined by solving an eigen problem. In all cases, experimental findings and numerical results show high agreement. The study determined the quantitative influence of the direction and value of compressive load eccentricity on the buckling load and rigidity of the structure in the post-buckling state. [ABSTRACT FROM AUTHOR]

Abstract Pultruded glass fiber reinforced polymer (GFRP) sections face a critical issue of premature web crippling failure when loaded in the transverse direction. However, limited research on the web crippling behavior of asymmetric sections like channel section was reported in the literature. In addition, the effect of specimen length on the web crippling behavior has not been explicitly investigated. This paper presents an experimental study on the web crippling behavior of pultruded GFRP channel sections under transverse bearing load. Four channel sections with various dimensions were tested under two transverse loading conditions, i.e. interior-two-flange (ITF) and exterior-two-flange (ETF). For each section, two specimen lengths were adopted to study the effect of specimen length on the web crippling behavior. Therefore, three variables including sectional dimensions, specimen length and loading conditions were considered in the experimental program. Two failure modes, namely web-flange junction failure and web buckling failure, were observed. The load-displacement curves and web crippling capacities of all specimens were reported and compared. Finally, design equations were proposed considering the failure mechanisms. The predicted web crippling capacities generally agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

Abstract The suggested before energy barrier criterion for design buckling pressure is extended to the case of clamped shallow spherical caps. It is developed for shells with geometrical imperfections and a new adjusted formula is obtained for design buckling load of imperfect structures. The method is applied to shells with elastic-perfectly plastic material. It is validated by experimental data and proved by numerical analysis based on finite element method. Calculation results were obtained and analysed for different values of shell geometrical parameter. A simple formula for design buckling pressure is suggested and validated. [ABSTRACT FROM AUTHOR]

Abstract The progressive instability behaviour of compressed dry-stone rectangular pillars loaded with an eccentric load is assessed experimentally and compared with the theory. Photoelastic compression tests were designed and executed on polymethyl-methacrylate brickwork pillars to reveal, i) the load-bearing capacity of the structure and the load-lateral displacement relation, ii) the effect of the eccentricity in the stress distribution along the structure, iii) the collapse mode of the system at high eccentricity. By employing a no-tension material model with linear behaviour in compression, new analytical, closed-form expressions for deformed shape of the structure, location of the neutral axis in a generic cross section and axial displacement are provided. The photoelastic stress analysis outcome fully confirms the analytical predictions for both low and high eccentricity loadings. [ABSTRACT FROM AUTHOR]

Abstract Wind turbine blades present different types of failure mechanisms and modes which are associated with specific loading conditions. Trailing edge failure mode has been documented in full-scale blade tests as one of the failure types observed in blades on service. Trailing edge failure is characterized by failure of the trailing edge adhesive joint and the buckling of the trailing edge sandwich panels. This failure is governed by the contribution of edgewise, flapwise and torsion moments, with edgewise moments being the main driver. This paper describes a blade sub-component test setup suitable for studying trailing edge failure on static and fatigue load conditions, which is an improvement in the experimental verification of a trailing edge blade design. The test setup and design drivers are described and studied via FE models. Static and fatigue test results are reported for a full-scale blade section sub-component obtained from a 34 [m] wind turbine blade. Moreover, experimental results are discussed and compared with FE models to describe and study the trailing edge failure mechanism. [ABSTRACT FROM AUTHOR]

Abstract The present paper deals with the description of the stability loss and postbuckling for multilayered composite structures. Both, the experimental results and theoretical predictions are presented and discussed. The wide literature review is also pointed out considering the issue of both experimental and theoretical buckling analyses for composite rectangular plates and shells. A special attention is focused on the buckling and postbuckling behaviour od structures with cutouts and reinforcement. [ABSTRACT FROM AUTHOR]

Graphical abstract fx1 Highlights • Similarity criteria are derived for thin-walled cylinders subjected to coupled thermo-mechanical loads. • Thermo-elastoplastic failure behaviors predicted by numerical model are validated by experiments. • Scaling laws are verified by numerical models, and source of error is discussed. [ABSTRACT FROM AUTHOR]

Abstract The critical buckling load of FRP pultruded columns of different shapes under static and dynamic load are presented. FRP columns with cross sections of sheet pile, square tube, I-section and T-section have been studied and the shape effect on the instability is discussed. The static buckling load calculated from the numerical simulations was then compared with the results from theoretical values and ratios reported for the different cross sections. The comparison shows that the outcomes of the FE analysis were more conservative than the theoretical values some cases. The simulation of dynamic buckling loads showed a considerable sensitivity to the model’s boundary conditions. The simulation of the horizontal loading suggested that local buckling tends to occur close to the base of the column. Based on the results, it is suggested that full numerical analysis including dynamic and horizontal loading needs to be conducted for the safe design of thin-wall FRP elements. [ABSTRACT FROM AUTHOR]

Thin-walled composite beams of complex sectional contour are widely used along with the traditional elements of reinforced structures. Based on the generalized theory of elasticity of thin-walled beams, the mathematical model of flexural–torsional deformation of open-profile thin-walled composite beams of non-uniform cross section under thermo-mechanical loading has been developed. To confirm the reliability of developed approach to determination of the spatial displacements of thin-walled composite beams of non-uniform cross section, several experimental studies were conducted. Based on the analysis of the range of typical profiles, for the further analysis we selected several compound cross sections for which the analytical dependences were obtained regarding displacements of their characteristic points. Our studies can serve as a base for development of the practical recommendations for the optimal designing and manufacturing of thin-walled anisotropic profiles, as well as proposing the measures to reduce the value of deformations caused by the production process. [ABSTRACT FROM AUTHOR]

The instability behaviour of eccentrically loaded circular masonry columns is investigated. Two approaches are considered for the analysis. One is based on a semi-analytical formulation of the relevant boundary-value problem for a no-tension material response; the other employs a plastic-damage-contact constitutive model, the CraftS model, to capture the complex microstructural behaviour of the material. The latter has been implemented in the finite element program LUSAS and has been already successfully employed to describe progressive instability in eccentrically loaded brickwork wallettes of rectangular cross section. Equilibrium paths and limit load estimates are computed for both analysis approaches for a range of column aspect ratios and load eccentricities. It is shown that the type of material response becomes less important for specimens with height-to-diameter aspect ratios greater than 7.5 and for loads applied to points in the kernel of the cross section, while for higher eccentricities the presence of a tensile strength increases considerably the limit load. The damage evolution predicted by the models is also investigated for selected cases, showing that the formulation based on the no-tension material is able to capture with good agreement the damaged zone of the column for loads with low eccentricities. For the same type of loading, a useful design formula is provided. [ABSTRACT FROM AUTHOR]

The Hencky bar-net model (HBM) has been shown to be a physical structural representation of the finite difference plate model (FDM). This paper extends the HBM to tackle buckling problems of rectangular plates under in-plane non-uniform loads. This class of problems requires a pre-buckling stress analysis involving plane-stress elasticity equations in order to establish the non-uniform stress distributions in the plate domain for input loads to the HBM. The converged results given by HBM compare well with existing reference solutions; thereby verifying the model. The HBM is also used to generate some new buckling solutions for rectangular plates under various point loads and partially distributed loads. [ABSTRACT FROM AUTHOR]

In terms of the interaction between buckling and snap-through for shallow structures affected by geometrical imperfections results have shown that, after the nonlinear bifurcation, load reductions occurs accompanied with a predictable tendency. In order to do it, the tracing of interaction domains and interaction curves presented in recent papers by the same Authors, has been proposed. In this study, every simple structural arrangement has been analyzed with regards to different shallowness ratios, slenderness, restraining conditions and imperfection patterns. It has been observed how the driving parameters could be led back to two original interaction ( Δ ) and form ( Ω ) factors. This procedure could shed new light on the application of the more burdensome imperfection pattern for the instability of geometrically nonlinear structures. Possible implications of these results have been presented, with a special attention to sensors and structural identification. The study accomplished numerous numerical simulations and showed good agreement with the theoretical expected results. [ABSTRACT FROM AUTHOR]

This paper examines the load bearing capacity of medium-length steel cylindrical shells with a circular cutout under the action of axial compression. Numerical simulations were performed for a radius-to-thickness ratio ( R / t ) ranging from 100 to 500, and an imperfection parameter ( α ) of between 1 and 4. Structural steel and the behavior of perfect plastic material were considered within the scope of the study. The investigation includes the influence of the cutout size and number, radius-to-thickness ratio. The paper also contains a comparison between theoretical predictions, ABAQUS ® FE results and experimental data for axially compressed cylinders. A reasonable correlation was obtained between numerical predictions and experimental tests. Details relating to the experimental procedure and FE model are provided. A parametric study was conducted to propose empirical equations, estimating the limit load of cylindrical shells as a function of geometry ( R / t , α and cutout number) and material properties ( E , v and σ y ). Empirical formulas were produced, fitting a surface plot using the Least Square method, for both the perfect shell structure (reference shell load) and the limit load reduction factor ( ϕ ). All variables in the empirical formula were normalized. A stochastic error analysis was used as a tool to measure how the results of proposed equations approach the FE predictions. Finally, based on experimental and numerical results, formulas are presented to calculate the limit load of medium-length shells with and without circular cutouts having a discrepancy not exceeding ± 10 % regarding error analysis. [ABSTRACT FROM AUTHOR]

This study investigates the stability of the structural systems assembled by system scaffolds. Loading tests were conducted on the indoor single-bay system scaffolds and the outdoor full-scale structural system assembled by system scaffolds. Test results were compared with the second-order inelastic analysis with semi-rigid joints to determine the reliability of various analytical parameters. The study reveals that, while the failure model of the single-bay two-storey system scaffold without diagonal braces is overall buckling failure of the structure, the failure model of the same structure with diagonal braces is buckling failure of the vertical standards between the upper and lower storeys. The critical load of the configuration with diagonal braces is about double that of the same structure without diagonal braces. At the moment of buckling failure of the outdoor full-scale two-row, two-bay, six-storey structural system assembled by system scaffolds, the vertical standards at the four corners appeared to have large horizontal displacements owing to without diagonal braces. However, the vertical standard in the center did not exhibit obvious horizontal deformation because it was reinforced with diagonal braces on four sides. In addition, the use of diagonal braces can significantly increase the load capacity of vertical standards. This study recommends that all vertical standards be reinforced with diagonal braces to ensure the load capacity of the structural systems assembled by system scaffolds. A second-order inelastic analysis with semi-rigid joints and various notional lateral forces is recommended to determine the critical loads of full-scale structural systems assembled by system scaffolds. [ABSTRACT FROM AUTHOR]

Elastoplastic buckling behaviors of rectangular plates made from functionally graded materials (FGMs) are investigated in this paper. The elastoplastic material properties are assumed to vary smoothly through the thickness of the plates. The three dimensional material constitutive relation of FGMs is found by introducing the material homogenization method, named Tamura-Tomota-Ozawa(TTO) model, into J 2 deformation theory or J 2 flow theory. The uniform strain hypothesis helps to simplify the prebuckling state and derive the analytical expression of the position of the material elastoplastic interface. The buckling governing equations and the buckling critical condition of the structures are formulated under the framework of the classical plate theory. An iterative algorithm is designed to obtain the elastoplastic buckling critical load, a converging result between the prebuckling and the buckling critical internal forces. ABAQUS simulation well verifies the present theoretical predictions from J 2 flow theory, and is resorted to investigate the postbuckling behaviors of FGM plates. Discussions are addressed for the effects of the constituent distribution, the material plastic flow, the preloaded states of the plates, and the regions of buckling types are plotted as well. [ABSTRACT FROM AUTHOR]

In the present work, attention is focused on the prediction of thermal buckling and post-buckling behaviors of functionally graded materials (FGM) beams based on Euler–Bernoulli, Timoshenko and various higher-order shear deformation beam theories. Two ends of the beam are assumed to be clamped and in-plane boundary conditions are immovable. The beam is subjected to uniform temperature rise and temperature dependency of the constituents is also taken into account. The governing equations are developed relative to neutral plane and mid-plane of the beam. A two-step perturbation method is employed to determine the critical buckling loads and post-buckling equilibrium paths. New results of thermal buckling and post-buckling analysis of the beams are presented and discussed in details , the numerical analysis shows that, for the case of uniform temperature rise loading, the post-buckling equilibrium path for FGM beam with two clamped ends is also of the bifurcation type for any arbitrary value of the power law index and any various displacement fields. [ABSTRACT FROM AUTHOR]

Mechanical structures are often simultaneously subjected to thermal and mechanical loading, both of which can lead to buckling failure. Developing efficient structural forms with better capacity for stability is important to keep structures safe. This study aims to optimize structural buckling capacity by using a density-based topology optimization scheme. Instead of treating the mechanical and thermal loadings as a single coupled part in the linearized buckling analysis, the effects of mechanical and thermal loadings are decoupled, which allows to separately analyze and optimize buckling aspects induced by mechanical or thermal loading. Two optimization models based on the decoupled analysis models are developed to respectively maximize the critical load factor of buckling induced by mechanical loading under a specified thermal loading and buckling induced by thermal loading under a specified mechanical loading. Further, based on a three-phase material model, a multi-material topology optimization scheme is employed to optimize the buckling capacity of active structures made of structural and actuating materials and prestressed structures containing prestressed components. The actuation effects are mimicked by the thermal loading of active material. The sensitivities of the objective functions and constraints are derived through the adjoint technique, and the method of moving asymptotes (MMA) is employed to solve the topology optimization problems. Numerical examples are adopted to verify the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

This article explores the local and global stability of CNT reinforced composite (CNTRC) sandwich shell panels consist of softcore material. The shell panel's face sheets are reinforced with functionally graded nanotube particles. The effective properties of CNTRC face sheets are determined considering the extended rule of mixture technique, and a multi-layer approach is used to examine the local and global stability phenomena. The material properties of the face sheets are assumed to be temperature-dependent. The formulation account for the core compressibility effect by considering higher-order polynomial terms for transverse core displacement. The governing equations for each layer of the sandwich panel are derived by minimizing the total potential energy of the system. The Galerkin's technique is adopted to obtain a set of non-linear algebraic equations from the derived partial differential equations. Global buckling and wrinkling loads of sandwich shell panels under thermomechanical loadings are obtained by solving standard eigenvalue problem. The nonlinear responses for sandwich shell panels subjected to mechanical and thermal stresses are traced through the arc-length approach and iterative approach, respectively. The obtained responses elucidate the influence of CNT gradation, volume fractions and core thickness on the local and global stability behaviour of CNTRC sandwich shell panels. • Semi-analytical higher order formulation of sandwich panels with FG-CNTRC face sheets is presented. • Buckling and wrinkling characteristics are elucidated for soft core sandwich panels. • Influences of temperature-dependent materials properties are studied under thermomechanical loadings. [ABSTRACT FROM AUTHOR]

The feasibility of probabilistic design methods to overcome conservatism associated with deterministic design methods for unstiffened cylindrical composite shells has been shown, but studies are frequently based on assumptions regarding relevant uncertainties due to the lack of available data. The reliability based calibration method suggested here relies on extensive measurements regarding the statistical characteristics of thickness, fibre volume fraction, fibre orientation, material stiffness and geometric imperfections of 11 previously tested cylinders. Furthermore, the stiffness of the potting of tested cylinders is estimated using Finite Element Analysis and the introduction of a pre-stress state through the potting process investigated. Following a sensitivity study, Bayesian inference is used to update the information of relevant uncertain variables. Monte Carlo simulation is employed to compute the distribution functions of the buckling load, and these are used to calibrate structural safety factors at a chosen reliability level. A multiplicative error model is established to compute safety factors covering the model uncertainty inherent to the approach. In combining these two safety factors in a Bayesian sense, a transparent, updatable safety-factor concept is developed, leading to less conservative design loads than currently considered. [ABSTRACT FROM AUTHOR]

The paper is devoted to mathematical modelling of multi-layered structures. The case of a metal seven-layer rectangular plate is considered. The plate is composed of a trapezoidal corrugated main core, two inner flat sheets, two trapezoidal corrugated cores of the faces and two outer flat sheets. The direction of the corrugation of the main core is orthogonal to the one of the face cores corrugations. The hypothesis of deformation of normal to middle surface of the plate after bending and the field of displacements and stresses is formulated. The plate is simply supported and subjected to a uniformly distributed compressive loads applied to the edges. Equations of motion are derived based on the Hamilton’s principle. These equations are analytically solved for static or pulsating loads. The influence of the trapezoidal corrugation pitch of the cores on the critical loads and natural frequency of the plates is analysed. The results obtained form the analytical solution are compared with the results given by the proposed finite element model. [ABSTRACT FROM AUTHOR]

A thin metallic glass foil of 100 mg mass forming a sinusoidal arc behaves as non-conventional flat micro-spring withstanding loads 10 5 times higher than its load. Upon a normal load applied on the top of the arc, the foil deforms elastically leading to sinusoidal wavy patterns of higher order. The lifespan of the novel spring is higher than conventional low cycle springs and can potentially be further improved by eliminating surface and edge preparation induced defects. This unique behavior of metallic glass foils has the potential to revolutionize the field of springs and can be exploited for numerous applications. [ABSTRACT FROM AUTHOR]

In order to understand the formation of one-dimension periodic structures by electrospinning, an approximate mechanical approach for the critical load and the number of half waves in the buckled shape have been conducted based on the energy method. Diameter of circular cross-section electrospun fiber is assumed to be equal to the length of the rectangular cross-section spitted fiber. Fiber with rectangular cross section buckles more easily than that with circular cross section because of the different flexural rigidity. For rectangular-section fiber, increase of length to width ratio can result in the increase of the number of half waves. Detailed simulation results for buckling responses of circular-section fiber and rectangular-section fiber have been conducted by commercial finite element analysis software (ABAQUS). [ABSTRACT FROM AUTHOR]

Influenced by numerous local features, the post-buckling analysis and optimization for hierarchical stiffened shells suffer from heavy computational costs. By smearing the minor stiffeners based on a novel numerical implementation of asymptotic homogenization (NIAH) method, a novel hybrid model for hierarchical stiffened shells is presented. Then, the high prediction accuracy and efficiency of the hybrid model for post-buckling analysis and imperfection sensitivity analysis are validated. Furthermore, a grid-pattern optimization framework of novel hierarchical stiffened shells allowing for imperfection sensitivity is established. The illustrative examples indicate that, the hierarchical stiffened shell with candidate sub-structures is more competitive in load-carrying capacity than that with the fixed grid-pattern, and the presence of imperfections would greatly affect the results of grid-pattern optimizations. [ABSTRACT FROM AUTHOR]

The experimental natural frequencies and buckling loads of aluminium slightly non-symmetric thin-Walled beams under axial force are compared with numerical results. A universal machine compressed the specimens by providing their ends with a relative axial displacement; suitable end constraints for warping were manufactured; PZT pickups, which revealed to be reliable in this field, helped extracting the natural frequencies under various compressive forces. An in-house code provided the corresponding numerical results, accounting for the effects of non-symmetric cross-sections and warping. The comparison provides a good agreement between the two sets of results, showing that the predictions of the code are verified by experiments, thus opening the way to possible applications in inverse problems. [ABSTRACT FROM AUTHOR]

The elastic buckling load of an axially compressed piecewise member was derived under various ideal boundary conditions based on the differential element method; then, the result was simplified for a symmetrical member. The theoretical results were found to be consistent with existing formulas for the elastic buckling load of uniform members. Then, the elasto-plastic buckling of an axially compressed piecewise member composed of steel and elastic materials was investigated and found to be quite different from that of a pure steel member, and a theoretical analysis approach was developed. In elasto-plastic buckling analysis, the load-bearing capacity of the steel section in the ultimate state is determined considering initial imperfections and steel hardening. Furthermore, the symmetric method for obtaining the load-bearing capacity of this member was obtained based on the ultimate state of the critical section, which is simple and reparative for design. The theoretical results of the elasto-plastic buckling analysis were consistent with experimental results, therein obtaining an average error of 4%. [ABSTRACT FROM AUTHOR]

This paper demonstrates the importance of including non-linearities in the design of textile reinforced concrete (TRC) shells. By two cases, the influence on the buckling load of considering geometrical non-linearity and material non-linearity, but also of considering geometrical imperfections is examined. For stiff shells mainly in compression, the buckling load is significantly reduced by including imperfections, analogue to observations with steel reinforced concrete shells. For shells with a low stiffness, experiencing large deformations, a non-linear analysis is essential and the buckling load is mainly reduced by considering material non-linearity. Conclusively, the shape and boundary conditions of thin TRC shells indicate which parameters should be taken into account in their design. [ABSTRACT FROM AUTHOR]

A new model depicting the full phase of tubular string buckling in vertical wellbores is proposed. The buckling modes of the tubular string are divided into: no buckling, 2D lateral buckling, 3D lateral buckling, continuous contact buckling and helical buckling. For the 2D lateral and 3D lateral buckling, the tubular string is respectively depicted by two and four suspended sections; for the continuous contact and helical buckling, the tubular string includes four suspended sections and one continuous contact section. With the suspended and continuous contact sections respectively depicted by beam-column model and buckling differential equation, the general buckling configurations of the entire tubular string are deduced. Substituting relevant continuity, boundary and stability conditions, the tubular string buckling problem is converted into a system of nonlinear equations. Solving these equations with iteration method, the critical buckling loads and the buckling configurations under different buckling modes for a weightless tubular string are obtained. Later, the weightless model is extended to the case for a tubular string with weight. On the basis of the new buckling model, the axial force and torque transfer along the tubular string under the coupling effect of friction force and buckling is discussed. The results show that the existence of tubular string weight increases the complexity of buckling mechanism and calculation. The continuous contact between the tubular string and wellbore reduces the axial force and torque transfer along the tubular string. To increase the axial force and torque transfer and inhibit buckling, the installation of stabilizers of low friction and buckling inhibition on the buckling-prone sections is wiser than unilaterally increasing the diameter and thickness of the tubular string. Compared with the previous results, the new model provides a more sophisticated description of tubular string buckling in vertical wellbores. [ABSTRACT FROM AUTHOR]

In the present paper, the post-buckling behavior of a simply supported piezoelectric hybrid microplate subject to thermal, electrical and mechanical loads is studied. The size effect in the mechanical behavior of the microplate is captured by using the modified couple stress theory. The Mindlin plate theory is adopted to describe its deflection behavior with the von Karman’s geometric nonlinearity taken into account. Based on these assumptions and the principle of minimum potential energy, the equilibrium equations of the microplate and associated boundary conditions are derived. By applying the Galerkin method to the equilibrium equations, closed-form solutions for the critical thermal/mechanical buckling load and the load–displacement relation in the post-buckling stage are obtained. Furthermore, the effects of the material length scale parameter to thickness ratio, the applied electric field and in-plane boundary conditions on the buckling and post-buckling behavior of the piezoelectric hybrid microplate are discussed in detail. [ABSTRACT FROM AUTHOR]

This paper presents an analytical solution for the buckling and free vibration analysis of laminated beams by using a refined and generalized shear deformation theory which includes the thickness expansion. The eigenvalue equation is derived by employing the Rayleigh quotient, and the Ritz method is used to approximate the displacement field. The functions used in the Ritz method are chosen as either a pure polynomial series or a hybrid polynomial-trigonometric series. The hybrid series is used due to the superior convergence and accuracy compared to conventional pure polynomial series for certain boundary conditions. The boundary conditions are taken into account using the penalty method. Convergence of the results is analyzed, and numerical results of the present theory are compared with other theories for validation. Nondimensional natural frequencies and critical buckling loads are obtained for a variety of stacking sequences. The effect of the normal deformation on the fundamental frequencies and critical buckling loads is also analyzed. [ABSTRACT FROM AUTHOR]

An analytical method for vibration and buckling behaviours of Functionally Graded (FG) beams with various boundary conditions under mechanical and thermal loads is presented. Based on linear strain-displacement relations, equations of motion and essential boundary conditions are derived from Hamilton’s principle. In order to account for thermal effects, three cases of the temperature rise through the thickness, which are uniform, linear and nonlinear, are considered. The exact solutions are derived using the state space approach. Numerical results are presented to investigate the effects of boundary conditions, temperature distributions, material parameters and slenderness ratios on the critical temperatures, critical buckling loads, and natural frequencies as well as load-frequencies curves, temperature-frequencies curves of FG beams under thermal/mechanical loads. The accuracy and effectiveness of proposed model are verified by comparison with previous research. [ABSTRACT FROM AUTHOR]

A semi-analytical approach is presented for the analysis and optimization of laminated panels with non-symmetric lay-ups, and with the possibility of introducing requirements on the buckling load, the postbuckling response and the eigenfrequencies. The design strategy relies on the combined use of semi-analytical techniques for the structural analysis and genetic algorithms for the optimization. The structural analysis is performed with a highly efficient code based on thin plate theory, where the problem is formulated in terms of Airy stress function and out of plane displacement, expanded using trigonometric series. Eigenvalue analyses are performed to determine eigenfrequencies and buckling load, while an arc-length method is adopted for the postbuckling computation. The genetic algorithm is implemented with proper alphabet cardinalities to handle different steps for the angles of orientation, while specific mutation operators are used to guarantee good reliability of the optimization. To show the potentialities of the proposed optimization toolbox, two examples are presented regarding the design of balanced non-symmetric laminates subjected to linear and nonlinear constraints. The accuracy of the semi-analytical predictions is demonstrated by comparison with finite element results and benchmark cases taken from the literature. [ABSTRACT FROM AUTHOR]

The paper proposes a novel type of stiffener designed to bear bending loads by exploiting internal pressure effects. The stiffener is made of two adjacent thin-walled pipes ( r / t ≥ 50 ) jointed with a connecting strip. Such a structure is shown to have higher performance against buckling failure compared to a single pipe and its geometry allows for good exploitation of internal pressurisation. The study is conducted by using the FEA software ANSYS and the analysis technique is the linear perturbation buckling analysis. Internal pressure ranges from 0 to 1.4 MPa. The buckling mechanisms are observed for a set of models with different values of length, wall thickness and geometric variation of the cross-section. It is shown that two different buckling modes can take place. However, for a given geometry, the level of pressure can alter the behaviour and lead to one mode rather than the other one. Potential of the presented structure is maximised by the use of high performance materials and a possible aerospace engineering application is presented. [ABSTRACT FROM AUTHOR]

Buckling strength is the most important design criterion for laminated composite structures subjected to compressive loading. The aim of the present work is to introduce an explicit procedure in designing laminated composite plates for maximum buckling load subjected to strength and stiffness constraints using the polar formalism, which relates stiffness to the critical buckling load in order to simplify the calculation and optimization of the buckling load. The polar representation of plane elasticity is effectively used in this work in order to introduce a unified optimization method. Design for maximum flexural stiffness as well as laminate effective elastic modulus was developed in order to achieve the optimal orientation of the layers giving the maximum buckling strength. Three optimization procedures were proposed. The first one is unconstrained optimization and the two other cases are constrained optimization subjected to the flexural stiffness and the elastic modulus constraints. The quasi-homogeneous laminates, which have been used as a special class of laminate stacks, were proposed as the general solution for the optimal stacking sequence of the layers. [ABSTRACT FROM AUTHOR]

A numerical parametric investigation into the response of axially and rotationally restrained compound cold-formed steel beams in fire has been carried out. A suitable finite element model was validated against experimental fire tests. Some parameters that could have influence on the behaviour of these beams were evaluated, such as the section geometry, initial applied load, slenderness and influence of the axial and rotational restraints. The results showed that the critical temperature of axially restrained beams may drop significantly (reaching a 50% reduction) and, beyond a certain value of axial or rotational restraint it may be no longer possible to change its fire resistance. Furthermore, it was still concluded that the methods established in EN1993-1.2:2004 are not appropriate for the fire design of these beams (reaching relative differences in the order of 20% and some predictions can be unsafe). [ABSTRACT FROM AUTHOR]

This paper presents a closed form solution for the analysis and design of composite steel concrete (SC) shear wall systems subjected to pure out-of-plane loads with partial interaction theory. This method takes into account the flexibility of connection between plate and concrete. SC walls under out-of-plane loads can be considered a slab under distributed loads; therefore, for obtaining the formulation of these systems, a strip beam-slab is considered. These walls are subjected to soil pressure when used in deep excavations water hydraulic pressure when used as marine structures, and ice moving pressure when used in offshore structures etc. For providing the interaction between steel and concrete, shear connectors and, for calculating the out-of-plane loadings, classic methods are utilized. The existence of concrete in composite shear walls not only prevents the steel plate from buckling, but also plays an important role in out-of-plane resistance. To investigate the effect of concrete on the behavior of these SC shear walls, two cases are considered in this study: shear walls with and without concrete. To validate the accuracy of the proposed method, a number of shear walls were modeled and analyzed by ABAQUS software and compared with the results from theoretical formulations. Results indicate that the proposed interaction theory is well capable of predicting the deformation and stress distribution of the composite shear walls. [ABSTRACT FROM AUTHOR]

In this study, the buckling and free vibration characteristics of three-phase randomly distributed carbon nanotube (CNT) reinforced fiber composite (RD-CNTRFC) beams subjected to in-plane compressive loadings and thermal environment are discussed in-depth through a semi-analytical approach. Displacement-based governing equations of motion are derived using Lagrange equation considering higher-order shear deformation theory (HSDT). The effective material properties of RD-CNTRFC are determined in two stages; firstly, effective properties of hybrid matrix (CNTs + Polymer) are evaluated using the Eshelbhy-Mori-Tanaka approach. Finally, overall effective properties of CNTRFC are estimated by implementing different homogenization techniques. The influences of temperature-dependent material properties and CNT-agglomeration are included in the derived formulation. The buckling loads and natural frequencies of RD-CNTRFC beams are computed using a typical eigenvalue solution. The influence of various boundary conditions, CNT mass fraction, CNT-agglomeration, length-to-thickness ratio, and various ply sequences are also addressed. • Semi-analytical higher order formulation of three-phase RD-CNTRFC beams is presented. • Buckling and vibration characteristics are elucidated for different boundary conditions. • Influences of CNT-agglomeration and temperature-dependent properties of materials are included. [ABSTRACT FROM AUTHOR]

Buckling analysis of nanobeam is significantly important for design of nano-electro-mechanical systems (NEMS), especially for those under non-uniform temperature induced commonly by the operation of NEMS. In this work, such issue is investigated with the aids of size-dependent model, i.e. nonlocal thermoelasticity, and size effect of heat conduction on buckling property is considered for the first time. Euler–Bernoulli beam is adopted and reformulated within nonlocal theory. Analytical solution to critical load for various boundary conditions, e.g. SS, CF, CS and CC, is obtained using eigenvalue method. And the temperature distribution is determined using nonlocal heat conductive law. The effect of elastic and thermal nonlocal parameter on the critical load is systematically discussed. It is observed that classical models over-predict the critical load, which may be dangerous in practical applications. The present work is expected to be helpful for design of nanobeam-based devices and systems. [ABSTRACT FROM AUTHOR]

A concept of hybrid-stiffness stiffened shell is proposed based on sub-panel elements to achieve a simultaneous buckling pattern, which can provide enhanced design flexibility to fully explore the load-carrying capacity of structures. Then, a novel hybrid model is established to improve the computational efficiency of post-buckling analysis for stiffened shells, where the Numerical Implementation of Asymptotic Homogenization Method is utilized to smear out the stiffeners. On this basis, an integrated optimization framework of sub-panel configurations and weld lands for stiffened shells is presented. Illustrative examples with single and multiple cutouts demonstrate the effectiveness of the proposed framework based on the concept of hybrid-stiffness stiffened shell. [ABSTRACT FROM AUTHOR]

Research on the structural behavior and buckling of vertical, aboveground tanks employed to store oil and fuels have significantly increased during the past two decades. Interest in this shell form is related not just to the cost of the infrastructure, but also because failures in cases of accidents or natural disasters may cause huge economic, environmental and social losses. This review concentrates on buckling problems of such tanks under static or quasi-static loads, including uniform pressure, wind, settlement of foundation, and fire. In all cases, buckling is considered as a static process. Attention is given to the load definition in each case, followed by buckling studies under previously defined pressures or temperatures. The structural configuration of tanks is first described in order to understand what is specific about this structural form. Next, the theoretical framework for stability and buckling is briefly described to place each contribution in a wider context. Each loading case is first explained, experiments or case-studies are briefly described, and computational analytical modeling is reviewed; finally, efforts towards improving design are mentioned. Most papers published in the literature have been motivated by wind effects on tanks, but the review shows that other areas, such as thermal buckling under an adjacent fire, are currently receiving increasing attention. [ABSTRACT FROM AUTHOR]

Submarine pipelines are important and influential structures in marine engineering because they transport important, useful, and common fuels around the world. The pipeline structure is affected by different environmental forces from the surrounding conditions such as the external uniform hydrostatic pressure, hydrodynamic pressure, seismic forces, installation forces, free span forces, and forces scouring the pipeline. These conditions cause the pipeline to express complicated behavior. Local buckling and buckling propagation along the pipeline are common examples of collapses under these conditions and loadings, which can destroy thousands of meters of pipeline. These post-buckling phenomena cause great damage and losses to the oil and gas industries and to the environment; the imposed costs for the repair and protection of pipelines and mitigation of environmental problems are high. The use of ring-stiffeners is one way of increasing the buckling capacity of a pipeline in order to prevent and control the buckling propagation in pipelines. In this study, the buckling and post-buckling behaviors of ring-stiffened pipelines were investigated at a small scale through experiments and the finite element method (FEM). Two different ring-stiffeners were attached to the specimens. Only the uniform hydrostatic pressure was considered as the main loading; the axial stress was neglected in this study. The buckling modes, lateral displacement of the pipeline, ring tilt, formation of yielding lines, and torsion of yielding lines were examined. The results indicated that increasing the number of ring-stiffeners greatly increases the buckling capacity and lateral displacement of the pipeline. The buckling modes were changed, the post-buckling region was shortened, and torsion in the yielding lines and tilting in the ring-stiffeners clearly appeared in the tests. The results of this study were compared with those of recent research and reliable guidelines and standards. [ABSTRACT FROM AUTHOR]

Stiffened panels are basic building blocks of weight sensitive structures. Design of laminated composite stiffened panels is more involved and requires the use of an optimization approach, which needs a computationally efficient analysis tool. This paper deals with the development of an analytical and computationally efficient analysis tool using artificial neural networks (ANN) for predicting the buckling load of laminated composite stiffened panels subjected to in-plane shear loading. The database for training and testing is prepared using finite element analysis. Studies are carried out by changing the panel orthotropy ratio, stiffener depth, pitch length (number of stiffeners). Using the database, key parameters are identified and a neural network is trained. The results shows that the trained neural network can predict the shear buckling load of laminated composite stiffened panels accurately and will be very useful in optimization applications where computational efficiency is paramount. [ABSTRACT FROM AUTHOR]

Unstiffened cylindrical shells are very sensitive to geometric imperfections such as production-related deviations from the ideal geometry (conventional imperfections) as well as imperfect boundary conditions, material and wall thickness imperfections (non-conventional imperfections). The load carrying capability of unstiffened shells is reduced significantly by those imperfections. The NASA SP-8007 design guideline from 1968 is currently used for shell design. This guideline provides knock-down factors for the buckling loads and is based on experimental data of isotropic and orthotropic test specimen. Therefore the structural behavior of composite material is not considered adequately. Based on the single-perturbation load approach (SPLA), this paper introduces a new physical based approach, to determine a lower bound for the buckling load of unstiffened composite cylindrical shells with respect to conventional and non-conventional imperfections, the constant single-buckle imperfection (CSBI) principle. The CSBI principle is based on the theory of the metastability of the geometric imperfect cylindrical shell which is introduced within this paper. The results indicate that the CSBI principle has the potential to provide an improved shell design in order to reduce weight and cost of thin-walled shells. [ABSTRACT FROM AUTHOR]

Two continuous lattice steel truss bridges spanning 190 m with subdivided top chord members were constructed on the same design across river Alaknanda at Dugadda and Srinagar, respectively, in Uttarakhand, India. Both bridges were similar in design and geometry having middle span of 110.0 m and two end spans of 40.0 m. Garudchatti bridge at Dugadda was constructed first and opened to traffic, but excessive vibrations and lifting of end supports under live load condition were observed. Construction of Chauras bridge at Srinagar started later, but it collapsed during casting of the deck slab due to buckling of one of its top chord compression members. Failure of Chauras bridge led to the serious concerns in the minds of people and technocrats about the safety of Garudchatti bridge also, because it was constructed using the same design of Chauras bridge. Therefore, it was decided to strengthen and carry out load testing of Garudchatti bridge before reopening to the traffic. In the present work analyses of Garudchatti bridge are presented to identify structurally unsafe members for most severe live loads given in IRC:6-2010 code, and recommendations for strengthening of the critical members. Finite element space frame analyses of the bridge were carried out using STAAD Pro. v8i software to find excessively stressed members beyond their permissible stress limit. The critical compression members were strengthened by welding additional channel sections. RCC anchor blocks were constructed to restrict lifting of end supports under live load. After strengthening, load testing of the bridge was performed to ensure the safety of the bridge. The bridge is now reopened for traffic. In the past a number of bridges have collapsed during load testing. In case of any shortcoming in the design or overloading during load testing, compression members of the truss may suddenly buckle and cause collapse of the bridge. Therefore, it is not advisable to load test steel truss bridges which do not have adequate margin beyond the service load condition. [ABSTRACT FROM AUTHOR]

The main aim of this paper is to present results of a full-scale pushover test of a 40 meter telecommunication tower under breaking load. A detailed description of the studied tower has been presented with emphasis on the geometrical imperfections of the selected members of the structure. The results of the experiment consisting of the axial forces in the tower's members, as well as the displacements of the observed nodes as a function of external load have been presented. A comparison of a wind load based on the current standards with the load based on the experimental breaking force has been discussed for a typical set of telecommunication equipment. The main conclusion was that the structure's overall carrying capacity depended on the buckling resistance of the legs. Additionally, theoretical buckling resistances (based on standards) of the tower's legs made with round solid bars were smaller than the experimental axial forces in compression. [ABSTRACT FROM AUTHOR]