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An effective way for improving the global load-carrying capacity of a steel arch with a welded hollow section is to increase the height of its webs. However, the high and thin web may buckle locally, which will affect the global load-carrying capacity and should be taken into account in predicting the global strength of the arch. This paper presents a numerical investigation for the in-plane strength and design for pin-ended circular steel arches with a welded hollow section, focusing on the effects of web local buckling by the large deformation inelastic analysis in association with a finite shell element model. The circular steel arches subjected to a radial load uniformly distributed along the arch length, a load uniformly distributed over the full span of the arch, or/and over the half span of the arch and their various combinations are considered in the investigation of their failure modes and strengths. The initial global and local geometric imperfections as well as residual stresses are included in the finite element model. It is found that web local buckling influences the global strength of the steel arches significantly and needs to be accounted in formulate their strength design formulas. The parameters related to the web local buckling and global buckling of the arch are thoroughly explored. It is found that the stability coefficients of arches under the nominal uniform axial compression are related to the equivalent normalized web height-to-thickness ratio of the cross-section and the normalized slenderness of the arch, and accordingly the design formula of the stability coefficients is proposed by including their effects. In addition, a design formula for predicting the strengths of the arches under a load uniformly distributed over the full span is developed by introducing a corrective coefficient into the stability coefficient, and it is found that the corrective coefficient is related to the arch rise-to-span ratio and slenderness of the arch. Furthermore, a general interaction design formula is developed for predicting in-plane strength of the arches under general in-plane loading such as a load uniformly distributed over the half span of the arch and various combinations of a full span uniform load and a half span uniform load. Comparisons with the finite element results demonstrate the proposed design formulas can provide good predictions and/or lower bound predictions for the strengths of the steel arches with a welded hollow section [ABSTRACT FROM AUTHOR]

This paper presents a theoretical and experimental analysis of buckling load of the circular tube with flattened ends. The buckling tests were conducted on the steel tubes with different length and diameter, and the critical buckling force was determined from the measured relation between the lateral displacement and axial force. Analytical solutions for the critical buckling force of the circular tubes were derived in the series form, and a numerical procedure based on the finite difference method and quasi-Newton method was developed to determine the critical buckling load. The results show that both analytical and numerical solutions were in agreement with those measured from the experiment. Moreover, the effect of flattened part length on the value of the critical buckling force was investigated there. The paper provides a mathematical model of mentioned case and gives us some simplifications calculating the critical buckling force. [ABSTRACT FROM AUTHOR]

NACA conducted extensive tests of z-stiffened panels under compressive load in the 1940s and 1950s in order to create direct-reading design charts. Because of the asymmetry of z-stiffened panels, the buckling behavior is complex and buckling analysis of the NACA data has not been conducted. In order to analyze the buckling of z-stiffened panels, a new tool for the buckling analysis of thin-walled structures is developed. This paper presents the results of the buckling analysis of the NACA data and investigates the buckling behavior of z-stiffened panels. It is found that the lateral buckling of the stiffener is critical in the short column region, while the torsional buckling of the stiffener is not critical. [ABSTRACT FROM AUTHOR]

A new type of core-separated buckling-restrained braces, namely a core-separated battened buckling-restrained brace (B-BRB) has been proposed. Its load-carrying capacity and hysteretic response are investigated theoretically and experimentally in this paper. The B-BRB has a remarkable advantage over a common buckling-restrained brace (BRB), in which the newly formed cross-section of the B-BRB is spread outwards by spacing two cores, hence resulting in higher material utilization efficiency in its structural design. In addition, the two independent all-steel BRBs, each having a single plate core simply in-filled in a narrow hollow section, are connected by longitudinally distributed battens rather than continuous plates. Based on the elastic-plastic FE analysis of a B-BRB under monotonic compressive load, its ultimate resistance and failure modes are investigated numerically, considering the effect of its overall initial geometric imperfection. An interaction formula between normalized slenderness ratio and buckling factor of the B-BRB is proposed for predicting its ultimate load-carrying capacity. Consequently, the hysteretic response of the B-BRB is explored through elastic-plastic FE analysis. The maximum normalized slenderness ratios of the B-BRBs required for a load-bearing type and an energy-dissipation type are proposed in their strength designs, respectively. Ultimately, hysteretic responses of five B-BRB specimens have been experimentally investigated. The experimental results are compared with the FE numerical analysis, which considers plate local buckling of all components of the B-BRBs. The comparison has verified the rationality of the proposed design method. [ABSTRACT FROM AUTHOR]

In this paper, we give a targeted review of the state of the art in the study of planar elastic beams in large deformations, also in the presence of geometric nonlinearities. The main scope of this work is to present the different methods of analysis available for describing the possible equilibrium forms and the motions of elastic beams. For the sake of completeness, we start by giving an overview of the nonlinear theories introduced for approaching this argument and then we account for the variational principles and deformation energies introduced for modelling beams undergoing large deformations and displacements. We then consider different kinds of loads treated in the literature and the corresponding induced beam deformations. We conclude by accounting for the available analysis for stability and some considerations about problems where live loads are applied, as well as by describing some relevant numerical methods of use in the applications we have in mind. The selection criterion for the reviewed papers is dictated by the need to study large deformations and the dynamics of pantographic sheets. (Large deformations of planar extensible beams and pantographic lattices: heuristic homogenization, experimental and numerical examples of equilibrium. Proc R Soc A 2016; 472(2185): 20150790), dell'Isola et al. (Designing a light fabric metamaterial being highly macroscopically tough under directional extension: first experimental evidence. Z Angew Math Phys 2015; 66(6): 3473–3498), Turco et al. (Hencky-type discrete model for pantographic structures: numerical comparison with second gradient continuum models. Z Angew Math Phys 2016; 67(4): 1–28)]. [ABSTRACT FROM AUTHOR]

In this paper, a new analytical approach is developed for global buckling of composite sandwich cylindrical shells with lattice cores under uniaxial compression by using the smeared stiffener method. The stiffness contribution of stiffeners is evaluated through the new force and moment effect analysis of the stiffener network on a general unit cell. In these analyses, outer skin-stiffener and inner skin-stiffener interactions are considered, appropriately. The equivalent stiffness of the composite sandwich cylindrical shells with lattice cores is then computed by superimposing the stiffness contribution of stiffeners, outer and inner skins. The critical buckling load is calculated by Rayleigh–Ritz method. Finally, various test examples with different scales of the structure, outer and inner skins ply stacking sequence, outer and inner skins thicknesses were analyzed and the results were compared with results obtained by finite element methods and other works. The results show that the proposed approach has high prediction accuracy and low computational cost for the global buckling analysis of composite sandwich shells with lattice cores. Also, another advantage of the developed approach is able to prediction of the global buckling load of stiffened composite cylindrical shells with better accuracy. Therefore, the proposed approach is highly attractive for the preliminary design of composite sandwich structures in the aerospace industry. [ABSTRACT FROM AUTHOR]

A general analytical procedure is proposed to design tapered laminated composite structures. It is based on: 1) the introduction of two variables representing a laminate configuration, 2) the analytical determination of the lower bound of the number of layers in each of the segments constituting the construction, 3) the definition of the reference sublaminate which configuration is transferred to all segments/parts of the construction, 4) the gradual building of configurations for symmetric balanced laminates having odd or even number of plies. The solution is verified by the comparison with results existing in the literature for both inner and outer tapers. A multi-panel composite structure is considered to demonstrate the applicability of the proposed method. As usual, in a such class of problems, the whole construction is divided into segments/panels. The individual segments are subjected to the simultaneous action of in-plane, tensile or compressive and shear loads. The present results demonstrate the simplicity and effectiveness of the method and non-uniqueness of solutions. The paper intends to clarify the physical sense of the discussed problem. [ABSTRACT FROM AUTHOR]

This paper deals with extending the domain of applicability of a recently developed Generalised Beam Theory (GBT) formulation intended to perform elastic linear buckling analyses of thin-walled members (i) exhibiting arbitrary flat-walled cross-sections (including those combining closed cells and open branches), and (ii) acted by general loadings. These loadings, which include transverse forces acting away from the member shear centre axis, are termed “general” in the sense that they may involve the presence of pre-buckling stress distributions associated with any possible combination of all the stress tensor membrane components ( σ xx , σ ss and τ xs , for a plane stress state), including cell shear flows – therefore, all the relevant geometrically non-linear effects need to be taken into consideration. After briefly presenting the main concepts and procedures involved in the development and implementation of the above GBT formulation, this same formulation is employed to analyse the buckling behaviour of beams with different types of cross-section geometry (containing closed cells) and exhibiting different loading and support conditions. In particular, they consist of (i) a RHS cantilever acted by two tip point loads, (ii) a closed-flange I-section simply supported beam subjected to a uniformly distributed load and (iii) a two-cell RHS section cantilever acted by tip transverse forces and couples. In all cases, the loads are applied both along the shear centre axis and also along axes parallel to it and located at the beam top and bottom surfaces. The results presented and discussed, which consist of pre-buckling stress fields, buckling curves and buckling mode shapes, are obtained by means of the newly released code GBTul 2.0 and validated by means of the comparison with shell finite element values obtained with the code Ansys . [ABSTRACT FROM AUTHOR]

Flexural tests on full-scale I-section beams built up from Q460 and Q890 high strength steel subjected to uniform moment about their major axis were carried out in this article to investigate the effects of geometric and material properties on the local buckling behavior. Failure modes, load–displacement responses, load–strain curves, critical local buckling loads, ultimate resistances, and rotation capacities of the specimens were studied. Then the test results were compared with the design results from current specifications to examine the appropriateness of extrapolating current design method to high strength steel flexural member. Three-dimensional finite element models were established and validated against the experimental results accounting for material nonlinearity, initial geometric imperfections, and welding-induced residual stresses. A parametric study was performed using the validated finite element model, which revealed the variation of normalized ultimate moment with interactive plate slenderness. And the comparisons between parametric analysis results, test results, and design results from ANSI/AISC 360-10 and Eurocode 3 were conducted. [ABSTRACT FROM AUTHOR]

Double-coped beams are usually employed to avoid spatial interference when similar elevations of both the top and bottom flanges of the connected beams are required. Due to the removal of the flange parts, the load resistance can be significantly compromised. This paper discusses the effectiveness of various reinforcing strategies aiming to increase the load resistance of newly designed double-coped beams or to upgrade the existing ones. A series of full-scale tests are conducted first, covering a set of reinforcement types and varying coping dimensions. Local web buckling is found to be the governing failure mode for the unreinforced specimens, and the presence of the considered stiffeners can effectively increase the load resistance. In particular, a pair of longitudinal stiffeners for the top cope edge is shown to completely mitigate the risk of local web buckling, and the final failure mode is tensile cracking at the bottom cope corner. The doubler plates, either full-depth or partial-depth, can delay the initiation of local web bucking, and as a result the load resistance is remarkably increased. The effects of the varying reinforcement types and coping dimensions on the utilisation efficiency of section capacities are discussed in detail. A finite element study is subsequently conducted to enable further understanding of key structural characteristics and to help explain some test phenomena. Preliminary design comments and recommendations are finally proposed based on the exiting test and numerical data. [ABSTRACT FROM AUTHOR]

This paper presents an exact model for studying the global buckling of concrete-filled steel tubular (CFST) columns with compliant interfaces between the concrete core and steel tube. This model is then used to evaluate exact critical buckling loads and modes of CFST columns. The results prove that interface compliance can considerably reduce the critical buckling loads of CFST columns. A good agreement between analytical and experimental buckling loads is obtained if at least one among longitudinal and radial interfacial stiffnesses is high. The parametric study reveals that buckling loads of CFST columns are very much affected by the interfacial stiffness and boundary conditions. [ABSTRACT FROM AUTHOR]

The design of cold-formed steel columns must consider flexural buckling, torsional buckling, and flexural-torsional buckling. The American Iron and Steel Institute incorporated equations for the critical elastic buckling loads corresponding to these failure modes in the North American Specification for the Design of Cold-Formed Steel Members. These equations were originally developed for columns with consistent boundary conditions for all three modes. However it is common in practice to have different unbraced lengths for major axis flexure, minor axis flexure, and torsion. Furthermore, it is common for certain members to be oriented such that intermediate bracing restraint directions do not align with the principal axes. This paper investigates and develops a general formulation of the column buckling equation to incorporate unequal unbraced lengths and non-principal axes. [ABSTRACT FROM AUTHOR]

The double rectangular tube assembled buckling-restrained brace is a new type of buckling energy consumption buckling-restrained brace. Because of its external restraining members, which are bound by high-strength bolts, its mechanical mechanism is more complicated and its failure modes are more varied. In this study, the double rectangular tube assembled buckling-restrained brace composition and three types of end constructions are introduced in detail. The influences of different design parameters on the performance of double rectangular tube assembled buckling-restrained brace are studied by numerical analysis methods; the possible failure modes and the influence of the end strengthening construction of double rectangular tube assembled buckling-restrained brace are also investigated, and a number of suggestions are proposed to improve this design. This study shows that the pinned double rectangular tube assembled buckling-restrained brace has four types of typical failure modes, namely, overall buckling failure, external end local pressure-bearing failure, bending failure of the extended strengthened core region and bolt threading failure. Rational design can prevent a buckling-restrained brace from losing its load-bearing capacity. In addition, compared with the end strengthening scheme with an external hoop, the end strengthening scheme with a strengthened bench can improve the load-bearing capacity of the double rectangular tube assembled buckling-restrained brace more effectively, and a reasonable design can also save materials. [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 this work, the bending-induced buckling of elliptical composite cylinders is significantly improved by using curvilinear fiber paths. The orientation angle in the composite plies are designed to circumferentially vary in elliptical multi-layered composite cylinders for the best bending-buckling performance. To this end, a metamodeling based design optimization approach is successfully employed. The resulting elliptical cylinders with so-called variable stiffness (VS) laminates are shown to have bending buckling capacities up to 70% higher than their constant stiffness (CS) counterparts made with traditional straight-fiber laminates. Unlike the circular cylinders, the non-uniform curvature of the elliptical cylinders adds more complexity to the buckling behavior when the direction of the bending moment is changed. The effect of loading direction on the buckling performance of VS and CS elliptical cylinders is then investigated. Finally, a VS elliptical composite cylinder is designed for having maximum bending buckling capacity in two opposite directions simultaneously, and its buckling performance in different directions is compared with its CS counterpart. [ABSTRACT FROM AUTHOR]

This paper aims at investigating the buckling load of fully deployed linear array deployable structure based on scissor-like element (SLE) under its own weight. The deployable structure has been widely researched both in geometric configurations and structural dynamic characteristics. However, when the number of elements or degree of deployment exceeds the predetermined range, even if there is no external load, deployable structure will automatically collapse under its own weight. To address this issue, this paper derives a new stability model based on linear elastic analysis and energy method to compute the buckling load caused by its own weight for avoiding the structural instability, which can be applied to a linear array deployable structure with n SLEs. In the process of calculation, the first SLE is taken for mechanical analysis and the results are extended to any unit. In the sequel of this process, the scissor deployable structure is equivalent to a uniform solid column and its buckling condition under self-weight is obtained based on the principle of potential energy. Also, the effect of various parameters that affect the instability of the structure, such as the number of elements, bar length and degree of deployment is investigated, and the results of the theoretical analysis are verified through a comparison with the simulation results in ANSYS, which show that the new stability model proposed here can predict the buckling load of scissor deployable structure. [ABSTRACT FROM AUTHOR]

Non-destructive methods to estimate the actual buckling load in particularly for imperfection sensitive thin-walled structures, are of severe interest among many fields. Particular techniques for validation of structural limit state and numerical model predictions for large scale structures are getting momentum. The vibration correlation technique (VCT) allows to correlate the ultimate load our instability point with rapid decrement of self-frequency response. Nevertheless this technique is still under development for thin-walled shells and plates. The current research discusses an experimental verification of extended approach, using vibration correlation technique, for the prediction of actual buckling loads on unstiffened cylindrical shells loaded in axial compression. Validation study include two laminated composite cylinders which were manufactured and repeatedly loaded up to instability point. In order to characterize a correlation with the applied load, several initial natural frequencies and mode shapes were measured during tests by 3D laser scanner. Results demonstrate that proposed vibration correlation technique allows one to predict the experimental buckling load with high reliability, without actually reaching the instability point. Additional experimental tests and numerical models are currently under development to further validate the proposed approach to extended composite and metallic structures. [ABSTRACT FROM AUTHOR]

A solution of the buckling problem for a shear loaded composite anisogrid lattice plate with the clamped edges based on the Galerkin method is presented in this paper. The lattice plate is modelled as an equivalent continuous orthotropic plate with effective stiffness parameters. The deflection of buckled plate is presented in the form of a double series containing clamped–clamped beam functions. The critical in-plane shear load is found solving the generalised eigenvalue problem for a homogeneous system of algebraic equations in which the unknowns are the coefficients of the double series. Based on this solution, the effects of the plate dimensions and parameters of lattice structure on the value of critical load are investigated and analysed. Results of these analyses are successfully verified using the finite element method. An approximate analytical expression providing fast and reliable way of calculation of the critical buckling load is obtained for the lattice plate composed of the ribs made of the same composite material and with the same size of their cross-sections. [ABSTRACT FROM AUTHOR]

Grid-stiffened composite structures not only allow for significant structural weight reduction but also are competitive in terms of structural stability and damage tolerance compared with conventional stiffened candidates. As the development of Automated Fibre Placement (AFP) technology matures, a unitized construction of skin and stiffeners is easily manufacturable. In this paper, a curved stiffener layout is optimized to enhance the structural buckling resistance. A linear variation of stiffener angles is used, resulting in the formation of a locally rhombic lattice pattern. Due to the spatial variation of angle and spacing induced by the use of curved stiffeners, analytic solutions for the responses are not generally applicable. Thus, global and local buckling loads are calculated based on finite element models by a previously-developed global/local coupled strategy. Since the stiffeners are not explicitly modelled in the finite element calculations, a fixed mesh is used for gradient-based optimization. Both parametric design and optimization are performed in order to find the optimal curved grid pattern, whose practical performances are assessed by post-buckling analysis. A comparison between the performances of structures with curved stiffeners, with straight stiffeners, and variable-stiffness skins with curved fibres, demonstrates the potential of curved stiffener configurations in improving the structural efficiency. [ABSTRACT FROM AUTHOR]

As a first attempt, optimum stacking sequences of thick laminated composite plate is obtained to maximize its buckling load via employing the finite element (FE), genetic algorithms (GAs) and particle swarm optimization (PSO) methods. The higher-order shear deformation theory (HSDT) is used to obtain governing equations of the plate. The finite element method (FEM) is employed to solve these equations and to gain buckling load of the plate. The FEM solution is linked with a developed optimization algorithm which is a mix of genetic algorithms (GAs) and particle swarm optimization (PSO) techniques. Some examples are solved to show applicability and usefulness of the proposed hybrid method for maximizing buckling load of the plate via finding optimum stacking sequences of the plate. Also, influences of different parameters on the optimum stacking sequences of the thick plate are studied. [ABSTRACT FROM AUTHOR]

The buckling of slender columns with functionally graded microstructures is studied. In such columns, the flexural modulus is varied in a controlled manner along the column length. The objective is to identify microstructures that maximize (and minimize) the critical buckling load when compared to a reference homogeneous column. Several microstructures are examined and a constraint is imposed so that the volume averaged flexural modulus remains the same in all columns. The buckling load is determined using both the linear perturbation analysis as well as the Rayleigh–Ritz method. A relationship between the material distribution and the corresponding mode shape is established. [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 work presents a study of the behavior, performance and failure of thinwalled composite channel section columns. The study is carried-out using nonlinear finite element models of laminated columns, including geometric imperfections and material failure, as well as approximate analytical solutions based on the Classical Lamination Theory. The accuracy of the numerical model is assessed using experimental results available in the literature and very good results were obtained. The results show the influence of the column layup and wall thickness on the structural behavior of laminated columns, including the buckling mode and ultimate failure load. Finally, the numerical model is used to assess the accuracy of approximate closed-form expressions for evaluation of the local buckling loads of composite channel section columns. [ABSTRACT FROM AUTHOR]

A complex finite strip method was used to study the buckling of functionally graded plates (FGPs) under thermal and mechanical (longitudinal, transverse, and shear in-plane) loading. The mechanical characteristics of FGPs were assumed to vary through the thickness, according to power law distribution. The nonlinear temperature distribution in the direction of the plate thickness was assumed according to thermal conduction steady state conditions. In complex finite strip method, the polynomial Hermitian functions were assumed in the transverse direction and the complex exponential functions were used in the longitudinal direction to evaluate the standard and geometric stiffness matrices that have the ability of calculating the critical shear stress in contrast to trigonometric shape functions. The solution was obtained by the minimization of the total potential energy and solving the corresponding eigenvalue problem. In addition, numerical results for FGPs with different boundary conditions were presented and compared with those available in the literature and the interaction curves of mechanical and thermal buckling capacity of FGPs were obtained. [ABSTRACT FROM PUBLISHER]

Research is limited with respect to load-deflection behavior of slender concrete columns internally reinforced with Fiber Reinforced Polymer (FRP) spirals and longitudinal bars. An analytical buckling model based on numerical integration is presented to predict the load versus deflection performance of slender concrete columns reinforced with FRP spirals and longitudinal bars, subjected to eccentric loads. The model can be used to predict the behavior of slender concrete columns with various configurations including FRP and/or steel reinforcement, single or double spiral, and number of longitudinal bars. The longitudinal bars considered include steel, FRP, or hybrid reinforcement consisting of steel and FRP bars. The model is found to predict the experimental performance of slender concrete columns reinforced with Glass FRP longitudinal bars and spirals with satisfactory accuracy. The model is used to create interaction diagrams for FRP spiral-confined circular concrete columns with various slenderness ratios, reinforced with steel, FRP or hybrid reinforcement. [ABSTRACT FROM AUTHOR]

The paper refers to the strengthening of doubly symmetric columns under load by welded plates. A validated numerical study containing more than 500 models was performed to question the currently used design procedures. These procedures are not unified but vary greatly in different countries. The overly conservative design approach used in the Czech Republic contrasts with the approach completely neglecting the effect of preload commonly used in the USA. The effect of various parameters on the flexural buckling resistance of columns strengthened under load was investigated. The selected parameters were the thickness of the strengthening flange, the column length, the initial bow imperfection, the preload magnitude and the direction of the axis which is pinned while the other axis is fixed. Several conclusions were reached from provided results and a simple analytical method is proposed. The load under which the column is strengthened weakens the column but only slightly. [ABSTRACT FROM AUTHOR]

Since economic quantities are more meaningful to decision makers than dynamic response parameters, this paper examines the economic benefits of using Buckling-Restrained Braces (BRBs) in hospitals located in the very soft soils of the lakebed zone of Mexico City. Since non-structural elements and contents are far more expensive than the structure itself, they are included in detail in the analyses. The results of analyses on three-, six-, and nine-storey frames, which represent short-period structures, show that the expected (or probable) losses and lifecycle costs are smaller when structures are equipped with BRBs. Different cases (defined by the contribution of the BRBs to the strength capacity of the structure) were analysed and compared. The best design options were identified from a comparison of lifecycle costs. As an example, a comparison of cost-benefit analysis between a bare frame and a frame designed under gravity loads and equipped with BRBs, shows that the latter is more economical; because, for the same initial cost, the lifecycle costs are significantly smaller. [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]

We present a nonlinear finite element method to investigate the nonlinear stability of stiffened functionally graded materials (FGM) plates considered as a whole unit. The plates are subjected to mechanical and thermal loads. The material properties are assumed to be temperature dependent and varied gradually across the thickness according to a power law distribution. The nonlinear equations of FGM plates are based on the first-order shear order plate theory. The influence of material, geometrical properties of stiffeners and initial deflections on the buckling and post-buckling response of the stiffened plates are studied in detail. Including the latest information no work has been oriented towards post-buckling analysis of stiffened FGM plates considered as a whole unit. [ABSTRACT FROM AUTHOR]

The buckling response and load carrying capacity of thin-walled open cross-section profiles made of Fibre Metal Laminates, subjected to static axial compression loading are considered. These include thin-walled Z-shape and channel cross-section profiles adopting a 3/2 FML lay-up design, made of 3 aluminium layers. The objective of the investigation is the comparison of standard thickness Fibre Reinforced Plastic layers versus thin-ply material technology. Whilst thin ply designs differ only by the layer thickness, they offer an exponential increase in stacking sequence design freedoms, allowing detrimental coupling effects to be eliminated. The benefit of different hybrid materials are also considered. The comparisons involve semi-analytical and finite element methods, which are validated against experimental investigations. [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]

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]

The effective method of transformed differential quadrature (TDQ) is improved for the buckling design optimization of functionally graded (FG) carbon nanotube‐reinforced laminated composite quadrilateral (FG‐CNTRCQ) plates with arbitrary straight‐sided based on the first‐order shear deformation theory. The laminated plates with both uniformly and FG distributions of single‐walled carbon nanotubes varied along the thickness of layers are considered. The TDQ method is used to directly discretize the governing differential equations for an arbitrary straight‐sided physical domain without any need to transform the equations to the computational domain. In the presented genetic algorithm, the orientation of fibers is considered as the design parameter to obtain the optimum critical buckling loads in terms of different parameters including distributions of the fibers, number of layers, stacking sequence, CNTs volume fraction, geometrical parameters, and boundary conditions. The edges of the plates can take arbitrary end supports of simply and clamped boundary conditions. The formulation is developed based on the invariant terms to provide a systematic procedure with minimum computational cost. Some parametric studies are conducted to examine the effectiveness of the model for the design purpose of the FG‐CNTRCQ plates. POLYM. COMPOS., 39:E853–E868, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Applicability of the vibration correlation technique (VCT) for nondestructive evaluation of the axial buckling load is considered. Thin-walled cylindrical shells with and without circular cutouts have been produced by adhesive overlap bonding from a sheet of aluminium alloy. Both mid-surface and bond-line imperfections of initial shell geometry have been characterized by a laser scanner. Vibration response of shells under axial compression has been monitored to experimentally determine the variation of the first eigenfrequency as a function of applied load. It is demonstrated that VCT provides reliable estimate of buckling load when structure has been loaded up to at least 60% of the critical load. This applies to uncut structures where global failure mode is governing collapse of the structure. By contrast, a local buckling in the vicinity of a cutout could not be predicted by VCT means. Nevertheless, it has been demonstrated that certain reinforcement around cutout may enable the global failure mode and corresponding reliability of VCT estimation. [ABSTRACT FROM AUTHOR]

In the present article, the buckling of a fluid-infiltrated porous plate is investigated using Mindlin plate theory and an analytical procedure. A cosine rule for the pore distribution across the plate thickness is assumed with a coefficient defining porosity level. The governing stability equations are rewritten in terms of four auxiliary functions and decoupled with the aid of some mathematical manipulations. The decoupled partial differential equations are solved analytically by assuming simply supported radial edges for the plate. The critical buckling loads are calculated by considering fluid-saturated and fluid free conditions for the interconnected network of pores for different sector angles, thickness-radius ratios, coefficients of plate porosity, aspect ratios, and boundary conditions. It is found that the pore fluid compressibility affects the buckling load significantly. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation into the buckling behaviour of cold-formed steel zed purlins when subjected to transverse distributed uplift loading. The study uses both linear and non-linear finite element methods (ABAQUS shell Finite Element analyses) to investigate the pre-buckling, buckling and post-buckling behaviour of zed-section purlins in purlin-sheeting systems. The numerical modelling strategy is carefully validated using the results of available experimental data. Influences of boundary conditions and restraints from sheeting on web shear buckling, local, distortional and lateral-torsional buckling behaviour, and the buckling interactions of the purlins are discussed. Furthermore, the strengths and failure modes of the purlins obtained from numerical results are compared with the design strengths predicted using the direct strength method (DSM) specified in the ‘North American Specification’ (AISI S100). The comparisons show that the ultimate strengths of buckling interactions are generally underestimated. Hence, the DSM is modified to cover the partially restrained zed-sections in purlin-sheeting systems. [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]

In this paper, an analytical model is developed to determine the torsional-flexural buckling load of a channel column braced by unevenly distributed batten plates. Solutions of the critical-buckling loads were derived for three boundary cases using the energy method in which the rotating angle between the adjacent battens was presented in the form of a piecewise cubic Hermite interpolation (PCHI) for unequally spaced battens. The validity of the PCHI method was numerically verified by the classic analytical approach for evenly battened columns and a finite-element analysis for unevenly battened ones, respectively. Parameter studies were then performed to examine the effects of loading eccentricities on the torsional-flexural buckling capacity of both evenly and unevenly battened columns. Design parameters taken into account were the ratios of pure torsional buckling load to pure flexural-buckling load, the number and position of battens, and the ratio of the relative extent of the eccentricity. Numerical results were summarized into a series of relative curves indicating the combination of the buckling load and corresponding moments for various buckling ratios. [ABSTRACT FROM AUTHOR]

In this paper, isogeometric finite element method (IGA) based on Non-Uniform Rational B-splines (NURBS) basis function is applied for the buckling analysis of generally laminated composite beam with various boundary conditions. A beam element with four degrees of freedom per control point is investigated, which has considered the bending-torsion deformation. The model for the buckling analysis of laminated composite beam is detailed by the principle of virtual work. Several numerical examples of symmetric and anti-symmetric, cross-ply and angle-ply composite beam are performed. Numerical results of critical buckling loads and mode shapes are presented, and compared with other available results to show the efficiency and accuracy of the present IGA approach. In addition, the impacts of the modulus ratios, slenderness ratios, stacking sequence and the fiber angle, especially the Poisson effect on the critical buckling loads of composite beam are clearly demonstrated. It should be noted the results with the Poisson effect neglected are only suit for the cross-ply composite beams. And the benchmark solutions presented in this work can be used as a reference for the buckling analysis of laminated composite beams in future. [ABSTRACT FROM AUTHOR]

This paper investigates the buckling mechanism of the steel core of buckling-restrained braces. The development of buckling mode is revealed with increasing axial load. The formulae of the maximum contact force and the maximum bending moment of the restraining member are obtained. The analytical results are validated by the finite element analysis. Compared to the results by conventional analysis, the number of contact points or buckling waves is much less; for hinged ends, the contact force for the lower mode is the identical while the contact force for higher modes is 1/4 lower; for fixed ends, the contact force is half of the conventional method. [ABSTRACT FROM AUTHOR]

The purpose of this paper was to study the effect of I-shape stiffener stiffness on the buckling and post-buckling, up to collapse behavior of stiffened composite panel under the uniform uniaxial compression load. Six stiffened composite panel configurations, which were orthogonally designed with two skin configurations and three I-shape stiffener configurations, were took into account in the experimental investigation. Three specimens for each configuration (18 specimens in total) were manufactured for test. Before tests, the key dimensions of I-stiffener and skin were measured. Furthermore, all the specimens were also inspected visually and detected by the ultrasonic C-scan system. No initial delamination or debonding area was found on all the specimens according to their C-scan images. The experimental results show that the equivalent compression stiffness of I-shape stiffener has great influence on the buckling load and failure mode of stiffened panel, but a little effect on the failure load of stiffened panel. The skin thickness has great impact on the buckling load and the final failure load. [ABSTRACT FROM AUTHOR]

Buckling mode interaction of elastic systems in the presence of initial imperfections is well known to have a detrimental effect on the response of a wide range of structural systems. This has been demonstrated mostly analytically for simple models, assuming small displacements, thus obtaining results with questionable validity in the post-buckling range. In order to acquire additional insight into this issue, in the first part of the present paper, two different versions of the well-known 2-DOF Augusti model, whose independent buckling modes are both stable, are studied analytically without any simplifying assumptions with respect to the magnitude of deformation, in order to accurately demonstrate the coupling phenomena in the presence of imperfections in the pre- and post-buckling range. Depending on the nature of the structure's rotational springs, its post-buckling equilibrium path may be either stable or unstable. Afterward, the elastic response of two examples of laced built-up columns is illustrated numerically, one characterized by interaction between in-plane global and local buckling and the other by in- and out-of-plane global buckling, featuring similar response to that of the two 2-DOF models, respectively, thus demonstrating occurrence of such behavior in actual structural systems. [ABSTRACT FROM AUTHOR]

Current study is concentrated on the extraordinary properties of defective carbon nanotubes (CNTs). The role of vacancy defects in thermal buckling response of precompressed CNTs is explored via molecular dynamics (MD) simulations. Defective CNTs are initially compressed at a certain ratio of their critical buckling strain and then undergo a uniform temperature rise. Comprehensive study is implemented on both armchair and zigzag CNTs with different vacancy defects including monovacancy, symmetric bivacancy and asymmetric bivacancy. The results reveal that defects have a pronounced impact on the buckling behavior of CNTs; interestingly, defective CNTs under compressive pre-load show higher resistance to thermal buckling than pristine ones. In the following, the buckling response of defective CNTs is shown to be dependent on the vacancy defects, location of defects and chirality. [ABSTRACT FROM AUTHOR]

Stiffened cylindrical shells are widely used in modern engineering structures, especially in aircraft, oil-transmitting pipeline, spacecraft industry and ocean engineering. Due to the increasing demands for high structures performances, this paper presents the effect of stiffeners on the nonlinear buckling of cylindrical shells with functionally graded (FG) coatings under torsional load. The cylindrical shell is reinforced with external axial stiffeners. The material properties are assumed to vary continuously through the thickness direction. Equilibrium and stability equations for cylindrical shells are derived by using the classical shell theory (CST) with von-Karman nonlinear kinematic relations. Using analytical approach, Galerkin procedure, and the Airy stress function, the resulting equations are employed to obtain the closed-form expression for the critical buckling loads and load–deflection relation. The influences of the number of stiffeners, volume fraction exponent, the thickness of the metal layer, and geometric parameters on the nonlinear buckling behavior of the cylindrical shell with FG coatings are examined in details. [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]

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]