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• A criterion for simulation of delamination is proposed. • An imperfection induced pre-buckling must be incorporated into failure analysis of open-hole laminate under in-plane compression. • Rules for selection of a scale factor for the pre-buckling analysis are set forth. • Various failures of notched laminate under compression are predicted with no parameter adjustment and no iteration. Failure prediction of open-hole laminates under compression still remains a great challenge. A number of unique mechanics theories for composites developed by the author are successfully applied to analyze in plane compression induced various failures of the notched laminates in this paper. A buckling mode must be incorporated into the analysis of the compression induced delamination, and the rules for selecting a scale factor for the buckling analysis through ABAQUS are established. To simulate delamination, the interlaminar matrix stress modification method is applied. A more pertinent criterion for delamination is proposed. When and where is delamination initiated, how can the initiated delamination be propagated and how much is the delaminated area to be attained can be easily reproduced. Intralaminar failures are estimated based on Bridging Model and the matrix true stress theory. The ultimate strength of a notched laminate is assumed when any primary layer element outside neighborhoods of the stress singularity and weak singularity points firstly attains an ultimate failure. A limited, if not the minimum, number of inputs are required all measurable independently and following existing standards with no data calibration. Except for the pre-buckling analysis, no iteration is needed for prediction of all the other failures. The predicted failure modes and ultimate compressive loads of several laminates with single or double holes agree well with our measured counterparts. [ABSTRACT FROM AUTHOR]

Thin-walled cylindrical shells under axial compression load are prone to buckling. The influencing factors leading to a reduction of the buckling load are a major design challenge. The sensitivity to imperfection increases with rising slenderness. In literature, cylinders with the same parameters and different slenderness are rarely tested in a larger number of samples. In this contribution, seven cylindrical shells, six of them nominally identical, are tested on two different test rigs and compared with twelve specimens with a smaller radius and same wall thickness from a previous series of tests. It is shown how the imperfection sensitivity is dependent on the R/t-ratio. Additionally, it is demonstrated how the quality of the test set ups corresponds with the achieved buckling load. Finally, the suitability of selected design approaches is determined based on the test results. Based on that, recommendations for the choice of a suitable approach are given. [ABSTRACT FROM AUTHOR]

We present a combined experimental and computational study of the elastic behavior of a series of highly anisotropic pyrocarbons, with crystallite sizes L a in the 2–10 nm range, under a -axis compressive load. The materials include a rough laminar and a regenerative laminar pyrocarbon, as-prepared by chemical vapor deposition and after various heat treatments up to 2600 °C, for which a -axis nanoindentation experiments have been performed, showing a significant decrease in the indentation modulus and hardness with increasing L a (or heat treatment temperature). To rationalize this behavior, molecular dynamics simulations of the uniaxial compression of accurate atomistic models of the materials as well as pristine graphite were performed, unraveling significant out-of-plane deformations in the models with increasing compressive strain, leading to elastic softening. More precisely, significant kinks were observed around extended screw dislocation-like defects in the most disordered pyrocarbon at rather large strain levels (∼ 3%). Conversely, graphite rather shows the formation of extended buckles, starting at very low strain values. Finite element modelling shows that such kinking/buckling transitions should take place in a large area under the indenter tip within usual nanoindentation conditions. Both finite element calculation and analytical approximation of the indentation modulus predict the correct trend of decreasing modulus with increasing L a when applied with the elastic tensors computed after the buckling/kinking transitions, certainly proving the importance of the latter in the observed experimental indentation moduli. [ABSTRACT FROM AUTHOR]

• A competitive-failure analysis framework of composite cylinder was proposed. • The material degradation model was adapted to judge the failure mode of composites. • The effectiveness and precision of the proposed framework were validated. • The effects of several design parameters on the competitive-failure were examined. When thin-walled composite cylindrical shells are subjected to combined loads, not only will they buckle, but they could fail under overstressing. Buckling-failure and stress-failure are two types of failure that compete mutually, and if one of them occurs, the structure loses its ability to carry the load. However, there is a lack of study, and very little attention was paid to the competitive-failure of the composite cylindrical shells under combined loads. To bridge this research gap, a competitive failure analysis framework of degraded composite cylindrical shells exposed to combined axial compression and external pressure loads was developed, considering the nonlinear buckling-failure interacting curve approach for buckling-failure analysis and the Tsai-Wu failure criterion for stress-failure analysis. The material degradation model was adopted to modify the properties of the failed ply based on two degrading philosophies. The proposed framework agrees well with the published results. Extensive parametric studies are accomplished and presented to detect the failure mode of composites. For material parametric study, the variation of material properties does not significantly affect the shape of the normalized buckling-failure interacting curve, while it appreciably affects the behavior of the stress-failure interacting curve. Moreover, it is found that as the proportions of the longitudinal compressive strength to longitudinal modulus and transverse tensile strength to transverse modulus of composite materials increase, the tendency for buckling-failure increases; otherwise, stress-failure happens. For a geometric parametric study, decreasing the radius-to-thickness ratio leads to an increase in the shape of the buckling-failure interacting curve and the possibility of stress-failure. [ABSTRACT FROM AUTHOR]

Cylindrical shells with corrugation are widely used in deep sea, underground pressure structures, and other fields. It is mainly subjected to uniform and concentrated external pressure. The current research mainly includes circumferentially corrugated shells and longitudinally corrugated shells. These two kinds of corrugations improve the strength of the cylindrical shell but also have some problems such as stress concentration, buckling extension, and so on. To solve these problems, a shell with composite corrugation is proposed and it has the structural characteristics of both circumferential and longitudinal corrugations. In this paper, the numerical analysis method is used to explore the stability of the composite corrugated shell under uniform and concentrated pressures. It is analyzed by Donnell's large deflection equation. In addition, it can reduce the area of damage caused by buckling. The excellent mechanical properties of the composite corrugated shell are proven. The influence of the number of corrugations and "diameter to thickness ratio" on the buckling performance is studied by using the control variate method. It is compared with a cylindrical shell without corrugation with equal volume and weight. The concentrated pressure tests of composite corrugated shells and shells without corrugation are finished. The results show that the curve of "radial compression-reaction load" obtained by the experiment is consistent with the simulation. The ultimate load of the composite corrugated shell is 34.96% higher than the shell without corrugation. The composite corrugation can effectively enhance the compressive strength and stiffness of the cylindrical shell. Composite corrugation can make more material of the shell to be involved in resisting external deformation. This method of increasing material utilization is effective. • The advantages of the composite corrugated shell are verified from mechanical theory, finite element analysis and test. • The influence of local curvature on the buckling performance of cylindrical shell is verified. • Donnell's large deflection equation has been applied and innovated in this paper. [ABSTRACT FROM AUTHOR]

Taking a biomimetic approach, this study introduces the use of a Voronoi diagram as an indicator of stiffener arrangement in stiffened composite panels. The locations of generator points that determine the shape of the Voronoi diagram are optimized for buckling problems under compression and shear load. An original optimization algorithm that combines the genetic algorithm and the finite element method is developed and implemented. The Voronoi diagram can also be used as an indicator for conventional, periodical stiffener shapes such as grid, lattice, honeycomb, and isogrid. We conducted parametric studies for periodical stiffener shapes, and demonstrated that these shapes can be designed using Voronoi diagrams. The results revealed that the optimized panel has a higher buckling load than that of conventional panels, and this methodology is effective for designing biomimetic stiffened CFRP panel structures. [ABSTRACT FROM AUTHOR]

Aramid Fiber Reinforced Polymer (AFRP) composites provide a companionable and beneficial technique to strengthen structures and noticeable advantages in terms of fire and heat resistance and vapor permeability. AFRP also improves the corrosion resistivity of the structural members, and it delays the buckling. These characteristics of AFRP materials have been catching attention of the technical community to study the mechanical behavior to define comprehensive strengthening design guidelines. This research work studied the effect of AFRP on a steel beam with five types of strengthening and without strengthening pattern. Several tests were carried out to find the compressive and flexural behavior of structure considering with strengthening and without strengthening. From the experimental result, it can be concluded that the load carrying capacity and stiffness of structure considerably enhanced due to external bonding of normal modulus AFRP. The wrapping of AFRP effectively delayed the local buckling and punching for the compressive and flexural loading, respectively. Then, the beam was modeled by using ANSYS 16.0 to authenticate the experimental results and the numerical results such as deflection and maximum load carrying capacity for the different patterns of strengthening quite agreed with the experimental results. Finally, this study concluded with showing different experimental failure modes and comparison made with the numerical results. It is expected that the outcome of this research will be of significant help for the strengthening of the structure. [ABSTRACT FROM AUTHOR]

• Distinct buckling modes of BLGSs on a foundation are studied. • New morphology evolutions of the post-buckling deformation are reported. • Novel finite element for analyzing atomic van der Waals interactions is developed. The buckling and the post-buckling of bilayer graphene sheets (BLGSs) on an elastic foundation subjected to an axial compressive load in plane-strain condition are studied. The solutions for the buckling strain and the characteristic wavelength at the onset of the buckling are obtained by using proposed continuum models describing deformations of BLGSs. The buckling analysis reveals that the buckling of BLGSs on an elastic foundation could be categorized into four. When the foundation is very soft, the Euler beam kinematics prevails in the entire BLGSs. On the stiffer foundation, the shear deformation on the cross-section of BLGSs occurs, and the characteristic wavelength changes sensitively as the stiffness of the foundation varies. With the foundation whose stiffness is almost the same as the shear modulus of the graphene interlayer, the buckling strain and the characteristic wavelength are nearly linear versus the elastic modulus of the foundation in logarithmic scale. When the foundation is much stiffer than the rigidities of the graphene interlayer, detachment between graphene layers could occur. Finally, we conduct the post-buckling analysis by using the proposed finite element model and obtain various morphology evolutions which contain detachment between graphene layers, period doubling, localization, period switching, and folding. Also, we present a diagram includes distinct deformation patterns according to the stiffness of the foundation and the magnitude of the applied compressive strain. [ABSTRACT FROM AUTHOR]

Steel bracing systems are usually introduced to assure the structural stability and seismic resistance of steel storage pallet racks, whose height over the last years has increased more and more to improve warehouse efficiency. In the present paper, the axial response, under monotonic and cyclic load, of perforated cold-formed steel diagonals of concentric bracing systems is investigated through experimental tests. To satisfy the design and detailing rules required by the capacity design approach, such as the ratio between overstrength coefficients and the value of the non-dimensional slenderness, tested diagonals are equipped with additional holes at one end. Results of monotonic tests, under compression and tensile load, provide useful information about the influence of the number and shape of holes on the ultimate strength, ductility and buckling load of bracings. Cyclic tests highlight how the member slenderness and the class of its cross-section affect hysteresis loops and energy dissipation. Finally, some novel considerations are presented concerning the influence of the shape, dimensions and distance of additional holes, in addition to member geometrical features like the cross-section class, on the cyclic response of tested members. In the framework of the "Design Assisted by Testing", results could be adopted for the capacity design of perforated concentric cold formed diagonal bracings as those adopted in steel storage pallet racks. • The axial response of CFS members with holes is experimentally investigated. • The effect on the ductility of holes, member compactness and slenderness is shown. • Segment with additional holes represents a ductile fuse for investigated members. • Ductility of very slender class 3 specimens is comparable to class 2 specimens. • Energy dissipation of class 3 specimens is lower than class 2 specimens. [ABSTRACT FROM AUTHOR]

The present study focuses on buckling and collapse behaviors of cracked steel panel by accounting for the crack opening/closure. A rectangular panel with a transverse through crack to the loading direction is selected to better understand the typical mechanical characteristics of a panel subjected to a sequence of tensile to compressive loading. When a tensile load is applied to the cracked panel, a through crack gradually opened and yielding occurs around the crack tip. When a compressive load is applied after the tensile load, the crack gradually closed and elastic/elasto-plastic buckling occur. A shell-solid mixed finite element (FE) model is adopted to effectively analyze the crack opening/closure. Shell FEs are employed in the rectangular panel (shell model), while solid FEs are partially adopted around the crack (solid model). Double nodes and contact condition are imposed on the crack face. The shell and solid models are joined together with a rigid body element (RBE). The buckling and collapse behaviors of the panel models under a sequence of tensile to compressive loading is critically examined, as well as its local behavior, i.e. , crack opening displacement (COD) varying displacement amplitude, panel aspect ratio and panel thickness. The results show that the crack opening/closure strongly affect the buckling and collapse behaviors of the cracked panel. • Buckling and collapse behavior are examined in a rectangular cracked panel. • Shell-solid FE modeling is adopted to analyze the cracked panel simulation. • The ultimate strength is analyzed under tensile and compressive load. • Crack opening distance is investigated by changing aspect ratio and plate thickness. [ABSTRACT FROM AUTHOR]

This paper presents a cross-sectional optimization procedure to increase the load carrying capacity of a perforated rack column under a compression load. The optimization method is based on a Genetic Algorithm (GA) combined with the Generalized Beam Theory (GBT), which allows to take perforations as well as sectional deformations into account. The results indicate that the optimal cross-section geometry depends on the dominant buckling mode. Therefore, a combined optimization criterion to consider distortional and global buckling is defined. Finally, nonlinear shell finite elements analyses are done in order to assess the structural behaviour of optimized cross-sections. • Cross-sectional optimization of rack columns under compression load. • Influence of perforations and sectional deformations. • Combination of Genetic algorithm and Generalized Beam Theory. • Influence of dominant buckling mode. [ABSTRACT FROM AUTHOR]

One of the most effective nondestructive methods to estimate the buckling load of imperfection sensitive thin-walled structures is vibration correlation technique (VCT). Although this technique can determine the buckling load for several types of structures without reaching the instability point, it is still under development for composite sandwich plates and shells. In this paper, experimental and numerical verification of VCT approach are presented for the estimation of the buckling load of the composite sandwich plates with iso-grid cores loaded in compression. In the experimental section, four specimens are designed and fabricated using a new silicone rubber mold, and hand lay-up technique. The modal test is performed on the first specimen by exciting the sandwich plates using the modal hammer method in the different applied loads. Then, the variation of the natural frequency with the applied compressive load is recorded up to actual experimental buckling load. Besides, numerical models, including nonlinear effects, are created in full details to calculate the variation of the natural frequencies with the applied load, and to be compared with the experimental results. Finally, the buckling test is carried out on all specimens to validate the experimental and numerical results of VCT approach. The results demonstrate that the maximum difference between the predicted buckling load using the VCT approach on the experimental and numerical results with an experimental buckling load is less than 3%. Also, VCT provides a reliable estimate of buckling load when the composite sandwich plates with iso-grid cores have been loaded up to at least 67% of the experimental buckling load. • Experimental and numerical validation of VCT approach were presented for the estimation of the buckling load of the composite sandwich plates with iso-grid cores. • The modal analysis of the composite sandwich plates with iso-grid-cores was performed using the modal hammer method. • Finite element models, including nonlinear effects such as geometric and thickness imperfection, was performed. • The maximum difference between the predicted buckling load using the VCT approach on the experimental and numerical results with an experimental buckling load was less than 3%. • It was shown that VCT provides a reliable estimate of buckling load when the composite sandwich plates with iso-grid cores have been loaded up to at least 67% of the critical load. [ABSTRACT FROM AUTHOR]

In this study, energy dissipation characteristics of covalently-bonded stochastic carbon nanotube (CNT) networks are comprehensively studied by means of molecular dynamic simulations. A previously-developed stochastic algorithm is used to generate three distinct numerical specimens which are subjected to two cycles of compression and relaxation for three different compression ratios with varied strain rates. One of the significant findings obtained in this study demonstrates that covalently-bonded stochastic CNT networks exhibit hysteretic stress – strain relationships and dissipate a significant portion of the energy absorbed during compression. Furthermore, it is observed that the hysteretic behavior of the covalently-bonded stochastic CNT network is enhanced by increasing the strain rate. Hence, the amount of energy dissipated by the covalently-bonded stochastic CNT network increases as the strain rate increases. [ABSTRACT FROM AUTHOR]

This paper presents an analytical and numerical investigation of the relationship between the compressive load level and the natural frequency variation toward a vibration correlation technique for the buckling load calculation of imperfection-sensitive isotropic cylindrical shell structures. Firstly, a back-to-basic s study is proposed and the linear equation between the applied load and the square of the loaded natural frequency is revisited. Such review considers the Flügge-Lur'e-Byrne's linear shell theory for the free vibrations of an isotropic unstiffened cylindrical shell under uniform axial loading. The demonstrated linear equation is rearranged for expressing the square of the applied load as a quadratic function of the square of the loaded natural frequency. The suggested formulation provides the analytical support to a novel vibration correlation technique that has been empirically proposed and experimentally validated for unstiffened cylindrical shells. Aiming a numerical verification based on finite element models, two cylindrical shells are defined. At first, the critical buckling load and the fundamental natural frequency for different load levels are determined and compared to the analytical results for validation of the numerical models. The finite element models are extended considering geometric nonlinearities, more realistic boundary conditions and three magnitudes of a benchmark measured initial geometric imperfection. The numerical results are considered for analyzing the variation of the natural frequency in the surroundings of buckling and for verifying the vibration correlation technique. • The free vibration of an axially loaded simply supported cylinder is revisited to verify an existing VCT. • A new insight to define a VCT which does not depends on the similarities between buckling and vibration modes is proposed. • The capability of the VCT to provide conservative estimations is corroborated through detailed numerical models. [ABSTRACT FROM AUTHOR]

Abstract A novel strengthening method using prestressed (PS) carbon fiber reinforced polymer (CFRP) strips was proposed. This method can be used for repairing existing steel columns or constructing new columns for high-rise buildings, power transmission towers and other buildings. Specifically, a prestressing system (PS system) can be used to prestress CFRP strips without using a hydraulic jack. A steel column, PS CFRP strips and the PS system comprise a self-balanced system that offers much greater stiffness against overall buckling than a pure steel column. To verify this strengthening method, axial compression tests are conducted. The results show that the buckling load of the PS-strengthened specimen is 2.5 times greater than that of an unstrengthened specimen, and the failure mode ranges between the first order symmetric and the second order asymmetric overall buckling mode. In addition, finite element analysis (FEA) was adopted to obtain the optimal prestress value, which can also be used as a guide in design. Finally, a simple calculation method of axial bearing capacity was proposed. [ABSTRACT FROM AUTHOR]

Abstract The study investigated thin carbon/epoxy composite plate elements with a central cut-out of regular shape, under uniform compression. The aim of the study was to investigate the possibility of using these elements as elastic elements whose stiffness depends on tailoring the cut-out geometry and laminate ply orientation. To ensure stable operation of the structure in the postbuckling range, the plate was assigned the properties of an unsymmetrical lay-up with extension-twisting and extension-bending couplings. The structure was analysed numerically by the finite element method. The scope of numerical simulations included linear analysis of an eigen problem using procedures for geometrically nonlinear analysis and the commercial simulation software ABAQUS®. The aim of the analysis was to determine a laminate ply orientation generating the lowest buckling mode (flexural-torsional) in order to ensure stable operation of the structure in the postbuckling range. [ABSTRACT FROM AUTHOR]

Abstract Experimental study is carried out to investigate the behavior and strength of square hollow structural section (SHS) columns, strengthened with an innovative polymer-mortar system. Thirteen specimens of cold-formed SHS columns with different variables are chosen. Three short-column and ten long-column SHS specimens were experimentally tested. The local and overall buckling of specimens are measured in the laboratory. The tested specimens are subjected to an axial compressive load. The effect of the thickness of polymer-mortar applied directly to the well-prepared steel surface was studied. The effect of slenderness ratio (kL/r) and width-to-thickness ratio (b/t) on the effectiveness of mortar strengthening was also discussed. Different failure modes are discussed as well as complete axial strength curves are drawn for different cross-sections and member lengths. A maximum axial strength gain of 31.6% was achieved for SHS short columns strengthened with 6 mm thickness polymer-mortar layer. For long columns, a maximum strength gain of 76.7% was achieved with 6 mm thickness polymer-mortar layer applied on four sides. In all mortar-strengthened SHS short and long columns, the axial and lateral deflection, and the axial strain were reduced. The axial strength of SHS long slender columns increased greatly as the overall slenderness ratio increases. Highlights • Cold-formed steel members is an economical alternative in design for low-rise buildings compared to hot-rolled. • Buckling is an important phenomenon to be considered by designers for steel members under compression. • Effectiveness of polymer-mortar strengthening system in increasing the axial strength of slender columns increases greatly as the overall slenderness ratio increases. • The axial strength of HSS columns increases as the plate slenderness ratio (b/t) increases. • Polymer-mortar strengthening system has a great effect on reducing axial, lateral displacement, and axial strain of the strengthened specimens. [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 In the present paper, a methodology for determination of an approximate value of the lowest buckling load of the thin-walled column under compression and with an arbitrary cross-section, affected by initial imperfections, whose amplitude does not exceed half the thickness of the wall, using a load-axial shortening plot, is presented. It has been shown that the load corresponding to an alternation in rigidity of the real structure on the load-axial shortening plot determines the buckling load with high accuracy. The attained results have been compared to the values corresponding to the bifurcation load and the lowest buckling loads determined with commonly used methods based on post-buckling equilibrium paths (i.e., P-w method, P-w 2 method, inflection point method). The formulated problem of nonlinear buckling has been solved with the analytical-numerical method and the FEM. An influence of the imperfection amplitude on an approximate value of the lowest buckling load of laminated thin-walled structures has been analysed on the determined post-buckling equilibrium paths and the load-axial shortening plot. Non-symmetric configurations of laminate layers that additionally exhibit various types of the membrane and bending state coupling have been selected. Detailed computations have been conducted for short angle sections (i.e. angle columns) under uniform compression. [ABSTRACT FROM AUTHOR]

Highlights • Applied the Hencky bar-chain model (HBM) for frame buckling analysis considering different configurations. • Used easy-to-code stiffness matrices with patterns to simplify the expression of HBM formulations. • Demonstrated the advantage of localized model modification of HBM in considering a local damage/stiffening. Abstract This paper presents the development of the Hencky bar-chain model (HBM) for the buckling analysis of non-symmetric portal frames under vertical compressive axial loads on the columns. Generic stiffness and geometric matrices are derived for the frame buckling analysis. Based on these matrices, a simple computer code is developed to determine the buckling loads. Illustrative frame buckling problems are solved to demonstrate the ease and simplicity of the HBM for analysis of different and complex design conditions imposed on the frames. The advantages of consistent formulation, localized model modifications, and convenience in obtaining the buckling modes are further noted for the HBM. [ABSTRACT FROM AUTHOR]

Highlights • A multiscale model is adopted to compute the buckling capacity of CLT walls. • The homogenization is sequentially carried out from nano to structural scale. • Experimental tests are conducted to determine buckling critical load of CLT walls. • The influence of openings on CLT wall buckling capacity is investigated. Abstract The recent trend towards the use of Cross-Laminated Timber (CLT) as a novel construction material in mid- and high-rise buildings has steered the research efforts into this subject over the last few years. Despite the considerable progress made on the structural response of CLT, there are still several unresolved issues related to the analysis and design of CLT. This is of great interest for engineers and designers working on the mass timber construction sector. In particular, the buckling behaviour of CLT walls is a problem not fully understood to date. Therefore, in this paper we investigate the buckling capacity of CLT subject to compressive loads. In order to capture the heterogeneities present in wood, a multi-scale modelling strategy is adopted. To improve the numerical predictions, an optimisation-based parameter identification procedure is performed to calibrate the micromechanical parameters of wood. The numerical predictions are compared with experimental results and are validated successfully. The numerical model is then used to study the influence of the number of layers and wall openings on the buckling capacity of CLT walls. [ABSTRACT FROM AUTHOR]

Abstract The ability to steer carbon fibre tapes, varying the tow angle, can widen the designs possibilities of cylindrical shells that are one of the main components of aerospace structures. This research presents experimental and numerical investigation of two carbon fibre reinforced plastic cylindrical shells – a cylinder with conventional layup made of unidirectional prepreg and a variable-stiffness cylinder manufactured by applying fibre placement technology. The shells were tested in compression until buckling and later subjected to a vibration analysis. Load-shortening curves and buckling shapes were acquired during the compression tests, while the natural frequencies and the mode shapes were measured during the vibration tests. Both tests provide a useful data set of the mechanical response of the cylinders which can be applied for further validation of models. The acquired experimental results were compared to a simple, approximated numerical model of the variable-stiffness cylinder showing good correlation with the test results. [ABSTRACT FROM AUTHOR]

Abstract To ensure the structural capacity of plates with multiple openings subjected compressive loads and to find a better design solution, the strength of different structural configurations is analysed here. A series of experimental buckling collapse tests have been carried out for steel plates with multiple openings, of three different degrees of openings. Each degree of opening is represented by two groups of openings, to investigate the effect of possible design solutions aiming for the maximum compressive strength. The effect of corrosion wastage is also studied, where the specimens are naturally corroded. The effect of manufacturing defects as the initial imperfection on both compressive capacity and the final deformed shapes is also studied. Several relationships as functions of the degree of openings and remaining volume of the corroded plates with multiple openings are developed, and recommendations regarding the early design stage are provided. [ABSTRACT FROM AUTHOR]

Abstract This research work presents a parametric numerical study on the resistance at elevated temperatures of stainless steel members, subjected to combined bending and axial compression. Previous studies have shown the need for the development of further research works aiming at better predicting the fire behaviour of stainless steel beam-columns. However they have only considered beam-columns composed of stocky I sections. Hence, this paper focuses on austenitic stainless steel (European grade 1.4301 also known as 304) beam-columns composed of square hollow sections (SHS) and circular hollow sections (CHS), considering different cross-sections classes (1 to 4), according to Eurocode 3 (EC3) classification. The numerical analyses were performed using the finite element program SAFIR, with material and geometric non-linear analysis considering imperfections. The influence of the following parameters was evaluated: bending moment diagram shape, cross-section slenderness considering the local buckling occurrence on the thin-walled sections, and member slenderness for the global instability due to flexural buckling. Comparisons between the obtained numerical results and the interaction curves of Eurocode 3 are presented. The results show that specific design approach should be developed for these stainless steel members under fire situation, taking into account the above mentioned parameters. Highlights • The behaviour of stainless steel beam-columns with square and circular hollow sections in case of fire is studied • Numerical analysis with material and geometric imperfections of stainless steel structural elements are performed • The accuracy and safety of EC3 design for beam-columns are not suitable for these stainless steel members in fire. [ABSTRACT FROM AUTHOR]

Abstract Face-to-face built-up cold-formed steel channel sections are becoming increasingly popular for column members in cold-formed steel structures; its applications include cold-formed steel trusses, space frames and portal frames. In such an arrangement, the independent buckling of the members is resisted by intermediate fasteners. In the literature, no research is available for such face-to-face built-up cold-formed steel columns. The issue is addressed herein. This paper presents the results of 36 experimental tests, conducted on face-to-face built-up cold-formed steel channel-sections covering a wide range of slenderness from stub to slender columns. A nonlinear finite element model is then described that shows good agreement with the experimental results. The finite element model includes material non-linearity, initial imperfections and modelling of intermediate fasteners. Both finite element and experimental results are compared against the design strengths calculated in accordance with the American Iron and Steel Institute (AISI), Australian and New Zealand Standards (AS/NZS) and Eurocode (EN 1993-1-3). The verified finite element model is used for the purposes of a parametric study comprising 90 models. The effect of fastener spacing on the axial strength was investigated. From the results of experiments and finite element investigations, it is shown that the design in accordance with the AISI & AS/NZS and Eurocode (EN 1993-1-3) is generally conservative by around 15%, however, AISI & AS/NZS and Eurocode (EN 1993-1-3) can be un-conservative by 8% on average for face-to-face built-up columns failed through local buckling. Highlights • Experimental tests were conducted on face-to-face built-up CFS channel-sections. • Initial geometric imperfections were measured for all test specimens using a laser scanner. • Nonlinear finite element models were developed which includes material nonlinearity and initial imperfections. • The column strengths were compared against the design strengths calculated in accordance with AISI & AS/NZS and EN 1993-1-3. • The AISI & AS/NZS and EN 1993-1-3 design strengths are generally conservative by around 15% but un-conservative by 8% on average for columns failed through local buckling. [ABSTRACT FROM AUTHOR]

The aim of the work was to assess the compressive strength of Fibre Metal Laminates after impact. The main objective of the evaluation of the compression after impact assessment of FMLs was the deep analysis of damage growth range, size and mechanisms during load from various initial damage states and final post-impact strength. The glass fibre/titanium and carbon fibre/titanium Fibre Metal Laminates were tested and analysed. Laminates previously subjected to impact energies ranging from 5 to 35 J were tested. Based on the research, three load bearing states of fibre-metal laminates were identified and characterized on the basis of an analysis of force reduction characteristics. In addition, it was found that the strength reduction of FMLs in relation to impact energy does not decrease significantly. One of the most crucial grounds for the above is the protective role of the elastic–plastic metal layers against rapid local buckling of the strength-carrying composite component. [ABSTRACT FROM AUTHOR]

• Buckling behavior of hybrid composites tubes. • Modal behavior or hybrid composites tubes before and after failure. • Analysis of variance of the structural responses in composites tubes with ply drop-off. • The results revealed that the hybrid structure with drop-offs is an appropriate option that offers the best cost-benefit. A comparative study of the static and dynamic behavior of a new type of tubular structure with drop-offs used in lower limb prostheses is presented in this paper. Composite structures that present mass reduction, low cost, and excellent performance are a great challenge for many researchers. In order to overcome these difficulties, numerical and experimental methods are performed, generating results regarding natural frequencies, damping loss factors, and maximum compression load for five different setups for tubes with drop-offs. For the manufacture of the structures, three types of fabrics are considered: carbon, glass, and a carbon/aramid hybrid fabric. Beyond the three types of tubes, two more setups are created considering hybridization, with the inner ply manufactured with glass fabric, the outer ply of the first setup manufactured with carbon fabric, and the outer ply of the second setup manufactured with carbon/aramid hybrid fabric. The structural hybridization and insertion of drop-offs provide a reduction in the cost of material. Firstly, an optimization strategy using the Lichtenberg algorithm is executed, aiming at the basic material properties in relation to elasticity modulus, strain modulus, Poisson ratio, and density. Then, it is possible to perform numerical modal analysis using the Finite Element Method in Ansys® software with the aim of obtaining the first natural frequencies for each setup. Modal experimental tests before and after failure obtained in the compression test are performed to measure the first natural frequency and damping loss factor for each setup, providing a comparison between the dynamic behavior of the undamaged and damaged structures, and, posteriorly, the numerical and experimental modal results before failure are compared. The compression test is performed to measure the maximum compression load supported by each structure. The results revealed that the hybrid structure with drop-offs is an appropriate option that offers the best cost-benefit for pylon tubes. [ABSTRACT FROM AUTHOR]

• The functionalized MWCNTs/HDPE based functionally graded nanocomposites are fabricated using 3D printing. • The micrographs of 3D printed FGNC samples reveal the seamless bonding between each layer of different compositions. • The highest P cr is noted for H5 and FGNC-2 among the 3D printed NC and FGNC samples, respectively. • The natural frequency of the NCs and FGNCs increases with increased MWCNTs % while decreases with increasing compressive load. • The numerical and experimental results are noted to be in good agreement. The experimental and numerical investigations are carried out for buckling and vibration of 3D printed functionalized MWCNTs/HDPE based nanocomposite (NC) and their functionally graded nanocomposite (FGNC) variants. P cr (critical buckling load) is computed through MBC (modified budiansky criteria) and DTM (double tangent method) techniques. It is observed that P cr of the 3D printed NCs and FGNCs increases with the functionalized MWCNTs content. The P cr values for the NCs (H0.5-H5) computed using DTM and MBC increased in the range of 16–79%, while for FGNC-1 (H0.5-H1-H3) and FGNC-2 (H1-H3-H5), the P cr increased from 54 to 91% compared to HDPE. Further, it is observed that the natural frequency of the NCs and FGNCs increases with the functionalized MWCNTs loading while decreases with rise in compression. The natural frequency of the NCs (H0.5-H5) and FGNCs increased up to 41% than HDPE. The highest P cr and the natural frequency is noted for H5 and FGNC-2 prints. The experimental and numerical results showed good agreement. [ABSTRACT FROM AUTHOR]

Identification of the boundary between failure by buckling, collapse and material failure in cylindrical tubes under axial compression is still challenging. The focus of this research is to investigate the response of carbon/epoxy filament wound cylindrical tubes under axial compression. Three approaches have been studied: (i) linear buckling; (ii) nonlinear buckling; and (iii) progressive damage modeling (PDM). For that, analytical, numerical and experimental approaches have been followed. Key results show that thinner tubes fail by buckling followed by a post-buckling field, whereas material failure due to transverse compression and in-plane shear stresses occur for thicker tubes. Both analytical and linear numerical models predicted very well the critical buckling load for all [±α] tubes, and nonlinear buckling model satisfactorily predicted axial displacement over the loading history. For multilayered tubes, the developed damage model provided better predictions compared to the nonlinear buckling model. Furthermore, for thicker tubes, a hoop layer at the outermost, instead of middle or innermost, improves buckling/compressive resistance. [ABSTRACT FROM AUTHOR]

To reveal the atomistic scale mechanism of buckling of single-walled carbon nanotubes (SWCNTs) under axial compression, we carried out molecular dynamics (MD) simulation and atomistic structural instability (ASI) analysis. The ASI analysis enables us to reveal the development of ‘latent’ instability modes until buckling of structure, which cannot be clarified with MD alone. Euler-type buckling was found in relatively thin and long nanotube models, while buckling triggered by change of cross-sectional shape (i.e., radial buckling) was found in thick and short models. With growing radius, a crossover between the Euler-type and radial buckling modes was clearly found in the ASI analysis. Even when the deformation behavior was apparently the same, the buckling can be triggered by different instability modes. We also analyzed the structural instability using the Flügge theory based on linear continuum mechanics (LCM) to compare the results with the ASI analysis. Initial eigenvalues and development of instability modes were different between the ASI and LCM results, leading to a significant deviation of buckling strain and instability crossover points. We investigated the effect of chirality of CNT which is difficult to explain by LCM. [ABSTRACT FROM AUTHOR]

The elastic buckling of shell structures such as spherical shells subject to external pressure and cylindrical shells loaded in axial compression is highly sensitive to imperfections and often catastrophic. Recent studies of spherical shells have provided accurate quantitative results for the relation between the buckling pressure and the amplitude and shape of geometric imperfections and, additionally, quantitative results for the energy barrier that must be overcome to buckle the shell by extraneous loadings or disturbances when it is loaded to pressures below the buckling pressure. Results for the simultaneous interaction of imperfections and energy barriers for spherical shells under external pressure will be presented. Numerical studies for probing forces illustrate their use in determining the buckling energy barrier, and new experimental results on energy barriers obtained by others by probing spherical shells will be discussed and compared with predictions. It will be argued that while imperfections determine the buckling load of a shell, the energy barrier at loads below the buckling load supplies important additional information about the relative safety or precariousness of the shell to additional disturbances. Results for the energy barrier for perfect and imperfect spherical shells under external pressure provide important insights into the shell's robustness, or lack thereof, at pressures below the buckling pressure. In particular, the energy barrier trends provide critical insights into the low knockdown factor usually employed in establishing the design load of unstiffened spherical and cylindrical shells. These design loads are shown to correlate with conventional predictions provided that imperfection amplitudes scale as the shell radius. [ABSTRACT FROM AUTHOR]

This paper presents the test results of an experimental program to investigate the structural performance of short and slender concrete-filled fiber-reinforced polymer (FRP)-tubes (CFFTs) columns under pure axial compression load. The test parameters include: transverse reinforcement type (steel spirals versus glass-FRP (GFRP-tube), type of longitudinal reinforcement (steel and carbon-FRP (CFRP) bars), GFRP tube thickness, and slenderness ratio. Comparisons between the experimental test results and the theoretical design equations are performed in terms of ultimate load carrying capacity. The design equation is modified to accurately predict the ultimate load capacities of CFFT columns reinforced with FRP bars. Furthermore, the experimental results showed that the axial compressive strength of CFRP-reinforced CFFT columns was reduced by 22% with increasing the slenderness ratio from 8 to 20. In general, the use of the FRP tube induces a confinement effect for concrete columns which enhances the strength and ductility of such column’s section. This enhancement resulted in a slender section which increased the possibility of buckling instability of the CFFT columns. Thus, a theoretical model was conducted to develop a simplified formula for critical slenderness limit of FRP-reinforced CFFT columns to control the buckling instability mode of failure. Results indicated that the slenderness limit of 14 was suggested as a safe value for the design purposes. A parametric study was conducted which showed the significant effect of the concrete compressive strength and hoop stiffness of FRP tube on the critical slenderness ratio of FRP-reinforced CFFT columns. [ABSTRACT FROM AUTHOR]

Experimental investigations of channel-section profiles subjected to compression after low-velocity impacts (20 J) leading to global failure are presented. The columns under discussion were made of an eight-layer GFRP laminate with quasi-isotropic, quasi-orthotropic and angle ply arrangements of layers. The profiles were impacted in mid-width of the web or mid-width of the flange in various locations along the profile length. An influence of the impact position and the layer arrangement on buckling and failure phenomena, post-buckling behaviour for impacted and non-impacted columns was thoroughly examined and described. It was found that the local degradation introduced by low-velocity impacts did not affect the global behaviour of the analysed structures to a considerable extent. Moreover, it was noted that the failure mechanism was initiated in the impact location in none of the cases analysed. Additionally, it was stated that a number of fracture points did not have any significant impact on the capacity reduction. [ABSTRACT FROM AUTHOR]

Due to mainly thermal and energy potentials, Insulated Glass Units (IGUs) are largely used in modern buildings to realize curtain walls and enclosures. The typical IGU consists of two glass layers, either monolithic and/or laminated, joined together by enclosing an hermetically-sealed air (or gas) cavity between them. There, maximum stresses and deformations derive from external pressures (wind loads, etc.) or environmental/climatic loads (temperature variations, etc.). While the common IGU application involves 4-side continuous supports, novel restraint configurations are increasingly used in practice (i.e. 2-side supports, point-fixings, etc.), hence resulting in additional loading scenarios that could compromise the integrity of these systems. In this paper, following earlier research contributions, a standardized buckling approach in use for structural glass elements mainly compressed or under combined compression/bending is assessed, for the specific case of IGUs with 2-side continuous supports. Analytical and Finite Element (FE) numerical studies are reported, giving evidence of their actual performance and buckling resistance, including parametric analyses and comparisons towards simplified design formulations for both external and internal pressures. [ABSTRACT FROM AUTHOR]

The focus of this paper is on the analytical buckling solutions of piezoelectric cylindrical nanoshells under the combined compressive loads and external voltages. To capture the small-scale characteristics of the nanostructures, the constitutive equations with the coupled nonlocal and surface effects are adopted within the framework of Reddy's higher-order shell theory. The governing equations involving the displacements and induced piezoelectric field are solved by employing the separation of variables. The derived accurate solutions conclude that bucking critical stresses should go down rapidly while the nonlocal effects reach a certain level. With the enhancing surface effects, the stability of piezoelectric cylindrical nanoshells can be improved significantly. Meanwhile, the induced electric field also plays an important role in elevating the buckling critical stresses. For the nanoshells with remarkable nonlocal effects, boundary conditions, shell length and radius have little influence on the buckling solutions. The detailed effects of the boundary conditions, geometric parameters, material properties and applied voltages are discussed. [ABSTRACT FROM AUTHOR]

High performance cementitious composites have made possible the manufacturing of thin cementitious shell structures which are prone to buckling. Perhaps the most comprehensive design procedure for such shells is provided by the design recommendations issued by the International Association for Shells and Spatial Structures (IASS) which, however, are inconsistent with the modern European design framework. The scope of this paper is to contribute to the development of a design methodology similar to the one recommended by Eurocode 3 part 1–6, which is based on a capacity curve that represents all the possible failure states. In this respect, the capacity curve of an axially compressed cylinder is produced by geometrically and materially nonlinear analyses for different fabrication quality classes, which are in the sequel approximated by parametric capacity curves based on parameters determined following the concept of Eurocode 3. [ABSTRACT FROM AUTHOR]

This paper reports on experiments addressing the buckling and collapse behavior of back-to-back lipped channel built-up cold-formed steel (CFS) columns assembled using 16 different CFS lipped channel sizes. The lipped channel sections are connected at the web using a pair of self-drilling screw fasteners at a specified spacing along the column length of 1.83 m (6 ft). These experiments aim to quantify the effect of two web fastener layouts on composite action for each section size, study member end fixity, observe buckling and collapse behavior, and provide benchmarks for design that includes specific considerations for thin-walled member buckling. A total of 32 monotonic, displacement-controlled, concentric compression tests are completed with up to 17 position transducers monitoring displacements at key locations. All tests are conducted with the built-up member seated in CFS tracks, as would be found in practice. Local–global interaction is shown to be a prevalent failure mode, and the stud-to-track end condition is determined to be semi-rigid, but generally closer to a fixed condition. End rigidities are estimated using a Southwell approach. Rational design approaches extending the application of the Direct Strength Method (DSM) and employing current state-of-the-art numerical modeling techniques are proposed and validated with test data. In addition, the development of definitive design recommendations that help reduce the complexity of fastener designs and incorporates the DSM framework when predicting built-up member strength is underway. [ABSTRACT FROM AUTHOR]

Offshore structures are often founded on long, slender piles that extend for a substantial distance above the ground surface. This paper presents a novel unified model to analyze the free vibration and buckling of partially embedded end-bearing piles subjected to axial compressive load. Consideration is given to the tapered piles of variable cross-sectional shape with constant volume. The governing differential equation of the motions is derived, and solved by using the Runge-Kutta method in combination with the Regula-Flasi method. The accuracy of the proposed model is confirmed by comparing the obtained calculations with existing closed-form and numerical solutions. Numerical results for the natural frequency, buckling load and corresponding modal displacements are provided, which are analyzed to highlight the effects of the parameters related to the cross-sectional shape, taper ratio and embedment of the pile, soil stiffness and compressive force as well as the end constraint. The geometry and material parameters that statically and dynamically yield the strongest piles with fixed volume are identified. The analytical model is beneficial for the optimum design of the soil-pile system in engineering applications. [ABSTRACT FROM AUTHOR]

Buckling analyses of laminated truncated conical shells subjected to external hydrostatic compression are carried out by employing the Abaqus finite element program. The critical buckling loads of these truncated conical shells with a given material system are maximized with respect to fiber orientations by using the golden section method. Through parametric studies, the influences of the end condition, shell thickness, shell length, shell radius ratio and cutout size on the optimal buckling loads, the associated optimal fiber orientations and the associated buckling modes are demonstrated and discussed. [ABSTRACT FROM AUTHOR]

This paper aims to explore the behaviour of substandard reinforced concrete (RC) columns confined with Steel-Reinforced Grout (SRG) jackets under monotonically increasing uniaxial compression. A total of 24 specimens of short RC columns of square cross section were designed to fail due to longitudinal reinforcement buckling. Single-layered SRG jackets were applied to 18 of these specimens, whereas the rest served for control without SRG jackets. Parameters of this investigation were the type and density of the steel fabric as well as the corner radius of the cross section. The employed SRG jacketing managed to increase the strength and strain capacity and postpone the buckling of the longitudinal steel bars to occur at higher compressive strain level. Confinement effectiveness with respect to the lateral confining pressure exerted by the used SRG jacketing is discussed along with the observed mode of failure. [ABSTRACT FROM AUTHOR]

A novel sandwich core topology – corrugated channels (periodic fluid-through wavy passages) – was proposed for simultaneous load-bearing and active cooling applications. Relative to a sandwich panel with parallel plate channels, the sandwich with corrugated channel core exhibits not only significantly enhanced convective heat transfer rate but also superior mechanical performance. To explore the underlying deformation and failure mechanisms, corrugated-channel-cored sandwich panels (3CSPs) with low relative densities (< 1.5%) were manufactured, with Ti-6Al-4V alloy used as the constituent material for both the core and the face sheets. The quasi-static, out-of-plane compressive behaviors of Ti-6Al-4V sandwich panels were systematically studied using a combined experimental, analytical and numerical approach. The compressive strength of the proposed 3CSP was also compared with competing core topologies on the material selection map. With superior structural and thermal efficiency, the corrugated channel core is promising for a wide variety of multifunctional lightweight sandwich constructions. [ABSTRACT FROM AUTHOR]

Due to the non-uniform in-plane stress distribution, variable-stiffness panel with curvilinear fiber paths is a promising structural concept for cutout reinforcement of composite structures under axial compression, due to the more diverse tailorability opportunities than simply choosing the best straight stacking sequence. However, traditional representation methods of curvilinear fiber path are usually not flexible for cutout reinforcement. In this study, the flow field function containing a uniform field and several vortex fields is utilized to represent the fiber path due to its inherent non-intersect and orthotropic features, and a bi-level optimization framework of variable-stiffness panels considering manufacturing constraints is then proposed. A typical rectangular composite panel with multiple cutouts is established to demonstrate the advantage of proposed framework by comparison with other fiber path functions. Results indicate that the flow fiber path only needs few variables to finely represent the fiber path, which can provide satisfying and manufacturable fiber paths by combination use of curvature constraint. [ABSTRACT FROM AUTHOR]

Single walled carbon nanotubes have excellent mechanical properties, are very tough, very rigid, the ability to withstand high working temperatures, and the highest strength-to-weight ratio of any known material. However, their buckling performance under compression and at high temperatures has not been studied to a sufficient extent. The aim of this work is to provide theoretical predictions concerning the compressive buckling response of SWCNTs of different chiralities and sizes under various thermal conditions. For this reason a structural mechanics numerical formulation is adopted that uses the temperature dependent molecular structure of the nanotubes while represents the interatomic interactions within the carbon nanostructures by introducing three dimensional, two-noded, bar finite elements. The temperature dependent stiffness matrices of the utilized finite elements are constructed in accordance with theoretical relationships which are provided by molecular theory. The critical buckling compressive loads and corresponding buckled shapes of variously sized zigzag, chiral, and armchair SWCNTs are thoroughly investigated with respect to the temperature. Then, some significant conclusions are discussed regarding the effect of the temperature, nanotube size and chirality on the structural stability performance of SWCNTs. [ABSTRACT FROM AUTHOR]

This paper presents analytical study of a non-uniform shallow arch under a central concentrated load. The non-uniformity is characterized by three constant stiffness regions. The least potential energy principle is used to obtain the equilibrium equations. The anti-symmetric buckling axial compression and buckling modes are shown to be identical with those of Euler-Bernoulli beam. The initial imperfection effect is also investigated theoretically and a parametric study on the different geometric parameters has been carried out on the snap-through symmetric buckling load and anti-symmetric buckling load. The comparison against the finite element analysis shows the accuracy of the theoretical model. We show that the stiffer center case is always economically better than the stiffer end case. The two limiting cases with largest degree of non-uniformity are analytically analyzed by using the augmented potential energy with the Lagrangian multiplier. The closed-form condition for the occurrence of symmetric snap-through buckling is presented for one limiting case. This paper serves to enhance the understanding of the effect of the non-uniformity of shallow arch on its load carrying capacity. [ABSTRACT FROM AUTHOR]

Cylindrical shell structures such as silos and wind turbine towers often feature openings for internal access, and these may have a significant detrimental effect on the buckling load. This paper numerically investigates the buckling of cylindrical shells with cutouts near the cylinder end using nonlinear finite element analysis. The finite element (FE) model was validated against published experiments on the axial compression of moderately thin-walled cylinders with cutouts of various sizes and shapes. The results indicate excellent qualitative and quantitative agreements for loads, deflections, and buckled mode shapes. Using the validated FE model, it was found that the opening width is the most critical geometric parameter in terms of loss of carrying capacity. The model was then extended to explore a variety of stiffener configurations aimed at recovering the capacity lost due to the opening. These configurations included a frame ring, as well as the simpler option of straight ribs on either side of and above the hole. Thickness and protrusion were also considered in the analysis. It was found that the frame ring achieved full recovery of the lost capacity, while the straight stiffeners were effective where only up to 67% recovery was required. The results also indicated that the optimum placement of stiffeners was immediately adjacent to the cutout. This study demonstrates that the optimum stiffener is a fully enclosed ring immediately adjacent to the cutout edge, and that full load recovery can be achieved with an appropriate design. [ABSTRACT FROM AUTHOR]

This paper investigates the buckling of screws loaded in compression inserted into timber members. Screws are often used as a reinforcement in timber structures. However, under compression forces, they are prone to axial buckling. The current model for the screw buckling, enclosed in the EC5 proposal, is based on the general framework of EC3 for the instability of compressed steel members. The main shortcomings of the current formulation for the buckling of screws are the following. (1) The analytical expression for calculating the theoretical buckling load does not follow the observed modes. (2) Due to the need for dedicated studies, the value of the imperfection coefficient is arbitrarily chosen. This paper fills the above gaps. Firstly, a simple analytical expression for predicting the buckling of screws is proposed and validated against experimental and finite element (FE) findings. Furthermore, the formulation adopts a more accurate expression for lateral deformation based on experimental observation. Secondly, a FE model calibrated on experimental tests is used to estimate the defect coefficients of the instability curves as a function of the amplitude of the geometric defects of the screw, expressed as a fraction of its length. Finally, a Markov chain Monte Carlo analysis is carried out to simulate the capacity of screws with different sizes, assuming the uncertainty of all input parameters sampled from suitable probability distributions. The results are used to validate the proposed deterministic capacity model and estimate the uncertainty factors of the design equation. • Buckling model for compressed timber screws. • Analytical model for the theoretical buckling load. • Numerical validation of the analytical model. • Experimental tests and numerical model calibration. • Calibration of the imperfection coefficients from Monte Carlo analysis. [ABSTRACT FROM AUTHOR]

The new Reference Resistance Design (RRD) method, recently developed by Rotter [1] , for the manual dimensioning of metal shell structures effectively permits an analyst working with only a calculator or spreadsheet to take full advantage of the realism and accuracy of an advanced nonlinear finite element (FE) calculation. The method achieves this by reformulating the outcomes of a vast programme of parametric FE calculations in terms of six algebraic parameters and two resistances, each representing a physical aspect of the shell's behaviour. The formidable challenge now is to establish these parameters and resistances for the most important shell geometries and load cases. The systems that have received by far the most research attention for RRD are that of a cylindrical shell under uniform axial compression and uniform bending. Their partial algebraic characterisations required thousands of finite element calculations to be performed across a four-dimensional parameter hyperspace (i.e. length, radius to thickness ratio, imperfection amplitude, linear strain hardening modulus). Handling so many nonlinear finite element models is time-consuming and the quantities of data generated can be overwhelming. This paper illustrates a computational strategy to deal with both issues that may help researchers establish sets of RRD parameters for other important shell systems with greater confidence and accuracy. The methodology involves full automation of model generation, submission, termination and processing with object-oriented scripting, illustrated using code and pseudocode fragments. [ABSTRACT FROM AUTHOR]

This study proposes a skin-added X-lattice composite structure consisting of corrugated ribs and a very thin skin, as an alternative form of anisogrid composites, for the efficient light weight structural concept under compression loading. The high mechanical capability of skin-added X-lattice structures is numerically analyzed, followed by introduction of the related manufacturing method. This manufacturing process is composed of preparation of corrugation units and co-curing of the units with a thin skin. The results of compression tests of fabricated X-lattice panels agree with numerical predictions in terms of buckling loads and buckling modes, while skin-added X-lattice panels exhibited somewhat lower buckling load than the prediction. Feasibility of the proposed skin-added X-lattice is demonstrated in this work by fabrication and mechanical characterization. [ABSTRACT FROM AUTHOR]