Search

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 • Explicit equations for 'tee' buckling are developed using energy method. • Influence of transverse bending of web is considered. • Parametric analysis is carried out using FEM for Litzka-type beams. • Influence of stress gradient in the 'tee' buckling is studied using GBT. • It is shown that this buckling mode be relevant for high-strength steel. Abstract This work presents the development of explicit equations for the prediction of elastic local buckling critical stress of castellated beams subjected to pure bending, considering the interaction between flange and web. Eigenvalue analyses are carried out for Litzka-type beams using Finite Element Method (FEM) to gather information on the buckling modes and critical stresses for combinations of usual flange-to-web width and thickness ratios. The representative compression 'tee' is analyzed using the Generalized Beam Theory (GBT) to study the influence of stress gradient and member length in the critical stress. The influences of flange torsional stiffness and web transverse bending in the 'tee' behavior are studied and an energy method is adopted to derive the prediction equations. It is shown that the proposed approach leads to a good agreement with the FEM results, with an average difference of 0.955 ± 0.063, whereas current guidelines may significantly over or underestimate actual critical stresses for low flange-to-web width ratios. It is finally shown that this buckling mode may become relevant for castellated beams using high-strength steel. [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]

This paper presents a comprehensive test database of concentric compression experiments on pultruded fiber-reinforced polymer (PFRP) specimens that failed in a global flexural buckling mode published in literature between 1969 and 2016. A new closed-form equation to determine the reduction factor for global flexural buckling of PFRP structural struts under axial compression is developed on the basis of the Ayrton-Perry formula and observed initial out-of-straightness of PFRP members measured by other researchers. Recognizing that data on initial imperfections may be unavailable, a second new empirical closed-form equation is derived based upon the experimental database. Validation of the two explicit expressions is performed by both comparison to experimental data and comparison with validated numerical simulations. In addition, the accuracies of the two proposed equations are compared with those of five closed-form solutions available in the literature; both results in more accurate predictions than the extant equations. Both new proposed equations can be conveniently used by structural engineers at the preliminary engineering design stage for accurately assessing the reliability and safety of composite structures under concentric compressive loading. [ABSTRACT FROM AUTHOR]

This paper proposes a new type of buckling-restrained braces (BRBs), namely shuttle-shaped buckling-restrained braces (SS-BRBs). The proposed SS-BRB is composed of a circular steel tube as the inner core, and a shuttle-shaped thin-walled steel tube as the external restraining member. The space between them is filled by a steel-plate isolation system. The shuttle-shaped restraining member of the SS-BRB significantly improves load-carrying efficiency and saves material in its strength design. Moreover, the SS-BRB is more aesthetically appealing and can be utilized as an exposed BRB in long-span or spatial structures. In terms of the concept of restraining ratio of a BRB, no design method of an SS-BRB is available currently because it concerns the solution of the elastic buckling load of an SS-BRB. Therefore, the elastic buckling load of a pin-ended SS-BRB is initially studied by adopting the equilibrium method and is further verified through finite element (FE) method. The lateral displacement function of an SS-BRB, and the longitudinal stress at the extreme fiber of the external restraining member are derived by considering an initial geometric imperfection that is consistent with the first order overall buckling shape of the SS-BRB. A correction factor considering shear deformation has been incorporated for a more accurate prediction. The lower limit of the restraining ratio for a load-bearing type of SS-BRBs is further obtained based on yielding of the extreme fiber of the restraining member. Furthermore, the proposed formula has incorporated a strain hardening factor for the SS-BRB that experiences strain hardening of the core after its initial yielding. The proposed formulas have been validated through FE numerical analysis. The findings in this paper provide fundamentals to develop the design method for an energy-dissipation type of SS-BRBs. [ABSTRACT FROM AUTHOR]

Due to its relatively good safety performance and aesthetic benefits, laminated glass (LG) is increasingly being used as load-carrying members in modern buildings. This paper presents a study into one application scenario of structural LG subjected to axial compression. The aim of the study is to reveal the flexural buckling behavior of the LG columns made up of multi-layered annealed glass plies. The LG specimens respectively consisted of two, three and four plies of annealed glass, bonded together by two prominent types of adhesives. To reach the research aim, both full-scale tests and nonlinear numerical simulations were carried out. Based on the test and numerical results, the influences of interlayer type, laminate number, load duration and ambient temperature on the buckling resistance of the LG columns were studied in detail. In addition, the applicability of the so-called Southwell plot method for LG columns was examined and discussed. Subsequently a characteristic initial geometrical imperfection for LG columns made of annealed glass was suggested. Finally design buckling curves were proposed for LG columns carrying axial loads with the various durations in various ambient temperatures. The results obtained are expected to provide supplementary information that is currently lacking in existing literature. [ABSTRACT FROM AUTHOR]

To meet the requirement of larger bearing capacity and better material economization than traditional main members in latticed transmission towers, a novel Y-section column is put forward in this paper. A series of full-scale tests is carried out to investigate the buckling behavior of 420 MPa high strength steel Y-section (HSSY) columns. 57 columns including three different sectional dimensions and nine slenderness ratios ranging from 30 to 80 are designed for axial compression tests. The width-to-thickness ratios, reduction factors accounting for the design stress or effective cross section area, material mechanical properties, initial geometric imperfections and longitudinal residual stresses are measured and discussed in detail. Based on the validated finite element results taking the initial imperfections into account, the buckling deformations and ultimate strengths are obtained and demonstrate a good agreement with the test results. The buckling factors are calculated and compared with different code results such as Eurocode 3, GB 50017-2003, ASCE 10-97, ANSI/AISC 360-10, CSA S16-09, AS4100-2012, BS 5950-1 and AIJ 2010. Related buckling curves and formulae are derived through nonlinear fittings and compared with the code design curves. It is concluded that the HSSY columns characterize very strong stability and high buckling strengths. Finally, the recommended buckling curves and design formulae are proposed to predict the buckling strengths of HSSY columns. [ABSTRACT FROM AUTHOR]

• Effect of single and double sided potting support design on compression buckling response of quasi-isotropic cylindrical shells under axial compression. • Possible causes of discrepancies between theoretical and experimental buckling loads due to changes in boundary conditions. • Empirical expressions for knockdown factors for evaluating initial margins of safety for testing cylindrical shells for different potting support sizes. • Validation of expressions for different thicknesses and different quasi-isotropic laminates. The design of thin-walled cylindrical shells under compression loading is mostly driven by buckling considerations. However, accurate experimental evaluation of the buckling load is challenging due to small variations in boundary conditions due to manufacturing tolerances in support conditions. To test a cylindrical shell under compression loading, potting support is usually created around its bottom circumference to avoid edge crippling that could otherwise drastically reduce its critical buckling load. Therefore, investigating the effects of the potting support on the buckling response of cylindrical shell structures is important to mimic boundary conditions as close as possible to real structural constraints of the boundary. The main objective of this work is to investigate the effects of single and double-sided potting supports on the critical linear buckling load of composite cylindrical shells under compression loading. Then, this paper provides insights into understanding underlying reasons for the deviations of theoretical buckling loads from their corresponding experimental values due to boundary conditions, which can occur independently from, or in combination with, geometric imperfection sensitivity. Finally, robust linear buckling expressions that can help designers estimate the reduction due to support conditions are presented. These expressions can be used for evaluating initial safety margins for the potting support design used for testing cylindrical shells. [ABSTRACT FROM AUTHOR]

• Investigated the effects of screw restraints on the distortional buckling behaviour of LSF walls. • Investigated the accuracy of numerical methods and idealised screw restraints on distortional buckling. • A detailed parametric study was conducted using a validated sheathed stud FE model. • Investigated the effects of screw connections and stud slenderness on the distortional buckling capacity. • Developed improved DSM design methods for the distortional buckling capacity of LSF walls. With the new advancements in constructions technologies, the use of cold-formed steel (CFS) construction is becoming popular due to its inherent advantages over conventional construction materials. These high performing CFS sections, such as the web stiffened lipped channel studs, are more likely to be subjected to distortional buckling under compression load. Although many numerical and experimental studies have been undertaken on unsheathed CFS columns subjected to distortional buckling, there is limited research on light gauge steel framed (LSF) walls subject to distortional buckling. The behaviour of sheathed wall studs is significantly different to that of columns due to the complicated boundary conditions provided by the stud-to-sheathing contact interactions and screw connections. Although CFS design standards recognize the sheathing boards as a means of providing lateral and rotational restraints, they do not provide any information on their effects on studs subject to distortional buckling. In this study, the suitability of currently available numerical modelling techniques on predicting the distortional buckling behaviour of LSF walls was investigated. It was identified that the distortional buckling capacity is highly sensitive to the in-plane restraints provided by screw connections. The effects of stud geometry, stiffness of screw connections and stud length on the distortional buckling capacity were investigated in a detailed numerical parametric study involving more than 3500 finite element analyses. Finally, the accuracy of the current direct strength method was investigated and suitable modifications are proposed. Moreover, alternative simplified design methods and their accuracy are also discussed. [ABSTRACT FROM AUTHOR]

Torsion and bending/torsion buckling may occur for compressed thin-walled open profiles used in engineering and architecture applications. We report experimental results provided by PZT pickups stuck on thin-walled aluminium beams with open modified cruciform cross-section, exhibiting non-zero warping stiffness. The buckling loads and the natural frequencies corresponding to various compressive forces were detected for free and (at least partially) restrained warping of the ends of the specimens. The results are compared with those of a FEM (commercial) and an in-house numerical code that examines the stability of non-trivial equilibrium paths in a dynamic setting. The results seem new and confirm that: (a) PZT pickups can be efficient in extracting modal parameters of thin-walled beams; (b) the numerical simulations are robust and accurate in finding the buckling loads in all analyzed configurations. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on the buckling behaviour of gusset plate connections under compression. The main focus is given to the post-buckling resistance of relatively slender gusset plate connections, cases which are commonly found in thin gusset plates in light-weighted structures, and also potentially, as driven by the recent development in steel manufacture industry, in high-strength steel (HSS) gusset plates. The numerical modelling strategy was carefully validated using the results of eight full scale tests previously conducted by the authors and co-workers, and an extensive parametric study was subsequently performed covering a reasonably wide range of geometric configurations and material properties of practical gusset plate connections. Stable post-buckling equilibrium paths were observed for the models with relatively thin gusset plates, and the use of HSS further promotes remarkable post-buckling resistance. The influences of initial imperfection and material strain hardening on the buckling behaviour of gusset plate connections have also been discussed in detail. Based on the results from the numerical study, two design approaches were proposed, namely, Column Buckling Approach, which is based on a modified column analogy from the current design practice, and Plate Buckling Approach, which is based on a plate analogy and modified Winter formulae. While both methods can be used by practicing engineers, the latter may take account of the plate action of gusset plates in a more reasonable manner, and it is also more consistent with the common design rules for plated structures. [ABSTRACT FROM AUTHOR]

Thin-walled columns with section are used widely as columns in aluminum alloy framed structures, offering high strength-to-weight ratios and convenience in connection with maintaining walls. In this paper, thin-walled aluminum alloy columns with section were studied experimentally and numerically to investigate the buckling behavior and to assess the accuracy of current design methods. A finite element model (FEM) was developed and used to perform parametric studies after being verified by tests. Effects of plate thickness on elastic buckling stress was studied using finite strip method (FSM) and to find the potential buckling failure mode at a given length. Tested ultimate strengths were compared with those predicted by the current American, European and Chinese specifications on aluminum alloy structures and the Direct Strength Method (DSM) on thin-walled structures. Following reliability analysis, the design strength predicted by current design specifications were found to be generally conservative, whereas DSM offered more accurate results. [ABSTRACT FROM AUTHOR]

High performance cementitious materials have made possible the construction of slender thin cementitious shells. For their design, the most relevant recommendations are those provided by the International Association of Spatial Structures (IASS), which, however, are inconsistent with the modern European design framework. In the case of steel shells, Eurocode 3 provides a simplified design approach based on the well-known buckling capacity curves. The aim of this paper is the determination of the capacity curve of a radially compressed spherical cementitious shell, for different fabrication quality classes and the determination of the four buckling parameters that describe the curve. [ABSTRACT FROM AUTHOR]

• Web compression buckling of wide-flange members were investigated with load width as the primary variable. • Specimens subjected to wider patch load demonstrated increase in the buckling strength. • Existing code equations significantly underpredict the strength of the specimens. • Using column buckling provisions for wide load widths provided a reasonable approach. • Tests confirmed that sustained load effects on web compression buckling were insignificant. A comprehensive study on web-compression buckling strength of wide-flange steel members subjected to concentric transverse loads spread over lengths longer than member section depth is presented in this paper. Calculation methodologies previously developed for web-compression-buckling strength of wide-flange steel members were established for use in beam-to-column moment connections, where the load width is relatively very narrow compared to the depth of the section, therefore does not include load width as a parameter in strength equations. More recently developed calculation procedures that account for load widths are typically limited to member section depth and are merely based on numerical models, and lack experimental evidence that validates these models. This study presents experimental research on steel wide-flange members subjected to transverse compression loading by having the load length as the primary variable. Experiments were conducted on specimens with measured imperfection levels and provided results on the buckling strength, displacement, and strain variation of the web portion during testing. The experimental program also investigated the potential of creep under sustained loading on web compression buckling strength of wide flange members at load levels near buckling strength. Benchmark numerical models using the finite element method were developed using the test results to obtain insights into the observed behavior and were employed in conducting numerical parametric studies to investigate the sensitivity of results due to load width and the angle of the applied load for various cross sections. The results obtained from the experimental and numerical studies were compared with the calculation methods provided in the North American and European design codes to evaluate their accuracy. The parametric study results were also used to develop an analytical calculation procedure for estimating the web-compression-buckling strength of steel wide-flange shapes subjected to vertical and inclined loading. [ABSTRACT FROM AUTHOR]

Built-up radially battened columns (RBCs), comprising several identical circular steel tubes interconnected by multiple radial-shaped battens, represent an innovative column design that combines aesthetic appeal with exceptional load-bearing capacity. This makes them well-suited for architectural applications in large public buildings such as stations and airports. The axial compressive strength design methods for the built-up RBC have been extensively explored in the authors' prior studies. However, in real-world engineering applications, built-up RBCs may experience simultaneous axial compression and varying directional bending moments, particularly when considering potential eccentric compression or wind and earthquake loads in public buildings. Currently, strength design methods for this loading condition are still lacking. To address this deficiency, this paper primarily delves into the failure mechanism and strength design methods for built-up RBCs experiencing combined axial compression and arbitrary directional bending moments. Initially, the sectional strength of the built-up RBC is investigated by using a shell finite element model (FEM) for the built-up RBC. It is revealed that the compression-bending sectional strength of the built-up RBC exhibits significant differences with varying bending directions and tube numbers. Moreover, in some bending directions, the M - N sectional strength curve of the built-up RBC exhibits convexity. By integrating theoretically derived equations grounded in the principles of materials mechanics with FEM numerical calculations, concise and practical design equations are proposed for accurately predicting the sectional strength of the built-up RBC under combined axial compression and arbitrary directional bending moments. Subsequently, The buckling strength of the built-up RBC is studied using the FEM, considering initial geometrical imperfections consistent with first-order flexural buckling and accounting for geometric nonlinearity. It is noted that the bending direction of the built-up RBC may deviate during loading. Besides, the M - N buckling strength curve of the built-up RBC is not as convex as its M - N sectional strength curve. Based on calculations from numerous examples, practical design equations for predicting the buckling strength for the built-up RBC under axial compression and any directional bending moments are introduced. The key findings of this paper contribute to the compression-bending strength design of RBCs, enriching RBC design theory and promoting the widespread application of built-up RBCs in actual engineering projects. [Display omitted] • The M - N strength of RBCs varies with different bending directions and tube numbers. • The M - N sectional strength curve of the built-up RBC is convex. • The built-up RBC's bending direction may deviate during loading. • The M - N buckling strength curve of RBCs is less convex compared to its M - N sectional strength. • The M - N strength of RBCs can be predicted by a quadratic function. [ABSTRACT FROM AUTHOR]

The local buckling behaviour and ultimate cross-sectional strength of tubular elliptical profiles in compression is examined in this study through numerical modelling. The numerical models were first validated against previous experimental data with good agreement observed, enabling an extensive parametric study to be performed. A total of 270 elliptical sections were simulated in order to examine the influence of cross-section aspect ratio, geometric imperfections and local slendernesses. The obtained ultimate capacities, load–deformation responses and failure modes are discussed. It was found that for lower cross-section aspect ratios the behaviour of the elliptical hollow sections (EHS) was similar to that of cylindrical shells across a number of metrics; however, as the aspect ratio increased, more plate-like stable postbuckling behaviour was observed. Imperfection sensitivity was found to decrease with increasing slenderness and aspect ratio. The influence of the shape of the initial imperfection on the strengths of the EHS columns was also assessed and was found to be generally limited. Finally, a design method has been proposed for Class 4 EHS members that reflects the reduction in capacity due to local buckling with increasing slenderness, but also recognises the improved postbuckling stability with increasing aspect ratio; the proposals were shown to provide safe and accurate predictions for the strengths of the EHS columns with nondimensional local slendernesses up to 2.5 and aspect ratios from 1.1 to 5.0. [ABSTRACT FROM AUTHOR]

Highlights • A stiffener on the compression diagonal increases the postbuckling shear strength. • The most important role of a stiffener is providing lateral restraint. • At ambient temperature, the axial force in the stiffener is negligibly small. • At 700 °C, the axial force in the stiffener is up to 35% of the shear strength. Abstract There are a growing number of bridge fire events and the National Fire Protection Association (NFPA) requires that critical structural elements of the bridge be protected from elevated temperatures due to fire. However, no guidance is given on how to protect these critical elements, nor how to identify them. Further, slender steel web plates have been shown to be vulnerable to shear buckling in fire events and recent research that indicates that the load path of shear forces in thin web plates is not well understood. The overall objective of this paper is to examine the effectiveness of stiffeners for enhancing the shear capacity of slender plates at ambient and elevated temperatures. Specifically, evaluations are made regarding the effectiveness of stiffeners for increasing the shear buckling capacity through various stiffener orientations, providing lateral restraint, and providing a load path for shear forces. In particular, the elastic shear buckling load, V cr , and the ultimate shear postbuckling load, V u , of the steel plate are examined. Finite element analyses, which have been validated with experimental data, are used as a basis for the study. The temperatures studied range from ambient to 1100 °C. This study provides some important insights on the behavior of plates under shear loads. For example, results indicate that the stiffener's role is not that of a load path for the shear forces, but one of lateral restraint, regardless of its geometric orientation. Further, it is shown that for lower temperatures a stiffener oriented along the compression diagonal (opposite to a tension field) provides the most improvement in postbuckling strength. [ABSTRACT FROM AUTHOR]

An experimental investigation into the structural performance of compressed high strength steel (HSS) square and rectangular hollow sections is described in this paper. Both hot-rolled and cold-formed HSS sections were examined. In total six S460NH and five S690QH hot-rolled section sizes and three S500MC, two S700MC and four S960QC cold-formed section sizes were tested. The experimental programme comprised tensile coupon tests on flat and corner material, measurements of geometric imperfections, full cross-section tensile tests and stub column tests. The results of the experiments presented in this paper have been combined with other available test data on high strength steel sections, and used to assess the existing design guidelines for high strength steels given in Eurocode 3. The focus has been on the material ductility requirements, the Class 3 slenderness limit for internal elements in compression and the effective width formula for Class 4 internal elements in compression.Reliability assessments of the Class 3 slenderness limit (both the current value of 42 and a proposed value of 38) and the effective width formula for Class 4 internal elements in compression were carried out. The analysis indicated that, based on the assembled test data considered in this study, and the assumptions made regarding the statistical distributions of material and geometric properties, a partial safety factor greater than unity is required for HSS. Similar findings have also recently been presented for ordinary strength steels. [ABSTRACT FROM AUTHOR]

This paper examines the behaviour of 29 square concrete-filled steel tubes (CFST) under concentric axial compression. The cross-section of the hot-rolled steel tubes ranges from 60 × 60 × 3.0 mm to 150 × 150 × 4.5 mm, and are grouped in three series (Series 1, 2 and 3). For the sections tested, the slenderness ratio (L/b) for Series 1, 2 and 3 ranges from 6.67 to 24.61, 27.00–45.00 and 18.00–27.0, respectively; and the depth-to-wall thickness (b/t) ranges from 33.87 to 42.86, 13.33–33.33 and 22.22–50.00, respectively. The slenderness ratio provides a range of columns, from relatively short to slender composite columns. Particular attention is paid to the existence of circumferential strain in the square composite columns. The compressive resistance of the composite columns are compared with the design strengths predicted by the South African standard (SANS 10162-1), as well as the European design standard (EN 1994-1-1). SANS10162-1 is based on the Canadian steel code (CAN/CSA-S160-01). A two-stage equation is proposed to model the results of short columns (Eq. (4)) and intermediate to slender columns (Eq. (5)). [ABSTRACT FROM AUTHOR]

The Ayrton-Perry (or Perry-Robertson) formula based stability resistance model (APF) is very popular in steel structural design standards. Although the original version of the model is more than 100 years old, it is still frequently used and continuously researched due to its simplicity and adaptability. The original and most widely accepted version of the APF is valid only for the flexural buckling of compression members yielding the basic formulation of the column buckling curves of several structural design codes. Recently there were more successful attempts for the extension of the APF type resistance model for other buckling modes such as torsional buckling or lateral-torsional buckling. The paper continues this research by deriving a complete closed-form universal APF type solution for steel beam-column stability problems. Rigorous mathematical solution is given for the so-called “fundamental case” which is defined by a simply supported prismatic beam-column with arbitrary cross-section subjected to uniform compression and biaxial bending. The exact interpretation and the universal form of the member slenderness, imperfection and reduction factors are presented for all possible buckling cases. The results of the paper can widen significantly the field of applicability of APF based design methods providing a theoretically consistent physical model for the beam-column stability problems. [ABSTRACT FROM AUTHOR]

It is widely accepted that for many buckling problems of plates and shells in the plastic range the flow theory of plasticity leads to a significant overestimation of the buckling stress while the deformation theory provides much more accurate predictions and is therefore generally recommended for use in practical applications. The present work aims to contribute to further understanding of the seeming differences between these two theories with particular regards to circular cylindrical shells subjected to axial compression. A clearer understanding of the two theories is established using accurate numerical examples and comparisons with some widely cited accurate physical test results. It is found that, contrary to common perception, by using a geometrically nonlinear finite element formulation with carefully determined and validated constitutive laws very good agreement between numerical and test results can be obtained in the case of the physically more sound flow theory of plasticity. The reasons underlying the apparent buckling paradox found in the literature regarding the application of deformation and flow theories and the different conclusions reached in this work are investigated and discussed in detail. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microcapsule cracking or microcapsule/matrix interface decohesion is considered. • Microcapsule size effect is discussed. • Buckling and post-buckling behavior are investigated. This paper shows an analytical approach to investigate buckling behavior of a carbon fiber reinforced resin (CFRR) cylindrical shell covered with a damaged porous microcapsule coating subjected to axial compressed loads under hygrothermal environment. The formulas are in view of the Donnell's shell theory considering the von Kármán geometric nonlinearity. The material parameters of microcapsule coating are predicted with the self-consistent model and Mori-Tanaka model. By utilizing Galerkin approach, the buckling behavior for simple-support damaged double-layered cylindrical shell are determined. The influence of temperature and moisture, interface debonding damages, material properties, geometry parameters of microcapsules and porosity upon the buckling behavior of the double-layered cylindrical shell are investigated. Results show moisture and geometry size of microcapsules are propitious to the critical buckling and post-buckling compressive load. In addition, the micro-structure damage greatly affects temperature and moisture. The geometric parameters of microcapsules significantly affect the buckling and post-buckling behavior of double-layered cylindrical shell. [ABSTRACT FROM AUTHOR]

• Axial compression tests were conducted on hat-stiffened composite panels and simulated by FE. • Local buckling was observed by strain bifurcation phenomena and full-field deformation. • Training and testing datasets of ANN are constructed by FE model group. • Two ANNs are selected to predict the buckling load and buckling mode respectively. • Performance and generalization ability of ANNs are verified. The composite hat-stiffened panel is a typical structure that embodies the concepts of high strength and light weight. It has many design parameters and multiple buckling failure modes. The prediction accuracy of the traditional simplified method of engineering calculation is not high. Although the finite element method can achieve high-precision prediction, it is time-consuming for engineering designers. In this study, two kinds of artificial neural networks are established to predict the compression buckling behavior of composite hat-stiffened panels. First, the buckling behavior of the composite hat-stiffened panel is studied using the combination of finite element simulation and experimental verification. Then, considering the variations of four mechanical properties of the stiffened panels, the finite element model group is used to generate the training dataset and test dataset of the neural network in batches. Two kinds of neural networks are comparatively selected to predict the buckling load and buckling failure mode. Based on the testing dataset and the new dataset, the performance and generalization ability of the artificial neural networks are examined. The results show that the trained artificial neural networks can accurately and efficiently predict the buckling behavior of composite hat-stiffened panels under axial compression. [ABSTRACT FROM AUTHOR]

• Overall buckling of Q420-Q960 steel welded columns was experimentally studied. • The higher the steel strength, the more conservative the current codes is. • The applicable buckling curves of the HSS H-section columns are presented. • The modification factor for overall buckling of Q420–Q960 steel columns is given. High-strength steel (HSS) has a broad application prospect in engineering structures owing to its high strength-to-density ratio. However, reliable research on the buckling behaviour of welded axial compression members according to current Chinese, European, and American specifications is lacking. In this study, the overall buckling of 12 welded H-section axial compression specimens made of Q420, Q550, Q690, and Q960 steels was investigated experimentally, and a parametric analysis was conducted via finite element simulation. The initial out-of-straightness and material properties of the specimens were measured. The imperfections were the same as those of the first-order buckling mode, and the strength and ductility of the steel met the specification requirements. The failure modes of the specimens were typical overall buckling about the minor axis. Through analysis of the axial compression deformation and the strain of the buckling section, it was found that as the strength of the steel increased, the axial ductility of the component decreased, and the size of the section where the strain entered the plasticity during buckling failure decreased. A comparison between the experimental and the current specification buckling factor revealed that the latter underestimated the overall buckling bearing capacity of HSS-welded H-section axial compression members; furthermore, the difference in the overall buckling factor increased as the steel strength increased. The finite element simulation of the specimens, which considers the measured initial out-of-straightness and material properties, verified the accuracy of the finite element model (FEM) and welding residual stress model. The FEM was used to analyse the steel grade parameters and slenderness ratio, which were compared with the current specification. The applicable buckling curves of the HSS-welded H-section axial compression members are presented. Finally, the modification factor function for calculating the overall buckling capacity of Q420–Q960 steel members using the recommended buckling curve in the specification is also given. [ABSTRACT FROM AUTHOR]

The cyclic behavior and design of a triple-truss-confined buckling-restrained brace (TTC-BRB) is investigated, especially when it is used in mega-frame high-rise buildings and long-span spatial structures as a long-span BRB. The TTC-BRB is formed by introducing an additional structural system of rigid truss frames to the outside of a common double-tube BRB in order to achieve a higher external restraining flexural stiffness as well as a high overall load-carrying capacity. An analytical method is utilized to derive a formula of the elastic buckling load of a pin-ended TTC-BRB, which is verified and modified through FE analyses. The effect of restraining ratio of the TTC-BRB on its cyclic behavior and failure mechanism is explored. The findings indicate that the TTC-BRB may have two different failure modes, namely in-plane and out-of-plane instability failures of the chord subjected to compression at the mid-span of the TTC-BRB. In addition, the load-carrying capacity of the TTC-BRB under cyclic loading is found to be proportional to the restraining ratio, and there exists a lower limit of the restraining ratio which ensures the core could reach its full cross-sectional yield load before overall instability failure of the TTC-BRB. Furthermore, in order for the TTC-BRB to be an energy dissipation type of BRBs, the lower limit requirement of the restraining ratio should be satisfied and its end constructional and strength design should be carefully carried out to avoid its premature failure. The investigation of the elastic buckling load and cyclic behavior as well as failure mechanism of the TTC-BRB provides fundamentals to the further development of a comprehensive design method of the TTC-BRB. [ABSTRACT FROM AUTHOR]

• The restrained non-uniform columns in the fire. • Temperature-dependent material properties. • The initial imperfection and geometric nonlinearity. • The convective–radiative condition. • Effects of fire source on the tapered column. This paper investigates the buckling and post-buckling behavior of restrained non-uniform columns in fire where the temperature surrounding the column varies along the longitudinal direction. The material properties of the column are considered to be temperature-dependent (TD). First, according to the convective–radiative condition on the surfaces of the column, a dimensionally reduced nonlinear heat transfer equation is proposed and is solved by the differential quadrature (DQ) method. Then, considering the geometric imperfection, the nonlinear governing equation is derived based on the von-Kármán theory when the column is subjected to an axial compression load at the column end. An improved DQ method is applied to the buckling and post-buckling analysis of the non-uniform column under the fire. Considering the yield strength of material at elevated temperature, the ultimate load of the column is obtained. A tapered H-section steel column surrounded by localized fire is taken as an example. The present results are verified by comparing with those in the literature and those obtained from the finite element (FE) method. The parameter analysis reveals the temperature distribution, the buckling and post-buckling behavior of the tapered column in the localized fire. [ABSTRACT FROM AUTHOR]

Double-skin composite walls (DSCWs) stiffened with perforated ribs (perfobond leiste in German, abbreviated as PBL) has gained popularity in large-scale structures due to their industrial construction potential. This study aims to explore the axial compressive behavior of PBL-stiffened DSCWs, considering the post-local buckling effect of the faceplates. Six PBL-stiffened DSCWs underwent an experimental investigation under axial compressive loads to evaluate their failure mode, load-axial behavior, ductility, and local buckling behavior. The study also examined the effect of the spacing of transverse and longitudinal PBLs and the introduction of headed studs on the axial compressive behavior of DSCWs. Results reveal that decreasing the spacing of transverse PBLs enhances the confining effect on the infilled concrete, increasing the axial compressive resistance of DSCWs. The introduction of studs delays local buckling and results in strain-hardening of the faceplates, improving the axial compressive resistance of DSCWs. However, increasing the longitudinal PBL spacing weakens the out-of-plane restraint of the faceplates, decreasing both local buckling load and compressive resistance. Assuming the longitudinal PBLs as out-of-plane continuous elastic supports, the elastic critical local buckling coefficient of PBL-stiffened plates with unilateral restraints was derived using the Ritz method. Based on this, the critical relative stiffness of the PBL can be determined, which helps in identifying the local buckling mode of the PBL-stiffened plates. To estimate the post-local buckling behavior of PBL-stiffened plates with unilateral restraints, an effective area method was proposed. Finally, a formula was proposed to predict the axial compressive resistance of PBL-stiffened DSCWs, considering the post-buckling effect. A suggested design procedure for PBL-stiffened DSCWs was also provided. • Axial compressive behavior considering local buckling of PBL-stiffened DSCWs is experimentally and theoretically studied. • Buckling coefficient of PBL-stiffened plates with unilateral restraints was derived. • Effective area method was developed to estimate post-buckling strength of PBL-stiffened plates. • Proposed formula accurately predicts axial compressive resistance of PBL-stiffened DSCWs. [ABSTRACT FROM AUTHOR]

• The least weight design of steel BRBs against global buckling is pinpointed. • Global buckling prevention criterion of BRB is expressed as stiffness and strength requirements. • Stiffness–strength relationship curve of BRB restraining member is derived. • Feasible designs of restraining member may be overdesigned in weight significantly. This paper is concerned with the optimal (or least weight) design of steel buckling-restrained braces against global buckling. First, the global buckling prevention criterion of steel buckling-restrained braces (BRB) is reconstituted to take on a symmetric expression, i.e., (P cr / P u −1) M r /(v 0 P u) −1] ≥ 1, so as to provide clarity on the equal importance of the stiffness and strength requirements of the restraining member, where P cr is the elastic buckling load, M r the yield moment resistance, and v 0 the initial imperfection of the restraining member whereas P u is the ultimate compressive load of the core under cyclic axial loads. It is shown herein that the optimal design of the restraining member satisfies (1) the boundary of the global buckling prevention criterion, and (2) the relationship between the stiffness term P cr / P u and the strength term M r /(v 0 P u) in view of the maximum feasible cross-sectional height-to-thickness ratio as specified by the adopted design code recommendation. The satisfaction of these two conditions furnishes a unique optimal design of the restraining member. The optimal design can be expressed as an explicit equation in terms of the second moment of area of the restraining member. A design example is presented to illustrate the material (or weight) efficiency of all-steel BRB designs based on the proposed design equation. [ABSTRACT FROM AUTHOR]

Current design rules for the member capacities of cold-formed steel columns are based on the same non-dimensional strength curve for both fixed and pinned-ended columns at ambient temperature. This research has investigated the accuracy of using current ambient temperature design rules in Australia/New Zealand (AS/NZS 4600), American (AISI S100) and European (Eurocode 3 Part 1.3) standards in determining the flexural–torsional buckling capacities of cold-formed steel columns at uniform elevated temperatures using appropriately reduced mechanical properties. It was found that these design rules accurately predicted the member capacities of pin ended lipped channel columns undergoing flexural torsional buckling at elevated temperatures. However, for fixed ended columns with warping fixity undergoing flexural–torsional buckling, the current design rules significantly underestimated the column capacities as they disregard the beneficial effect of warping fixity. This paper has therefore recommended the use of improved design rules developed for ambient temperature conditions to predict the axial compression capacities of fixed ended columns subject to flexural–torsional buckling at elevated temperatures within AS/NZS 4600 and AISI S100 design provisions. The accuracy of the proposed fire design rules was verified using finite element analysis and test results of cold-formed lipped channel columns at elevated temperatures except for low strength steel columns with intermediate slenderness whose behaviour was influenced by the increased nonlinearity in the stress–strain curves at elevated temperatures. Further research is required to include these effects within AS/NZS 4600 and AISI S100 design rules. However, Eurocode 3 Part 1.3 design rules can be used for this purpose by using suitable buckling curves as recommended in this paper. [ABSTRACT FROM AUTHOR]

• Cyclic tests were conducted on nine full-scale BRB specimens. • Steel cores involved three grades of low yield point steels with the nominal yield strengths of 100–225 MPa. • The failure modes, hysteresis behaviour, and mechanical indexes were analysed. • The cyclic hardening and tension–compression asymmetry were evaluated. Low yield point steel is an advanced high-performance material that was deemed to provide reliable cyclic properties based on previous research. This paper presents experimental investigations into low yield point steel buckling-restrained braces (BRBs). Cyclic tests were conducted on nine full-scale specimens made of three grades of low yield point steels in China, including LY100, LY160, and LY225, with the nominal yield strengths of 100 MPa, 160 MPa, and 225 MPa, respectively. The failure modes, hysteresis behaviour, and mechanical indexes were analysed. Results showed that low yield point steel BRBs featured cyclic hardening behaviour with the strain hardening adjustment factor ω of 1.35–2.94, and the LY100 BRB exhibited more significant cyclic hardening (ω = 2.50–2.94) than the other two. Moreover, specimens showed tension–compression asymmetry behaviour with the compression strength adjustment factor β of 1.07–1.51, proving that the maximum compressive loads exceeded 7–51 % of tensile ones. The low yield point steel BRBs could produce stable cyclic behaviour and energy dissipation with the cumulative ductility factor of 491.16–3279.23 upon the acceptance stipulated in American and Chinese codes. Based on the test results, the performance of low yield point steel BRBs was evaluated, and suggestions were proposed for design purposes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Interactive buckling tests on eight welded stainless steel box section columns. [•] Numerical modelling and systematic parametric studies were carried out. [•] Assessment of existing design methods by the generated test and numerical results. [•] Modifications to the current EN 1993-1-4 design curves and the DSM are proposed. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present a proposal for the design of steel structures sensitive to buckling due to compression in order to fill in the gaps in the current Standard EN 1993-1-1 guidelines for obtaining the magnitude of the geometric equivalent imperfection. The proposal generalizes the approach provided in Clause 5.3.2(11) of EN 1993-1-1 (EC-3) for cases in which a torsional or flexural–torsional buckling mode may occur. The extension of the procedure also allows designers to obtain the magnitude and shape of the imperfection as well as the worst direction of the imperfection due to the external loads applied. It also identifies the cases in which it is necessary to consider the shape of the imperfection given by higher buckling modes. [ABSTRACT FROM AUTHOR]

Pre-compression loads are conducted in BRBs if the installation of frames and BRBs are performed simultaneously. In this paper, the load-carrying and energy-dissipating behavior of BRBs under pre-compression are investigated by subassemblage tests and additional finite element (FE) analyses. A total of five specimens were tested, in which two specimens were tested by cyclic pure compression loads and three specimens were tested by hysteresis loads; four of them maintained stable load-carrying behavior during loading process. The load-carrying and energy-dissipating behavior of the specimens were satisfactorily simulated using a refined FE model with a combined isotropic and kinematic hardening rule of the core material, and the compression strength adjustment factor and the stress enhancement coefficient were well predicted by the FE analytical results with a relative error less than 3.0%. The FE analytical results of BRBs with different pre-compression strains are presented, indicating that the pre-compression in a BRB would aggravate the stress enhancement of the core material in both tension and compression, yet it would hardly influence the value of the compression strength adjustment factor. [ABSTRACT FROM AUTHOR]

• A new type of DSC slab with stiffening ribs and tie plates (SDSC slab) is proposed. • The buckling stress, bearing capacity and ductility of the SDSC slabs are enhanced. • Formulas for the bending capacity and service behavior of the SDSC slab are proposed. • A modified theoretical model is established for predicting the buckling stress. • The design process of the steel plate in SDSC slabs is illustrated in detail by two examples. Double steel plate concrete (DSC) composite slabs consist of two outside steel plates and a concrete core that are connected by welded studs or cross tie bars. If weak restraints are designed for the interface between the steel plates and concrete core, the surface steel plate of the DSC slabs may suffer local buckling when subjected to a compressive load. In this paper, a new type of DSC slab with stiffening ribs and tie plates (SDSC slab) is proposed to improve the stability of surface steel plates. Two groups of bending tests are carried out to investigate the buckling behavior of both SDSC slabs and ordinary DSC slabs (ODSC slabs). Furthermore, the influence of the B/t ratio, that is, the ratio between the stud spacing and the steel plate thickness, is intensively analyzed. The experimental results reveal that compared with that of the ODSC slabs, the buckling behavior of steel plates in the SDSC slabs is delayed or even prevented owing to the additional stiffening ribs and tie plates. Thus, the bending capacity and ductility of SDSC slabs are both enhanced. According to the test results, calculation formulas are derived to predict the bending capacity of the ODSC slabs and SDSC slabs, respectively. In addition, design models for buckling analysis are proposed to determine the buckling stress and critical B/t ratio for different types of DSC slabs. The accuracy of the theoretical methods is validated against the test data, and two examples are provided in detail to illustrate the design process of the steel plate in SDSC slabs. [ABSTRACT FROM AUTHOR]

• Effects of translational and rotational constraints on the linear buckling response. • Groups of boundary conditions based on identical linear buckling load and mode shape. • Transitions between various mode shapes by changing relevant stiffness of springs. • Coupling effect of radial and tangential constraints on the linear buckling response. Cylindrical shells under compressive loading are highly sensitive to boundary conditions. Considering that these structures are connected by surrounding structural components with finite stiffness, an accurate evaluation of the effects of their boundary stiffness is crucial in their design. As such, this work investigates the effect of elastic boundary conditions on the linear buckling behaviour of cylindrical shells under compressive loading. To achieve this goal, a virtual testing investigation on the effect of translational and rotational constraints to the linear buckling response of a quasi-isotropic cylinder subjected to axial compression is performed. Subsequently, the effect of many kinds of constraints on linear buckling behaviour is discussed and interesting insights regarding a significant coupling effect between the radial and tangential translational constraints are given. Results obtained from virtual testing show that seven recurrent buckling mode shapes occur with seven corresponding similar linear buckling loads. Therefore, based on these similarities, seven groups of classical boundary conditions are introduced to classify all possible linear buckling behaviours exhibited by the cylinder under consideration. Finally, these findings can support the development of theoretical models for cascade, or flange, designs of multiple connecting cylinders. [ABSTRACT FROM AUTHOR]

Buckling and postbuckling behavior of shear deformable anisotropic laminated composite beams with initial imperfection subjected to axial compression is presented. The material in each layer of beams is assumed to be linearly elastic, anisotropic and fiber-reinforced. The governing equations are based on the higher order shear deformation beam theory with a von Kármán-type of kinematic nonlinearity. Composite beams with the fixed–fixed, fixed–hinged, and hinged–hinged boundary conditions are considered. A generic imperfection function for one-dimensional composite beams is adopted to model various possible initial geometric (e.g., sine, local, and global type) imperfections. The nonlinear prebuckling deformation and initial geometric imperfection of the beam are both taken into account. A numerical solution of nonlinear partial–integral differential form in terms of the transverse deflection is employed to determine the buckling load and postbuckling equilibrium path of composite beams. The results obtained by combining the Newton’s iterative method with the Galerkin’s method are theoretically exact from the transverse and longitudinal displacements for anisotropic laminated beams under the axial compressive loads using the secondary parameter conversion technique, and they are validated by comparing with those available in the literature. The numerical illustrations are presented for the postbuckling response of laminated beams with different types of boundary conditions, ply arrangements (layups), geometric and physical properties. The results reveal that the geometric and physical properties and boundary conditions have a significant effect on postbuckling behavior of anisotropic laminated composite beams. [ABSTRACT FROM AUTHOR]

• The flexural buckling behaviour of concrete-filled double skin aluminium alloy columns is studied. • 8 columns are tested under axial compressive load. • A numerical parametric study including 81 columns is conducted. • A design methodology is proposed on the basis of Eurocode 4. • A design buckling curve is suggested. Concrete-filled double skin steel tubular columns consisting of two hollow steel tubes and concrete infill between their interspace, have become popular in modern construction owing to their high ultimate load, less self-weight and good ductility. The weight of these columns can be reduced further by using lightweight aluminium alloy hollow tubes instead of steel ones. This paper experimentally and numerically studied the flexural buckling behaviour of the concrete-filled double skin aluminium tubular (CFDSAT) columns subjected to axial compression. A total of 8 CFDSAT columns were tested using a pin-ended set-up. The test results are presented in terms of failure modes, ultimate load and load versus mid-height lateral displacement curves. Non-linear finite element (FE) models of the specimens were developed and their accuracy was evaluated by comparing the FE and test results. A numerical parametric investigation was conducted to study the influence of the hollow ratio, the member slenderness, the cross-sectional slenderness of the hollow tubes and the concrete strength on the structural behaviour of CFDSAT columns. The parametric study results revealed that the cross-sectional dimensions of outer section, the member slenderness and the concrete compressive strength have a significant effect on the flexural buckling response of the columns, while the influence of the cross-sectional dimensions of inner section is less prominent. In the absence of design standards for CFDSAT members, a design methodology is proposed with a design buckling curve to predict the ultimate load of CFDSAT columns based on the Eurocode 4 framework. Moreover, a revised concrete correction factor is suggested to determine the effective flexural rigidity of CFDSAT columns according to Eurocode 4. [ABSTRACT FROM AUTHOR]

• Column member of Guadua subjected to axial compression was experimentally conducted. • Buckling reduction factor is ultimate compressive load to critical buckling load ratio. • Buckling reduction factor can be fitted by linear or non-linear regression. An experimental study was conducted to evaluate the buckling behavior of 190 Guadua bamboo culms of various lengths. These were subjected to an axial compressive load until failure. The geometrical and physical properties of each culm were measured, as well as its compressive strength and load carrying capacity. The buckling reduction factor (ψ) – which is the ratio of the ultimate buckling load (F cr) to the ultimate compressive load (F u) or the ratio of the ultimate buckling stress (σ cr) to the ultimate compressive stress (σ u) – was determined for each specimen. Several formulas were investigated by means of linear and non-linear regression in order to find the best fit for ψ. Separate models for intermediate and long members, as well as models combining the whole range of the slenderness ratios (λ) were proposed. Rankine-Gordon's and Ylinen's buckling formulas proved to be suitable to determine the buckling reduction factor for the whole range of slenderness ratios for the Guadua bamboo specimens studied, whilst Euler's formula is more appropriate for longer columns. For the intermediate columns, the Newlin-Gahagan's buckling formula was initially evaluated; however it was deemed unsuitable due to its unsatisfactory statistical performance. As a replacement, the Johnson buckling formula was derived. Ylinen's buckling formula appears to provide the best fit and it is therefore recommended for Guadua column design. A maximum slenderness ratio was calculated at the ψ = 0.057, which resulted in a slenderness ratios of 139, 214, and 161, when calculated by Rankine-Gordon's, Ylinen's, and Euler's buckling formula, respectively. Those ratios are approximately equivalent to 43, 67, and 50 length to diameter ratios (L / D). Since Ylinen's equation is the best fit buckling formula among others, it is recommended that the length does not exceed 67 times the diameter (L / D < 67). When the buckling reduction factor is used in combination with characteristic value, the load carrying capacity of a column of any length can be safely used in design of Guadua bamboo culms. [ABSTRACT FROM AUTHOR]

Abstract: Glass elements are widely used in modern buildings as structural columns, beams, stiffeners. Nevertheless, due to accidental eccentricities, additional loads, boundary conditions or imperfection factors, glass beam–columns are frequently subjected to in-plane compressive actions combined with bending moments. Because of this reason, the paper focuses on the buckling resistance of glass elements subjected to eccentric compressive loads. Based on large experimental numerical results available in literature for monolithic and laminated glass columns or beams in out-of plane bending, verification criteria for these simple loading conditions are firstly recalled from previous contributions. Subsequently, numerical static incremental simulations are performed with a finite-element model able to predict the buckling strength of imperfect glass elements eccentrically compressed. In it, also the effects of various geometrical imperfection shapes are deeply investigated. Finally, an analytical interaction curve is proposed for a conservative and rational buckling verification of monolithic and laminated structural elements. [Copyright &y& Elsevier]

• Optimized stiffened plate is 88.50% more resistant to buckling than reference plate. • Constructal Design is effective to improve the stiffened plate's mechanical behavior. • The best geometry has more plate regions submitted to material yield stress. • The Constructal principle of optimal distribution of imperfections has been verified. Several engineering structures used in civil, aeronautical and, mainly, naval and offshore industries consist of steel stiffened panels formed by beams welded into thin plates. These beams are called stiffeners, being arranged longitudinally and/or transversely aiming to increase the mechanical strength of the plate. So, it is desirable to obtain an optimal geometric configuration for these structures which maximizes its ultimate buckling stress. In this context, it has been used the Constructal Design Method associated with the Exhaustive Search technique and the Finite Element Method (by ANSYS software) in a geometric optimization study of plates with stiffeners subjected to elasto-plastic buckling. Initially, it was adopted a simply supported thin plate without stiffeners (called reference plate), using its ultimate buckling stress as a reference value for the study. After that, part of its volume has been transformed into stiffeners, which were incorporated into the plate. For this, the volume fraction (ϕ) parameter, which represents the ratio of the volume of stiffeners (V s) and the total volume of the structural element plate/stiffeners (V T), has been adopted, without varying the final volume of the plate. Moreover, the number of longitudinal (N ls) and transverse (N ts) stiffeners, as well as the ratio between the height of the stiffener and its thickness (h s /t s), were considered as degrees of freedom. The study considered two total steel volume values V T 1 = 0.040 m3 and V T 2 = 0.028 m3. The results indicated that the variation of the geometrical configuration significantly affects the mechanical behavior of stiffened panels under buckling. Therefore, it was possible to determine the optimum geometry that leads to a maximized ultimate buckling stress, near the yield strength of the material. The stiffened plates with volume V T 1 did not present relevant improvements if compared with the reference plate, since the optimal geometry achieved an improvement of 7.38% concerning the ultimate buckling stress of the reference plate. On the other hand, the study of the plates with volume V T 2 showed significant improvements in the value of the ultimate buckling stress, so that the optimized geometric configuration among all analyzed geometries reached an improvement of 88.50% when compared with the ultimate buckling stress of the reference plate. [ABSTRACT FROM AUTHOR]

• Six T-shaped double skin composite walls are tested. • Seismic behavior of T-shaped double skin composite wall is evaluated. • Impact of strength of concrete is explored. • Failure mechanism, load-displacement responses, energy dissipation capacity, etc. are discussed in detail. • Buckling behavior of steel faceplates is investigated. This study investigates the seismic performance of T-shaped double-skin composite walls (DSCWs), which are comprised of double-skin composite flange and web walls and concrete filled steel tubular (CFST) boundary elements, through experimental tests. Six T-shaped DSCW specimens, which are categorized into three groups, according to flange width and type of mechanical connectors (shear studs/tie bars), are tested under combined axial compressive loads and lateral cyclic loads. The DSCWs fail in a ductile flexural mode with similar damage patterns, characterized by buckling of steel tubes and faceplates, concrete crushing, and fracture of steel tubes at the wall base, and exhibit asymmetric hysteresis behaviors, with higher stiffness and strength but lower deformation capacities when the flange walls are under tension. Special focus should be placed on the design of CFST boundary element connected to the web wall, whose compressive failure triggers the loss of load carrying capacity of the specimens. The comparisons between the behaviors of two specimens in each group, which are infilled with high strength (C70) and normal strength concrete (C30) respectively, suggest that employment of high strength concrete improves the seismic behavior of T-shaped DSCW significantly regardless of the flange wall width when shear studs are used. Tie bars may impair the seismic behaviors of DSCWs by inducing premature local buckling of perforated steel faceplates. Numerical studies are conducted using detailed finite element models to investigate the buckling behaviors of steel faceplates which are connected to infilled concrete by tie bars and shear studs. The simulation results reveal that the former buckles earlier than the latter due to smaller critical stress. The slenderness ratio limits to prevent local buckling prior to yielding of steel faceplates are also suggested when these two types of mechanical connectors are used. [ABSTRACT FROM AUTHOR]

An assessment method is developed for the panel reliability of ship-shaped Floating, Production, Storage and Offloading units (FPSO). Not only axial compressive loads but also internal and external lateral pressures are taken into account in the reliability assessment. Beam-column buckling and flexural-torsional buckling are regarded as two primary failure modes of stiffened panels. Variability of corrosion wastage and material properties are accounted for in modelling the panel’s time-dependent ultimate strength. Uncertainty of axial compressive loads induced by hull girder bending is evaluated based on probabilistic characteristics of still-water bending moment (SWBM) and vertical wave-induced bending moment (VWBM). A case study is performed to demonstrate this method and the effects of the lateral pressure, the return period of the extreme value of VWBM, the environmental severity factor, and the corrosion wastage on the panel reliability are investigated. Sensitivity measures for random variables are also carried out. [ABSTRACT FROM AUTHOR]

A stress-strain model is proposed to define the relationship between axial compressive stress and strain for square steel tube stub columns, which have been widely used as predominant gravity-sustaining structural components in high-rise buildings and skyscrapers. The proposed model consists of two equations, defining the ascending branch and descending branch of the stress-strain curve, respectively, and has a significant advantage over previous models in that it can trace effects of both the residual stress induced during manufacturing process and the local buckling of steel plate on the compressive stress-strain behavior of square steel tube stub columns. Another feature of the proposed model is that it can be used to the stub columns made of very thin steel plates. In order to calibrate the new stress-strain model and verify its reliability and accuracy, sixty-eight hollow square steel tube stub columns under monotonic axial compression are collected. The previous tests cover a wide range of structural factors such as yield strength and width-to-thickness ratio of steel plates. In particular, the previous tests include stub columns made of steel plate with high yield strength of up to 835 MPa. Comparisons between the experimental results and the calculated ones indicate that the proposed model cannot only predict the local buckling strength and the corresponding strain very well, but also trace the compressive stress-strain behavior of square steel tube stub columns up to large strain with high accuracy. [ABSTRACT FROM AUTHOR]

Closed form expression for the buckling load of generally anisotropic laminated composite simply supported thin plates is derived. The Rayleigh-Ritz displacement field approximation based on the energy approach introduced an upper bound solution compared to the FE results. Therefore, the critical stability matrix is used to obtain an accurate buckling formula. The effective axial, coupling and flexural stiffness coefficients of the anisotropic layup is determined from the generalized constitutive relationship using dimensional reduction by static condensation of the 6 × 6 composite stiffness matrix. The resulting explicit formula has an additional term, which is a function of the effective coupling and axial stiffness. This formula reduces down to Euler buckling formula once the effective coupling stiffness term vanishes for isotropic and certain classes of laminated composites. The closed form results are verified against finite element Eigenvalue solutions for a wide range of anisotropic laminated layups yielding high accuracy. Comparisons with a limited number of experiments are also performed showing good correspondence. A brief parametric study is then conducted to examine the effect of ply orientations and material properties including hybrid carbon/glass fiber composites. Relevance of the numerical and closed form results is discussed for all these cases. [ABSTRACT FROM AUTHOR]

• Three slender MCFSTW specimens were tested under axial compressive load. • Test results were validated by FE models considering boundary constraints. • The failure modes of specimens were discussed and summarized. • Existing stability curves exhibited large discrepancies in global stability design. • A stability curve was proposed by fitting FE points and modified test points. Multi-celled concrete-filled steel tubular wall (MCFSTW) is a composite structural system. In engineering practice, MCFSTWs are always orthogonally arranged to form wall limbs with different section forms. For slender wall limbs, their global stability is widely concerned and deserves further investigation. To evaluate their global stability performance, the single wall limb isolated from the whole wall limb is commonly regarded as a wall member with lateral edges constrained by simple supports. In this study, experimental and numerical studies were conducted to predict the global stability resistance of MCFSTWs with three simply-supported edges. Firstly, three specimens were tested under axial compressive load. Based on the test results, the failure modes were discussed and summarized. Secondly, a refined FE model considering boundary constraints and deformations was developed. According to the orthotropic plate theory, the theoretical formula of the elastic buckling load for MCFSTW with three simply-supported edges was derived and validated. Then, the existing stability curves were verified by comparing them with numerical results. The results indicated that they are not adequately accurate for practical engineering applications. Finally, a stability curve was proposed by fitting the FE points and validated against the modified test points, indicating that the proposed curve is capable of predicting the global stability resistance of MCFSTWs with three simply-supported edges. [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]

In this work, the influence of initial geometric imperfection modes on the ultimate strength of a ship’s hull is studied, with a focus on the buckling behavior of stiffened panels that initiates the structural hull failure. A numerical model of a cargo compartment at the midship of a Suezmax tanker is developed by using the finite element method and by considering both geometric and material nonlinearities. Analyses are conducted under hogging conditions to evaluate the double bottom stiffened panels experiencing axial compression by hull girder bending. Different imperfection modes on the bottom and inner bottom plates are considered in the model. Two cases are studied. In the first one, a half-wave imperfection mode is employed in the longitudinal and transversal directions. In the second case, the imperfection mode coincides with the main natural buckling mode of the plate between the stiffeners. Experimental tests were performed using small-scale models that are representative of the bottom panels, and the results are correlated with those from numerical simulations to define a proper mesh refinement to reproduce the buckling phenomenon. The ultimate strength of the ship hull, in full-scale, employed the same mesh refinement for the bottom panels, assuming the two proposed initial imperfections. The results from the ultimate strength are compared with the reference values for the design bending moment recommended by a classification society. [ABSTRACT FROM AUTHOR]

Abstract: The buckling behavior of slender unreinforced masonry (URM) walls subjected to axial compression and out-of-plane lateral loads is investigated through a simplified “homogenized” procedure. After a preliminary analysis performed on a unit cell meshed by means of elastic FEs and non-linear interfaces, macroscopic moment–curvature diagrams so obtained are implemented at a structural level, discretizing masonry walls by means of rigid triangular elements and non-linear interfaces. The non-linear incremental response of the structure is accounted for a specific quadratic programming routine where second order effects are suitably considered adding a further term, quadratic in the nodal displacements, within the total energy of the discretized system. The finite element model, applicable under general load and restraint conditions, incorporates material and geometric nonlinearity and may be used to analyze slender URM walls, having the capability of capturing post-cracking and post-buckling behavior in an approximate but suitable way. As validation of the approach proposed, the instability behavior of some existing experimental pre-compressed four-point bending tests is reproduced. Square panels in two-way bending, exhibiting classical Rondelet’s mechanisms, are also studied. Finally the results obtained are compared with those provided both by commercial FE programs and specifically developed analytical models. [Copyright &y& Elsevier]

• The behavior of octagonal CFT columns under compression is investigated. • Local buckling of thin-walled tubes depends on b/t ratio and section shape. • The compression behavior is estimated by strain-compatibility analysis. • Effective stress-strain relationships of thin tube and concrete are suggested. • Applicability of AISC 360 strengths to octagonal CFT columns is investigated. The compression behavior of octagonal concrete-filled thin-walled tube (OCFT) columns was investigated. Eight OCFT columns with different tube sections were tested under monotonic compressive loading. The tests showed that the thin-walled tubes underwent elastic or inelastic local buckling, and the slenderness ratio (or width-to-thickness ratio) and section shape of the tubes significantly affected their buckling modes. Despite such local buckling, the load-deformation behavior of the OCFT columns all was highly ductile, due to confinement to the infilled concrete. The design strengths of AISC 360-16 agreed well with the test strengths. In this study, effective stress–strain relationships of the tube and infilled concrete were proposed to account for the local buckling and confinement. The maximum strength and post-buckling behavior were estimated through the strain-compatibility analysis, and the results were compared with the tests. [ABSTRACT FROM AUTHOR]

• GA and DSM used for cross-section optimisation of anti-symmetric CFS beam-columns. • Manufacturing constraints and practical construction limitations were imposed. • 132 CFS elements were optimised using different lengths and load eccentricities. • Capacity improved by 62%, 92% and 188% for short, medium and long length elements. • FE models are developed considering material nonlinearity & geometric imperfections. Flexibility in the manufacturing of cold-formed steel (CFS) cross-sectional shapes provides a unique opportunity to improve the load-carrying capacity of these elements, leading to more efficient and economic structural systems. This paper presents a practical constrained optimization methodology for pin-ended anti-symmetric CFS beam-columns members with different lengths subjected to various combinations of axial compression and bending moment. The optimization process is carried out using a Genetic Algorithm (GA) with respect to buckling resistance of CFS elements determined according to the Direct Strength Method (DSM). In total, 132 CFS beam-columns with three different lengths (1000, 2000 and 3000 mm) and eleven different cross-sections are optimized under concentrically compressive loads with different levels of eccentricities varying from 0 to 30 mm. Each cross-section is formed using a certain number of fold-lines of steel plate, while the length and angle of the constituent elements of the cross-section are considered as the main design variables. To provide more practical beam-column elements, end-use constraints as well as a range of practical manufacturing and construction limitations are imposed on the selected cross-sections during the optimization process. A standard commercially available anti-symmetric Z section is taken as a starting point of optimization and used to assess the efficiency of the optimized sections. The results show that, for the given plate width and thickness, the adopted optimization process can significantly increase the strength of beam-column members on average 62%, 92%, and 188% for the short, medium and long length elements, respectively, compared to those with the standard section. It is also demonstrated that using more complex cross-sectional shapes does not necessarily provide higher strength for beam-column members. Finally, to verify the efficiency of the optimized sections, detailed nonlinear finite element models are developed using ABAQUS software. The developed models should prove useful for the efficient design of CFS beam-column elements in practice. [ABSTRACT FROM AUTHOR]