Search

The article presents continued considerations presented in a prior publication on the development of a model for calculating the bending stiffness BS of cellular honeycomb paperboards, applying the strength properties of paper raw materials used for the production of paperboard and the geometric parameters of cellular board. The results of BS calculations obtained by using the analytical model presented in the prior publication were significantly overestimated in relation to the value obtained by measurements. The calculation error in relation to the measurement value for the tested group of paperboards in the case of bending stiffness in the machine direction MD was within the range from 23% to 116%, and the average error was 65%, while in the cross direction CD, it was within the range from 2% to 54%, and the average error was 31%. The calculation model proposed in this work based on the physical properties of cellular paperboard reduces the error values for bending stiffness in both the machine and cross directions. The value of the average error for both main directions in the paperboard plane was 10%. The method enables more accurate determination of BS in the machine direction MD and in the cross direction CD at the paperboard design stage. In order to validate the proposed analytical model, the calculation results were compared with the results of BS laboratory measurements performed using the four-point bending method and, in order to expand the group of tested paperboards, with the measurement results presented in the prior article for cardboards with different raw material composition and different geometric parameters. [ABSTRACT FROM AUTHOR]

This paper proposes a meso-structural model for the discrete fibrous network of paper, which is able to upscale the irreversible phenomena from the underlying hygro-mechanics towards the effective behaviour at the macro-scale. The swelling of individual fibres, induced by moisture content variations, is transmitted to the network through inter-fibre bonds and governs the resulting effective material response. The present approach is based on a recently developed discrete meso-structural model for the reversible part of the response, which distinguishes between the influence on the hygroscopic behaviour of free-standing fibre segments and inter-fibre bonds. The network structure, fibre and bond geometries and hygro-elastic properties are explicitly incorporated. The major novelty of this contribution is the extended fibre constitutive model, enabling to describe some typical irreversible mechanisms and instability effects related to the history of the manufacturing. This extension strongly affects the effective material behaviour beyond the elastic range. Despite the valuable work in the literature, no papers can be found dedicated to meso-structural models including these phenomena. Using an appropriate homogenization strategy, the unit-cell is solved analytically, capturing irreversible shrinkage in restrained dried paper and the occurrence of local buckling within the bond for freely dried material. The proposed scale transition offers a deeper insight into the complex relation between the events occurring at the different length scales. The potential of the proposed methodology is demonstrated through the convincing agreement with experimental data obtained from the literature. [ABSTRACT FROM AUTHOR]

In the companion paper, test results were presented to explore the flexural performance of cold-formed ferritic stainless steel (FSS) closed built-up beams. Each specimen was fabricated by joining two lipped channels in a face-to-face configuration and securing them with spot welds at intermediate points along the beam span. Sectional aspect ratio, compression flange's sectional slenderness and moment gradient were the key parameters varied to explore their influence on the flexural response of such members through tests. The current paper establishes a simplified finite element (FE) model of cold-formed FSS closed built-up beams and verifies it against the test results. Further, an extensive parametric study is carried out using the validated FE model to generate a large pool of data points. A wider database comprising of test results, numerical results obtained from this study and numerical results available in the companion paper were used to critically examine the adequacy of the current Australian Specifications (AS/NZ), American Standard (SEI/ASCE-8), European Code (EN 1993-1-4), Modified Eurocode approach suggested by Gardner and Theofanous, and Direct Strength Method (DSM) in North American Specification (AISI-S100: 2016), Modified DSM approach proposed by the authors in the literature and Continuous Strength Method (CSM) for cold-formed steel (CFS) flexural members. This makes the current study the first to extensively assess the accuracy of the various design guidelines available in the codes and other relevant literature, which explicitly highlighted their grave limitations. Accordingly, through suitable modifications and recommendations, new design rules are proposed to reliably and safely predict the flexural capacity of cold-formed FSS closed built-up beams. [ABSTRACT FROM AUTHOR]

This article analyzes the influence of the initial deflection of the flat layers on the bending stiffness (BS) of honeycomb paperboards and presents two methods for its calculation. Both methods allow for the determination of BS in the main directions in the plane of the paperboard, i.e., the machine direction (MD) and the cross direction (CD). In addition, they have been verified by comparing the calculation results with the results of the BS measurements. The first method allowed for the calculation of the BS of cellular paperboard based on the mechanical properties of the paper used for its production. The second method allowed for the estimation of the BS of cellular paperboard based on the bending stiffness of other honeycomb paperboards with the same raw material composition and the same core cell size but with different thicknesses. In the first analytical method for the calculation of the bending stiffness of cellular paperboard, which does not include the deflections of the flat layers, the calculation results significantly differ from the measurement results, and they are overestimated. The second of the presented BS calculation methods allowed for a much more accurate assessment of paperboard's bending stiffness depending on its thickness. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the local buckling of curved special-shaped pylons, which are becoming increasingly common in bridge construction. Three kinds of steel plate specimens with different radii of curvature were selected to study the local buckling of curved special-shaped pylons. Both model tests and finite element analyses were conducted. Modal solutions for elastic buckling analysis of the steel plate specimens were obtained using finite element method (FEM). The relationships between load and deformation, and load and strain were determined through testing. The results showed that the sequence of elastic buckling modes from the FEM was consistent with theoretical solutions, and the trends from the test and FEM were generally consistent. It was observed that an increase in curvature led to a decrease in bearing capacity, and the thickness-to-width ratio (t/b) was found to have a greater effect on the reduction factor than the radius-to-width ratio (R/b). Therefore, the thickness of the curved plate was determined to be critical for ultimate strength. The findings from this study offer insights into the behavior of curved special-shaped pylons under load, and provide a basis for their design and construction. [ABSTRACT FROM AUTHOR]

In this paper, a failure analysis of the TMT90m + composite wind turbine blade performed by combining numerical simulation and full-scale destruction tests is presented. The complex failure characteristics of the skin were studied in detail and a driving relationship was obtained. From the results, it was found that the stress concentration leading to local buckling was due to the geometric and layup nonlinearities of the destruction region. This in turn contributed to the successive occurrence of matrix failure and fiber failure. Further, by using the method of finite element secondary development, the accuracy of four commonly used failure criteria for wind blade failure prediction is discussed. From the results, it was found that the Chang-Chang model has ideal prediction accuracy and is more suitable for engineering applications in blade structure design. [ABSTRACT FROM AUTHOR]

Packages made of corrugated paper are fundamental to the protection, transportation and handling of the appliance product market. During the storage and sales stages of a product, the package must resist compressive loads in different directions beyond moderate impacts. In this context, the objective of this work is to develop and implement a post-processor that allows the simultaneous analysis of two of the most common failure modes of packages made of corrugated paper: failure due to tensile or compressive stress limit, and failure due to local buckling, when the buckling of the faces of the corrugated paper between two peaks of the fluting waves occurs. It was realized that the current procedure proposed by the literature expend a series of operations, what became the failure analysis for corrugated boxes too lengthy for the immediacy of the industry. Thus, it was chosen to apply a procedure to simplify the failure limit surface. Tensile tests were performed for the characterization of corrugated material used in numerical simulations. Experimental tests were performed on corrugated boxes used on household appliance products. The Tsai-Wu criteria for the material failure evaluation was applied and a modified Nyman-Gustafsson criteria for the local buckling analysis on the numerical simulations was proposed. A good correlation between experimental tests and numerical results was obtained. This work brings high expectations to the agility requested by the industry in the launching of new products. [ABSTRACT FROM AUTHOR]

The durability of profiled metal-faced insulating sandwich panels (MFISPs) in terms of exposure to high temperatures and thermal cycles is critical for their use in civil engineering applications. In this paper, a total of 20 full-scale panels made with two different thicknesses were tested under instantaneous lateral pressure loading at ambient conditions as well as under various combinations of high temperatures, thermal cycles, and lateral pressure. The pressure was applied through a vacuum chamber whereas thermal blankets were used for sustained and cyclic thermal exposure of the panels. Each thermal cycle entailed 24 h of time duration with a temperature range of 20–80°C. The results show a consistent reduction in the initial stiffness, local buckling pressure, and strength of the panels when they were loaded at high temperatures. These reductions were more substantial (up to 24%) under the combined effects of high temperature (80°C), thermal cycles, and pressure loading. The study also shows that the thickness of the foam core can play an important role in controlling the local buckling capacity and strength of the MFISPs. A nonlinear finite-element analysis was also conducted with a relatively good correlation with the test results. The numerical results provide further insights into the structural response and explain certain aspects that could not be obtained from the tests. Given that MFISPs are typically used for roof panels, where the combination of high temperatures and wind load is inevitable at certain regions, the results presented in this work are recommended for consideration in their design. [ABSTRACT FROM AUTHOR]

Japanese buildings are generally designed as moment‐resistant frames, and beam ends are required to have high bending strength and high plastic deformation capacity. With H‐shaped beams, the contribution of the web to the bending strength is small, so H‐shaped beams with thick flanges and thin webs are used to reduce the amount of steel required for construction. However, H‐shaped beams with thin webs are prone to local buckling at the ends of the beam, resulting in poor plastic deformation performance. The authors have developed a structural system of steel structures in which the ends of beams are reinforced by stiffener plates with the aim of improving the plastic deformation capacity. Especially when these structural systems are applied to a high‐rise building with large‐sized beams, the effect of reducing the amount of steel is high by reducing the thickness of the web. Reducing the amount of steel can be expected to reduce the loads on the environment and the construction cost. In this paper, the simple stiffening method is proposed with stiffeners that can improve factory manufacturability. Secondly, to confirm the plastic deformation capacity of a stiffened steel beam, a series of cyclic loading tests is carried out using 1/2 scale specimens. [ABSTRACT FROM AUTHOR]

An ordinary double steel plate–concrete composite wall (ODSC wall) is composed of core concrete, the faceplates, and shear connectors such as studs, etc. Based on an ODSC wall, a new type of stiffened double steel plate–concrete composite wall (SDSC wall) is conceived by incorporating additional stiffeners and tie plates on the internal surface, which aims to improve the local stability of the faceplates. In the authors' previous study, a series of axial compression tests were conducted on the SDSC walls. The SDSC walls in the test showed better mechanical performance, as the presence of stiffeners changed the buckling deformation mode and significantly improved the corresponding local buckling stress and ultimate strength. In this paper, a comprehensive summary of the prior research on SDSC walls is provided, and the effect of the constructive parameters on the local stability is discussed. The results reveal that the modified formula of the critical stress can degrade to the Euler formula when the stiffener-to-stud spacing ratio (i.e., a/B ratio) approaches infinity. What is more, the analysis model is also applicable for DSC walls with enclosed side plates, and the proposed formula can predict the buckling stress of the SDSC walls with different a/B ratios. In addition, according to the analysis of the numerical simulation, a design approach for SDSC walls to prevent local buckling is provided, which is applicable in practical engineering applications. [ABSTRACT FROM AUTHOR]

The paper addresses the issue of local buckling of compressed flanges of cold-formed thin-walled channel columns and beams with nonstandard flanges composed of aluminium alloys. The material behaviour follows the Ramberg–Osgood law. It should be noted that the proposed solution may be also applied for other materials, for example: stainless steel, carbon steel. The paper is motivated by an increasing interest in nonstandard cold-formed section shaping in local buckling analysis problems. Furthermore, attention is paid to the impact of material characteristics on buckling stresses in a nonlinear domain. The objective of the paper is to propose a finite element method (FEM) model and a relevant numerical procedure in ABAQUS, complemented by an analytical one. It should be noted that the proposed FEM energetic technique makes it possible to compute accurately the critical buckling stresses. The suggested numerical method is intended to accurately follow the entire structural equilibrium path under an active load in elastic and inelastic ranges. The paper is also focused on correct modelling of interactions between sheets of cross section of a possible contact during buckling analysis. Furthermore, the FEM results are compared with the analytical solution. Numerical examples confirm the validity of the proposed FEM procedures and the closed-form analytical solutions. Finally, a brief research summary is presented and the results are discussed further on. [ABSTRACT FROM AUTHOR]

This paper proposes an optimization study for both structure and materials to obtain an affordable, long-span, light-weight, and fast-constructing T-shape lightweight concrete-filled steel tubular (LWCFST) girder in order to be used in bridge construction. This research was performed on a hollow steel tube of Steel-52 (yield limit 360 MPa), which was filled with LWC. A set of parameters had been investigated to illustrate its effect on T-shape LWCFST girder stiffness, toughness, resilience, and ultimate carrying load capacity in order to obtain an equivalent stiffness to that of the typically used precast concrete girder. Based on design codes (EN 1994-1-1/Euro code 4 and ANSI/AISC 360-10) that permit the use of LWC as a filler material, the parameters considered were: the thickness of the steel tube, compressive strength of the filler concrete, and the bond condition between the steel tube and filler lightweight concrete. The yielding and ultimate bending capacity were determined based on the interpreted failure criteria of T-shape LWCFST girder, considering non-linear analysis for both material and loads using ANSYSWORKBENCH software. The results showed that T-shape LWCFST girder can be employed as a significant relative economic alternative to a typical precast girder in the bridge construction field, thanks to its high stiffness/weight ratio. The lightweight concrete inside was effectively employed to delay the local web buckling of the steel tube to increase its bending capacity. In addition, it reduced the total self-weight of the bridge's superstructure by 20% compared with a typical precast concrete girder. The dominant failure of T-shape LWCFST girders was found in the upper concrete slab due to the compression stress, even though the tensile cracks in the filler concrete occurred after reaching tensile yield stress in the steel tube. Additionally, increasing the value of friction coefficient between steel tube and lightweight concrete up to 0.8 was found to significantly affect the girder stiffness and has a slight effect after, no matter how high it is. [ABSTRACT FROM AUTHOR]

The paper develops a stiffness reduction factor to be used in geometric nonlinear beam-element type elastic analysis of cold-formed steel structures. The factor accounts for the reduction in flexural and warping torsion rigidities resulting from local and distortional buckling as well as residual stresses, particular to cold-formed steel structures. The purpose of applying the factor is to accurately account for the geometric second order effects when predicting the internal distributions of moments of cold-formed steel structural frames. The stiffness reduction factor arising from local and distortional buckling is first determined followed by the stiffness reduction factor caused by residual stresses. Subsequently, the two effects are combined in a single expression, which is a format suitable for incorporation in the North American specification for cold-formed steel structures, AISI-S100. [ABSTRACT FROM AUTHOR]

This paper investigates the ultimate resistance of aluminum circular hollow sections (C.H.S.) under simple load cases as affected by local buckling and material strain hardening. Following the development of advanced non-linear shell finite element models and their validation against existing test data, extensive non-linear numerical analyses were carried out, varying several key parameters such as alloy types, load case (compression or pure bending) and various section dimensions. The numerical results are used as references to analyze the structural performance of aluminum C.H.S., and to assess the accuracy of design equations based on the Overall Interaction Concept (O.I.C.). The O.I.C.-based proposal is shown to yield more accurate, consistent, and continuous resistance predictions than Eurocode 9 recommendations. [ABSTRACT FROM AUTHOR]

Aluminum appears as a promising structural material as it shows many benefits such as a great strength to weight ratio, low maintenance costs, resistance to corrosion, recyclability, etc. Accordingly, characterizing the behavior and resistance of different aluminum sections under various loading conditions is essential. The current paper presents an experimental investigation on aluminum sections with simple and complex geometries to study the effect of cross-section shape on the buckling response of the aluminum sections. Firstly, eight tensile coupon tests were conducted on coupons of aluminum alloy 6061-T6 to accurately determine its material properties. Geometrical imperfections on the surface of each specimen were then measured using a 3D scanner. Further, eight stub column tests were also performed to study the behavior of I, H and complex cross-sections under pure compression. In addition to this, 12 cross-section tests under combined compression and bending are currently under way to study the buckling behavior of these specimens under eccentric compression. [ABSTRACT FROM AUTHOR]

In this paper, an in‐depth nonlinear finite element analysis is carried out on longitudinally unstiffened and stiffened welded I‐steel plate girders subjected to patch loading. The most realistic load case is during the incremental launching of multi‐span steel and composite bridges over temporary or permanent supports. Bridge plate girders are usually reinforced by longitudinal and transverse stiffeners in order to prevent web panel buckling and to increase the bending and shear strength. The current European design standard EN 1993‐1‐5 also requires a stability control check for concentrated transverse forces (patch loading) since it can be a decisive design criterion. By using longitudinal stiffeners for flexural and shear resistance, the patch loading carrying capacity can be increased as well. Previous experimental studies showed that the EN1993‐1‐5 patch loading resistance model significantly underestimates the ultimate strength of longitudinally stiffened plate girders. The paper is primarily dealing with numerical research of the post‐buckling behavior and ultimate strength of longitudinally stiffened I‐steel plate girders reinforced by one longitudinal stiffener. The main objective of the present work is to investigate the influence of different geometrical parameters, including patch load length, web panel aspect ratio, and initial geometrical imperfections, on the ultimate strength of longitudinally stiffened plate girders. We showed in this study that for all the considered initial geometrical imperfections, the patch load resistance increases as the patch load length is increased. The lowest ultimate strength of longitudinally stiffened plate girders was determined for initial geometrical imperfections that resembled the deformed shape at collapse (collapse‐affine imperfections). The web panel aspect ratio also influenced the patch load resistance and lower ultimate strengths were returned for bigger web panel aspect ratios. Finally, further research recommendations are presented. [ABSTRACT FROM AUTHOR]

This paper investigates the behaviour and design of duplex stainless steel stub columns with a circular hollow cross‐section (CHS) at elevated temperature. A numerical model is developed to supplement the limited number of test results available in the literature. Following validation, the numerical approach is employed to gain an understanding of the critical behavioural characteristics which have not previously been studied. In addition, the paper considers and extends the continuous strength method (CSM) to include duplex stainless steel for CHS stub columns in fire. This approach employs a base curve linking the cross‐sectional resistance to the deformation capacity and is implemented herein using an elastic, linear hardening material model. The cross‐sectional resistances obtained from the CSM are compared with those from the numerical analysis, as well as with the standardised procedures in the European, American and Australia/New Zealand design standards. It is demonstrated that the proposed design method can lead to more accurate and less scattered strength predictions compared with current design codes. [ABSTRACT FROM AUTHOR]

The structural response and design of normal strength and high strength steel I-sections at elevated temperatures are investigated in this paper. The shell finite element models of steel I-section elements capable of replicating their behavior in fire are developed and validated against experimental results from the literature. The validated shell finite element models are then utilized to generate extensive structural performance data for steel I-sections, considering a broad range of plate slenderness values for cross-section elements, elevated temperature levels, cross-section aspect ratios as well as different loading conditions and normal strength and high strength steel grades. The accuracy of the existing methods provided in the European structural steel fire design standard EN 1993-1-2 and its upcoming version prEN 1993-1-2 for the ultimate strength predictions of normal strength and high strength steel cross-sections in fire is assessed. Scope for improvement is observed. Considering this, a new method for the ultimate strength predictions of normal strength and high strength steel sections at elevated temperatures is put forward. It is shown that the proposed method leads to more accurate ultimate strength predictions for normal strength and high strength steel I-sections in fire with a higher level of reliability relative to the existing design methods provided in EN 1993-1-2 and prEN 1993-1-2. [ABSTRACT FROM AUTHOR]

Corrugated steel web (CSW) sections are utilized worldwide in civil and mechanical engineering because of their advantages over flat sections, including enhanced lateral stability, a higher strength-to-weight ratio, improved energy absorption, and a reduced need for vertical stiffeners. The stability of such thin-walled structures becomes critical due to the small thickness of components and complex geometry. While lateral torsional buckling (LTB) can be avoided through lateral restraints, individual components of a girder, i.e. web and flanges, may undergo failure due to local instability. This paper focuses on summarizing the approaches for evaluating the local stability behavior of the flange and web sections. The review presents a holistic overview of the existing analytical, numerical and experimental studies on the web and flange instability of CSW girders. A numerical evaluation of local shear and flexural stability is presented using existing approaches. The influence of different geometrical parameters is summarized and important observations are highlighted for future research in this area. [ABSTRACT FROM AUTHOR]

This paper presents a method to optimize the dimensions of z-stiffened panels under a compressive load. Buckling coefficient curves for local buckling and stiffener lateral buckling are developed. The effects of transverse shear, coupling of buckling modes, and stiffeners on one side of the skin are considered in the column buckling stress estimation. An optimization tool is developed using MS-Excel. Examples of the design charts are presented and a design guideline is derived. [ABSTRACT FROM AUTHOR]

This paper presents a method to optimize the dimensions of z-stiffened panels under a compressive load. Buckling coefficient curves for local buckling and stiffener lateral buckling are developed. The effects of transverse shear, coupling of buckling modes, and stiffeners on one side of the skin are considered in the column buckling stress estimation. An optimization tool is developed using MS-Excel. Examples of the design charts are presented and a design guideline is derived. [ABSTRACT FROM AUTHOR]

This paper describes experiments addressing the buckling and collapse behaviour of cold‐formed stainless steel cruciform section columns. To build doubly symmetrical flanged cruciform section columns, six individual press‐braked plain channels made of austenitic grade EN 1.4307 were assembled back‐to‐back. Two channel geometries were used – with cross‐section height 200 mm and 100 mm. They were connected using bolts M8 of class 8.8, with equidistant spacings along the column length. Six columns with three different lengths – namely, short (600 mm), intermediate (1200 mm) and long (2400 mm) – were tested under pure axial compression load and under end semi‐rigid support conditions. Two tests were included for each length. It was observed that the buckling patterns in the built‐up cruciform section specimens were affected by their global slenderness and by the spacing between the fasteners. However, in the cases of long specimens, where global torsional buckling was critical, the fastener spacing had a minor influence on the ultimate capacity of the columns. [ABSTRACT FROM AUTHOR]

The local buckling of I-section columns is investigated in this paper, where the interaction between the web and flanges is taken into account. An analytical method is first developed based on the classical theory of the elastic buckling of thin plates, with which the main parameters affecting the interaction between the web and flanges are analyzed. The interactive behaviors of the buckling deformations of the I-section with different parameters are then revealed by employing finite element analyses. Simple approximate solutions for the buckling coefficients of the web and flanges are proposed using the energy method, which is capable of providing very accurate predictions compared to the analytical results. Using the simple solutions for buckling coefficients, the limits for the width-to-thickness ratio of I-section columns are proposed. Comparisons between the existing solutions and provisions in design codes indicate that the proposed limits for width-to-thickness ratio are capable of precisely considering the web–flange interaction at the local buckling of I-section columns. [ABSTRACT FROM AUTHOR]

Wide-flange columns are commonly used for the construction of special moment frames and braced frames. For special moment frames, design engineers routinely use deep sections to meet the stringent code-specified story drift limits in order to achieve economy in recent years. Columns with shallow and stocky sections are common for braced frame construction. Observation made from two recent experimental studies involving both deep and shallow columns under axial compression and cyclic drifts showed a variety of buckling modes. A classification with three cyclic buckling modes is proposed in this paper; subsets of each buckling mode are also presented. A parameter measuring the relative rotational restraint that the web provides to each flange is derived. After calibrating this parameter with the test results, a practical procedure that can predict the governing cyclic buckling mode is proposed. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical investigations on the cross-sectional behavior and compressive capacities of aluminum alloy channel section stub columns after exposure to fire. A testing program was performed, including heating tests, postfire material tests, geometric imperfection measurements, and 16 stub column tests. The testing program was followed by a numerical modeling program. Finite-element models were developed to simulate the test responses and conduct parametric studies to obtain additional numerical data. The obtained test and numerical data were analyzed and adopted to perform design analyses, in which the applicability of the relevant room-temperature design rules in the American, European, and Australian/New Zealand codes to the postfire design of aluminum alloy channel sections under compression were examined. The results of the design analyses reveal that all three examined design codes yield excessively conservative and scattered predictions of postfire strengths, owing to the neglect of significant postfire material strain hardening. Then, a new design approach was proposed by rationally considering the material strain hardening. The new proposal was found to offer greatly improved design accuracy and consistency compared to the American, European, and Australian/New Zealand codes, especially for aluminum alloy channel sections after exposure to elevated temperatures above 400°C. [ABSTRACT FROM AUTHOR]

The possible failure modes of cold-formed steel (CFS) lipped angle (LA) compression members are yielding, local, flexural torsional, or flexural buckling, and any possible interaction among these buckling modes. In general, the strength estimated by current design guidelines are conservative for these members when flexural-torsional buckling (FTB) is the first global buckling mode because the postbuckling strength of this mode is not accounted for in the global buckling strength equations. The initial part of this paper reports the results of an experimental and numerical study of CFS-LA members undergoing independent FTB. Modifications are suggested to global buckling strength equations based on these results. Subsequently, the reduction in the ultimate strength from strength corresponding to independent buckling modes for LA members undergoing interaction between buckling modes such as local-flexural torsional, flexural-flexural torsional, local-flexural, and local-flexural torsional-flexural are studied systematically using finite-element analysis results. A simple and more accurate interaction equation that accounts for these interactions among buckling modes in CFS-LA compression members is proposed. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on the static behavior and cyclic behavior of UHPC-filled steel tube (UHPCFST) columns. A novel fiber element model is developed based on the effective distribution width method to consider the influence of local buckling. The parameters of the descending branch of the stress–strain curve of constrained concrete have been modified and proposed according to the existing experimental results. Thereafter, the impact parameter analysis of the seismic performance of UHPCFST columns under the pseudo static load is conducted, and the strength of steel and UHPC, width–thickness ratio, length–diameter ratio and axial compression ratio are considered. The results indicate that the proposed fiber element model can accurately predict the static and cyclic nonlinear behaviors of the UHPCFST columns. The bearing capacity and the post-peak ductility of UHPCFST columns can be overestimated, such as neglecting the local buckling of the steel tube, which will lead to the insecurity of structures. [ABSTRACT FROM AUTHOR]

This paper investigates the structural behaviour and design of duplex and ferritic stainless steel stub columns with a circular hollow cross-section (CHS) at elevated temperature. A numerical model is developed to supplement the limited test results on stainless steel CHS stub columns in the literature. Following validation, the numerical approach is employed to gain an understanding of the critical behavioural characteristics which have not previously been studied. In addition, the paper considers and extends the continuous strength method (CSM) to include duplex and ferritic stainless steel for CHS stub columns in fire. The CSM employs a base curve linking the cross-section resistance to its deformation capacity and implements an elastic, linear hardening material model. The cross-sectional resistances obtained from the proposed CSM are compared with those from the numerical analysis, as well as with the standardised procedures in the European, American and Australia/New Zealand design standards. It is demonstrated that CSM can lead to more accurate and less scattered strength predictions than current design codes. [ABSTRACT FROM AUTHOR]

The paper presents a set of Direct Strength Method (DSM) formulae for cold-formed stainless steel I-section beams. On basis of a carefully calibrated FE model for stainless steel open-section beams featuring local-global interaction buckling, an extensive database was first established. The existing DSM formula of the best prediction performance was commented on for its drawbacks. For improved strength prediction, a traditional-form DSM formula was proposed first, and novel two-phase DSM formulae were derived on basis of a deep insight into the varying trend of the member strengths. The two-phase DSM formulae were found to be very powerful predictors yielding more accurate strength predictions over the whole range of slenderness and avoiding undue conservatism for intermediate and short members. A considerable boost in design strength by up to 39% can be achieved with the two-phase DSM formula. The DSM curves were developed with a due reliability level to fit into the current design codes. [ABSTRACT FROM AUTHOR]

The paper deals with the experimental analysis of the local stability of short axially compressed rectangular concrete-filled steel tubes (CFSTs), in which the load acted on the steel pipe. This analysis is one part of the research oriented to the local and global stability of rectangular concrete-filled steel tubes. This part presents the comparison of the coefficients of critical stress, which were obtained from experimental tests of investigated members with standard value in Eurocode 3. Some results and research findings of this analysis are published in the paper. [ABSTRACT FROM AUTHOR]

In detailed three-dimensional (3D) finite-element modeling, two-dimensional and/or 3D elements are widely used because of their high accuracy and ease of use despite the high computational cost. In contrast, simplified modeling based on fiber beam element (FBE) formulation is preferred for developing macro models to simulate structural frames due to its simplicity and computational efficiency. As for the FBE simulation of concrete-filled steel tubular (CFST) columns, its accuracy largely depends on the input steel and concrete material models, which should implicitly consider the material nonlinearity and interaction between the steel and concrete components. The authors have previously developed a FBE model for circular CFST columns, and this paper is a continuation of the previous work. In this paper, uniaxial effective stress–strain relationships are developed for the steel and concrete materials in rectangular CFST columns based on rigorous analysis of data generated from 3D finite-element modeling of stub columns. Thus, the material models have implicitly considered the effects of yielding and local buckling of the steel tube and passive confinement to the concrete. Meanwhile, the size effect is also considered in the concrete model. The accuracy of the proposed material models is verified against a database of rectangular CFST stub columns covering a wide range of material and geometric parameters. The developed material models are further used to simulate rectangular CFST slender columns and beam-columns, and a reasonably good agreement is achieved between the experimental and predicted load–deformation curves. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubes present excellent structural and constructional performances because they ideally combine the advantage of concrete and steel tube. Thus, they are widely used in civil infrastructures. However, they inevitably suffer from either hard compacting or high costs. Thus, convenient and rapid construction for compacting concrete and cost saving are the urgent challenges for concrete-filled steel tubes. Therefore, this study investigates filling a thin-walled steel tube with self-compacting concrete to solve the challenges presented by traditional concrete-filled steel tube columns, such as poor compacting performance and high costs. This experimental study tests self-compacting concrete-filled thin-walled steel tube (SCCFTST) columns under concentric compression from loading to failure. Effects of wall thickness of the thin-walled steel tube on the failure modes, load-deformation behaviors, and the ultimate loads of the SCCFTST columns are comprehensively investigated. The ultimate loads between experiments and their calculated values in terms of design codes are also compared. The results suggest that buckling on thin-walled steel tube surface is the typical failure mode. The amount of local buckling increases with decreasing wall thickness, and the decreasing rate of the load-deformation curves in the descending branch decreases by increasing the wall thickness, as well as the ultimate load increasing with increases wall thickness. The ACI and CECS are the most conservative and accurate design codes, respectively, for predicting the ultimate load. Therefore, the SCCFTST columns can be used as structural components in civil infrastructures and their peak loads can be calculated using design codes for conventional concrete-filled steel tube columns. However, modification measures must be taken while predicting the ultimate loads of the SCCFTST columns by design codes. The experimental results of this paper can contribute towards the application of SCCFTST columns in practice. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results from nine full-scale concrete-filled double-skin tubular (CFDST) beam-columns. The test specimens exploited two fabrication strategies, featuring either hollow steel inner skins with corrugated geometry or ultrahigh-strength steel corner tubes to enhance the seismic performance of noncompact CFDST beam-columns for potential use in low-to-moderate seismicity regions. The effects of loading sequence, axial load ratio, and cross-sectional geometry were investigated. The experimental results suggested that the current AISC specification may be used to predict the axial strength of composite members with a relatively good accuracy. In the postbuckling range, conventional CFDST beam-columns and those with corrugated inner skins are prone to fracture at the corner welds of the built-up cross section. However, the latter exhibited up to two times larger drift capacities than conventional CFDST counterparts prior to losing axial load carrying capacity. Noncompact beam-columns retrofitted with ultrahigh-strength steel corner tubes exhibited a 4% lateral drift demand without experiencing more than 25% flexural strength loss. The presence of ultrahigh-strength steel increases the plastic hinge length of CFDST beam-columns by up to four times relative to CFDST beam-columns with corrugated inner skin, regardless of the employed loading history. [ABSTRACT FROM AUTHOR]

Composite action between the components of the concrete-filled steel tube (CFT) is complex and it is difficult to accurately obtain the experimental relationship between the steel tube and the core concrete of CFT columns. The triaxially stressed core concrete has been studied by hydrostatic test in past research, while little research has been focused on the mechanical behavior of steel tube of CFT columns. It is difficult to obtain the experimental constitutive relationship of the steel tube of CFT columns to reflect the real-time influence of biaxial stress state and local buckling of steel plate on the steel tube. To clarify the mechanical behavior of the steel tube of CFT columns, this paper proposed an elastoplastic analytical method considering biaxial stress state and local buckling of steel tube to obtain the stress–strain curve of the steel tube. This method applied the Hook's law and the plasticity theory to interpret the information conveyed by the measured vertical and hoop strain histories of the steel tube. To verify its effectiveness, 11 circular concrete-filled steel tube stub columns were fabricated and tested under axial compression. Superposition results of the axial load–strain of steel tube and core concrete were compared against the experimental curves. The widely used Sakino–Sun model of the confined concrete was adopted to calculate the axial load–strain curve of the core concrete. Satisfactory agreements between the calculated and experimental results confirmed the rationality of the proposed method in tracing the constitutive relation of the biaxially stressed steel tube even after the occurrence of the local buckling. The obtained stress–strain relationship is critical for establishment of mathematical constitutive model and finite element model of steel tube. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on the nonlinear behaviors of UHPC-filled square steel tubular (UHPCFST) columns under complex actions. A novel fiber model was developed considering the local buckling effects of steel tubes. The reliability and robustness of the model were validated by a large amount of experimental data in the reported literature. Then, the current design codes were evaluated and discussed on the basis of the collected experimental data, and a practical calculation method was finally proposed to predict the bending moment capacities of UHPCFST beam–columns. The results indicate that the proposed fiber model can accurately predict the nonlinear behaviors of UHPCFST beam–columns, including axial compression, eccentric compression, pure bending, and hysteretic behaviors. Compared with current design codes, the practical calculation method presents high precision and can accurately predict the bending moment capacities of UHPCFST beam–columns. [ABSTRACT FROM AUTHOR]

Local buckling in steel tubes was observed to be capable of reducing the ultimate loads of thin-walled concrete-filled steel-tube (CFST) columns under axial compression. To strengthen the steel tubes, steel bars were proposed in this paper to be used as stiffeners fixed onto the tubes. Static-loading tests were conducted to study the compression behavior of square thin-walled CFST columns with steel bar stiffeners placed inside or outside the tube. The effect and feasibility of steel bar stiffeners were studied through the analysis of failure mode, load–displacement relationship, ultimate load, ductility, and local buckling. Different setting methods of steel bars were compared as well. The results showed that steel-bar stiffeners proposed in this paper can be effective in delaying local buckling as well as increasing the bearing capacity of the columns, but will decrease the ductility of the columns. In order to obtain a higher bearing capacity of columns, steel bars with low stiffness should be placed inside and steel bars with high stiffness should be placed outside of the steel tubes. The study is helpful in providing reference to the popularization and application of this new structural measure to avoid or delay the local buckling of thin-walled CFST columns. [ABSTRACT FROM AUTHOR]

This paper presents an energy‐based approach to obtain the critical length and stress of local (L) and anti‐symmetric distortional (D2) modes of simply supported lipped channel columns. For each mode, deformed shapes are assumed and the Rayleigh Quotient Method is applied to obtain analytical expressions for the buckling stress. The shape functions adopted for local buckling ensure compatibility of rotation and bending moments at wall junctions and at the stiffener's free end. For the D2 mode, equilibrium of bending and twisting moments are considered leading to an analytical derivation of the mode's warping stress distribution. While for L mode it is not feasible to obtain a closed expression for the critical length (but a simple length testing procedure is sufficient), for D2 mode an expression dependent on geometrical properties is derived. The developed equations for L and D2 modes are validated against CUFSM's pure local modes and GBTul's pure D2 mode (mode 6 in GBTul convention) respectively. For sections with flange‐to‐web width ratio, bf/bw, ranging from 0.2 to 1.0 and lip‐to‐web width ratio, bs/bw, from 0.1 to 0.4 the average ratios obtained for critical stresses (σcr,reference/σcr,proposed) are 1.014±0.019 and 1.011 ± 0.014 for L and D2 modes respectively. [ABSTRACT FROM AUTHOR]

This article explores a novel approach to inhibit local premature failures in cold-formed steel (CFS) beams and enhance their flexural capacity by introducing external web stiffeners to buckling prone regions. An experimental and finite element investigation on the behaviour of doubly symmetric CFS built-up channel beams with adhesively bonded glass-fiber reinforced polymer (GFRP) stiffeners is presented in this paper. Unlike previous attempts, where flat plates have been used, the results of pultruded T-shaped GFRP stiffeners on the flexural capacity and local failure inhibition of the CFS beams are presented. The viability of suggested strengthening arrangement is assessed by comparing the results from CFS beams strengthened with steel stiffeners of equivalent stiffness. One control and six reinforced beams, stiffened with different configurations of both steel and GFRP stiffeners in the moment span, were tested up to failure under four-point bending. The change in the mode of failure from buckling at discrete regions to global failures with an improvement in the flexural capacity by up to 39% was achieved using adhesively bonded external stiffeners in the present study. It can be concluded that adhesively bonded GFRP stiffeners provide a cost-effective and adequate alternative to enhance the flexural performance and inhibit the local failures in thin-walled beams. Finite element models were developed and verified against test results. FE models were found to be capable of predicting the ultimate capacity and failure of stiffened beams with fair accuracy. [ABSTRACT FROM AUTHOR]

This paper investigates the post-buckling behaviour and axial capacity of thin-walled steel stiffened single-channel sections (ISSCS) and back-to-back stiffened channel sections (BISCS). BISCS were connected using fasteners at a spacing of 200 mm and with an edge distance of 100 mm. Under axial compression, 10 new ISSCS and BISCS columns with fixed-ended conditions were tested. In the experimental tests, the back-to-back channel sections failed due to a combination of local and global buckling, whereas the single-channel sections generally failed as a result of local buckling. The behaviour of both ISSCS and BISCS shows a 20% increase on an average in axial capacity through adding stiffeners at the junction of the flange and the web, in addition to stiffeners in the web. A nonlinear finite element model (FEM) with material and geometric nonlinearities was then developed. The FE model was validated against the experimental results. A comprehensive parametric study comprising 64 face-to-face intermediate stiffened channel sections (FISCS) was then conducted to study the influence of stiffener length on its axial capacity. The axial capacity obtained from the tests and FEA shows that design in accordance with the Direct Strength Method (DSM) is accurate and conservative by only 4% on average. [ABSTRACT FROM AUTHOR]

Abstract \nHIGHLIGHTS: Three-dimensional lattice structures with high specific strength, specific stiffness and low apparent density, are widely employed across multiple engineering fields. Under uniaxial compressive loading, the lattice structure may experience local buckling or global buckling. This paper conducted a systematic parametric study of the various factors affecting the buckling behavior of multilayer pyramid lattice structures to investigate the mechanism of the two main instability modes, local and global buckling. It was found that the critical buckling load increases with the increase in the size of the unit cell and decreases with the increase in the total height of the structure for the same relative density. As the relative density increases, the buckling resistance of the lattice structure increases. It is possible to examine various buckling modes by varying the geometrical properties of the pyramid unit cell (slenderness ratio, rod inclination angle, cross-sectional size of strut connection parts). Finally, numerical simulations were performed to calculate the yield strength and buckling strength of the lattice structure under uniaxial compression load, in order to estimate the threshold relative density for structural buckling and yield failure. The results demonstrated that buckling failure should be considered for aluminum alloy pyramid lattice when the relative density is below 4.07%. This study provides design criteria for lattice structures dominated by buckling and offers ideas for improving the buckling capacity of truss-type lattice structures.Global and local buckling failures of lattice structure were studiedStructure height and unit cell size have significant effects on both buckling mode and critical buckling loadsAnalyzed the threshold relative density for two failure modes of buckling and yielding [ABSTRACT FROM AUTHOR]

This paper presents a hybrid simulation (HS) with a proposed substructuring technique that captures the effect of first‐story column local buckling and axial shortening on the frame behavior. The HS is applied to examine the seismic response of a two‐dimensional seven‐story, two‐bay steel dual system. The experimental substructure consists of a full‐scale interior column and beam cruciform subassemblage, including a moderately ductile first‐story built‐up box column and two I‐shaped beams. Under combined axial and lateral loads, local buckling can occur near the column base, resulting in column shortening. The specimen is loaded through a four‐degree‐of‐freedom (DOF) mixed‐mode control (three displacement‐ and one force‐control) actuation system that simplifies the actual complex boundary conditions of the frame structure. To account for column shortening in the HS, a new approach consisting of a set of fictitious equivalent forces applied to columns in the numerical model to achieve compatible displacements with the experiment is implemented. Shortening of the two exterior columns in the model is simulated through finite element analysis using the computer program ABAQUS in an attempt to capture the redistribution of axial loads with column shortening. The test results confirm that the proposed modeling and control methods successfully integrate the experimental substructure and ABAQUS simulation into the HS, resulting in a more realistic frame response that captures the effect of column shortening in the analysis. The moderately ductile built‐up box column is verified to perform well in near‐fault earthquake loadings. [ABSTRACT FROM AUTHOR]

• The double-layer optimization algorithm solves truss topology with local buckling. • Buckling constraints as linear functions ensure efficient computation. • Algorithms address transient hinges and matching bar sections in truss topology. • Topaz plug-in enables rapid topology optimization in Rhino-Grasshopper. • The optimization meets strength, buckling, and slenderness ratio requirements. This paper proposes the double-layer optimization algorithm to solve the truss topology problem with bar local buckling constraints. With this algorithm, the constraints on the local buckling are treated as linear functions of the optimized variables, which ensures efficient computation. In addition, two practical algorithms are proposed to solve the problems of the existence of transient hinges and the difficulty in matching the bar sections with standard sections. In addition, the topology optimization plug-in, named Topaz, is developed in this paper in the Rhino-Grasshopper parametric modeling platform to facilitate rapid model building. Finally, numerical examples show that the optimization results satisfy the requirements of strength, local buckling, and slenderness ratio of the bar, which demonstrates the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]