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Reduced beam section (RBS) connections are ductile connections that have been widely used in steel structures. Because of the reduction of web resistance, local buckling usually occurs under large deformations and is associated with decreased strength. In addition, the complex deformation of beams prevents determining the residual strength, hence posing a challenge in postearthquake repairs. In this study, a buckling-restrained system (BRS) including steel channels and a mortar was proposed for deformed RBS regions to provide lateral support on buckled plates so as to recover the connection strength. Two full-scale RBS connections with various cutting ratios were first tested, and then the connection was repaired with BRS loaded again. The test results indicated that the repaired connections were loaded at a drift angle of up to 4% without fracture or strength deterioration. The negative strength increased by approximately 18%, and the maximum strength was similar to that of the original connection, indicating that the column-to-beam flexural strength ratio of the connection did not change. The strain at the heat-affected area also did not increase and rather decreased because of the additional support of the restraint. The dissipated energy capacities of the repaired specimens were approximately 92% and 87% of the values of the original specimens. These results confirmed that BRS provided sufficient lateral resistance and helped recover the connection performance. • This paper proposed a new postearthquake repair method for recovering the performance of the locally buckled reduced beam section connections. • Two full-scale connection specimens with different cutting ratios were prepared and tested. • The results indicated that the method notably enhanced the strength of the locally buckled connection, and the maximum strength was similar to that of the original connection, indicating that the column-to-beam flexural strength ratio of the connection did not change. • The strain at the heat-affected area also did not increase, and the dissipated energy capacities of the repaired specimens were closed to the values of the original connections. • The repair method does not require field cutting, welding works, and temporally support structures. [ABSTRACT FROM AUTHOR]

In the current work, an innovative fixture was designed and made to test local buckling of the notched plates under tensile loading. The conducted experimental measurements include the symmetric and for the first time the anti-symmetric modes of the buckling. Both monotonic and cyclic loading were applied on the specimens and the effect of the buckling on the fracture capacity and fatigue life of the specimens were investigated. The main interest of the paper is to describe the fixture and some experimental techniques. The buckling load was obtained from the tests as well as fracture capacity and fatigue life. Based on the obtained results, the buckling can reduce the fracture capacity as well as the fatigue life by 35% and 59%, respectively. Due to the mix mode of I-III, the anti-symmetric buckling shows a greater effect on the fracture capacity, however, the sliding crack closure due to mode III prevents the crack growth in the case of anti-symmetric buckling. [ABSTRACT FROM AUTHOR]

In this work, explicit equations to determine local buckling critical stress of thin-walled fiber reinforced polymer (FRP) profiles in pure bending or compression are proposed. Interaction between flange and web is considered and the expressions allow for different orthotropy ratios and ranges of flange-to-web widths and thicknesses. To obtain the equations, Rayleigh Quotient energy method is adopted for assumed approximate buckled shapes. As quality of selected functions affects the accuracy, different shapes are investigated and the results are compared with those obtained with Generalized Beam Theory (GBT) for typical I-section dimensions and material properties. A comparison is made to the solutions based on discrete plate with simplified support conditions as well as to a recently proposed equation for major-axis bending. Finally, a general form for the local buckling critical coefficient is also presented along with tabulated parameters for prompt assessment of critical stresses, consisting in a simple and reliable alternative for design approach. [ABSTRACT FROM AUTHOR]

An analytical study to investigate the local buckling capacity of steel I-section beams under elevated temperatures is presented. The study is based on an inelastic local buckling stability model that was developed by the author. The study is focused on I-section beams loaded in pure bending and subjected to either uniform or linear temperature gradient through the section depth. A parametric study is presented to investigate the effect of section geometry, steel type, and temperature gradient on local buckling capacity. The parametric study results are used to propose a new method to estimate the local buckling capacity of I-section beams under elevated temperatures. A numerical example is presented to illustrate the use of the proposed method. [ABSTRACT FROM AUTHOR]

This paper describes an experimental program investigating the local-global interaction buckling of stainless steel I-section beams. Three alloys were included: austenitic S30401, ferritic S44330, and lean duplex S32101. Extensive coupon tests were conducted to determine the specific properties of stainless steel sheets, including nonlinearity, anisotropy, and strain hardening. The test program encompassed six laterally braced tests and 24 unbraced tests with spans ranging between 1.9 and 4.0 m. The unbraced specimens were tested in a specially designed setup featuring clearly defined loading and support conditions. Interaction buckling was successfully achieved in the tests. The geometric imperfections, bearing capacity, and sectional and global deformations of each specimen were carefully recorded before or during the tests. Key factors affecting the test conditions were identified. The research addressed the lack of experimental data for local-global interaction buckling of stainless steel beams with open cross section and establishes the foundation for further theoretical study, as described in a companion paper. [ABSTRACT FROM AUTHOR]

This paper discusses unified criteria for the local buckling of multi-walled carbon nanotubes in both compression and bending deformations from a standpoint of atomic simulations. Defective and non-defective five-walled carbon nanotubes are subjected to compression and bending deformation by the molecular dynamics method using the adaptive intermolecular reactive empirical bond order potential. The atomic elastic stiffness of each atom, B ij α , is then evaluated during the deformations to discuss the onset of local buckling. The B ij α corresponds to the second-order derivatives of the atomic energy, i.e. , the gradient of the local stress–strain surfaces in six-dimensional strain space. If B ij α has a negative eigenvalue, a local unstable path will exist in the direction of the strain. Under compression, the smallest eigenvalues, λ ( 1 ) α , of the B ij α for all atoms changes to a negative value long before buckling occurs, while the second-smallest eigenvalues, λ ( 2 ) α , of the B ij α of some atoms change to a negative value just prior to buckling. Under bending deformation, the change in the positivity of λ ( 2 ) α corresponds to a rippling deformation on the side of compressive bending stresses. A variation in the location of defects in the carbon nanotubes affects the peak stresses under compression and the peak moments under a bending deformation. However, for all models, local buckling occurs from the dense region of atoms whose λ ( 2 ) α < 0 in some outer layers. This suggests that the atomic elastic stiffness is capable of acting as an evaluation criterion for local buckling in multi-walled carbon nanotubes. [ABSTRACT FROM AUTHOR]

A higher order beam model for the buckling analysis of thin-walled structures is presented in this paper.The model considers an enrichment of the displacement field so as to accurately represent the three-dimensional behaviour of thin-walled structures. The definition of an uncoupled set of deformation modes allows a meaningful definition of hierarchical higher order solutions, which are useful for the linear buckling analysis of thin-walled structures. A criterion for the definition of local and global buckling modes, as well as possible interaction between modes is put forward. A comparison between the results obtained with the higher order beam model and results obtained from a shell finite element model implemented in Abaqus allows to conclude not only the efficiency of the beam model but also its simplicity of use. [ABSTRACT FROM AUTHOR]

The ultimate performance and deformability of frames composed of H-shaped non-plastic sectional steel members (NP member) were investigated. Firstly, the failure mechanism, resistance, deformability and energy dissipation capacity of NP members were summarized through experimental studies, which indicate that NP members can be employed as energy dissipation components in seismic areas despite their limited ductility. Subsequently, a concept named 'buckling hinge' reflecting the features of NP members along with the requirements for realizing buckling hinges were put forward. Furthermore, by adopting the buckling hinge model, non-linear performance of NP frames was numerically simulated. It is found that with the redistribution process of internal forces, certain degree of stable deformability of statically indeterminate NP frames can be expected even though the individual NP member possesses limited ductility. Finally, based on the ultimate failure mechanism model of steel frames and buckling hinge model of NP members, the ultimate resistance of low rise frames can be predicted through ultimate analysis method with satisfactory accuracy, which was verified by two series of frame tests. [ABSTRACT FROM AUTHOR]

This study investigates the reliability of the buckling formulas usually employed for designing bolted built-up columns of pultruded fibre reinforced polymer (FRP) material. Several papers have been published on buckling and instability analysis of pultruded FRP columns, but the same studies do not deal with built-up type. In this case, it is necessary not only to take into account the effect of the high deformability of the FRP material, but also to clearly identify the extent of each element in the overall bearing capacity as well as in the type of connection – i.e. it can play a key role by increasing the axial stiffness or it may contribute to the shear stiffness. The investigation compares the results predicted by the existing formulas to experimental data as well as to an appropriate finite element analysis previously carried out. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a study of the inelastic local buckling of flange outstands in thin-walled steel beams at elevated temperatures. A spline finite strip method of buckling analysis is modified in order to model the properties of the steel section at elevated temperatures, so that slenderness limits can be proposed. These limits are needed in describing the behaviour of members under fire loading, since the development of benign catenary action in a restrained beam that has received widespread research attention in fire engineering design is reliant on the formation of plastic hinges, and of the influence of local buckling on the formation of these hinges. A sensitivity analysis is undertaken in order to propose plasticity and yield slenderness limits at elevated temperature, and it is shown that these limits depend on the parameters describing the uniaxial stress–strain relationship at the elevated temperature. The local buckling temperature is predicted for two different boundary conditions for a flange outstand, and it is shown that at high temperatures the local buckling of the beam is highly significant in accelerating the favourable development of catenary action. [Copyright &y& Elsevier]

Circular thin-walled elastic tubes under concentric axial loading usually fail by shell buckling, and in practical design procedures the buckling load can be determined by modifying the local buckling stress to account empirically for the imperfection sensitive response that is typical in Donnell shell theory. While the local buckling stress of a hollow thin-walled tube under concentric axial compression has a solution in closed form, that of a thin-walled circular tube with an elastic infill, which restrains the local buckling mode, has received far less attention. This paper addresses the local buckling of a tubular member subjected to axial compression, and formulates an energy-based technique for determining the local buckling stress as a function of the stiffness of the elastic infill by recourse to a transcendental equation. This simple energy formulation, with one degree of buckling freedom, shows that the elastic local buckling stress increases from 1 to $\sqrt{3}$ times that of a hollow tube as the stiffness of the elastic infill increases from zero to infinity; the latter case being typical of that of a concrete-filled steel tube. The energy formulation is then recast into a multi-degree of freedom matrix stiffness format, in which the function for the buckling mode is a Fourier representation satisfying, a priori, the necessary kinematic condition that the buckling deformation vanishes at the point where it enters the elastic medium. The solution is shown to converge rapidly, and demonstrates that the simple transcendental formulation provides a sufficiently accurate representation of the buckling problem. [ABSTRACT FROM AUTHOR]

Abstract: Slender section columns can carry additional loads up to failure after local buckling has happened in its elements. This post-local buckling capacity depends mainly on the width–thickness ratios of elements forming the section as well as the state of stresses within it. This paper presents tests to examine the influence of these factors on this additional capacity. The experimental local buckling and ultimate loads of two series of specimens are presented. Each series contains a group of slender I-sections varying in their flange and web width–thickness ratios. In the first series the loads are applied axially through the CG. of the sections, while in the other one they are applied eccentrically about the major and minor axis. Additionally, the tested specimens are simulated numerically by a non-linear finite element model considering different values of overall geometric imperfections. Generally, the post-local buckling strength gained by the sections is higher for axially loaded columns than that of bi-axially loaded ones, and it decreases with increasing eccentricity for the same web and flange width–thickness ratios. [Copyright &y& Elsevier]

Abstract: Although fibre reinforced polymers exhibit several advantages over traditional materials, their widespread acceptance is being delayed by the lack of appropriate design codes. In fact, additional and comprehensive experimental data are needed to assess the accuracy of recently developed analytical and numerical design tools. This work reports an experimental study on the first-order, buckling and post-buckling behaviours of I-section beams made of GFRP pultruded profiles. Tests were first carried out on small-scale (coupon) specimens, in order to determine the most relevant material mechanical properties. Full-scale tests were then conducted on (i) simply supported beams with spans varying from 1.0m to 4.0m under 3-point bending and (ii)cantilevers with spans ranging from 2.0 m to 4.0 m subjected to a tip point load applied at the end cross-section centroid or top/bottom flange mid-point. While the first series is aimed at investigating the flexural behaviour under service and failure conditions (including the local buckling of the top flange), the objective of the second series is to study the collapse behaviour stemming from lateral-torsional buckling. The results obtained confirm that, due to the GFRP low Young’s modulus and high strength, the beam structural integrity is often governed by excessive deformation and/or local and global buckling phenomena, rather than by material strength limitations. Moreover, the low shear-to-Young’s modulus ratio implies that the role played by the shear deformation is quite relevant, particularly in stocky beams. The experimental data presented here is used to validate and assess the accuracy of numerical simulations reported in a companion paper (Part 2). [Copyright &y& Elsevier]

Abstract: Cross-section classification is an important concept in the design of metallic structures, as it addresses the susceptibility of a cross-section to local buckling and defines its appropriate design resistance. For structural stainless steel, test data on cross-section capacity have previously been relatively scarce. Existing design guidance has been developed based on the limited experimental results and conservative assumptions, generally leading to unduly strict slenderness limits. In recent years, available test data for stainless steel cross-sections have increased significantly, enabling these slenderness limits to be re-assessed. In this paper all available stainless steel test data have been collected and additional moment–rotation curves have been presented. The study covers both cold-formed and welded plated elements as well as CHS. Following analysis of the test results, new slenderness limits for all loading conditions have been proposed and statistically validated. In addition to re-assessment of the current slenderness limits, a new approach to the treatment of local buckling in structural elements–the Continuous Strength Method–has been outlined. The Continuous Strength Method (CSM) is based on a continuous relationship between cross-section slenderness and deformation capacity and is applied in conjunction with accurate material modelling. The method enables more rational and precise prediction of local buckling than can be achieved with the traditional cross-section classification approach, thus allowing better utilization of material and more economic design. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to provide and verify a new design method for the in-plane compressive strength of steel sandwich panels comprised of steel face sheets and foamed steel cores. Foamed steel, literally steel with internal voids, provides enhanced bending rigidity, exceptional energy dissipation, and the potential to mitigate local instability. In this work, Winter''s effective width expression is generalized to the case of steel foam sandwich panels. The generalization requires modification of the elastic buckling expressions to account for panel non-composite bending rigidity and shear deformations. In addition, an equivalent yield stress is introduced to provide a single parameter description of the yielding behavior of the steel face sheets and steel foam core. The provided analytical expressions are verified with finite element simulations employing three-dimensional continuum elements and calibrated constitutive models specific to metallic foams. The developed closed-form design expressions are employed to conduct parametric studies of steel foam sandwich panels, which (a) demonstrate the significant strength improvements possible when compared with solid steel, and (b) provide insights on the optimal balance between steel face sheet thickness and density of the foamed steel core. This work is part of a larger effort to help develop steel foam as a material with relevance to civil engineering applications. [Copyright &y& Elsevier]

Cold-formed thin-walled sections are prone to local buckling caused by residual stresses, geometrical imperfections and inconsistency of material properties. We present a real case of buckling failure and conduct a numerical and experimental study aimed to identify methods capable of predicting such failures. It is important because designers of structures are getting more FEA-oriented and tend to avoid lengthy procedures of cold-formed structures design. Currently adopted methods are complicated and require patience and caution from a designer which is reasonable in case of the most important structural members but not necessarily so in ordinary design. Since it is important, we offer an insight into several FEA and manual methods which were sufficient to predict the failure while remaining fairly simple. Using a non-uniform partial safety factor was still necessary. We hope that this paper will be of interest for people performing a lot of routine analyses and worrying about reliability of their computations. [ABSTRACT FROM AUTHOR]

One of the most concerned problems for analytical estimation of ultimate strength and ductility of steel bridge columns is the consideration of local buckling. Stress-strain curves with softening behavior to include local buckling in fiber model analysis method were proposed by several researchers. However, accuracy of those models is still relatively low. As a consequence, most steel bridge designs have been done using fiber model analysis method without consideration of local buckling. In order to improve the analytical response estimation of steel bridge columns, a fiber model analysis method considering local buckling is proposed in this study. In this method, multi-fiber elements were used to model the local buckling length to simulate local buckling deformation. The proposed method shows good results not only for estimating peak strength but also post-peak strength compared to previous experimental results. However, further research should be directed to improve the accuracy of the deformation modes. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a general formulation for the analysis of steel hollow structural beams subjected to biaxial bending. The model has been developed within the framework of lumped damage mechanics. In this approach, the models are based on methods of continuum damage mechanics and the concept of plastic hinge. The model was implemented in a commercial finite element program. In order to calibrate the model, a set of experimental tests were carried out in the Structural Mechanics Laboratory at the Lisandro Alvarado University. The model was evaluated by the numerical simulation of these tests finding a good agreement between the experimental tests and the numerical simulations. [Copyright &y& Elsevier]

Abstract: This paper describes the flexural strength of welded sections based on a series of flexural tests performed on H-sections fabricated from steel plates of thickness 6.0mm with nominal yield stress of 315.0MPa. Thin-walled flexural members undergo local, lateral-torsional or their interactive buckling according to the section geometries and lateral boundary conditions. Flexural members with the flanges or the web of large width-to-thickness ratios may undergo local buckling before lateral-torsional buckling and their interaction before the final collapse of the section. The local buckling has a negative effect on the flexural strength based on the lateral-torsional buckling. This phenomenon should be considered in the estimation of the nominal flexural strength of thin-walled flexural members. Welded H-section beams composed of the flanges and the web with various width-to-thickness ratios were tested to failure. The initial imperfections in local and lateral buckling mode, and residual stresses were included in the FE analyses. Simple design flexural strength formulas for the direct strength method (DSM) were proposed based on the test and FE results of welded sections to account for interaction between local and lateral-torsional buckling. The design strength curves were compared with the AISC specifications (2005), Eurocode3 (2003) and test results. The adequacy of the strength curve for the DSM was confirmed. A set of conclusions on the flexural strength and structural behavior of thin-walled welded H-sections was drawn from the experimental studies. [Copyright &y& Elsevier]

Current models to determine the local buckling stress of inelastic plates under in-plane loading are based on plastic deformation theory and semirational or empirical relationships. A successful J2 flow theory describing inelastic local buckling of initially perfect plates needs to avoid two well-known pitfalls known as the “inelastic column buckling paradox” and the “plastic buckling paradox.” While the former problem, which found its origin in 1895 in Engesser’s double modulus approach, was resolved by Shanley in the late 1940s, a convincing solution of the plastic buckling paradox has not yet been presented. This paper proposes a modification to the J2 flow theory which hinges on the determination of the shear stiffness from second-order considerations. A differential equation is derived which describes the incremental plate deformations at the inelastic local buckling load. The differential equation is studied for two cases of boundary conditions: a plate simply supported along four edges and a plate simply supported along three edges with one longitudinal edge free. [ABSTRACT FROM AUTHOR]

This paper presents a special thin-walled plane beam finite element that accounts for the in-plane cross-section local deformation. The element is based on the superposition of a classical beam displacement field and of an additional field describing local effects, with an approximation on the local second-order membrane stress field. The theoretical formulation is summarized and an application of the resulting numerical tool to the post-buckling analysis of RHS thin-walled members with moderate local and global slenderness susceptible to both global and local buckling is then performed. Different types of analyses are presented (computation of critical bifurcation loads, geometrically non-linear analysis, geometrically and materially non-linear analysis). The results obtained with the proposed beam finite element are compared to values provided by shell FE models. [ABSTRACT FROM AUTHOR]

Long-term large deformation geohazards can impose excessive deformation on a buried pipeline. The ground displacement field may initiate pipeline deformation mechanisms that exceed design acceptance criteria with respect to serviceability requirements or ultimate limit states. The conventional engineering approach to define the mechanical performance of pipelines has been based on combined loading events for in-air conditions. This methodology may be conservative, as it ignores the soil effect that imposes geotechnical loads, and also provides restraint, on buried pipelines. The importance of pipeline-soil interaction and load-transfer mechanisms that may affect local buckling of buried pipelines is not well understood. A three-dimensional continuum finite element model, simulating the local buckling response of a buried pipe, using the software package ABAQUS/Standard was developed and calibrated. A comprehensive parametric study was previously conducted to investigate the effect of several parameters on local buckling response of pipelines buried in firm clay. A new strain criterion for local buckling of buried pipelines in firm clay through response surface methodology was developed. In this paper, the new criterion is compared with several existing in-air criteria to study the effect of soil restraint on the local buckling response of buried pipelines. The criterion developed in this study predicts greater characteristic critical strain capacity than in-air based criteria that highlights the influence of soil restraint. [ABSTRACT FROM AUTHOR]

Abstract: Box columns are often used as main strength members of various types of thin-walled structures such as ships, ship-shaped offshore structures, and aerospace structures. Until and after the ultimate limit state is reached, box columns exhibit highly nonlinear structural behavior in terms of geometrical and material aspects. In particular, the effects of local buckling, global buckling, and their interaction play a significant role in the resulting consequences of box columns under extreme actions. In order to calculate the maximum load-carrying capacity of box columns, it is thus highly required to perform the progressive collapse analysis to take into account progressive failures of individual components and their interacting effects. The aim of the present study is to demonstrate a method that is useful for the progressive collapse analysis of thin-walled box columns in terms of computational efficiency and accuracy. Theoretical outline of the method is addressed. Short, medium and long box columns in length are studied in terms of interacting effects between local component failure modes and global system failure modes. The effect of unloaded edge conditions of individual plate elements is also studied. A comparison of the method with more refined nonlinear finite element method computations is made. [Copyright &y& Elsevier]

In order to study the effect of damage caused by local buckling on the seismic behavior of steel frames under severe earthquakes, beam element model and fine shell element model were respectively established by ABAQUS. The differences caused by damage of two models were compared. Shell element model was proved correct and applicable comparing with typical quasi-static tests, which was considered to accurately describe the degraded behavior. Base on this confirmation, beam element model and shell element model were performed for quasi-static and nonlinear time history analysis. The characteristics of structural deformation, hysteresis energy and failure modes were compared. The results show that: before the occurrence of damage and degradation, seismic indices calculated by the two models are in accordance. However, once local buckling causes damage, the results of the two models are remarkably different. Beam element model underestimated the structural deformation and plasticity development level. [ABSTRACT FROM AUTHOR]

Abstract: The bifurcation equations for locally buckled point symmetric sections are derived in a companion paper [Rasmussen KJR. Bifurcation of locally buckled point symmetric columns—analytical developments. Thin-walled Struct, submitted for publication]. In the present paper, two series of experiments are reported, one on narrow flange Z-sections and one on wide flange Z-sections. The main objective of the tests was to validate the bifurcation load predictions derived in [Rasmussen KJR. Bifurcation of locally buckled point symmetric columns—analytical developments. Thin-walled Struct, submitted for publication] against experimental values. A further objective of the tests on narrow flange sections was to investigate the change in the direction of overall buckling, as predicted by the theory, from principal axis directions to non-principal directions. A further objective of the tests on wide flange sections was to investigate the possible change of the critical overall buckling mode from a flexural mode to a torsional mode as a result of local buckling. Agreement is generally found between analytical and experimental results. [Copyright &y& Elsevier]

This paper investigates the effects of precondition characteristics on the residual compressive strength (RCS) of 16-ply carbon/epoxy panels through the establishment of their compressive and buckling response characteristics. The preconditions of varying sizes include impact damage and embedded artificial delaminations of both circular and elliptical shapes. A sequence of prebuckling, local and global buckling, and postbuckling is found in both the longitudinal and transverse directions. The possibility of delamination propagation is examined using the response characteristics on the basis of the sequences. A damage threshold is found at the 25% panel width or 455mm² damage area. Both the global buckling loads and the RCSs suffer substantial degradation but in a different manner, depending on the threshold. For small damages, the global buckling loads are unaffected but the RCSs suffer substantial degradation, though there is little evidence for the delamination propagation. For large damages, while the global buckling loads are reduced moderately with an increase of the damages due likely to the unstable global buckling-to-postbuckling transition, the RCSs do not suffer further reduction, though evidence is found for the delamination propagation. These panels fail soon after the unstable global buckling-to-postbuckling transition. Panels with multiple delaminations suffer a greater reduction in RCS than the impact-damaged panels. A combination of the delamination size and number is shown to have the most dominant effect on the RCSs. It is demonstrated that the present method of embedding artificial delaminations proves to be very useful for studying the RCS of impact-damaged panels via the establishment of response characteristics and their links to the effects of the preconditions on them. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the results of an investigation of the non-linear behavior of delaminated sandwich panels with a compressible core. The delaminated zone, at one of the face-core interfaces, consists of through-the-width crack, which is free of shear stresses but is capable of accommodating partial contact with compressive stresses only within the debonded zone. The governing non-linear equations along with the appropriate boundary conditions and the continuity conditions are derived through variational principles. The governing equations include moderate deformations type of kinematic relations, and include the high-order effects due to the transverse flexibility of the core. The governing equations along with the stress and displacements fields for the core and the appropriate continuity conditions are presented. The effects of the non-linear response and the partial contact are described through some numerical cases of three points bending typical sandwich panels with inner delaminations in the vicinity of a concentrated load, in the vicinity of a stiffened core and, finally, far from the load. Numerical results in the form of displacements, bending moments, shear stresses in the core and vertical interfacial normal stresses at the upper and lower face-core interfaces along the panel length and at the delamination crack tips are presented. Buckling curves of load versus various extreme structural parameters are included. The analyses show that a full contact type of delamination transforms into a partial contact area with buckling of the compressed face sheet, as the load is increased and it is associated with extreme large displacements and stresses. [Copyright &y& Elsevier]

The stress–strain state and local buckling of thin plates with an oblique edge crack are studied. An expression for critical stresses is derived [ABSTRACT FROM AUTHOR]

An experimental study of the in-plane compression failure of sandwich panels consisting of glass/epoxy face sheets over a range of PVC foam cores (H45, H100, and H200) and a balsa wood core containing one or two circular or square interfacial debonds is conducted. For the great majority of the specimens, failure occurred by local buckling of the debonded lace sheet followed by rapid debond growth towards the panel edges, perpendicular to the applied load. Panels with the largest debond (10cm diameter or 9cm length) displayed some post-buckling strength. Examination of the face and core failure surfaces after total separation showed that the tendency for interface (core/resin) failure increases with increasing core density. It was found that the compression strength strongly decreases with decreasing core stiffness and increasing debond size. The compression strength of panels with H45 core decreased with reduced core thickness. Failure loads for panels with symmetric debonds at both face/core interfaces were practically the same as those for panels containing a single debond. Panels with square debonds failed at lower loads than those with circular debonds of the same area. Circular debonds of 50 mm diameter and square debonds of 45 mm length set the threshold for debond failure of the panels considered here. [ABSTRACT FROM AUTHOR]

Hot rolled angles are classified into two categories: equal-leg and unequal-leg. Owing to the difference in cross sectional symmetry, these two kinds of angles, when subjected to axial compression, behave differently. Whether the flexural buckling about the minor axis or the flexural-torsional buckling about the major axis predominates in the inelastic range for equal-leg angle struts is a controversial issue. Analysis in this regard ascertains that, in the inelastic as well as in the elastic range, angles fail by flexural buckling. But for angles of high-strength steel, with large width- thickness ratios, it is necessary to take into account the effect of leg local buckling. Unequal-leg angles always fail by flexural-torsional buckling. The calculation of the critical load of these members is rather complicated. Through analytical calculations, an equivalent slenderness ratio is derived to transform the problem into a flexural buckling one. This approach applies to both elastic and inelastic ranges. Comparison with available test data shows that suggested approaches for the equal-leg and unequal-leg angles are both qualified for design use. [ABSTRACT FROM AUTHOR]

Abstract: The paper derives the differential equations for the overall bifurcation of locally buckled point-symmetric columns. It is shown that flexural buckling about the minor and major principal axes are coupled in a locally buckled point-symmetric column whereas the buckling modes are uncoupled in a non-locally buckled column. The governing equations are solved for simply supported and fixed-ended columns and applied to Z-sections. Overall bifurcation curves are obtained for five Z-sections with increasingly slender flanges. It is shown that local buckling reduces the elastic torsional buckling load more so than the flexural buckling load for Z-sections, and that local buckling can cause a mode switch from the flexural to the torsional mode in Z-sections with very slender flanges. [Copyright &y& Elsevier]

Abstract: Built-up columns are often used in steel buildings and bridges providing economical solutions in cases of large spans and/or heavy loads. Two main effects should be taken into account in their design that differentiate them from other structural members. One is the significant influence of shear deformations due to their reduced shear rigidity. The second is the interaction between global and local buckling. These effects are addressed here from both a numerical and an analytical point of view for laced built-up columns. It is concluded that the largest loss of capacity occurs when the local and global Euler critical stresses and the yield stress all coincide. This reduction in capacity becomes more prominent in the presence of imperfections, reaching magnitudes in the order of 50%. Despite the detrimental effects of mode interaction many major design codes do not provide sufficient pertinent guidance. In order to address this issue, a simple analytical method is proposed for calculating the collapse load of laced built-up members taking into account the above effects as well as global imperfections, local out-of straightness and plasticity, which is then verified by means of nonlinear finite element analysis, using either beam or shell elements. The proposed method is found to provide improved accuracy in comparison to EC3 specifications in cases of global elastic failure. [Copyright &y& Elsevier]

In the current work, the results of full-scale laboratory testing of 114.3 and 168.3 mm in diameter steel gas distribution pipes buried at different depths and in two different soil types under a reverse fault offset of 0.6 m are presented and discussed in terms of longitudinal strain distribution, pipe deformation, and cross-section distortion. Results show that the pipe deformation and accordingly its failure mode, and soil failure planes change with increasing burial depth. It was also found that severe cross-section distortion occurs at about 2.3 times the strain limit for onset of wrinkling suggested by various guidelines. [ABSTRACT FROM AUTHOR]

This work is part of an ongoing investigation aimed at comparing the mechanics underlying the application of generalized beam theory (GBT) and the constrained finite strip method (cFSM), two alternative modal approaches to analyze the elastic buckling behavior of open-sectional unbranched thin-walled members. Previous work included an overall comparison between the numerical results yielded by the two approaches for lipped channel columns and beams, which were shown to be essentially identical - the few minor discrepancies were fully explained. The next step consists of revisiting the kinematical assumptions and procedures adopted by GBT to identify and characterize the cross-sectional deformations modes, presenting, explaining, and interpreting them from a novel perspective, deemed more suitable for a true comparison with the displacement field constraints employed in cFSM - the main objective of this paper. The starting point is the derivation of the conventional finite strip method (FSM), intended to show that some of the corresponding matrices also appear in GBT. Indeed, it is demonstrated that the determination of the GBT deformation modes involves a set of particular FSM matrices, termed "cross-sectional matrices." After a brief comparison between the GBT and cFSM assumptions and procedures, an illustrative example is presented and discussed, in order to provide a better grasp of the concepts and procedures involved in the new approach to the GBT deformation mode determination. Finally, the paper closes with a few concluding remarks that also address the work to be carried out in the near future. [ABSTRACT FROM AUTHOR]

The works that have been already published on sandwich face wrinkling consider isotropic or almost isotropic sandwich configurations. Hence, only the critical wrinkling load needs to be evaluated in the principal compressive stress direction. This is insufficient for a sandwich panel with a higher degree of anisotropy. This paper presents a method for estimating the wrinkling behavior of highly anisotropic sandwich panels under biaxial loading. The method is based on the assumption that wrinkling occurs at the angle where the ratio of applied load to sustainable wrinkling loads reaches a global maximum. In addition to the description of the analytical theories, the paper presents comparisons with finite element calculations and testing of real sandwich configurations. The results indicate that the derived model works excellently both for uni- and biaxial loadings, though a small factor of safety is required as with all other standard wrinkling theories. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a comprehensive experimental and numerical investigation on the cyclic response of cold-formed steel columns with hollow rectangular sections. The present study examined the columns׳ post-buckling strength and rigidity degradation, deformation and failure modes, ductility, and energy dissipation capacity. The cold-formed steel members exhibited stable hysteretic performance up to the point of local buckling with considerable degradation in strength and ductility. The energy dissipation mechanisms from the in-plane plastic behavior and out-of-plane elastic buckling deformation were identified. The influence of the height-to-width ratio and axial-compression ratio on energy-dissipation and failure mode was also investigated. [Copyright &y& Elsevier]

Local buckling of steel structural members has to be well understood in order to design accurately steel structures in seismic areas. Induced softening moment-curvature law leads to a well known ill-posedness elastoplastic evolution problem. Localization is chosen to be controlled with a gradient plasticity approach. The concept of cross-section behavioural classes, classically adopted in modern rule design, should be substituted by the concept of member behavioural classes. To cite this article: N. Challamel, C. R. Mecanique 331 (2003). [Copyright &y& Elsevier]

This paper addresses a nonlinear finite element method for the crippling analysis of composite laminated stringers. For the finite element modeling, a nine-node laminated shell element based on the first order shear deformation theory is used. Failure-induced stiffness degradation is simulated by the complete unloading method. A modified arc-length algorithm is incorporated in the nonlinear finite element method to trace the post-failure equilibrium path after a local buckling. Finite element results show excellent agreement with those of previous experiment. A parametric study is performed to assess the effect of the flange-width, web-height, and stacking sequence on the buckling, local buckling, and crippling stresses of stringers. [Copyright &y& Elsevier]

Abstract: This experimental project investigates and validates an innovative method to confine the potential plastic hinge zone of hot-rolled H-shape (or wide-flange) steel column for improved seismic behavior. Based on fundamental mechanics, the concept aims at controlling the local buckling of the flange and web elements of the H-shape steel in the potential plastic hinge region of a column. In the experimental program, six model columns were tested under constant axial load and cyclic lateral forces acting in either the weak or the strong axes. Compared with the conventional H-shape steel model columns, the model columns with their potential plastic hinge zone confined by either steel strips or reinforced concrete cover, exhibited excellent seismic performance with large ductility. Analytical efforts to compare with the test results were also made using simple moment-curvature analysis. [Copyright &y& Elsevier]

Abstract: The plastic collapse response of structural steel elliptical hollow section (EHS) profiles in compression is examined in this paper. As an initial step, a parametric study to identify the factors that determine which plastic mechanisms would arise has been carried out using finite element (FE) results from the current work and experimental data from the literature. All investigated EHS had a cross-sectional aspect ratio of two. The parametric study revealed four plastic collapse mechanisms and showed that the “split flip disc” plastic collapse mechanism is the most likely to appear in compressed EHS. Thus, the present work is focussed on this failure mechanism, for which an analytical model to describe the relationship between load and deformation is developed. Coupled with the consideration of the elastic, yielding and strain hardening characteristics of steel, the derived analytical model enables construction of the full load–deformation behaviour of compressed EHS to be established. The parameters controlling the shape and size of the plastic hinges have been investigated and found to be of key importance; hence, special care has been taken in their definition. Finally, the developed load–displacement curves have been compared with both finite element results and experimental data. The comparisons have revealed good agreement, confirming the ability of the analytical model to predict the collapse response of elliptical tubes. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the behaviour and design of axially loaded concrete filled stainless steel circular and square hollow sections. The experimental investigation was conducted using different concrete cube strengths varied from 30 to 100 MPa. The column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with existing design methods for composite carbon steel sections — Eurocode 4 and ACI. It was found that existing design guidance for carbon steel may generally be safely applied to concrete filled stainless steel tubes, though it tends to be over-conservative. A continuous strength method is proposed and it is found to provide the most accurate and consistent prediction of the axial capacity of the composite concrete filled stainless steel hollow sections due largely to the more precise assessment of the contribution of the stainless steel tube to the composite resistance. [Copyright &y& Elsevier]

For medium and large spans of trusses efficient solutions can be achieved with members made of cold formed sections due to the easiness of production and the nearly unlimited variety of cross-section types and the high-strength steels available today. The use of ‘pentagon’ cross-sections with a large radius of gyration for both axes offers statical and constructional advantages for the chords. The low-cost design of the truss joints using a gusset plate welded onto the ridge of the cross-section can lead, however, to great section deformations and consequently also to an early failure of the entire construction. This local load-bearing behavior can be described by the following analytical calculation model based on the Generalized Beam Theory (GBT). Furthermore this analytical model has been compared with tests on truss segments and results of an numerical analysis using the finite element program system ABAQUS. [Copyright &y& Elsevier]