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Design specifications in North America, unlike their European counterpart, use same equations for design of rolled and welded shape beams for lateral torsional buckling (LTB). A recent study by MacPhedran and Grondin (2011) has shown that the current Canadian design equations might overestimate the capacity of welded wide flange (WWF) beams, which are welded I-shapes, requiring further investigation. This paper evaluates the performance of the current design equations for LTB capacities of welded I-shape beams. Nonlinear Finite Element (FE) analysis is performed for simply supported WWF beams subjected to constant moment, linear and nonlinear moment gradient. Three types of linear moment gradients are investigated: end moment ratios of 0.5, 0.0, and − 1.0. Also, two types of transverse loadings are considered: a concentrated load at mid-span and uniformly distributed load along the length, and applied at the top flange, shear center, and at the bottom flange. In total, 416 FE models are analyzed and it is observed that for constant moment loading both CSA and AISC overestimate the LTB capacity of welded I-shape beams by as much as 37%. FE analysis also shows that current CSA strength curve overestimates significantly the strength of WWF beams by as much as 40% for end moment ratio of 0.5. For transverse loading, current CSA strength curve overestimates the capacity significantly for top flange loading and underestimates for bottom flange loading. Also, Eurocode is found to be conservative for all cases and the proposed equation by MacPhedran and Grondin (2011) provides better predictions of LTB strengths of WWF shapes than the current CSA approach. [ABSTRACT FROM AUTHOR]

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

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

Experimental study on thin-walled welded steel beam-to-column connections under cyclic large plastic strain loading was conducted. Severe shear buckling in panel zones was observed during the testing. The connections have stable and excellent seismic performance, and finally failed due to the post-buckling ductile fracture. This paper aims to numerically simulate the post-buckling ductile cracking process using a proposed micro-mechanism based ductile fracture model, and further investigate critical factors, such as equivalent panel zone width-to-thickness ratio, axial load ratio and initial geometrical imperfection, that affect cracking behaviors of the connections. The cyclic ductile fracture model is verified with the experimental data, and employed to conduct the parametric analyses. Deterioration of stress-carrying capacity is also considered, so the fracture model can successfully simulate the load decrease in the load-displacement curves of the experimental results. [ABSTRACT FROM AUTHOR]

Abstract The present paper shows an experimental and numerical modelling investigation of the flexural-torsional buckling behaviour and load-carrying capacities of fixed-ended hot-rolled austenitic stainless steel equal-leg angle section columns. The testing programme was conducted on four austenitic stainless steel angle sections and involved material testing, initial global and torsional imperfection measurements and sixteen fixed-ended column tests. This was followed by a numerical simulation study, where the numerical models were firstly developed to validate against the experimental data and then utilised to perform numerical parametric studies to generate additional results over a broader range of member lengths and cross-section geometric dimensions. The derived test and finite element results were carefully analysed and then utilised to evaluate the accuracy of the established design rules in Europe, America and Australia/New Zealand. Comparisons of the failure loads derived from the experimental and numerical studies with the corresponding codified flexural-torsional buckling strength predictions revealed an unduly high level of conservatism and scatter. Extension of the direct strength method to carbon steel equal-leg angle section columns has been recently made, and the applicability of the approach to fixed-ended hot-rolled austenitic stainless equal-leg steel angle section columns was also assessed. The new approach was generally shown to yield more precise flexural-torsional buckling resistance predictions than the existing design standards, but a large portion of the predictions were unsafe, indicating that further improvements are required. Highlights • 16 fixed-ended hot-rolled austenitic stainless steel equal-leg angle section columns have been tested. • FE models have been validated against tests and used to perform parametric studies. • Current international design codes and other recent proposals have been described and discussed. • The accuracy of each approach has been evaluated against test and FE results. [ABSTRACT FROM AUTHOR]

Cellular and castellated members are usually produced by performing cutting and rewelding operations on a hot-rolled I-section member. As illustrated in previous work, these operations will influence the residual stresses present in the members in a manner which is detrimental for the flexural buckling resistance. Up to now, this has not been considered in the limited amount of literature concerning the flexural buckling resistance of these members. In this paper, the weak-axis flexural buckling resistance is examined, taking into account the influence of the modified residual stress pattern and the modified geometry of cellular and castellated members. Therefore, the critical buckling load and the buckling resistance of simply supported cellular and castellated members were investigated numerically. In the numerical model, a modified residual stress pattern was introduced, based on earlier measurements. As the amount of measurements was relatively limited, the results of these simulations should be considered as preliminary results, in attendance of a confirmation of the utilized residual stress pattern. The results of the simulations illustrate the detrimental influence of the expected residual stress pattern modification on the buckling resistance. By comparing the results with the European buckling curves, preliminary best fit curves could be selected. This comparison was executed with a 2T approach, in which all cross-sectional properties are calculated for the 2T section at the centre of the opening. [ABSTRACT FROM AUTHOR]

The effect of distortional deformation on the elastic lateral buckling of thin-walled box beam elements under combined bending and axial forces is investigated in this paper. For the purpose, an analytical model is developed for the stability of laterally unrestrained box beams according to higher order theory. Ritz and Galerkin's methods are applied in order to discretize the governing equilibrium equations and then the buckling loads are obtained by requiring the singularity of the tangential stiffness matrix. The different solutions are discussed and then compared to the finite element simulation using Abaqus software where shell elements are used in the mesh process. The numerical results reveal that classical stability solutions as those adopted in Eurocode 3 overestimate the real lateral buckling resistance of thin-walled box beam members, particularly for the ones with high ratios between the height and the thickness of the cross-section. Numerical study of incidence of compressive forces on lateral buckling resistance of thin-walled box beam is investigated. [ABSTRACT FROM AUTHOR]

Abstract: Various methods can be used to investigate buckling phenomena in a steel compression member. Among these methods, experimental formulas, semi-empirical formulas, closed-form solutions and classic methods based on differential equations as well as numerical methods based on finite elements are most commonly used. All of these methods have associated complexities. Thus, it is very difficult to perform a comprehensive parametric study on the buckling phenomenon of a compression member using these methods. The simplicity of the mathematical concepts used in ANNs (artificial neural networks) and their ability to model complex problems have led to the popularity of ANNs. After the learning step of an ANN, a function can be determined as a relationship between the input variables and output parameters, which is a load–displacement relationship in this article. It is then possible to perform an extensive parametric study on the buckling behavior of a compression member. In this research, the network can also extract the critical load–slenderness relationship. Using this network, it is possible to conduct an accurate study on the effects of various parameters at the critical load as well as to evaluate the sensitivity of the critical load to each variable used in the ANN training. [Copyright &y& Elsevier]

Abstract: Large parabolic dish concentrators have been widely employed in solar thermal applications. The supporting structure of a solar dish concentrator consists of a circular frame, a central post, and front and rear cables connecting the frame to the post. The tensions in the cables cause compressive stresses in the circular frame and the central post, and this support structure must be designed for stability. In this paper, the nonlinear buckling behavior of the supporting structure of a cable-stayed circular frame is studied in detail. A three-dimensional finite element model of the supporting structure is developed to predict the critical cable tensions that would cause buckling of the circular frame and to determine the associated buckling mode shapes of the supporting structural system. The results show that the buckling load of a cable-stayed circular frame depends not only upon the cross-section of the frame, but also upon the number of cables and the inclinations of the cables. In all cases, in-plane buckling modes are predominant. The concentrated torques resulting from unbalanced cable tensions tend to induce the out-of-plane buckling modes. [Copyright &y& Elsevier]

Abstract: The detrimental effect due to perforations on the buckling resistance of perforated hot-rolled steel L-shaped members in compression is evaluated in the current paper. FEM numerical models are used in order to carry out buckling and non linear analyses with the aim of detecting both the critical and the collapse load of the studied elements in case of one or more holes. The obtained results show that, although the critical load is not strongly influenced by the presence of holes, the load bearing capacity, when members are characterized by middle–low slenderness, could be significantly diminished when drillings of common sizes are applied on one of the two section legs, meaning that current methods given by the codes are not fully conservative. As a consequence, specific stability curves are determined and proposed as useful alternative design procedure. [Copyright &y& Elsevier]

The paper presents the results of cyclic loading tests on all-steel buckling-restrained braces (BRBs), with the aim of investigating the contact phenomena and the associated lateral thrust occurring when the inner core of a BRB, after buckling, comes into contact with the external restraining case. A special test set-up was employed to detect the shape and extension of the contact zones, as well as the local contact pressures. Attention was focused on the role of certain key parameters governing the high-mode plastic buckling of the core, such as the size of the gap between the core and the restraining members, the stiffness of the containing case, and the cyclic loading history. The results show that the value of the lateral thrust generated by the core during its high-mode buckling increases, possibly up to very high values, with the gap/core thickness ratio, the axial core strain, and the cumulated plastic deformation of the core. The results might be a useful tool both to validate analytical expressions and numerical models for the assessment of the lateral thrust. Moreover, test results on full-size all-steel bolted BRBs showed that the design of the containment profiles and relevant connections cannot be made without an accurate estimate of the lateral thrust exerted by the buckled core under the adopted loading conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper first briefly reviews the modified effective length method in the literature for design of steel columns considering the inter-column interaction with the limitations outlined. To overcome these limitations, a new storey-buckling approach for steel frames is presented, where each storey is treated as a whole at the sway buckling, and its resistance is evaluated using the presented storey-buckling factor, which can be obtained from the defined storey slenderness using the relationships illustrated by the column curves in current codes. In total, 30 frame examples, considering the effects of storey number, the span number and the configuration of axial forces in columns, are adopted to examine the proposed method. Comparisons between FE results show that the presented method has good performances in predicting the failure load of considered frames. In FE analysis, the geometric and material nonlinearities as well as two types of geometric imperfections and longitudinal residual stresses are considered. Predictions from the notional load approach are also compared with FE results for some cases, which shows that these predictions may underestimate or overestimate the failure load of certain frames. The interaction between the sway buckling of the whole storey and the non-sway buckling of the weakest column may reduce the failure load of steel frames. In this study, a reduction factor is presented to consider this mode interaction, and comparisons with FE results show that this method can reasonably assess the adverse effects of this mode interaction. [Copyright &y& Elsevier]

Progressive collapse is disproportionate failure of the structure due to the failure of a relatively small part of it. Catenary action is a load mechanism that is developed to resist the additional loads as a result of sudden column loss and prevent disproportionate collapse. Buckling restrained braces (BRBs) have been widely adopted as a dependable lateral load mechanism since the early 1990s. The impact of BRBs on the performance of steel frames subjected to lateral seismic forces suggests that BRBs might be beneficial to steel frames that are subjected to progressive collapse loads as well. The objective of this research is to conduct a detailed study on the impact of BRBs on the catenary action demands in steel framed structures. Push-down analysis of three, five and eight story steel frames with and without BRBs was carried out. The results showed that buckling restrained braced frames had a higher load carrying capacity compared to the bare steel frames. Different BRB placement scenarios and building heights were considered for this study. The BRB placement scenarios had more impact on the catenary action demands of the steel frame compared to the different building heights. Different loading types were studied and results showed that the loading of the model has significant impact on developed catenary forces. Finally, the results of the study highlight the importance of incorporating BRBs in future guidelines addressing the progressive collapse resistance of steel structures. [ABSTRACT FROM AUTHOR]

Submarine pipelines are important and influential structures in marine engineering because they transport important, useful, and common fuels around the world. The pipeline structure is affected by different environmental forces from the surrounding conditions such as the external uniform hydrostatic pressure, hydrodynamic pressure, seismic forces, installation forces, free span forces, and forces scouring the pipeline. These conditions cause the pipeline to express complicated behavior. Local buckling and buckling propagation along the pipeline are common examples of collapses under these conditions and loadings, which can destroy thousands of meters of pipeline. These post-buckling phenomena cause great damage and losses to the oil and gas industries and to the environment; the imposed costs for the repair and protection of pipelines and mitigation of environmental problems are high. The use of ring-stiffeners is one way of increasing the buckling capacity of a pipeline in order to prevent and control the buckling propagation in pipelines. In this study, the buckling and post-buckling behaviors of ring-stiffened pipelines were investigated at a small scale through experiments and the finite element method (FEM). Two different ring-stiffeners were attached to the specimens. Only the uniform hydrostatic pressure was considered as the main loading; the axial stress was neglected in this study. The buckling modes, lateral displacement of the pipeline, ring tilt, formation of yielding lines, and torsion of yielding lines were examined. The results indicated that increasing the number of ring-stiffeners greatly increases the buckling capacity and lateral displacement of the pipeline. The buckling modes were changed, the post-buckling region was shortened, and torsion in the yielding lines and tilting in the ring-stiffeners clearly appeared in the tests. The results of this study were compared with those of recent research and reliable guidelines and standards. [ABSTRACT FROM AUTHOR]

Abstract: Nine square concrete-filled box column (CFBC) specimens were fabricated and tested under monotonic axial loading. The loading tests were simulated with the commercial finite element program ABAQUS. The feasibility of the finite element models was verified. Based on tests and FEM simulation results, the following conclusions can be made. The development procedure of the concrete confinement mechanism of CFBCs was identified. After concrete crushing occurs, concrete confinement provided by the horizontal arch action starts to become noticeable. After buckling of the column wall, vertical arch action, which provides additional concrete confinement, is developed. Horizontal arch action acting together with vertical arch action provides significant confinement for the concrete to gain and recover its strength. A larger width-to-thickness ratio of the column wall results in the earlier development of vertical arch action. From the concrete confinement mechanism, there will be a strength drop and a strength recovery in the concrete component of the load versus axial strain curve. As a result of these findings, Mander''s concrete confinement model and Sakino''s concrete analytical model were not able to reasonably predict the stress–strain behavior of the concrete inside CFBCs. [Copyright &y& Elsevier]

Abstract: The critical buckling load of a structure undergoing lateral buckling can be determined experimentally by using the extrapolation or plotting techniques, without having to subject the structure to loading in the vicinity of critical. To achieve this, it is only necessary to have data relating load to a deformation characteristic. A search of the literature reveals that only certain and just a few deformation characteristics such as lateral displacement and/or twist have mostly been used by researchers in this regard. In this paper, the feasibility of application of various deformation variables for experimental determination of the critical buckling load is investigated in case of I-beams with different initial geometrical imperfections undergoing the elastic lateral–distortional mode of buckling. It is demonstrated that lateral displacement of the I-beams is directly coupled with different deformation variables such as web transverse and longitudinal strains, vertical deflection, and angles of twist of top and bottom flanges. Based on these key findings, the Southwell, Massey, Modified, and Meck Plot methods are applied on these various deformation variables, and consequently satisfactory and reliable estimates are obtained for the critical buckling loads. Finally, it may be concluded that the application of the extrapolation techniques does not actually need to be limited to some certain deformation variables. [Copyright &y& Elsevier]

Abstract: Concentric braced frames are commonly used in steel structures to withstand lateral forces. However, brace hysteretic behavior is asymmetric in tension and compression. These frames typically exhibit substantial strength deterioration when loaded in compression. Consequently, the concept of Buckling Restrained Brace (BRB) has been introduced to overcome this deficiency. The length of a BRB steel core could have a significant effect on its overall behavior since it directly influences the energy dissipation of the member. Furthermore, BRB could be effectively utilized as a damper to dissipate seismic input energy, particularly when used as a fuse within the brace in a frame. Modified BRBs with shorter lengths may be called damper BRBs, because they function as if a typical damper is utilized along any brace member. These damper BRBs are fabricated and tested in this study both experimentally and analytically. Useful insights into local retrofitting of core plates and connections are also provided. [Copyright &y& Elsevier]

Abstract: A full scale experimental investigation into the strength and behaviour of prestressed steel stayed columns in compression has been conducted. Results, including full load versus end-shortening curves, for a total of 18 test specimens are presented. Two critical modes of buckling — symmetric and antisymmetric — with interactive post-buckling are demonstrated experimentally and the imperfection sensitivity of the stayed columns is investigated. Interactive buckling is observed primarily when the individual buckling loads of the antisymmetric and symmetric modes are close or when the antisymmetric mode is critical. Analysis of the results reveals that increased prestress leads to an increased load-carrying capacity when instability occurs in the symmetric mode, but the reverse trend is found when the antisymmetric mode is critical. [Copyright &y& Elsevier]

Abstract: Compression buckling tests were performed on four full-scale W-shaped column specimens to investigate the buckling response of columns in multi-storey braced steel frame structures subjected to seismic strong ground motions. The test protocols included monotonically and cyclically applied concentric and eccentric axial loading. One test was conducted under dynamic cyclic loading. End moments were applied on one cyclic test. The columns were W310×129 compact (class 1) sections made with ASTM A992 steel. Weak axis buckling was studied and the column had an effective slenderness ratio of 48. The response of the test columns was also examined using numerical simulations based on fibre discretization of the member cross-section. Column residual stresses and strain rate effects on the material properties were both characterized and accounted for in the numerical models. The study showed that steel columns can sustain several cycles of inelastic buckling under seismic induced loading while maintaining sufficient compressive resistance to support the applied gravity loads. Residual stresses affected the column response only at the first buckling occurrence with a gradual reduction of the columns’ tangent stiffness prior to buckling as well as a reduction of the column’s compressive resistance. High strain rates anticipated during strong earthquakes increased the column buckling and post-buckling strengths. The cyclic buckling response of steel columns can be predicted adequately when using nonlinear beam–column elements and cross-section fibre discretization provided that residual stresses and strain rate effects are included in the modelling. [Copyright &y& Elsevier]

ABSTRACT Physical theory models for strut members have been proposed in the past few years to efficiently and accurately investigate the influence of member buckling on the dynamic failure mechanism of long-span spatial structures. However, most of them can only simulate the Bauschinger effect without considering the reduction behavior of critical loads under cyclic load reversals. This study devoted to propose an improved physical theory model based on the authors' previous work. Cyclic loading tests on circular and square members were conducted. The range of slenderness ratio of the specimens is from 60 to 130, which is commonly used in long-span spatial structures. Based on the experimental results, empirical coefficients are introduced to the improved model, in which each member can be discretized by only one beam element. Using this model, the cyclic buckling behavior of members can be efficiently and accurately considered with various section types, slenderness ratios, and boundary conditions. Finally, the improved model is verified by experiments conducted in this study and in previous studies. A close agreement is found between the simulated and experimental results. Highlights • An improved physical theory model is proposed to predict the cyclic buckling behaviors of strut members in long-span spatial structures. • 12 specimens are tested to propose the improved physical theory model. • The reduction behavior of the critical loads after the member yields and the Bauschinger effect can be accounted. • A close agreement is found between the simulated and experimental results conducted in this paper and in previous studies. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation into locally unstable ultra-light-gauge steel storage rack frames that are prone to flexural-torsional buckling. The aim of the research was to understand how local instabilities and interactive buckling affect the strength of ultra-light gauge frames and to create reliable data through a controlled experimental investigation. A total of twelve full scale tests were conducted in the Civil Engineering Structures Laboratory at the University of Sydney. Prior to testing, the geometric imperfections of each member were measured, as were the material properties of the cold-rolled sections and the virgin steel from which the sections were formed. The cross-sectional deformations, ultimate loads and observations regarding failure modes were accurately captured and documented. The tests were also successful in capturing the post-ultimate response of the frames as well as the rotational stiffness of the beam-to-upright connections. Results from nominally identical tests were in good agreement. The tests provide comprehensive data for assessing the effects of interactive buckling and the extent to which cross-sectional deformations amplify the second-order deformations in locally unstable storage rack frames. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports an investigation aimed at developing a Direct Strength Method (DSM) approach to estimate the ultimate strength of lipped channel columns affected by local/distortional buckling mode interaction. Following a brief presentation of a few relevant aspects concerning the shell finite element analysis of the geometrically and materially non-linear behaviour of thin-walled members, one illustrates the methodology adopted to obtain a lipped channel column ultimate load “data bank” intended to be used in the development and assessment of a DSM design approach. Next, the current DSM expressions to predict the load-carrying capacity of columns failing in local and distortional modes are briefly reviewed, devoting special attention to an approach that takes into account the above mode interaction. Then, the results of a parametric study, carried out by means of the code Abaqus, are presented and discussed — this study involves the evaluation of the “exact” ultimate loads of 276 lipped channel columns with various geometries and two boundary conditions (pinned and fixed end supports), all exhibiting local/distortional interaction. Finally, these ultimate strength data are compared with the estimates provided by the available DSM expressions and, on the basis of this comparison, one identifies several features that a DSM approach successfully accounting for local/distortional interaction must incorporate. [Copyright &y& Elsevier]

Local and distortional buckling reduces the flexural and warping rigidities of steel frames. As a result, the sway buckling load of locally unstable unbraced frames is reduced and sway deflections increase at a faster rate than corresponding locally stable unbraced frames. This leads to greater second order moments and potentially premature collapse, since commonly, unbraced steel frames are designed using elastic analyses (2nd order or 1st order with moment amplification) which assume unreduced values of the flexural and warping rigidities. This paper investigates the effects of second order moments induced by local and/or distortional buckling of the uprights of steel storage rack frames. Using results from the accompanying experimental investigation, calibrated FE models are used to predict the strength of steel storage rack frames with increasingly slender cross-sections. The FE strengths are compared to design strength predictions and conclusions are drawn about the extent to which current specifications are able to accommodate second order moments generated by local and/or distortional buckling. [ABSTRACT FROM AUTHOR]

Abstract: In previous studies, a proliferation of research work has been undertaken on the buckling behavior of shell structures particularly conical shells. Nonetheless, no experimental studies are found in the literature on the buckling of a full and real configured model of a slender shell reducer with two cylindrical end boundaries. To this end, buckling behavior of three conical shell reducers under uniform peripheral pressure was investigated and evaluated experimentally in this paper. In addition, relevant FE simulations as well as theoretical predictions were taken into account to compare buckling load and modes of deformation. Derived results were aimed at generalizing the data for conical reducers in full scale within the range of this study. [Copyright &y& Elsevier]

Abstract In this paper elastic and inelastic buckling analysis of the bolted double shear lap connections (DSL) are investigated, which are commonly used in concentrically braced steel frames comprised of cold-formed hollow structural section (HSS), as brace members. By the lack of any approach to evaluate the compression strength of a DSL connections, their design is usually relied on the tension load demand developed in the brace member. The results of quasi-static cyclic tests performed on six full-scaledX-bracing specimens have shown that the discontinuous brace member with DSL connection, not designed for compression, failed and fractured by the buckling at the connection. In all the specimens, the typical brace buckling only occurred in the continuous members, as expected. In this study. a simplified elastic stability analysis is employed to calculate elastic buckling load and effective length factor usable for the design of DSL connections. Anon-linear static analysis is also performed on a suggested numerical model comprised of beam-column elements to predict the response of the studied X-bracings, exhibiting the connection and member buckling. It is shown that the results of the both suggested design procedure based on the stability analysis and the numerical model agree well with the buckling load of the test specimens. It is also indicated that the slip of connection plates decreases the compression capacity and should be considered in the analysis and design procedures. Highlights • A procedure for the design of bolted double-shear-lap connection under compression load was presented. • The anti-symmetrical buckling mode is the governing compression behavior of the X-bracingmid-connection of type DSL. • For the corner connections, the three-hinge buckling strength can be evaluated through the presented design procedure. • DSL connection compression strength decreases when slip occurred between the plate. [ABSTRACT FROM AUTHOR]

In the construction of single layer domes and vaulted structures manufactured ball-node type connections are widely used. These ball-nodes deform due to the action of a three-dimensional state of stress while offering their resistance. These deformations result in a loss of connection stiffness, which influences the overall stability of these domes, and is usually ignored in the analysis. This work presents an investigation on the effect of ball-node deformations in the inelastic post-buckling behavior of domes and vaulted structures. A model for the load-deformation properties of the ball-nodes has been proposed in this study, in the lines of EC3-8. This connection flexibility model is integrated into a corotated–updated Lagrangian finite element formulation. Results for single layer domes and a braced barrel vault are presented. Although the present investigation deals with ball nodes only, the computational framework is still relevant for other type of connections of space structures, with modifications. [ABSTRACT FROM AUTHOR]

Abstract: Self-Compacting Concrete (SCC) use is spreading worldwide and it is becoming a regular solution in some special applications, including steel–concrete composite columns. In the particular case of Concrete Filled Tubes (CFT), the main advantage from a practical point of view in the use of SCC consists in employing the steel tube as a formwork to directly cast concrete inside it, without the need of vibration. The study of three different concretes for structural applications as composite elements is presented, each of them designed for a 28-day cylindrical compressive strength of 50 MPa: (i) a Normal Vibrated Concrete, (ii) a Self-Compacting Concrete, (iii) an expansive SCC (with the goal of an increase in bond strength as a consequence of the expansion). CFT with critical length ranging from 131 cm to 467 cm have been experimentally and analytically investigated in uniaxial compression. In each case the steel case presents a cross section of 139.6 mm of external diameter and 4.0 mm thickness and with a fixed eccentricity of the applied load equal to 25 mm. The bond strength at the steel–concrete interface is reported for each of the three mixes. The experimental and analytical results show that the behavior of eccentrically loaded columns is governed by the bending moment–axial load interaction. As a consequence, perfect bond at the interface can be assumed and the axial capacity of the column is only a function of its geometry and of the mechanical properties of the materials. A numerical procedure is proposed to evaluate the increase in the axial capacity of the composite columns consequent to the confinement of the internal concrete in case of zero-eccentricity of the applied axial load with respect to the column’s axis. Finally, the obtained numerical results are introduced into code provisions to evaluate modified axial force -bending moment interaction diagrams to predict the axial capacity of the column in the particular test configuration. [Copyright &y& Elsevier]

Abstract: The present research is devoted to the study of out-of-plane buckling of trusses with elastic side bracing. In this paper, a sensitivity analysis of critical buckling loads of a truss due to bracing stiffness is carried out. A method based on the sensitivity analysis for the determination of the threshold bracing stiffness condition for full bracing of a truss is proposed. The influence lines of the unit change of the bracing stiffness on the buckling load, for different initial bracing stiffness, are investigated. The approximations of an exact relation between the buckling load and bracing stiffness are found. The buckling length related to the side-support distance as a function of bracing stiffness is also determined. It is shown that the buckling length of truss chords with elastic side supports is larger than that assumed in design codes. [Copyright &y& Elsevier]

This study investigates the stability of the structural systems assembled by system scaffolds. Loading tests were conducted on the indoor single-bay system scaffolds and the outdoor full-scale structural system assembled by system scaffolds. Test results were compared with the second-order inelastic analysis with semi-rigid joints to determine the reliability of various analytical parameters. The study reveals that, while the failure model of the single-bay two-storey system scaffold without diagonal braces is overall buckling failure of the structure, the failure model of the same structure with diagonal braces is buckling failure of the vertical standards between the upper and lower storeys. The critical load of the configuration with diagonal braces is about double that of the same structure without diagonal braces. At the moment of buckling failure of the outdoor full-scale two-row, two-bay, six-storey structural system assembled by system scaffolds, the vertical standards at the four corners appeared to have large horizontal displacements owing to without diagonal braces. However, the vertical standard in the center did not exhibit obvious horizontal deformation because it was reinforced with diagonal braces on four sides. In addition, the use of diagonal braces can significantly increase the load capacity of vertical standards. This study recommends that all vertical standards be reinforced with diagonal braces to ensure the load capacity of the structural systems assembled by system scaffolds. A second-order inelastic analysis with semi-rigid joints and various notional lateral forces is recommended to determine the critical loads of full-scale structural systems assembled by system scaffolds. [ABSTRACT FROM AUTHOR]

Abstract: According to section D1.2 of AISI S100-2007 for compression members composed of two sections in contact whose buckling mode involves shear forces in the connectors, a reduction must be made, must be replaced by . This new modified slenderness ratio takes into account the connection weld spacing and the minimum radius of gyration of an individual shape in the built-up member. Under the provisions of section D1.2 a reduction in load capacity must be made for built-up welded box members, which are the subject of this study. An experimental investigation on 48 samples was addressed to determine the comparative behaviour under compression load of box sections composed of two C-section members in contact by seam welds with different weld spacings (ranging from 100 to 900 mm). The studs were tested simulating rigid and flexible end support conditions. The length of the samples was 900 mm with a cross-section of 100 mm×100 mm. The base material thickness was 1.5 mm (gauge 16) for 24 samples and 2.0 mm (gauge 14) for the rest. The testing done on the samples did not show a statistical reduction in the ultimate compression load capacity for these members except for a weld spacing of 900 mm and a flexible end support condition. The reduction considered in AISI S100-2007is not applicable to determine the ultimate load capacity for the rest of the members. [Copyright &y& Elsevier]

Abstract: A numerical model is developed to predict the behavior of castellated beams with hexagonal and octagonal openings up to failure. The numerical model takes into account both material and geometric nonlinearities. To initiate buckling, an initial small out-of-plane geometric imperfection, obtained from an eigenvalues buckling analysis, was imposed to the model. Results of experimental data obtained from previous works have shown that the model is able to predict, with good accuracy, the ultimate load and to some extent the mode of failure. A parametric study is then realized to assess the cross-section classification given in the Annex N and to compare between the ultimate load behavior of castellated beams with hexagonal and octagonal openings when subjected to flexure and shear force. The numerical results have been compared with those obtained with the design method presented in ENV1993-1-1 Annex N. [Copyright &y& Elsevier]

Abstract: In this paper, linear buckling analyses of plates with longitudinal stiffeners having various shapes and positions and subjected to axial force, in-plane bending and shear are developed. The aim is to give some new practical insights about the shape and optimum position of longitudinal stiffener in webs when axial force, bending moment and shear act. By means of a comprehensive numerical investigation, some practical issues for buckling phenomena in stiffened plates, taking into account (a) dimensions and shape (square and rectangular) of the plate, (b) dimensions and shape of the stiffener (with open and closed cross-sections), (c) location of the stiffener, and (d) load configuration (uniform compression, pure bending, combinations of axial compression and bending, and shear) are developed. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an overview of the mechanics of distortion in members which have restrained thin-walled steel sections. First, the basic features that characterize the distortion of thin-walled sections under compression and/or bending are explained and the generally adopted kinematical assumptions are presented and discussed. On the basis of these assumptions, a simple procedure to build the distortional displacement fields is proposed. Then, two illustrative examples of restrained sections are given and their distortional displacement fields are built. The I-section illustrates the case of a symmetric section having a distortional displacement field with a single d.o.f. The Z-section exemplifies the case of a non symmetric section having a distortional field with two d.o.f. Based on an energy formulation, the equilibrium equation for buckling analysis of simply supported thin-walled members is derived. For two illustrative examples, the distortional displacement field is used to obtain distortional analytical formulae. Finally, some results (buckling loads and moments) were determined and validated by means of comparison with fully numerical obtained from finite strip analysis. [Copyright &y& Elsevier]

This paper deals with the design of an innovative type of bolted junction that shows a high plastic range in the load displacement. The schematization studied and reported in this paper is generally valid for steel structures and can be applied where high ductility is required (for example structures subjected to earthquakes) or statically indeterminate structures. In this case due to the high ductility of the junction there is a redistribution of stress/load in the elements. For this implementation the bolted junction was studied and applied to the arches of a bridge (designed by the University of Brescia). The developed junction described in this paper will solve the problems described above and permit an adjustment of the arch length until a balanced configuration is reached. The design procedure includes a preliminary analytical computation using the most important buckling theories; subsequently it is carried out a numerical analysis which results are validated executing several experimental analyses on a scale model. The final scope is the design of an innovative junction for tubular elements with circular section which permits the modification of the post-buckling curve in order to increase the ductility of the entire junction. The geometric solution studied was verified numerically and experimentally tested on a scale model. The results show a meaningful increase in elastic plastic performance of the junction. Indicatively this innovative geometry increases the elastic plastic behavior on the experimental geometry approximately 2 times when compared with the junction of the tubular elements without the designed junction. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the study of the low-yield-point (LYP) steel plate shear walls under in-plane load. In the LYP steel plate shear wall system, LYP steel was selected for the steel plate wall while the boundary frame was constructed by the high strength structural steel. A series of experimental studies examined the inelastic shear buckling behavior of the LYP steel plate wall under monotonic in-plane load. The effects of width-to-thickness ratio on the shear buckling of LYP steel plates were examined. The stiffness, strength, deformation, and energy dissipation characteristics were investigated by performing cyclic loading tests on the multistorey LYP steel plate shear walls. Excellent deformation and energy dissipation capacity were obtained for all specimens tested. The LYP steel plate shear wall system is able to exceed 5% of storey drift angle under lateral force. [Copyright &y& Elsevier]

Abstract: Elliptical structural steel hollow sections represent a recent addition to the range of steel sections available to structural engineers. However, despite the extensive interest in their use on the basis of both architectural attraction and structural efficiency, a complete absence of fire resistance design guidance is restraining applications. This paper presents the first study ever conducted to investigate the fire resistance of steel columns with Elliptical Hollow Sections (EHS). Six columns of two slenderness and were tested under three loading levels ( and 0.6) and subjected to a hydrocarbon fire curve. The paper provides the recorded data of axial displacements and temperature profiles of the EHS steel columns, while highlighting the unique local and overall buckling failure modes of the Elliptical Hollow Section. [Copyright &y& Elsevier]

The main aim of this paper is to present results of a full-scale pushover test of a 40 meter telecommunication tower under breaking load. A detailed description of the studied tower has been presented with emphasis on the geometrical imperfections of the selected members of the structure. The results of the experiment consisting of the axial forces in the tower's members, as well as the displacements of the observed nodes as a function of external load have been presented. A comparison of a wind load based on the current standards with the load based on the experimental breaking force has been discussed for a typical set of telecommunication equipment. The main conclusion was that the structure's overall carrying capacity depended on the buckling resistance of the legs. Additionally, theoretical buckling resistances (based on standards) of the tower's legs made with round solid bars were smaller than the experimental axial forces in compression. [ABSTRACT FROM AUTHOR]

Abstract: Although several studies of the out-of-plane strength and design of steel arches with a solid web section have been reported, little research of the out-of-plane strength and design of spatially trussed arches has been reported in the open literature or design codes. In deference to the steel arch with a solid web section, the shear deformations play important parts in the out-of-plane inelastic buckling behavior of spatially trussed arches. In addition, global out-of-plane inelastic buckling of a spatially trussed arch is associated with local buckling of its components such as chord and diagonal web tubes and hence local component buckling influences the out-of-plane strength of the arch. This paper investigates the out-of-plane inelastic strength and design of spatially trussed circular arches with a rectangular lattice section under general loading using a three-dimensional nonlinear inelastic numerical approach. Methods for the out-of-plane inelastic strength and design of spatially trussed arches under uniform compression or under uniform bending are developed, based on which interaction equations for the design of spatially trussed steel arches under general loading against their out-plane failure are proposed. These interaction equations provide good lower bounds for the out-of-plane strength of spatially trussed arches. [Copyright &y& Elsevier]

Abstract: Thin-walled cylindrical shells are extensively used in numerous kinds of industrial applications under different cases of load combination. Nonetheless, quite few are the experimental researches that point out the real behavior of cylindrical shells under pure bending and external pressure. In the present experimental study, the buckling behavior of long cylindrical steel shells was investigated under combined bending and uniform peripheral pressure. Relevant FE simulations were also carried out and the results were compared with the experiments. The study shows that the theoretical outcomes predicted by nonlinear finite element analyses agree acceptably with the experimental results in terms of bucking load and modes of deformation. Furthermore, it was found that the initial sectional out of circularity developed by bending (especially higher values) considerably influences the buckling capacity of such shells under uniform external pressure. Ultimately, an interaction formula was proposed to generalize the interaction behavior of the test results within the range of this study. [Copyright &y& Elsevier]

Abstract: This paper presents compression tests of cold-formed plain and dimpled steel columns. A series of compression and tensile tests were conducted on plain and dimpled steel of different geometries. For each group of geometries the source of material for both the plain and dimpled steel columns was taken from a single coil. Within each group the sections were fabricated either by press-braking or cold-rolled forming. The buckling and ultimate strength of the columns was investigated. The change in strength of the dimpled columns resulting from the cold working associated with the dimpling process was also considered. This paper contains the results obtained when comparing the test strengths of short plain and dimpled steel columns using a compression test. In outlining the work the test setup and testing procedure will be described. Enhancements in buckling and ultimate strengths were observed in the dimpled steel columns-caused by the cold-work of the material during the dimpling process. The results showed that the buckling and ultimate strengths of dimpled steel columns were up to 33% and 26% greater than plain steel columns, respectively. [Copyright &y& Elsevier]

Abstract: A new type of lateral force-resisting system, a framed modular building with double skin steel panels of slender thin steel plates is presented. Modular construction leads to faster construction, improved quality and reduced resources and waste. A steel panel strengthened framed modular system is developed for the lateral load resisting system instead of in situ concrete core walls. The proposed double skin steel panel systems showed moderate ductility and energy dissipation due to their post-buckling strength. Full-scale experiments on a framed modular system with double skin steel panels were conducted. The test of the frame with steel panel systems showed that all steel panel systems reached a yielding point before the frame structure started to yield, so that severe damage to the frame as a primary structure was controlled. Also, the steel panel systems increased the initial lateral stiffness of the total system and maintained the elastic range of the panels up to near the yielding point of plates without local buckling driven from its shear behavior. By rigid-plastic analysis, the post-buckling strength of thin plates under in-plane bending was predicted and compared with experimental results. Based on the experimental data of the panels, the analytic model of these panel systems was constructed and compared with the experimental results of frames with double skin steel panel systems. [Copyright &y& Elsevier]

Abstract: Steel conical vessels with upper cylindrical caps are widely used as liquid containments in elevated water tanks. This type of structure for containing water is referred to as “combined conical tank”. A number of catastrophic failures of combined conical tanks occurred during the past decades in various locations around the globe. Previous studies available in the literature focused on pure conical tanks, where the vessels have no upper cylindrical caps. The current study focuses on characterizing the buckling behaviour of combined conical tanks under the effect of hydrostatic pressure. The study is conducted numerically using a three-dimensional finite element model developed in-house. The effects of geometric imperfection and residual stresses as well as the variation of the geometric and material parameters on the buckling capacity of combined conical tanks are investigated. Finally, a comparison between the buckling capacities of combined and equivalent pure conical tanks is conducted. [Copyright &y& Elsevier]

Abstract: In this paper, a half-scaled substructure test was performed to evaluate the failure mode of an existing transmission tower subjected to wind load. A loading scheme was devised to reproduce the dead and wind loads acting on the prototype transmission tower. The load was enforced on the model structure using two actuators and a triangular jig mounted on the reduced model. Preliminary numerical analysis was carried out to evaluate the stability and member force of the specimen for the design load. When the substructured transmission tower was loaded by 270% of its maximum allowable buckling load, local buckling occurred in joints of leg members with weak constraints. From the experimental results, such as load–displacement curves, displacements, and strains of members, it was concluded that the local buckling was due to the additional eccentric force caused by unbalanced deformation of the specimen. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental investigation of the elastic-plastic out-of-plane buckling response of roller bent circular steel arches subjected to a single force applied to the crown. The experiments are used to validate a finite element model described in a related paper. A series of 15 tests was performed on full-scale and model arches where the developed length of the arches was kept constant. The subtended angle was varied between 90° and 180°. Each full-scale arch configuration was tested at least twice to monitor experimental scatter and assess the repeatability of the tests. Special attention was paid to the boundary conditions: at the crown the load was introduced at the centroid of the arch-rib with the use of hydrostatic bearing to eliminate any torsional restraint. Loading was applied by means of a tension rod affixed to the centre of the baseline, rendering a directed load. The supports were designed such that they acted as hinges in-plane while they were fixed out-of-plane. Geometric imperfections were measured prior to loading. All arches failed by elastic-plastic out-of-plane buckling featuring the presence of plastic zones in the arch-rib and out-of-plane arch deformation. [Copyright &y& Elsevier]

Abstract: The paper describes 36 experimental tests conducted on rectangular and square tubular columns filled with normal and high strength concrete and subjected to a non-constant bending moment distribution with respect to the weak axis. The test parameters were the nominal strength of concrete (30 and 90MPa), the cross-section aspect ratio (square or rectangular), the thickness (4 or 5mm) and the ratio of the top and bottom first order eccentricities etop/ebottom (1, 0.5, 0 and −0.5). The ultimate load of each test was compared with the design loads from Eurocode 4, presenting unsafe results inside a 10% safety margin. The tests show that the use of high strength concrete is more useful for the cases of non-constant bending moment, whereas if the aim is to obtain a more ductile behavior the use of concrete-filled columns is more appealing in the cases of normal strength concrete with non-constant bending moments because, although they resist less axial force than the members with HSC, they obtain a softened post-peak behavior. [Copyright &y& Elsevier]

This paper approaches the elastic critical moment of web-corrugated beams (WCB), either subjected to a uniform bending moment, gradient bending moments, or a uniformly distributed load. Previous research on the subject of lateral-torsional buckling (LTB) of WCB is presented and critically reviewed. Based on earlier studies on the cross-section properties of beams with trapezoidal corrugations, a new method is proposed to obtain the warping or torsional constant of WCB with sinusoidal corrugation. Furthermore, based on an extensive numerical study for a wide range of different corrugation profiles and lengths, it is demonstrated that the present design formulae for the moment modification factor for flat web beams (FWB) could be improved, in order to predict satisfactorily the buckling capacities of WCB under non-uniform bending distributions. Therefore, a new closed-form expression for the moment modification factor is proposed and successfully verified. Finally, by comparing the analytical results with those obtained from a linear buckling analysis (LBA) carried out using shell finite elements, it is demonstrated that the proposed modifications lead to an accurate prediction of the buckling strength of WCB. [ABSTRACT FROM AUTHOR]

Abstract: Steel structural members and frames always indicate imperfections to various degrees. These include initial out-of-straightness and initial out-of-plumb due to manufacturing and erection tolerances. In general, the shape and magnitude of geometric imperfections may have a significant influence on the response of a structure, and hence need to be modelled accurately when determining the load carrying capacity of a steel frame by advanced structural analysis. Most conveniently, geometric imperfections can be introduced in structural models as scaled eigenmodes obtained a priori from an elastic buckling analysis. However, it remains unanswered how many eigenmodes need to be incorporated and how to choose the scaling factors of each mode. This paper presents a study of how the strength of steel frames varies with the number and magnitudes of eigenmodes. Frames with random geometric imperfections are produced using the statistics of measurements of out-of-plumb and member imperfections, and analysed using advanced geometric and material nonlinear analysis. The imperfections are then resolved into eigenmodes and a second set of advanced analysis is carried out using a finite number of modes to represent the imperfections. Conclusions are drawn about the appropriate number and magnitudes of eigenmodes to use in advanced structural analyses of steel frames. [Copyright &y& Elsevier]

Abstract: This paper proposes a new and simple method for estimating the collapse load of a steel cable-stayed bridge. A new convergence criterion for iterative eigenvalue computations is suggested to consider the beam–column effect of a cable-stayed bridge system. The collapse loads of two example bridges representing medium and long-span models are evaluated by the proposed method and compared to a nonlinear inelastic analysis. The results demonstrate that the proposed method is a good substitute for a complex nonlinear inelastic analysis to approximately evaluate the collapse loads as well as failure modes of steel cable-stayed bridges. [Copyright &y& Elsevier]

Abstract The system of governing differential equations of stability of centrically loaded members with rigid open cross-sections was presented by Kappus in 1937 and by Vlasov in 1940. In 1941 Goľdenvejzer published a solution of this system by Bubnov-Galerkin's variational method using eigenfunctions of flexural vibration modes as fundamental functions. The result is a formula for torsional-flexural critical force calculation. The simplified formula for torsional-flexural critical force calculation is in EN 1993-1-3 as formula (6.35). This formula gives exact values of elastic critical force for torsional-flexural buckling of centrically loaded members with monosymmetric cross-section only if the flexural boundary conditions are the same as the torsional boundary conditions at both member ends. The Goľdenvejzer's formula differs from (6.35) by allowing different flexural boundary conditions to the torsional ones. Goľdenvejzer takes this into account by introducing factor α. The purpose of this paper is to verify whether the factor α can correctly include the influence of combinations of flexural and torsional boundary conditions which Goľdenvejzer did not investigate, and to verify if the simplified formula (6.35) may be used for any boundary conditions. The authors used Goľdenvejzer's method for 8 different shapes of monosymmetric cross-sections for all 100 theoretical possible combinations of boundary conditions, and for two different fundamental functions: a) eigenfunctions of flexural vibration modes (which were also used by Goľdenvejzer) and b) eigenfunctions of buckling modes (which is a more natural choice). All results are verified by the finite element method with 1D member elements. Research field Stability of metal members under axial compression. Highlights • Elastic critical force • Torsional-flexural buckling • Monosymmetric cross-section • Combination of flexural and torsional boundary conditions • Thin-walled metal member [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the lateral stability of cellular steel beams is numerically investigated. The study is carried out using three-dimensional finite element modeling of simply supported I-shaped cellular steel beams with a broad spectrum of cross-sectional dimensions, span lengths and web perforation configurations. Stability analyses are carried out for beams subjected to equal end moments, mid-span concentrated loads and uniformly distributed loads. Finite element results reveal that, unlike the case of conventional beams with solid webs, the moment-gradient coefficient is significantly influenced by the beam geometry and slenderness. In addition, the coefficient of cellular beams depends on the web perforation configuration. Moment-gradient coefficient values that fluctuate closely to those values recommended by design codes are associated with pure elastic lateral torsional buckling (LTB) deformations. As the beam slenderness decreases, the web distortion increases, leading to the lateral distortional buckling (LDB) mode, which is associated with lower values than code-recommended ones. Severe reduction in the coefficient to values less than 1.1 is noticed for shorter-span beams where the response is dominated by non-lateral local buckling modes. A simplified approach is developed to enable accurate prediction of a moment modification factor for cellular beams. The proposed factor is provided by an empirical formula that is derived based on the best fit of the finite element results related to lateral buckling (LTB and LDB) modes only. The proposed approach allows for accurate and conservative evaluation of the critical moment associated with the lateral torsional/distortional buckling of cellular beams. Several numerical examples are worked out to illustrate the application of the proposed procedure. [ABSTRACT FROM AUTHOR]