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The application of design by finite element analysis (FEA) is becoming increasingly prevalent in applied engineering; however, codified provisions remain scarce. The vision of CEN/TC 250/SC 3 was to develop a new comprehensive document based on the existing provisions currently distributed throughout the different Eurocode 3 parts, and with extension where necessary to cover all fields of structural steel design. Within the development process, two documents are being prepared: (i) the code, prEN 1993‐1‐14 and (ii) a Technical Report. The new code aims to provide rules on the use of finite element analysis and other numerical methods for verifying ultimate limit states, serviceability limit states and fatigue. In parallel, the Technical Report will provide background information and explanations of all aspects of the code, as well as benchmark cases and design examples to support the correct application of the prEN1993‐1‐14 design rules and the necessary benchmarking required for model validation. The assumed stakeholders are mainly designers who can find direct guidance for design by finite element analysis in daily engineering practice. This current paper gives an overview of the new code and accompanying Technical Report, as well as the development process and harmonisation within the current Eurocode 3 framework. [ABSTRACT FROM AUTHOR]

The behaviour and design of homogeneous and hybrid high strength steel (HSS) beams are addressed in the present study. Six in‐plane three‐point bending tests on three different welded I‐sections were first conducted. Following the experimental investigation, a finite element (FE) modelling programme was performed, which included a validation study confirming the accuracy of the developed FE models in replicating the flexural behaviour of HSS welded I‐section beams, and a parametric study generating additional FE data on HSS welded I‐section beams over a broader range of cross‐sectional slendernesses, steel grades and loading configurations. Then, the suitability of the current Eurocode 3 cross‐section slenderness limits for HSS homogeneous and hybrid welded I‐sections in bending were evaluated. It is shown that the current Eurocode Class 2 and Class 3 slenderness limits are suitable for the classification of the outstand flange (in compression) and internal web (in bending) elements of both HSS homogeneous and hybrid welded I‐sections subjected to major axis bending, while stricter Class 1 slenderness limits are considered necessary to achieve sufficient rotation capacity for plastic design. The findings indicate that plastic design can be used for HSS structures, provided the proposed stricter Class 1 slenderness limits are employed. Further work is underway to develop advanced design approaches using second‐order inelastic analysis with strain limits for HSS welded I‐section members. [ABSTRACT FROM AUTHOR]

The behaviour and design of cylindrically‐pinned stainless steel equal‐leg angle section members under compression and compression combined with strong‐axis bending are investigated herein. Numerical models are developed by means of shell finite element modelling formulated within ABAQUS and validated against experimental data. A numerical parametric study is then presented considering both hot‐rolled and cold‐formed stainless steel equal‐leg angle section columns alongside beam‐columns with a wide range of cross‐section and member geometries. Finally, new design proposals for pin‐ended stainless steel equal‐leg angle section members under compression and compression plus major‐axis bending are developed and verified against the results of physical experiments and numerical simulations. The proposed design rules are shown to offer substantially more accurate and consistent resistance predictions compared to existing codified design rules. [ABSTRACT FROM AUTHOR]

Recent disruptive technological advances, including wire arc additive manufacturing (WAAM) and the concept of digital twins, have the potential to fundamentally transform the way in which we design, build and manage structures. WAAM is a method of metal 3D printing that is well suited to the price‐sensitive construction industry and has been used to manufacture the MX3D bridge – the world's first metal 3D printed bridge. The intricate geometry, undulating surface finish and particular material properties rendered the bridge outside the scope of any existing structural design standards; hence, physical testing and advanced numerical modelling were carried out for its safety assessment. The key features of the finite element model of the bridge, and its validation against in‐situ structural tests, are described herein. Subsequent numerical studies undertaken to verify the structural performance of the bridge under various loading scenarios are presented, while the basis for the development of the smart digital twin of the bridge is also introduced. The presented research provides insight into the use of advanced computational simulations for the verification and ongoing assessment of structures produced using new methods of manufacture. [ABSTRACT FROM AUTHOR]

The structural behavior and residual capacity of S700 high-strength steel circular hollow section (CHS) columns after exposure to elevated temperatures were studied through testing and numerical modeling. The testing program was conducted on 10 S700 high-strength steel CHS columns and comprised heating and cooling of the specimens as well as postfire material testing, measurements of initial geometric imperfections, and pin-ended column tests. Numerical simulations were subsequently performed, where finite element models were built and validated with reference to the experimental results and afterward used to conduct parametric studies to obtain further numerical data. Given that there are no specific provisions for the design of steel structures after exposure to elevated temperatures, the relevant room-temperature design buckling curves were evaluated, using postfire material properties, for their applicability to S700 high-strength steel CHS columns after exposure to elevated temperatures, based on the experimental and numerical data. The evaluation results indicated that the buckling curves prescribed in the American specification and Australian standard lead to accurate and consistent residual capacity predictions for S700 high-strength steel CHS columns after exposure to elevated temperatures, while the Eurocode buckling curve yields conservative predictions of residual capacity. A revised Eurocode buckling curve was then proposed, and resulted in a higher level of accuracy than its original counterpart. [ABSTRACT FROM AUTHOR]

Highlights • Results of experimental study on stainless steel I-section beam-columns presented. • FE models validated against new and existing test results. • Numerical parametric studies carried out to generate further data. • Existing structural design provisions for stainless steel beam-columns assessed. • New design provisions developed, and reliability assessed against EN 1990 requirements. Abstract The stability and design of laser-welded stainless steel I-section beam-columns are explored in this study. Owing to the high precision and low heat input of laser-welding, structural cross-sections produced using this fabrication method have smaller heat affected zones, lower thermal distortions and lower residual stresses than would typically arise from traditional welding processes. Eighteen laser-welded stainless steel beam-columns were tested to investigate the member buckling behaviour under combined compression and bending. Two I-section sizes were considered in the tests: I-50 × 50 × 4 × 4 in grade EN 1.4301 and I-102 × 68 × 5 × 5 in grade EN 1.4571 austenitic stainless steel. The two cases of minor axis bending plus compression and major axis bending plus compression with lateral restraints were investigated. The initial loading eccentricities in the beam-column tests were varied to provide a wide range of bending moment-to-axial load ratios. The test results obtained herein and from a previous experimental study were used to validate finite element (FE) models, which were subsequently employed for parametric investigations to generate further structural performance data over a wider range of cross-section sizes, member lengths and loading combinations. The obtained test and FE results were utilized to evaluate the accuracy of the beam-column capacity predictions according to the current European and North American design provisions and a recent proposal by Greiner and Kettler. Finally, an improved approach for the design of stainless steel I-section beam-columns is proposed. [ABSTRACT FROM AUTHOR]

Abstract Stainless steel is widely used in construction due to its combination of excellent mechanical properties, durability and aesthetics. Towards more sustainable infrastructure, stainless steel is expected be more commonly specified and to feature in more substantial structural applications in the future; this will require larger and typically welded cross-sections. While the structural response of cold-formed stainless steel sections has been extensively studied in the literature, welded sections have received less attention to date. The stability and design of conventionally welded and laser-welded austenitic stainless steel compression members are therefore the focus of the present research. Finite element (FE) models were developed and validated against a total of 59 experiments, covering both conventionally welded and laser-welded columns, for which different residual stress patterns were applied. A subsequent parametric study was carried out, considering a range of cross-section and member geometries. The existing experimental results, together with the numerical data generated herein, were then used to assess the buckling curves given in European, North American and Chinese design standards. Following examination of the data and reliability analysis, new buckling curves were proposed, providing, for the first time, design guidance for laser-welded stainless steel members. Highlights • Finite element models of welded stainless steel I-sections are developed • Finite element models are validated against existing experimental data • Parametric studies are presented for both laser-welded and conventionally welded columns • Existing design provisions are described and evaluated • New design proposals are made and assessed through reliability analysis [ABSTRACT FROM AUTHOR]

Abstract Structural design formulae for beam-columns require accurate end points (i.e. accurate resistance predictions for pure compression and pure bending), should be of suitable form to capture the interaction between the different components of loading and should take due account of the influence of a moment gradient along the member length. However, existing design rules for stainless steel beam-columns do not fully capture the interaction responses observed in experiments and numerical simulations, and are often tied to inaccurate end points; the adopted equivalent uniform moment factors can also be unconservative in the case of high moment gradients. As a consequence, previous comparisons of stainless steel beam-column experimental and finite element results with codified strength predictions have often revealed a rather high degree of scatter. This prompted the present research, to develop improved design proposals for stainless steel square hollow section (SHS) and rectangular hollow section (RHS) beam-columns under moment gradients. To this end, revised design approaches are proposed firstly through the derivation of more accurate design interaction curves for stainless steel SHS and RHS beam-columns under uniform bending moment and then through the employment of more suitable equivalent uniform moment factors, underpinned by and validated against over 1500 test and numerical data points. The new design approaches are shown to lead to improved (safe-sided, accurate and consistent) resistance predictions for stainless steel SHS and RHS beam-columns under moment gradients over the current codified design rules. Finally, statistical analyses are performed to demonstrate the reliability of the proposed approaches, according to the requirements specified in EN 1990. Highlights • Current codified design rules for stainless steel beam-columns under moment gradients were briefly reviewed. • Shortcomings in the existing design codes were identified, and methodologies for overcoming them were described. • Improved design approach for stainless steel beam-columns under moment gradients was proposed. • Assessment of the new proposal indicates a higher level of design accuracy and consistency. • The reliability of the new proposal has been confirmed by means of statistical analyses. [ABSTRACT FROM AUTHOR]

Cold-formed steel purlin systems with overlapped or sleeved connections are alternatives to continuous two-span systems and exhibit different degrees of continuity. Both connection types are highly favourable in practice since they are both strategically placed over an interior support to provide additional moment resistance and rotational capacity where the corresponding demands are at their largest, thus improving the overall structural efficiency. Until recently, full-scale testing has been the most common way of investigating the structural behaviour of such systems. In this study, numerical modelling, capable of capturing the complex contact interactions and instability phenomena, is employed. The developed finite element models are first validated against data from physical tests on cold-formed steel beams featuring sleeved and overlapped connections that have been previously reported in the literature. Following their validation, the models are employed for parametric studies, based on which the structural behaviour of the examined systems is explored, while the applicability of conventional plastic design as well as of a previously proposed design approach is investigated. Finally, the efficiency of these systems in terms of load-carrying capacity is compared with their equivalent continuous two-span systems. [ABSTRACT FROM AUTHOR]

Highlights • FE models validated against test results on cold-formed steel SHS/RHS. • Validated FE models used to perform parametric studies considering key parameters. • EN 1993-1-1 and AISC-360-16 provisions assessed using test and FE data. • CSM extended and modified to cover the design of cold-formed steel SHS/RHS. • Reliability of different methods evaluated by means of statistical analyses. Abstract Cold-formed steels typically exhibit a rounded stress-strain response with gradual yielding merging into strain hardening. This form of stress-strain curve is at odds with the elastic, perfectly plastic material model that underpins many of the provisions set out in current structural steel design standards. In particular, the beneficial influence of strain hardening on cross-section capacity is neglected. The continuous strength method (CSM) is a deformation-based design method that enables material strain hardening properties to be exploited, thus resulting in more accurate and consistent capacity predictions. The aim of this study is to extend the CSM to the design of cold-formed steel non-slender tubular cross-sections subjected to compression, bending and combined loading, and to verify the proposals through comparisons with existing test data from the literature and finite element results generated herein. The finite element models were first developed and validated against test results on cold-formed steel cross-sections collected from the literature. An extensive parametric study was then conducted to generate additional data over a wider range of cross-section geometries, slendernesses and loading conditions. The numerical results together with the experimental results were then compared with capacity predictions, calculated according to the current design rules in European Standard EN 1993-1-1 (2005) and American Specification AISC-360-16 (2016) as well as the CSM. The CSM is shown to provide more accurate and consistent design predictions for cold-formed steel cross-sections under different loading conditions than those obtained from existing design methods. The improvements arise from the use of the continuous deformation based design approach, as well the rational exploitation of strain hardening. Finally, the reliability levels of the different design methods were assessed by conducting reliability analyses in accordance with EN 1990 (2002). [ABSTRACT FROM AUTHOR]

Abstract The structural behaviour and design of hot-rolled and cold-formed steel continuous beams with square and rectangular hollow sections are studied in the present paper, with a focus on the beneficial effects of material strain hardening and moment redistribution. Finite element (FE) models were first developed and validated against existing test results on hot-rolled and cold-formed steel square and rectangular hollow section continuous beams. Upon validation against the experimental results, parametric studies were carried out to expand the available structural performance data over a range of cross-section geometries, cross-section slendernesses, steel grades and loading conditions. Representative material properties and residual stress patterns were incorporated into the FE models to reflect the two studied production routes – hot-rolling and cold-forming. The experimental results, together with the parametric numerical results generated herein, were then used to evaluate the accuracy of the design provisions of EN 1993-1-1 (2005) as well as the continuous strength method (CSM) for indeterminate structures, the latter of which is extended in scope in the present study. It was shown that the current provisions of EN 1993-1-1 (2005) for the design of hot-rolled and cold-formed steel continuous beams are rather conservative, while the proposed CSM yields a higher level of accuracy and consistency, due to its rational consideration of both strain hardening at the cross-sectional level and moment redistribution at the global system level. Finally, statistical analyses were carried out to assess the reliability level of the two design methods according to EN 1990 (2002). Highlights • Numerical models validated against test results for structural steel continuous beams. • Validated numerical models used to perform parametric studies considering key parameters. • Current design provisions in EN 1993-1-1 assessed using the experimental and numerical data. • The Continuous Strength Method extended to cover the design of structural steel continuous beams. • Reliability of the CSM evaluated by means of statistical analyses according to EN 1990. [ABSTRACT FROM AUTHOR]

An innovative concept, whereby the load-carrying capacity and serviceability performance of cold-formed steel beams are enhanced by utilising prestressing techniques, is presented. The prestressing force is applied by means of a high-strength steel cable, which is housed at a location eccentric to the strong geometric axis within the bottom hollow flange of the cold-formed steel beam, inducing initial stresses in the beam that are opposite in sign to those introduced during the subsequent loading stage. As a consequence, the development of local instabilities during loading is delayed and thus the capacity of the beam is enhanced. Furthermore, the pre-camber induced during prestressing, as well as the contribution of the cable to the bending stiffness of the system, decrease the overall vertical deflections of the beam. The conceptual development of prestressed cold-formed steel beams and a study investigating the potential benefits are presented. The mechanical behaviour of the proposed beams in both the prestressing and imposed loading stages is described in terms of analytical expressions, while failure criteria for the design of the cold-formed steel beam and the cable are also developed by employing interaction equations in conjunction with the Direct Strength Method. Geometrically and materially nonlinear finite element analysis with imperfections is employed to simulate the behaviour of the proposed beams. Sample numerical results are presented and compared with the developed analytical expressions and failure criteria, demonstrating the substantial enhancement in moment capacity and serviceability performance offered by these beams. [ABSTRACT FROM AUTHOR]

The findings from a numerical investigation into the degree of composite action that may be mobilised within floor systems comprising cold-formed steel joists and wood-based particle boards are presented herein. Finite element models have been developed, simulating all the components of the examined systems, as well as the interaction between them. The models include initial geometric imperfections, the load-slip response of the fasteners employed to achieve the shear connection as well as both geometric and material nonlinearities. The developed models were first validated against 12 physical tests reported in the literature, which showed them to be capable of accurately capturing the load-deformation curves and failure modes exhibited by the tested specimens. Parametric studies were then performed to examine the influence of key parameters on the structural behaviour of these systems, including the depth and thickness of the cold-formed steel section, as well as the spacing of the employed fasteners; in total, about 100 systems have been examined. Significant benefits in terms of structural response have been identified from the presented numerical study as a result of the mobilisation of composite action; for the systems investigated, which were of typical, practical proportions, up to 140% increases in moment capacity and 40% increases in stiffness were found. The presented research reveals the substantial gains in structural performance and the influence of the key governing parameters for this novel form of composite construction. [ABSTRACT FROM AUTHOR]

A stiffness reduction method for the design of laterally restrained web-tapered steel structures fabricated through the welding of individual steel plates is presented in this paper. Stiffness reduction functions for welded members, accounting fully for the deleterious influence of the spread of plasticity and imperfections on the structural resistance, are developed. The method is implemented through (i) dividing tapered members into prismatic segments along their lengths, (ii) reducing the flexural stiffness of each segment by means of the developed stiffness reduction functions considering the first-order forces and cross-section properties of each segment, (iii) performing Geometrically Nonlinear Analysis and (iv) making cross-section strength checks. Essentially, it is proposed to replace the current typical approach to structural design of conducting a simple elastic (with nominal stiffness) structural analysis followed by elaborate member checks with an integrated process utilising more sophisticated second-order analysis (with stiffness reduction) but very simple design checks. The distribution of internal forces within the structure is captured more accurately due to the allowance for imperfections, residual stresses and plasticity through stiffness reduction and the allowance for frame and member instability effects through the use of second-order analysis. The need for determining effective lengths and for conducting member buckling checks is also eliminated. Verification of the proposed approach against the results obtained from nonlinear shell finite element modelling is presented for various tapering geometries, slenderness values and loading conditions. Assessment of the proposed method against the European and North American steel design codes for tapered steel structures is also provided. [ABSTRACT FROM AUTHOR]

An experimental and numerical study of the flexural buckling behavior of hot-finished high-strength steel (HSS) square and rectangular hollow section (SHS and RHS, respectively) columns is described in this paper. A total of 30 hot-finished S460 and S690 hollow section column specimens have been tested in compression with pin-ended boundary conditions. Finite element (FE) models have been developed to replicate the experiments and employed in a subsequent parametric study considering a range of member geometries. Based on the test and FE results, the applicability of the current column design curves in European, North American, Chinese and Australian structural steel design standards to hot-finished HSS SHS and RHS columns has been verified by means of reliability analyses [ABSTRACT FROM AUTHOR]

Formulae for calculating the elastic local buckling stresses of doubly-symmetric thin-walled I-section girders subjected to combined shear and direct stresses, accounting for the interaction between the plate elements are presented. The interaction between the plate elements (i.e. the flanges and web) is bounded by a theoretical lower-bound, where there is no interaction and the critical plate is considered to be simply-supported, and a theoretical upper-bound where interaction is strongest and the critical plate is considered to have rotationally fixed edges. The interaction is accounted for by introducing an interaction coefficient ζ that quantifies the relative level of fixity between the aforementioned lower and upper bounds. Expressions to calculate ζ are calibrated using results from finite element analyses generated in Abaqus. Doubly-symmetric I-sections of varying geometric proportions loaded in shear, major axis bending, compression and a full range of combinations thereof are considered. Using the developed formulae, the elastic local buckling stresses of the studied cross-sections are accurately predicted, typically within 5% of the values obtained from FE models; this is a significant improvement over the results determined in the traditional manner in which plate element interaction effects are ignored, where the full cross-section buckling stress is shown to be underestimated by as much as 40%. [Display omitted] • Elastic buckling stress of thin-walled I-sections under shear stress is determined. • Interaction coefficient quantifies restraint of critical plate element boundaries. • Elastic buckling stress predicted to within 5% of FE results. • Buckling stress under combined shear and direct stresses also predicted accurately. • Significantly improved predictions when compared to the current EC3 provisions. [ABSTRACT FROM AUTHOR]

A study into the mechanical behaviour and design of steel equal-leg cruciform section members subjected to axial compression is presented. Experimental data from the literature are used to validate shell finite element models developed within the commercial package ABAQUS for their load-deformation and ultimate behaviour. A numerical parametric study then considers cruciform section columns with a wide range of slenderness ratios and various common boundary conditions. The mechanical response and load-carrying capacity are shown to be dependent not only on the column slenderness but also on the torsional to flexural elastic buckling load ratio. Finally, a recently established design approach for steel angle section columns is extended to include cruciform section members, and verified against the available results. It is found through reliability analysis based on the EN 1990 procedure that the new proposal also offers substantially improved accuracy and consistency in strength predictions compared to the existing codified design rules for cruciform section columns; a recommended partial safety factor of 1.0 is determined. • Critical buckling behaviour of cruciform sections under compression described. • Shell FE models of cruciform columns developed in ABAQUS and validated against test results. • Numerical parametric study considering a range of steel cruciform section columns described. • Experimental and numerical results are used to develop a new design approach. • Accuracy and reliability of the new design approach is verified in accordance with EN 1990. [ABSTRACT FROM AUTHOR]

This paper reports the second part of the study on the structural behaviour of stainless steel circular hollow sections subjected to combined axial load and bending moment. A series of numerical parametric studies is presented, using the validated finite element (FE) models from the companion paper, with the aim of generating further structural performance data over a wider range of stainless steel grades, cross-section slendernesses and combinations of loading. The considered parameters include the outer cross-section diameter, the ratio of outer cross-section diameter to thickness and the initial loading eccentricity. Both the experimentally and numerically derived section capacities were compared with the strength predictions determined from the current European code, the American specification and the Australian/New Zealand standard, allowing the applicability of each codified method to be assessed. The comparisons revealed that the current design standards generally result in unduly conservative and scattered strength predictions for stainless steel circular hollow sections under combined loading, which can be primarily attributed to the neglect of strain hardening in the determination of cross-section resistances and to the use of linear interaction formulae. To overcome these shortcomings, improved design rules are proposed through extension of the deformation-based continuous strength method (CSM) to the case of circular hollow sections subjected to combined loading. Comparisons between the proposals and the test and FE results indicate a high level of accuracy and consistency in the predictions. The reliability of the proposed approach was confirmed by means of statistical analyses according to EN 1990. [ABSTRACT FROM AUTHOR]

The aims of this study are to generate experimental data and develop numerical models for aluminum alloy continuous beams, and to utilize the results to underpin the development of revised design methods for indeterminate structures. This paper presents an experimental program and finite-element (FE) analyses for two-span continuous beams (i.e., five-point bending) of square and rectangular hollow sections (SHSs and RHSs). The experimental program comprised 27 five-point bending tests with three different positioning of loads. The testing procedures and key results are reported. The test specimens were manufactured by extrusion, with 18 of grade 6061-T6 and 9 of grade 6063- T5 heat-treated aluminum alloys. The test specimens were nonslender sections, and mostly of Class 1 proportions. Generally, the specimens failed by the formation of a collapse mechanism comprising three plastic hinges. The distances between the supports and the loading points were varied in order to form the first plastic hinge in different locations, to achieve different load levels between the first hinge and collapse, and to change the rotation demands on the first hinge that formed. The FE models were developed and failure was defined as either when a plastic collapse mechanism was formed or the material fracture strain was reached on the tension flange, whichever occurred first. The numerical models were first validated against the experimentally obtained load-deflection responses, as well as the failure modes. The experimental and FE ultimate loads were both found to be beyond the theoretical loads corresponding to the formation of the first hinge as well as the calculated plastic collapse loads. A key characteristic of aluminum alloy, strain hardening, is shown to be particularly significant in both the experimental program and the numerical investigation. The validated FE models are used to generate numerical results through parametric studies in the companion paper. The development of design rules for indeterminate aluminum alloy structural systems is then described. [ABSTRACT FROM AUTHOR]

Aluminum alloys are employed in a range of structural engineering applications, supported by many international design standards, but plastic design methods are generally not permitted. In the second part of this study, an extensive numerical parametric study is conducted to assess the effect of key parameters, such as cross section slenderness, cross section aspect ratio, and moment gradient on the strength, strain hardening, and moment redistribution behavior of aluminum alloy continuous beams. The key input parameters and findings are reported herein. Based on both the experimental and parametric numerical results, the design provisions of the American, Australian/New Zealand, and European specifications as well as the traditional plastic design method, the plastic hinge method, and the continuous strength method (CSM) for indeterminate structures, the scope of which is extended in the present study, have been evaluated. The design strengths predicted by the three specifications were found to be rather conservative, while the predications of the latter three methods are more precise and consistent. The results reveal that strain hardening at the cross-sectional level and moment redistribution at the global system level have significant influence on the performance of stocky (plastic and compact sections) aluminum alloy members, which should be accounted for in design. Following reliability analysis, proposals are made for revised design provisions. [ABSTRACT FROM AUTHOR]

This paper presents a stiffness reduction approach utilising Linear Buckling Analysis (LBA) with developed stiffness reduction functions for the lateral–torsional buckling (LTB) assessment of steel beams. A stiffness reduction expression is developed for the LTB assessment of beams subjected to uniform bending and modified for the consideration of moment gradient effects on the development of plasticity. The proposed stiffness reduction method considers the influence of imperfections and plasticity on the response through the reduction of the Young's modulus E and shear modulus G and obviates the need of using LTB buckling curves in design. The accuracy and practicality of the method are illustrated for regular, irregular, single and multi-span beams. In all of the considered cases, the proposed method is verified against the results obtained through nonlinear finite element modelling. [ABSTRACT FROM AUTHOR]

Experimental and numerical studies into the structural behaviour of reinforced concrete columns confined by circular steel tubes after exposure to standard fire conditions are presented. These elements differ from conventional concrete-filled steel tubular (CFST) columns in that breaks in continuity are present at the member ends, which limit the longitudinal stresses in the steel and maximise the level of confinement afforded to the concrete through the generation of hoop stresses in the tube. The temperature distributions in the specimens were measured during the heating and cooling phases, while the load-displacement relationships and longitudinal and transverse strains in the steel tube were recorded during the subsequent compressive tests. 3D finite element (FE) models were also developed using the program ABAQUS to investigate the post-fire performance of circular steel tube confined reinforced concrete (CSTCRC) columns, including both heat transfer and stress analyses. The FE models were used to identify the influences of key parameters on the residual capacity of CSTCRC columns, following exposure to the ISO-834 standard fire. The considered parameters included heating time, cross-sectional dimensions, strength of the materials, steel tube to concrete area ratio and ratio of reinforcement. Finally, a design method was proposed for predicting the residual load bearing capacity and compressive stiffness of CSTCRC columns after standard fire exposure. [ABSTRACT FROM AUTHOR]

Highlights: [•] Stiffness reduction method developed based on the European column buckling curves. [•] Finite element models validated against existing experimental results. [•] Comprehensive verification of the stiffness reduction method against FE results. [•] Illustration of the application and accuracy of the method for irregular members. [Copyright &y& Elsevier]

Prestressed stayed columns offer an innovative and aesthetically attractive solution where designs demand long and slender elements under compression. The addition of cross-arms and pretensioned cables to the columns provides significant lateral and rotational support that can result in a marked increase of the buckling capacity. The current work presents a simplified model, comprising discrete rigid links and springs with a mathematically exact formulation including the destabilising effect of cable slackening, which mimics the response of stayed columns and reveals the governing physical parameters that drive the behaviour. A recent finite-element study had indicated that these structural components are likely to exhibit interactive buckling phenomena, particularly if the critical buckling mode is antisymmetric, leading to highly unstable responses. However, by its very nature, that study could not reveal the bifurcational structure of the equilibrium response. The results from the present model reveal similar behaviour to that observed in the earlier finite-element study. A sequence of bifurcations is found that switch the post-buckling response from one mode to another by way of a path of interactive buckling. [ABSTRACT FROM AUTHOR]

The structural behaviour of prestressed stayed columns is investigated through nonlinear finite element modelling. The models were developed using the commercial software ABAQUS and validated against a series of recently conducted experiments. The sensitivity of the load-carrying capacity to the geometry of the stayed column, the initially applied prestress level within the stays and the initial global imperfection is investigated through parametric studies. It is found that there is a substantial increase in load-carrying capacity with increasing cross-arm length, provided the critical buckling mode remains symmetric. Once the critical buckling mode becomes antisymmetric, mode interaction becomes significant and the load-carrying capacity reaches a plateau and the component generally becomes more sensitive to imperfections. It is also found that the relative level of initial prestress required to maximize the load-carrying capacity of a given stayed column tends to reduce with increasing cross-arm length. [ABSTRACT FROM AUTHOR]

Abstract: General design procedures for prestressed stayed columns with a single cross-arm system are presented. The accuracy of the proposed design expressions is confirmed by comparison with the results of physical experiments and validated finite element simulations. Reliability is assessed by following the approach set out in Annex D of EN 1990. The presented resistance expressions for prestressed stayed columns are a function of the system geometry, the level of initial prestress in the cables and the global imperfection level. Worked examples are also presented to illustrate the application of the developed design approach. [Copyright &y& Elsevier]

Abstract: In this work, a non-linear three-dimensional finite element model is presented in order to study the behaviour of axially loaded concrete filled elliptical hollow section (CFEHS) columns exposed to fire. This study builds on previous work carried out by the authors on concrete filled circular hollow section (CFCHS) columns both at room temperature and in fire. The numerical model is first validated at room temperature against a series of experiments on CFEHS stub columns available in the literature and subsequently extended to study the performance of slender columns at elevated temperatures. The aim of this work is to understand and represent the behaviour of axially loaded CFEHS columns in fire situations and to compare their effectiveness with that of the circular concrete filled tubular (CFT) columns. Parametric studies to explore the influence of variation in global member slenderness, load level, cross-section slenderness and section size are presented. Finally, guidance on the fire design of CFEHS columns is proposed: it is recommended to follow the guidelines of Clause 4.3.5.1 in EN 1994-1-2, but employing the flexural stiffness reduction coefficients established in the French National Annex with an equivalent EHS diameter equal to P/π, where P is the perimeter of the ellipse. [Copyright &y& Elsevier]

Abstract: Stainless steel''s characteristic nonlinear, rounded stress–strain behaviour requires accurate recognition in numerical modelling. Its response to cold-working is far more pronounced than that of ordinary carbon steel and hence appropriate modelling of the cold-worked corner regions is very important. Despite the importance of geometrical imperfections, their measurement is not a very common practice and assumed models are generally adopted in numerical investigations—often without proper verification. This paper investigates all important aspects for modelling stainless steel cross-sections through carefully designed parametric studies. Different cross-section types have been considered and the numerically obtained load–deformation responses have been compared with selected experimental results; the findings form the basis for specific guidelines. These proposals have been verified by application to all available stainless steel stub column tests obtained from different sources. The predicted numerical results have shown excellent agreement with those obtained experimentally. [Copyright &y& Elsevier]

The behaviour and design of cylindrically-pinned stainless steel equal-leg angle section members under compression and compression combined with strong-axis bending are investigated herein. An experimental investigation, including material testing, initial geometric imperfection measurements and physical tests on hot-rolled stainless steel equal-leg angle section members is first presented. Numerical models are developed by means of shell finite element modelling formulated within ABAQUS and validated against experimental data. A numerical parametric study is then presented considering both hot-rolled and cold-formed stainless steel equal-leg angle section columns alongside beam–columns with a wide range of cross-section and member geometries. Finally, new design proposals for cylindrically-pinned stainless steel equal-leg angle section members under compression and compression plus major-axis bending are developed and verified against the results of physical experiments and numerical simulations. The proposed design rules are shown to offer substantially more accurate and consistent resistance predictions compared to existing codified design rules. The reliability of the new design provisions, with a recommended partial safety factor γ M1 = 1. 1 , is verified following the EN 1990 procedure. • Physical tests on pin-ended stainless steel equal-leg angle columns and beam–columns conducted. • Shell FE models developed in ABAQUS and validated against test results. • Numerical parametric study considering a range of stainless steel equal-leg angle columns and beam–columns describd. • Experimental and numerical results are used to develop a new design approach. • Accuracy and reliability of the new design approach is verified in accordance with EN 1990. [ABSTRACT FROM AUTHOR]

The post-fire performance of concrete-filled stainless steel tubular (CFSST) columns subjected to an entire loading–fire history, including four characteristic phases: (i) ambient temperature loading, (ii) heating, (iii) cooling with constant external loads, and (iv) post-fire loading, is investigated in this paper. Sequentially coupled thermal-stress analyses are performed using ABAQUS to establish the temperature field and structural response of CFSST columns. To improve the precision of the finite element analysis (FEA) models, the influence of moisture on the thermal conductivity and specific heat of the concrete in the heating and cooling phases is considered by using subroutines. Existing fire and post-fire test data on CFSST columns are used to validate the FEA modelling. Comparisons between FEA and test results indicate that the accuracy of the model is acceptable; the FEA model is then extended to simulate CFSST columns subjected to the four characteristic phases. The behaviour of the CFSST columns during the four characteristic phases is explained by analysis of the temperature distribution, load versus axial deformation relations, failure modes and internal force redistribution. The excellent post-fire performance of CFSST columns is examined in comparison with traditional concrete-filled carbon steel tubular (CFST) columns with the same total cross-sectional area. The residual strength index is studied with respect to a series of parametric analyses. It is found that the residual strength of CFSST columns is higher than that of CFST columns after the same fire exposure, and that the diameter of the stainless steel tube, slenderness, heating time ratio and load ratio have a significant influence on the residual strength index. • FEA model established to simulate fire and post-fire performance of CFSST columns. • User subroutines developed for automatic selection of thermal properties in heating and cooling phases. • Behaviour of CFSST column during full loading–fire history explored and compared to CFST column with the same steel ratio. • Parametric analysis on residual strength index of CFSST columns after fire conducted and design tables proposed. [ABSTRACT FROM AUTHOR]

Stainless steel tubular members are employed in a range of load-bearing applications due to their strength, durability and aesthetic appeal. From the limited existing test data on stainless steel circular hollow sections (CHS) columns it has been observed that the current Eurocode 3 provisions can be unconservative in their capacity predictions. A comprehensive experimental programme has therefore been undertaken to provide benchmark data to validate numerical models and underpin the development of revised buckling curves; in total 17 austenitic, 9 duplex and 11 ferritic stainless steel CHS column buckling tests and 10 stub column tests have been carried out. Five different cross-section sizes (covering class 1 to class 4 sections) and a wide range of member slendernesses have been examined. The experiments were initially replicated using finite element (FE) simulations; the validated FE models were then used to generate 450 additional column buckling data points. On the basis of the experimental and numerical results, new design recommendations have been made for cold-formed stainless steel CHS columns and statistically validated according to EN 1990 [1] . [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive numerical study into the in-plane member stability and design of normal and high strength steel (NSS and HSS) non-slender welded I-section beam–columns subjected to compression plus uniaxial bending. Finite element (FE) models were firstly developed to replicate the structural performance of welded I-section beam–columns made of different steel grades, as observed in existing tests collected from the literature. The validated FE models were then employed in a comprehensive parametric study to generate extensive numerical data covering a wide range of cross-section geometries, steel grades, member slendernesses and loading combinations. The numerically obtained data were utilised to evaluate the accuracy of the current design methods set out in the European Standards EN 1993-1-1:2005 and EN 1993-1-12:2007 as well as the American Specification AISC 360-16 for both NSS and HSS non-slender welded I-section beam–columns. The comparisons revealed that the codified design methods yield varying levels of accuracy in predicting the ultimate capacities of welded I-section beam–columns depending on the steel grade. To address this issue, new design proposals that are compatible with the European beam–column design framework have been developed, featuring more accurate yield strength-dependent interaction curves anchored to improved resistance predictions for members subjected to isolated loading scenarios (i.e. the compression and bending end points of the interaction curves). The new design proposals have been found to provide more accurate and consistent resistance predictions than the existing codified design provisions for NSS and HSS non-slender welded I-section members under compression plus uniaxial bending. The reliability of the new proposals has been confirmed through statistical analyses according to EN 1990: 2002. • Existing test data on NSS and HSS non-slender welded I-section beam–columns​ have been collected. • Finite element models have been developed and validated against test results. • Numerical parametric studies have been carried out considering key parameters. • Current European and American specifications have been examined and their shortcomings have been highlighted. • A new design approach has been proposed leading to more accurate and consistent resistance predictions. [ABSTRACT FROM AUTHOR]

• Existing stress–strain models for conventional structural steels are reviewed. • Constitutive models are proposed to represent stress–strain curves of WAAM steels. • Over 600 experimental stress–strain curves on WAAM steels are collected and analysed. • Predictive expressions or values for the required input parameters are developed. • Accuracy of model demonstrated through comparisons with measured stress–strain curves. Interest in the use of wire arc additive manufacturing (WAAM) in construction has increased rapidly in recent years. Key to facilitating wider application is an improved understanding of the material behaviour. In particular, with structural design by finite element analysis in mind, constitutive models to describe the full range stress-strain response of WAAM steels are needed; development of such models is the focus of the present study. WAAM normal-strength steels generally exhibit a stress-strain response featuring a well-defined yield point, a yield plateau (for machined material) or slightly inclined yield plateau (for as-built material) and subsequent strain hardening, while the stress-strain response of WAAM high-strength steels is typically rounded, with no distinct yield point or plateau. This behaviour is similar to that of conventionally-produced steels, and hence can be represented analytically using existing material models, but with suitable modifications — a quad-linear or bilinear plus nonlinear hardening model and a two-stage Ramberg-Osgood model are proposed for WAAM normal- and high-strength steels, respectively. Predictive expressions or standardised values for the input parameters required in the models are developed and calibrated against a comprehensive database of WAAM steel coupon test results collected from the literature. The experimental database comprises over 600 engineering stress-strain curves and covers different feedstock wires, surface finishes (i.e. machined and as-built), material thicknesses, directions of testing and printing strategies. The proposed material models are shown to accurately predict the full stress-strain curves of WAAM steels, and are considered to be suitable for incorporation into analytical, numerical and design models for WAAM steel structures. [ABSTRACT FROM AUTHOR]

The structural behaviour of sheathed cold-formed steel lipped channel section columns (studs) subjected to combined compression and major axis bending is investigated herein by means of numerical modelling. Finite element (FE) models of single studs, set in tracks and connected to oriented strand board (OSB) and gypsum plasterboard sheathing under varying combinations of axial compression and horizontal loading were developed in ABAQUS and validated against experimental results reported in the literature. The developed numerical models incorporated cross-sectional and global geometric imperfections, while geometrical and material nonlinearities for both the steel and the sheathing were considered in the analyses. Particular emphasis was given to replicating the "as-built" boundary conditions at the ends of the columns, controlled by the screws connecting the column to the track and by the column–track contact interaction. The interaction between the sheathing and the column, as well as the behaviour of the fasteners connecting the two components, were also explicitly modelled. Both the shear and pull-through characteristics of the fasteners were considered and simulated based on experimental findings. Following successful validation of the finite element models, parametric studies were conducted. The results showed that substantial structural performance benefits can be achieved by the addition of sheathing to cold-formed steel members and that the spacing of the connectors has a strong influence on the member response. For a typical system, decreasing the connector spacing from 300 mm to 75 mm was found to increase stud capacity and stiffness by up to 12% and 10% respectively when in pure compression and up to 26% and 22% respectively when in pure bending; under combined loading, capacity increases of up to 29% were found. • Numerical simulation of sheathed studs under combined compression and bending. • Advanced modelling of fasteners, sheathing and boundary conditions at the stud ends. • Validation of developed finite element models against physical tests. • Addition of sheathing found to substantially enhance structural performance. • Decreasing fastener spacing shown to increase capacity and stiffness by up to 29%. [ABSTRACT FROM AUTHOR]

Tubular profiles, such as square and rectangular hollow sections (SHS and RHS) are widely used in a range of structural engineering applications. Their thin-walled nature means that local buckling is a key design concern, which is usually addressed by adhering to specified slenderness limits. An alternative approach is to employ local plate stiffeners, which can be practically achieved in extruded aluminium alloy sections through the introduction of internal cross stiffeners. The flexural behaviour and design of aluminium alloy SHS and RHS with internal stiffeners is the subject of investigation of the present paper. The primary aims of the study are to generate experimental and numerical data for these new types of cross-section in bending, as well as to assess the applicability of different approaches to their design at cross-sectional and system levels. First, an experimental investigation was performed on aluminium alloy SHS and RHS beams with internal stiffeners subjected to three-point bending, four-point bending and five-point bending (i.e. continuous beams over three supports) of three different configurations. Finite element (FE) models were also developed and validated against the presented test data. Once validated, the models were employed to generate additional structural performance data through numerical parametric studies. Comparisons are then made between the experimental/numerical capacities and the design capacities predicted using a series of international design specifications for aluminium alloy structures, as well as the continuous strength method (CSM). The design strengths predicted by the American and Australian/New Zealand specifications were found to be conservative, while improved predictions are achieved by Eurocode 9. The most accurate and consistent predictions are obtained using the CSM, which was able to capture the significant observed strain hardening at the cross-sectional level and moment redistribution at the global system level. [ABSTRACT FROM AUTHOR]

The post-fire behaviour of eccentrically loaded reinforced concrete columns confined by circular steel tubes, also known as circular steel tube confined reinforced concrete (STCRC) columns, is investigated in this paper. A total of 12 experiments were conducted on eccentrically loaded circular STCRC stub columns after exposure to the ISO 834 standard fire, including both the heating and cooling phases. The temperatures across the tested sections, the axial load versus lateral displacement responses and the strains in the steel tubes were all measured and discussed. A finite element (FE) model was developed using the program ABAQUS, and validated against the test results from the present study, as well as related studies. Parametric studies were then performed to identify the influences of key parameters on the residual capacity of the eccentrically loaded STCRC columns, including eccentricity ratio, heating time, cross-sectional diameter, slenderness ratio, material strengths, steel tube to concrete area ratio and reinforcement ratio. Finally, a simplified method was proposed for predicting the residual load-bearing capacity of the eccentrically loaded STCRC columns after fire exposure. [ABSTRACT FROM AUTHOR]

In parallel with the experimental study described in the companion paper (Zhao et al., submitted for publication), a numerical modelling programme has been carried out to investigate further the structural behaviour of stainless steel cross-sections under combined loading. The numerical models, which were developed using the finite element (FE) package ABAQUS, were initially validated against the experiments, showing the capability of the FE models to replicate the key test results, the full experimental load–deformation histories and the observed local buckling failure modes. Upon validation of the FE models, parametric studies were conducted to generate additional structural performance data over a wide range of cross-section slenderness and combinations of loading. The experimental and numerical results were then compared with the design capacity predictions from the current European Standard EN 1993-1-4 (2006) and American Specification SEI/ASCE-8 (2002) for stainless steel structures. The comparisons revealed that the current design standards can significantly under-estimate the resistance of stainless steel cross-sections subjected to combined loading; this under-prediction of capacity can be primarily attributed to the lack of consideration of strain hardening of the material under load. The Continuous Strength Method (CSM) is a deformation-based design approach that accounts for strain hardening and has been shown to provide accurate predictions of cross-sectional resistance under compression and bending, acting in isolation. In the present paper, proposals are made to extend the scope of the CSM to the case of combined loading. Comparisons between the CSM design proposals and the test and FE results indicated a high level of accuracy and consistency in the predictions. The reliability of the proposals was confirmed by means of statistical analyses according to EN 1990 (2002). [ABSTRACT FROM AUTHOR]

Two series of simply supported bending tests on aluminium alloy square and rectangular hollow sections have been performed. The test program comprised 14 three-point bending tests and 15 four-point bending tests. The test specimens were fabricated by extrusion from grades 6061-T6 and 6063-T5 heat-treated aluminium alloys, with width-to-thickness ratios ranging from 2.8 to 20.5. Measured geometric and material properties, together with the full load–deflection histories from the test specimens, were reported. Observed failure modes included local buckling, material yielding and tensile fracture. Further experimental data were gathered from the literature. Finite element (FE) models were developed and validated against the test results, and then used to perform parametric studies, in which a total of 132 numerical results were generated. The experimental and numerical results were used to evaluate the bending resistance provisions of the American [1], Australian/New Zealand [2] and European [3] Specifications, as well as the continuous strength method (CSM). The moment capacities predicted by the three design specifications were found to be generally conservative, while the CSM provided more accurate and more consistent predictions due to the recognition and systematic exploitation of strain hardening. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical investigation into the post-fire behaviour and residual capacity of S700 high strength steel circular hollow section (CHS) beam–columns. The experimental investigation was performed on ten S700 high strength steel CHS beam–columns and included heating and cooling of the specimens as well as post-fire material testing, initial global geometric imperfection measurements and pin-ended eccentric compression tests. A subsequent numerical investigation was conducted, where finite element models were developed and validated against the test results and then employed to carry out parametric studies to generate further numerical data over a wide range of cross-section dimensions, member lengths and loading combinations. In view of the fact that there are no specific provisions for the design of steel structures after exposure to fire, the relevant room temperature design interaction curves were evaluated, using post-fire material properties, to assess their applicability to S700 high strength steel CHS beam–columns after exposure to fire, based on the test and numerical data. The evaluation results revealed that the interaction curves provided in the American Specification and Australian Standard result in a high level of design accuracy and consistency, while the Eurocode interaction curve leads to more conservative and scattered failure load predictions. Finally, a revised Eurocode interaction curve, with more accurate end points, was proposed and shown to offer improved failure load predictions for S700 high strength steel CHS beam–columns after exposure to fire. • Tests on ten S700 high strength steel CHS beam–columns after exposure to fire are conducted. • The post-fire member behaviour and residual capacity are studied. • FE models are developed to validate against the test results and then used to conduct parametric studies. • The applicability of the ambient temperature codified design interaction curves is assessed. • A revised Eurocode design interactive curve is proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fire tests on concrete-filled RHS columns subjected to fire on 3 sides were conducted. [•] Finite element models were validated against the experiments. [•] The influence of a range of parameters on fire resistance was investigated numerically. [•] Simplified methods were proposed for the prediction of fire resistance. [Copyright &y& Elsevier]

Reinforced concrete-filled steel tubular (RCFST) members possess excellent load-bearing properties and fire resistance, and have been applied in a range of practical engineering projects. In addition to static and seismic loads, RCFST members may also be subjected to transverse impact loads, such as those from vehicle/vessel collisions and terrorist attacks. An experimental and numerically study into the dynamic behaviour of RCFST members subjected to transverse impact is therefore the focus of the present paper. Nine specimens were tested using a drop-weight experimental setup, and the instantaneous impact force and deformation states were recorded. A finite element model was established, considering strain rate effects, and validated against the test results. Parametric studies were then conducted in which the effects of the material selection, cross-section characteristics, specimen scale and impact conditions were analysed. Finally, design proposals for RCFST members under transverse impact loading are presented. [Display omitted] [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) is being increasingly used in structural applications due to its high strength-to-weight ratio, ease of construction and versatility. The performance of CFS structures in fire has received signification recent attention, but the fracture behaviour of thin-walled CFS at elevated temperatures, which is fundamental to the fire response of the key components, like connections has yet to be extensively studied; this is therefore the subject of the present paper. First, using experimental data on cold-formed grade S280GD+Z275 steel at elevated temperatures from the literature, damaged true stress-strain curves considering the post-necking behaviour are determined. Then, a fracture prediction approach, implemented in the finite element analysis software Abaqus and considering ductile damage and a damage evolution law is calibrated and validated against the experimental data. Finally, the applicability of the proposed approach to different types of CFS material, including high-strength CFS, is assessed. The results show that the proposed model can accurately predict the fracture behaviour of CFS at elevated temperatures. • Description of post-necking damaged true stress-strain behaviour of cold-formed steel using weighted average method. • Proposal of empirical formula for determining suitable values for weighting factor. • FE modelling of fracture in cold-formed steel coupons at elevated temperatures. • Validation of developed FE models against existing coupon tests covering a range of grades and temperatures. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical investigations into the web crippling behaviour and load-carrying capacity of stainless steel built-up I-section members under End-Two-Flange (ETF) concentrated transverse loading. An experimental programme was conducted on 23 austenitic and duplex stainless steel built-up I-section specimens, with each consisting of two identical press-braked channel sections assembled back-to-back by means of self-tapping screws. Following the experimental programme, a numerical modelling programme was performed, where finite element models were firstly developed to replicate the tests and then used to conduct parametric studies. Based on the test and numerical data, the existing design rules for stainless steel built-up I-section members failing by web crippling, as set out in the current European, American and Australian/New Zealand design standards, were assessed. The comparisons indicated that the European and Australian/New Zealand design standards resulted in overly conservative and rather scattered failure load predictions, while the American design standard led to less scattered failure load predictions, but with many predictions on the unsafe side. Therefore, an improved design approach was proposed and shown to provide substantially improved failure load predictions for stainless steel built-up I-section members under End-Two-Flange loading. • The web crippling behaviour of stainless steel built-up I-sections under ETF loading was studied. • Tests were conducted on 23 stainless steel built-up I-section specimens. • FE models were developed and validated against test results and then used for parametric studies. • The existing codified design rules were assessed and a new design approach was proposed. [ABSTRACT FROM AUTHOR]

• Tests and numerical analysis were conducted on concrete-filled double skin sections. • Structural behaviour of stub columns was studied. • The applicability of the existing design provisions was assessed. • Use of an effective concrete strength is recommended for the higher concrete grades. • Use of a higher buckling coefficient to consider the local buckling of the steel tubes. • Modification to existing design rules shown to provide improved capacity predictions. The use of concrete-filled double skin tubular (CFDST) cross-sections for compression members has become increasingly popular in construction. A recently proposed innovative form of CFDST cross-section, ultilising stainless steel for the outer tube, offers the combined advantages of the composite action seen in CFDST member alongside the durability and ductility associated with stainless steel. CFDST sections with stainless steel outer tubes, for which there are currently little experimental data, are the focus of the present study. A comprehensive experimental and numerical investigation into the compressive behaviour of CFDST sections with square stainless steel outer tubes is presented in this paper. A total of 19 specimens was tested under uniform axial compression, and the test observations are fully reported. The ultimate loads, load-displacement curves and failure modes from the tests were used for the validation of finite element (FE) models. Parametric finite element analyses were then performed. The combined set of experimentally and numerically derived data was employed to assess the applicability of the existing European, Australian and American design provisions for composite carbon steel members to the design of the studied CFDST cross-sections. Overall, the existing design rules are shown to provide generally safe-sided (less so for the higher concrete grades) but rather scattered capacity predictions. Modifications to the current design codes are also considered—a higher buckling coefficient k of 10.67 to consider the beneficial restraining effect of the concrete on the local buckling of the stainless steel outer tubes, as well as a reduction factor η to reflect the reduced relative effectiveness of higher concrete grades. Overall, the comparisons demonstrated that improved accuracy and consistency were achieved when the modified design rules were applied. [ABSTRACT FROM AUTHOR]

• Prestressed stayed beam-columns studied for the first time analytically. • Zones of mechanical responses relating buckling load to prestressing forces identified. • Asymmetry in configuration demonstrated to make system more efficient. • Nonlinear FE analyses demonstrate existence of significant post-buckling strength. • Potential alternative to heavy long span struts for supporting temporary excavations. The instability of beam-columns with crossarms and externally prestressed cable stays is studied analytically, where the combination of bending and compression is assumed to be derived from the system self-weight acting orthogonally to the applied axial load. Three principal zones of behaviour are identified with two of these each having two sub-zones that relate the critical buckling load to the initial prestressing force applied to the stay cables. The ultimate load-carrying capacity of the beam-columns is evaluated by conducting nonlinear finite element analysis within the commercial package ABAQUS. Results show that the analytically derived critical buckling loads generally provide safe predictions of the ultimate loads due to significant post-buckling strength. It is found that releasing the geometric double symmetry of the system can make for a significantly more efficient structure due to the effect of pre-cambering against the self-weight. The strength and efficiency of stayed beam-column systems opens up a range of potential applications, including lighter alternatives to conventional props to support wide excavations, which currently utilize very heavy steelwork. [ABSTRACT FROM AUTHOR]

Abstract The local cross-section behaviour of stainless steel channel sections under the combined actions of axial compression and minor axis bending moment is investigated in the present paper and its companion paper, based on a comprehensive experimental and numerical study. Two channel section sizes were considered in the experimental programme, with the test specimens laser-welded at the two flange-to-web junctions from hot-rolled EN 1.4307 and EN 1.4404 austenitic stainless steel plates. The experiments involved initial local geometric imperfection measurements and 15 eccentrically loaded stub column (combined loading) tests. The loading eccentricity was varied to achieve a range of ratios of axial compression to minor axis bending moment; both orientations of bending (web in compression and web in tension) were considered. The test setup and procedures, together with the key experimental observations, including the load-carrying and deformation capacities, load-end rotation histories and failure modes, are fully reported. A finite element simulation study is then presented, in which the models were first validated against the obtained test results and then employed, in the companion paper, for parametric investigations and the assessment of design provisions. Highlights • Laser-welded stainless steel channel sections under combined compression and minor axis bending moment has been studied. • An experimental programme including 15 combined loading tests has been carried out. • Finite element models have been developed and validated against experimental results. [ABSTRACT FROM AUTHOR]

Abstract Following the experimental study and finite element (FE) model validation described in the companion paper, numerical parametric studies and the evaluation of design provisions for stainless steel channel sections under combined axial compressive load and minor axis bending moment are presented herein. The parametric studies were carried out to generate additional structural performance data over a wider range of cross-section aspect ratios and slendernesses, loading combinations and bending orientations. The test data and numerical results have been carefully analysed to develop a comprehensive understanding of the structural performance of stainless steel channel sections under combined compression and minor axis bending moment, and to assess the accuracy of the existing design provisions in Europe and North America. Comparisons of ultimate loads from the tests and FE simulations with the codified resistance predictions revealed that the current design standards typically under-estimate the capacity of stainless steel channel sections under combined compression and minor axis bending moment; this is attributed primarily to the neglect of material strain hardening and the employment of conservative interaction formulae. Improved design rules featuring more efficient interaction curves, anchored to more precise end points (i.e. cross-section resistances under pure compression and bending moment), are then proposed and presented. The new design proposals are shown to yield both more accurate and more consistent resistance predictions over the existing design provisions. Finally, statistical analyses are presented to confirm the reliability of the new design proposals according to EN 1990. Highlights • Parametric studies were carried out to generate further structural performance data. • Design provisions in EC3 and AISC were assessed against test and FE data. • New proposals were made, leading to substantial improvement in resistance prediction. • The reliability of the new proposals was confirmed according to EN 1990. [ABSTRACT FROM AUTHOR]

• Eight large-scale frames made of S690 welded I-sections were tested. • Digital Image Correlation was employed to obtain detailed information. • Out-of-plane displacement was restrained by using a bespoke lateral bracing system. • Test setup, instrumentation, loading procedures and observations were fully described. • The potential for plastic design of HSS structures were highlighted. Physical experiments are widely used in structural engineering for the validation of finite element models and the establishment and assessment of design provisions. However, while there exists an abundance of member-level test data, there is a clear need for further benchmark frame-level test data, particularly given the growing trend for advanced system-level simulation and design. Towards meeting this need, and exploiting state-of-the-art measurement techniques, tests on eight high strength steel frames are presented herein. The tested frames were fixed-base, single storey, unbraced in-plane and made up of welded S690 steel I-section members. Two section sizes, of different local slenderness, were employed to assess the influence of local buckling on cross-section strength and the potential for plastic redistribution of forces within the frames. All the frames were laterally restrained out-of-plane using a bespoke lateral bracing system, but free to deform in-plane. The frames were subjected to different combinations of horizontal and vertical loading, in order for beam, sway and combined mode mechanisms to form. Extensive use was made of digital image correlation in order to obtain detailed information on the deformation of the frames and their components. The test setup, instrumentation, loading procedures and frame structural response, including load-deformation characteristics, failure modes and connection rotational stiffnesses are fully reported. The experimental data indicated that, despite the lower ductility and strain hardening of HSS relative to normal strength steel (NSS), HSS frames with stocky cross-sections have the ability to form plastic hinges with sufficient rotation capacity to achieve a considerable amount of inelastic moment redistribution; the potential for extending plastic design to HSS structures has therefore been demonstrated. The test results also provide a firm basis for the validation of advanced numerical models and system-level design approaches. [ABSTRACT FROM AUTHOR]