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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]

Steel and steel-concrete composite construction is employed in a substantial proportion of low-rise and multi-storey buildings. Design codes for these forms of structure have evolved over many years, but are currently essentially founded upon the assumption of elastic-plastic or rigid-plastic material behaviour and largely disregard the beneficial influence of strain hardening. This simplificaton can result in overly conservative predictions of capacity, particularly in the case of stocky, bare steel cross-sections and composite beams under sagging bending moment. The continuous strength method is an alternative deformation-based design approach that allows for strain hardening, provides more accurate predictions of member capacities and, thus, enables more efficient structural solutions to be achieved. In this paper, the development and application of the continuous strength method to steel structures is explained and extension of the method to steel-concrete composite design is outlined. [ABSTRACT FROM AUTHOR]

Under significant seismic loading conditions, the response of concentrically braced frames largely depends on the behaviour of the diagonal braces, which represent the key energy dissipating zones. Although the hysteretic response of steel braces under cyclic axial loading has been examined in previous studies, there is a need for further assessments that focus on quantifying failure. This paper describes the development of detailed finite-element models of hollow sections subjected to cyclic axial loading. The effects of initial imperfections and cyclic hardening are taken into consideration and the models are validated against data from 19 tests. A method to predict the fracture life of bracing members under cyclic loading is also described. Using the numerical models, parametric studies are undertaken to assess the influence of global and local slendernesses on the performance of the braces - both are found to affect the occurrence and severity of local buckling under cyclic loading, which causes high localised strains at the corner areas of sections, leading to fatigue fracture. A predictive equation addressing the coexisting influence of global slenderness and local slenderness on displacement ductility is presented. The observations in the current study are compared with conclusions from other experimental programmes, and the discrepancy between the findings is discussed. [ABSTRACT FROM AUTHOR]

The stability and design of steel equal-leg angle section members subjected to uniaxial bending are studied herein. An experimental investigation, comprising material testing, initial geometric imperfection measurements and physical tests on hot-rolled steel equal-leg angle section beams is first presented. The test results, in combination with existing experimental data on steel equal-leg angle section beams collected from the literature, are then used for the validation of numerical (shell finite element) models, developed within the commercial package ABAQUS. Next, a numerical parametric study is presented considering both hot-rolled and cold-formed steel angle section beams with a wide range of slenderness values. In major-axis bending, both lateral-torsional and local buckling were observed, with the former characterised by lateral deflection and twist of the cross-section along the member length but no cross-section deformation and the latter by relative twist and transverse bending of the outstands. In minor-axis bending, lateral-torsional buckling and Brazier flattening were observed, with the latter characterised by splaying of the outstands. Note that, for equal-leg angles under minor-axis bending, lateral-torsional buckling is dominant when the cross-section tips are in compression, while Brazier flattening is more influential when the cross-section tips are in tension. When designing for major-axis bending according to Eurocode 3, both local and lateral-torsional buckling are considered; it is shown herein that equal-leg angle section beams under major-axis bending can be designed using a normalised slenderness based on the minimum of the local and lateral-torsional elastic buckling moments, while also considering the ratio of the local to the lateral-torsional elastic buckling moments. For minor-axis bending, Eurocode 3 only requires cross-section checks; this is found to result in unsafe predictions in some cases. It is shown that both safer and more accurate resistance predictions can be achieved when lateral-torsional buckling and Brazier flattening are accounted for in the design of equal-leg angle section beams under minor-axis bending, using a normalised slenderness, based on the minimum of the lateral-torsional and Brazier flattening critical buckling moments. Finally, new design proposals for steel equal-leg angle section beams, covering both major- and minor-axis bending, are developed and verified against the experimental and numerical results. 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. 0 , is verified following the EN 1990 procedure. • Critical buckling behaviour of equal-leg angles under uniform bending is described. • Experiments on hot-rolled steel equal-leg angle section beams are presented. • Numerical parametric study considering steel angle section beams is described. • Experimental and numerical results are used to develop a new design approach. • Accuracy and reliability of the new proposals is verified in accordance with EN 1990. [ABSTRACT FROM AUTHOR]

• Tests on ten cold-formed S700 circular hollow section (CHS) beam-columns were performed. • Digital image correlation (DIC) was employed in the experimental programme. • Finite element simulations were carried out to expand test data pool for CHS beam-columns. • Existing EC3 beam-column design rules for Class 1–3 CHS were assessed. • New stability design method was proposed to capture influence of increased yield strength. An experimental and numerical study into the global buckling behaviour of structural steel circular hollow section (CHS) beam-columns with normal and high strength steel grades is presented in this paper. Two cold-formed S700 CHS profiles – 139.7×4 and 139.7×5 (diameter × thickness, in mm), were used in the beam-column testing programme. Ten CHS specimens were tested under eccentric compression, resulting in a combination of axial compressive force and uniform first-order bending moment. Digital image correlation (DIC) was used in the experiments to enable full-field monitoring of the strain and deformations in the specimens. Finite element (FE) modelling was also carried out with the aims of first replicating the test results and then generating further numerical data to complement the test data pool. Assessment of the existing EC3 design provisions was carried out against the test and FE data, which revealed that the lack of account taken for the full influence of varying yield strengths leads to inaccuracies in the EC3 resistance predictions. Improved design rules were proposed accordingly and shown to result in considerably more consistent predictions of buckling strength across a wide spectrum of steel grades. Lastly, a reliability assessment of both the EC3 and proposed design approaches was performed in accordance with EN 1990. The statistical results confirmed that the current EC3 partial safety factor is suitable for use with the new design proposals. [ABSTRACT FROM AUTHOR]

The stability and design of fixed-ended stainless steel equal-leg angle section members subjected to axial compression are studied herein. An experimental investigation, comprising material testing, initial geometric imperfection measurements and tests on hot-rolled austenitic stainless steel equal-leg angle section columns is first presented. The test results, in combination with existing experimental data on stainless steel equal-leg angle section columns collected from the literature, are then used for the validation of numerical (shell finite element) models, developed within the commercial package ABAQUS. Validation is performed by means of comparisons between the test and numerical results, considering ultimate loads, failure modes and the load–deformation responses, all of which are shown to be generally in good agreement. A numerical parametric study is then presented considering angle section columns in the three main families of stainless steel (austenitic, ferritic and duplex) with a wide range of slenderness values. The behaviour and normalised load-carrying capacity of the studied members is shown to be dependent on not only the column slenderness, but also the ratio of the elastic torsional-flexural buckling load to the elastic minor-axis flexural buckling load. Finally, a design approach recently proposed for carbon steel angle section columns is extended for application to stainless steel, and verified against the experimental and numerical results. The proposed approach offers substantially improved accuracy and consistency in strength predictions compared to the 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. • Experiments on hot-rolled austenitic stainless steel equal-leg angle section columns are presented. • Shell finite element models are developed in ABAQUS and validated against test results. • Numerical parametric study considering a range of stainless steel equal-leg angle section columns is 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]

• EN 1995 design expressions underestimate ultimate loads and overestimate slip moduli. • Analytical model validated against available push-out test results. • Analytical model can accurately describe the ultimate load and the slip moduli. • Analytical model can accurately predict failure modes. • Proposed model offers a significant improvement over current design provisions. An analytical model that can describe the load-slip response of cold-formed steel-to-timber connections, based on three components: timber embedment, screw bending and the axial pull-through, is presented. The model takes into consideration the screw inclination and the damage to the timber caused during the screw drilling process. The model was validated against available push-out test results, where it was shown that the model can accurately describe the ultimate load, the slip at ultimate load, and the two slip moduli, k s and k s,m , with mean model-to-test ratios of 1.01, 1.03, 1.09 and 0.96, respectively. The observed failure modes were also accurately predicted. Comparisons between the test data and the predictions of the EN 1995-1-1 design expressions showed that the Eurocode underestimated the ultimate loads by around 50% on average and overestimated the slip moduli by around 500% on average; the proposed model therefore offers a significant improvement over current design provisions. [ABSTRACT FROM AUTHOR]

Following the introduction of hot-finished elliptical hollow sections to the construction industry, recent research has been performed to develop supporting structural design guidance. This paper focuses on shear resistance. Twenty-four shear tests were performed on hot-finished steel elliptical hollow section members. The shear tests were arranged in a three-point bending configuration with span-to-depth ratios ranging from 1 to 8. This enabled the study of cross-section resistance in shear and the interaction between shear and bending. Measurements were taken of cross-section geometry, local initial geometric imperfections and material properties in tension. Test results, including moment--rotation histories, are presented. Additional results were generated numerically. These results have been used to verify proposed design expressions for shear resistance and resistance to combined shear and bending. Further investigations into design criteria for shear buckling are currently under way. [ABSTRACT FROM AUTHOR]

The article presents a study that examines the life-cycle costs of aluminium alloy and stainless steel and compares them to ordinary structural carbon steel. The study’s results show that on an initial cost basis, carbon steel offers the most competitive solution. However, with additional life-cycle costs including maintenance, end-of-life costs and the residual value of the structure, aluminium alloy and stainless steel offer more competitive solutions.

The initial material cost of structural stainless steel is about four times that of structural carbon steel, largely owing to the expense of the alloying elements and the relatively low volume of production. Given broadly similar structural performance, additional areas of benefit need to be identified and exploited in order to establish stainless steel as a viable alternative material for construction. In addition to the familiar benefits of corrosion resistance, low maintenance, high residual value and aesthetics, one such area is fire resistance. Stainless steel generally displays superior strength and stiffness retention at elevated temperature when compared to carbon steel, but also exhibits greater thermal expansion. The current paper describes experimental, numerical and analytical investigations into the elevated temperature response of stainless steel structures. Comparisons are made with the behaviour of carbon steel structures in fire and proposals for improved structural fire resistant design guidance for stainless steel are described. [ABSTRACT FROM AUTHOR]

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]

Abstract: The material stress–strain behaviour of structural carbon steel may be suitably accurately reflected for design purposes by an idealised elastic, perfectly-plastic material model; such material behaviour lends itself to the concept of section classification. There are, however, a number of structural materials, such as aluminium, stainless steel and some high strength, cold-worked steels, where this idealised model becomes inaccurate due to non-linearity of the stress–strain response below the yield point and considerable strain hardening beyond the yield point. Resulting design methods, developed on the basis of the idealised material behaviour, are necessarily overly conservative. A new method has been developed that utilises a more accurate material model and a continuous measure of cross-section deformation capacity (rather than the discretised system of section classification) to provide more rational and efficient designs. This paper describes the basis for the proposed design method and presents a comparison with results obtained from laboratory testing and those predicted by the current Eurocode approach. The proposed design method offers average increases in member resistances of around 20% over the current Eurocode approach, and a reduction in scatter of the prediction. [Copyright &y& Elsevier]

In this paper, the in-plane behaviour and design of duplex and ferritic stainless steel welded I-section beam–columns fabricated through the welding of individual hot-rolled stainless steel plates are explored. Finite element models able to replicate the structural response of stainless steel I-section members are created and validated against experimental results from the literature. Using the validated finite element models, extensive numerical parametric studies are performed, the results of which are utilised to investigate the accuracy and reliability of existing design provisions for duplex and ferritic stainless steel I-section beam–columns. Scope for improvement is revealed, prompting the development of new beam–column design rules that are compatible with those provided for carbon steel members in EN 1993-1-1. The new proposals are shown to offer improved accuracy and consistency over existing design provisions for duplex and ferritic stainless steel I-section members under combined axial compression and bending, and are recommended for inclusion in the upcoming revision to EN 1993-1-4. The reliability of the proposed design rules, with a partial safety factor γ M 1 = 1. 1 , is demonstrated. • Behaviour and design of duplex and ferritic stainless steel welded I-section beam–columns are investigated. • Finite element models able to mimic the behaviour of stainless steel beam–columns are developed. • Accuracy of existing beam–column design methods is investigated. • New design rules for duplex and ferritic stainless steel welded I-section beam–columns are proposed. • Proposed beam–column design rules lead to more accurate results relative to the existing design methods. [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. 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 influence of yield strength on the in-plane stability and design of structural steel square and rectangular hollow section (SHS and RHS) beam-columns under compression plus uniform bending is investigated in this study. Ten buckling tests were carried out on hot-finished S690 SHS 100×100×4 (in mm) specimens under combined compression plus uniaxial bending. Finite element (FE) models of SHS and RHS beam-columns were established, validated and employed to perform parametric studies, where supplementary buckling resistance data were numerically derived. Through comparisons with the test and FE data, shortcomings of the current EC3 beam-column interaction curves were revealed, particularly in the higher yield strength domain. A modified EC3 approach was developed accordingly, featuring more accurate compression end points and re-calibrated interaction factors, and was shown to significantly improve the design accuracy and consistency for both hot-finished and cold-formed SHS and RHS beam-columns over a wide spectrum of steel grades. Subsequent reliability analysis confirmed the applicability of the current EC3 partial safety factor to the proposed modified EC3 design approach. [Display omitted] • Ten hot-finished S690 square hollow section beam-columns were tested. • Finite element modelling of SHS and RHS beam-columns was carried out. • Current EC3 design rules for SHS and RHS beam-columns were assessed. • Modifications were proposed to improve the accuracy of EC3 interaction curves. • Reliability of the new design proposals was confirmed through statistical analysis. [ABSTRACT FROM AUTHOR]

The mechanical behaviour and design of fixed-ended steel equal-leg angle section members subjected to axial compression are addressed in this study. First, the critical buckling behaviour is described. Experimental data on steel equal-leg angle section columns collected from the literature are then used for the validation of numerical (shell finite element) models, developed within the commercial package ABAQUS. Validation is performed by means of comparisons between test and numerical results, considering ultimate loads and failure modes, all of which are shown to be generally in good agreement. A numerical parametric study is then presented considering steel angle section columns with a wide range of slenderness values. The behaviour and load-carrying capacity of the columns is shown to be dependent on, not only the column slenderness, but also the ratio of the elastic torsional-flexural buckling load to the elastic minor-axis flexural buckling load. Finally, the collected experimental and generated numerical results are used to develop a new design approach, suitable for incorporation into future revisions of Eurocode 3, for fixed-ended steel equal-leg angle section columns, reflecting the observations made. The proposed approach offers improved accuracy and consistency in strength predictions compared to the existing codified design rules. The reliability of the new design approach, with a recommended partial safety factor γ M1 = 1.0, is verified following the EN 1990 procedure. [Display omitted] • Critical buckling behaviour of fixed-ended equal-leg angle section columns is described. • Developed finite element models are validated against existing test results from the literature. • Numerical parametric study is conducted considering steel equal-leg angle section columns. • Elastic post-buckling behaviour of fixed-ended equal-leg angle section columns is studied. • Collected experimental and generated numerical results are used to develop a new design approach. • Accuracy and reliability of the new design approach are assessed and verified. [ABSTRACT FROM AUTHOR]

Additive manufacturing, also referred to as 3D printing, has the potential to revolutionise the construction industry, offering opportunities for enhanced design freedom and reduced material use. There is currently, however, very limited data concerning the performance of additively manufactured metallic structural elements. To address this, an experimental and numerical investigation into the cross-sectional behaviour of circular hollow sections (CHS), produced by powder bed fusion (PBF) from Grade 316L stainless steel powder, is presented. The experimental programme comprised tensile coupon tests, initial geometric imperfection measurements and five axially loaded stub column tests on specimens with a range of diameter-to-thickness (D / t) ratios. Similar cross-sectional behaviour to that of conventionally produced stainless steel CHS was observed, with the more slender cross-sections displaying increased susceptible to local buckling. In parallel with the experimental study, numerical simulations were carried out initially to replicate the experimental results and then to conduct parametric studies to extend the cross-sectional capacity data over a wider range of D / t ratios. The generated experimental and numerical results, together with other available test data on stainless steel CHS from the literature, were used to evaluate the applicability of existing design approaches for conventionally formed sections to those produced by additive manufacturing. • Additively manufactured stainless steel CHS stub columns were tested under axial compression. • Numerical models were validated against test results for additively manufactured CHS under axial compression. • Validated numerical models were used to perform parametric studies considering key parameters. • Applicability of existing design provisions in EN 1993-1-4 and the Continuous Strength Method was assessed. [ABSTRACT FROM AUTHOR]

A comprehensive experimental and numerical study into the cross-sectional behaviour of structural steel circular hollow sections (CHS), with an emphasis on high strength steel, is presented in this paper. Six cold-formed high strength steel S700 CHS profiles – 168.3×4, 139.7×4, 139.7×5, 139.7×6, 139.7×8 and 139.7×10 (diameter × thickness, in mm), spanning from Class 1 to Class 4 in compression according to EN 1993-1-1, were experimentally examined. The test programme consisted of twelve tensile coupon tests, local geometric imperfection measurements, six stub column tests, six four-point bending tests, six three-point bending tests and fifteen short beam-column tests. In parallel with the experimental study, finite element (FE) models of CHS were established and validated against the obtained experimental results, and parametric studies were subsequently carried out using the developed models to expand the cross-sectional resistance data pool. Finally, the cross-section design provisions specified in the European code prEN 1993-1-1:2018 and the American Specification ANSI/AISC 360-16 were assessed using the freshly generated experimental and numerical results as well as the existing test data on hot-rolled and cold-formed CHS from the literature. The present study provides the basis for the development of improved cross-section design rules for normal and high strength steel CHS in future research. • Six cold-formed S700 circular hollow section profiles were examined. • Six stub columns, twelve beams and fifteen short beam-columns were tested. • Digital image correlation was employed in the experiments. • Numerical models were developed to replicate the test results and to generate additional data. • Codified design provisions in EN 1993-1-1 and ANSI/ASIC 360 were assessed. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing (WAAM) is a method of metal 3D printing that is suited to the requirements of the construction industry in terms of scale, speed and cost. Using this technology, a 10.5 m span footbridge, the first of its kind, has been printed. The testing, analysis and initial verification of the bridge and its components are described herein. The experiments performed included advanced geometric analysis, material testing, compressive testing of cross-sections and full-scale load testing of the bridge at various stages throughout and post construction. Parallel finite element modelling of the full bridge and its constituent elements has also been performed as part of the verification. Confirmation that the bridge was able to sustain its full serviceability design load enabled to the bridge to be unveiled to the public, with controlled access, for Dutch Design Week 2018. Further testing under ultimate limit state design loading is planned before the bridge is placed in its final location and fully opened to the public. The project highlights the potential for metal 3D printing in structural engineering, as well as the necessary considerations for design. Unlabelled Image • Initial verification of the world's first metal 3D printed bridge is undertaken. • Material behaviour of the bridge is determined by tensile coupon testing. • Compressive structural response of the key bridge components is assessed by stub column testing. • Full-scale structural load testing of the bridge both during and after construction under different load cases is described. • Finite element simulations of the bridge are carried out and comparisons are made with the test results. [ABSTRACT FROM AUTHOR]

The flexural-torsional buckling response and design of stainless steel I-section beam-columns are investigated in this paper. First, a series of laboratory tests on laser-welded stainless steel I-section beam-columns susceptible to flexural-torsional buckling is presented. The results obtained are supplemented by further data generated by means of numerical parametric studies on both conventionally arc-welded and laser-welded stainless steel members covering a wide range of member slenderness and combinations of loading. Existing provisions for the design of welded stainless steel I-section elements against flexural-torsional buckling are then assessed and found to require improvement. Finally, new formulae for the design of stainless steel I-section beam-columns susceptible to flexural-torsional buckling are proposed. The new proposals yield improved accuracy and consistency over existing provisions and their suitability for inclusion in the upcoming version of the European structural stainless steel design code EN 1993-1-4 is confirmed by reliability analysis in accordance with EN 1990. • Flexural-torsional bucking response of stainless steel I-section beam-columns is investigated. •Experimental study on laser-welded stainless steel I-section beam-columns undergoing flexural-torsional buckling are presented. •FE models able to mimic flexural-torsional buckling response of stainless steel beam-columns are created and validated. •Numerical parametric studies are performed, whose results are utilised to assess accuracy of existing design provisions. •New design provisions are established, whose reliability is verified against the criteria set out in EN 1990. [ABSTRACT FROM AUTHOR]

Steel framed structures are affected, to greater or lesser extent, by (i) geometrical nonlinearity associated with the change in geometry of the structure under load and (ii) material nonlinearity related to the onset and spread of plasticity. In traditional design approaches, the design forces and moments within structural members are usually determined from simplified structural analyses (e.g. first or second-order elastic analysis), after which member design checks are performed to assess the strength and stability of the individual members. The extent to which the strength and deformation capacity of cross-sections is affected by local buckling is typically assessed through the concept of cross-section classification. For example, only compact (Class 1) cross-sections are considered to possess sufficient rotation capacity for plastic hinges to develop and for inelastic analysis methods to be used. This approach results in step-wise capacity predictions and is considered to be overly simplistic. Since the structural analysis of steel framed structures is typically performed using beam finite elements, which are unable to explicitly capture local buckling, a more sophisticated treatment of the available deformation capacity is required if inelastic analysis methods are to be used for all cross-section classes. A novel method of design by advanced inelastic analysis has recently been developed (Gardner et al., 2019a; Fieber et al., 2019a, 2018a, 2018b 1–4), in which strain limits are employed to represent the effects of local buckling in beam finite element models and thereby control the spread of plasticity and level of force/moment redistribution within a structure. It is thus possible to use a consistent advanced analysis framework to design structures composed of cross-sections of any class. In the present paper, application of the proposed design method to continuous beams and planar frames is illustrated and assessed. Ultimate load capacity predictions are compared against results obtained from benchmark shell finite element models that explicitly capture local buckling and to conventional steel design. It is found that the proposed method predicts safe-sided ultimate capacities that are consistently more accurate than current design methods, particularly for structures benefiting from strain hardening and for structures composed of non-compact cross-sections where inelastic redistribution is typically ignored. • Novel method for the design of steel structures using advanced analysis with strain limits is presented. • Capacity predictions compared against benchmark shell FE models for continuous beams and frames with I-section, SHS/RHS profiles. • Cross-section slenderness dependent levels of force/moment redistribution and effect of local moment gradients are captured. • The proposed design method is consistently more accurate than current EN 1993-1-1 design. [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]

Previous research has revealed shortcomings in the current Eurocode 3 (EC3) provisions for the design of semi-compact (Class 3) cross-sections. These shortcomings arise primarily from the lack of utilisation of partial plastification in bending, leading to a step in the design resistance function at the boundary between Class 2 and 3 cross-sections and an underestimation of the available capacity. This affects the accuracy of resistance predictions in bending and under combined loading, and applies at both cross-sectional and member level. To address this issue, the use of an elasto-plastic section modulus, which lies between the plastic and elastic section moduli, has been proposed and employed in the design of semi-compact I- and box sections. The aim of the present study is to develop new cross-section and member buckling design rules incorporating the elasto-plastic section modulus for semi-compact circular hollow sections (CHS), and to assess their accuracy against existing experimental and freshly generated numerical data. Firstly, an experimental database, consisting of previous cross-section and member buckling test results on steel CHS, was established. A comprehensive numerical simulation programme was subsequently carried out; in this programme, finite element (FE) models were developed, validated and used for parametric studies, where over 600 numerical structural performance data on semi-compact CHS were generated. New sets of cross-section and member buckling design expressions featuring elasto-plastic section properties were then proposed and assessed against the test and numerical data. The proposals were shown to offer improved accuracy and design efficiency over the elastic EC3 methods. The reliability of the proposed elasto-plastic design rules was then confirmed through statistical analyses in accordance with EN 1990, demonstrating their suitability for inclusion into the next revision of EN 1993-1-1. • Existing cross-section and member buckling test data on CHS were collected. • Numerical simulation was conducted to generate further data on CHS. • New design rules were developed to capture the elasto-plastic behaviour of semi-compact CHS. • Accuracy of the current Eurocode 3 and proposed methods were assessed and compared. • Reliability of the proposed design rules was confirmed through statistical analyses. [ABSTRACT FROM AUTHOR]

An experimental investigation into the cross-sectional behaviour of hot-finished high strength steel tubular sections, to support the assessment and development of structural design guidance, is presented. Two grades of quenched and tempered high strength steel – S690 and S770 and eight cross-sections – seven square hollow sections (SHS) and one rectangular hollow section (RHS), covering a wide range of local slenderness, were examined. This test programme consisted of twelve tensile coupon tests, five stub column tests and 30 short beam-column tests, with various initial loading eccentricities employed to achieve a spectrum of compression and bending combinations. Local geometric imperfection measurements were carried out on each test specimen using 3D laser-scanning, and a rational approach to analysing the local imperfection distributions using the scanned data was subsequently proposed. Following the experimental study, the current Eurocode 3 cross-section design provisions were evaluated through comparisons with the results from the present research and additional results from the literature. The experimental results and findings from the present study provide a basis for the development of numerical models and the enhancement of existing design methods in the future. • Hot-finished S690 and S770 square and rectangular hollow sections were examined. • Twelve tensile coupons, five stub columns and 30 short beam-columns were tested. • Local geometric imperfections were investigated by means of 3D laser-scanning. • Current Eurocode 3 design provisions were assessed using the experimental data. [ABSTRACT FROM AUTHOR]

• Structural behaviour and design of semi-compact (Class 3) EHS were studied; • Parametric studies were conducted to numerically expand the existing data pool; • New design methods were developed to exploit partial plastification in semi-compact EHS; • Accuracy of both the existing and proposed design methods were assessed; • Reliability of the design proposals was confirmed through statistical analyses. Current structural steel design codes typically feature a step in the cross-sectional resistance functions at the Class 2 slenderness limit due to the abrupt switch between elastic and fully plastic capacities. To address this issue, new design rules, featuring a gradual transition between elastic and plastic resistances, have been recently developed for semi-compact (Class 3) I- and box sections to account for the partial spread of plasticity. This approach is extended herein to the cross-section and member buckling design of semi-compact elliptical hollow sections (EHS). Finite element models were first established and validated against previous test results; particular attention was given to the modelling of local geometric imperfections. Parametric studies were then conducted, where over 4000 structural performance data were numerically generated covering a wide range of cross-section aspect ratios, material properties, local and global slendernesses and load combinations. Upon completion of the numerical simulation programme, structural design rules of semi-compact EHS were developed. The classification of EHS under biaxial bending and compression plus biaxial bending was initially addressed. Following this, new design expressions featuring elasto-plastic section properties were developed to exploit partial plastification at both cross-section and member buckling levels. The accuracy of the design proposals was evaluated through comparisons between the test/numerical data and the resistance predictions; the comparisons revealed that the proposed elasto-plastic cross-section and member buckling design rules lead to both improved accuracy and consistency over the existing elastic provisions. The reliability of the proposals was verified through statistical analyses in accordance with EN 1990, demonstrating their suitability for incorporation into the next revision to EN 1993-1-1. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is a method of metal three-dimensional (3D) printing that has the potential for a significant impact on the construction industry due to its ability to produce large parts with reasonable printing times and costs. However, there is currently a lack of fundamental data on the performance of structural elements produced using this method of manufacturing. Seeking to bridge this gap, the compressive behavior and resistance of WAAM square hollow sections (SHS) are investigated in this paper. In a previous study by the authors, testing reported of sheet material produced in the same manner as the studied SHS is first summarized. The production, measurement, and testing of a series of stainless steel SHS stub columns are then described. Regular cross-section profiles were chosen to isolate the influence of 3D printing and enable direct comparisons to be made against equivalent sections produced using traditional methods of manufacturing. A range of cross-section sizes and thicknesses were considered to achieve variations in the local cross-sectional slenderness of the tested specimens, allowing the influence of local buckling to be assessed. Repeat tests enabled the variability in response between specimens to be evaluated; a total of 14 SHS stub columns of seven different local slendernesses was tested, covering all cross-section classes of AISC 370 and Eurocode 3. Advanced noncontact measurement techniques were employed to determine the as-built geometric properties, while digital image correlation measurements were used to provide detailed insight into the deformation characteristics of the test specimens. Owing to the higher geometric variability of WAAM relative to conventional forming processes, the tested 3D printed stub columns were found to exhibit more variable capacities between repeat specimens than is generally displayed by stainless steel SHS. Comparisons of the stub column test results with existing structural design rules highlight the need to allow for the weakening effect of the geometric undulations that are inherent to the WAAM process in order to achieve safe-sided strength predictions. [ABSTRACT FROM AUTHOR]

The hyperbolic paraboloid (hypar) form has been widely used in long-span roof structures and is the subject of much research under out-of-plane loading. However, the behaviour of hypars under in-plane loading has been less keenly studied, and there is no suitable guidance for their design in current codes of practice. A nonlinear analytical model treating the hypar as a deliberate imperfection applied to a flat plate is presented. A Rayleigh–Ritz formulation using appropriate shape functions is developed and the resulting equations are solved using numerical continuation techniques. The results are verified with nonlinear finite-element models, showing good correlation across a range of thicknesses and degrees of initial curvature. Key modal contributions that influence the behaviour of the hypar are identified, providing insight into the nonlinear behaviour of hypars subject to in-plane shear. The main differences in behaviour between the flat plate and the hypar panel are shown to be most prevalent in the early stages of loading, where the influence of the initial geometry is at its greatest. [ABSTRACT FROM AUTHOR]

• Design of steel members using advanced inelastic analysis with strain limits. • Strain limits mimic local buckling and control spread of plasticity in beam FE. • Capacity predictions were compared against 6188 benchmark shell finite element models. • Proposed design method is consistently more accurate than current EN 1993-1-1 design. Structural steel design is traditionally a two step process: first, the internal forces and moments in the structure are determined from a structural analysis. Then, a series of design checks are carried out to assess the strength and stability of individual members. The structural analysis is typically performed using beam finite elements, which are usually not able to capture local buckling explicitly. Instead, the assessment of local buckling and rotation capacity is made through the concept of cross-section classification, which places class-specific restrictions on the analysis type (i.e. plastic or elastic) and defines the cross-section resistance based on idealised stress distributions (e.g. the plastic, elastic or effective moment capacity in bending). This approach is however considered to be overly simplistic and creates artificial steps in the capacity predictions of structural members. A more consistent approach is proposed herein, whereby a second-order inelastic analysis of the structure or structural component is performed using beam finite elements, and strain limits are employed to mimic the effects of local buckling, control the spread of plasticity and ultimately define the structural resistance. The strain limits are obtained from the continuous strength method. It is shown that not only can local buckling be accurately represented in members experiencing uniform cross-sectional deformations along the length, but, by applying the strain limits to strains that are averaged over a defined characteristic length, the beneficial effects of local moment gradients can also be exploited. The proposed method is assessed against benchmark shell finite element results on isolated members subjected to bending, compression and combined loading. Compared to conventional steel design provisions and even to existing advanced design approaches utilising second-order elastic analysis, the proposed design approach provides consistently more accurate capacity predictions. [ABSTRACT FROM AUTHOR]

Concrete-filled stainless steel tubular (CFSST) columns combine the advantages of composite action seen in concrete-filled steel tubular (CFST) columns with the durability benefits associated with stainless steel. An effective means of reducing the material usage in the outer stainless steel tube in CFSST columns is to embed an inner carbon steel profile. This enables the material costs to be reduced, while achieving similar load-bearing capacity and durability, as well as enhanced fire resistance. The behaviour of such steel reinforced composite columns, i.e. concrete-filled stainless steel tubular (CFSST) columns with outer square cross-sections and embedded carbon steel profiles, under ISO 834 standard fire conditions is investigated in this study by finite element (FE) analysis. Firstly, FE models are developed and validated against relevant published experimental data on CFSST and steel reinforced CFST columns under fire conditions. Based on the validated FE models, the working mechanisms of the studied steel reinforced CFSST columns under fire conditions are investigated by analysis of the temperature field, failure modes, axial deformation versus time response and internal force distribution. The fire performance of the studied steel reinforced CFSST columns is also evaluated in comparison with CFST and CFSST columns with the same total cross-sectional area of steel or the equivalent cross-sectional load-bearing capacity at ambient temperature. Finally, with respect to fire resistance, the optimal ratio of the cross-sectional areas of the inner carbon steel profile to the outer stainless steel tube is investigated. • Finite element analysis models were developed to simulate the behaviour of steel reinforced CFSST columns in fire. • The working mechanisms of steel reinforced CFSST columns with square cross-sections in fire were analyzed. • Parametric analyses and comparisons were conducted to assess and optimize the fire performance of steel reinforced CFSST columns. [ABSTRACT FROM AUTHOR]