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Three types of geometric imperfection need to be considered in the design of structural systems: global frame out‐of‐plumbness, also referred to as sway imperfections, member out‐of‐straightness, also known as bow imperfections, and local cross‐section imperfections. For modelling convenience, equivalent geometric imperfections are often employed to account for the combined influence of initial geometric imperfections and residual stresses. For design by geometrically and materially nonlinear analysis with imperfections (GMNIA), amplitudes for equivalent bow imperfections for members are provided in prEN 1993‐1‐14; however, no provisions exist for global sway imperfections. Therefore, equivalent sway imperfections suitable for use in the design of steel structures by GMNIA, expressed by the out‐of‐plumbness Φ0,GMNIA are established herein. Two proposals for calculating Φ0,GMNIA are presented: (1) Φ0,GMNIA = Φ0,geom + α/100 with Φ0,geom representing the amplitude of the pure geometric sway imperfection, and (2) Φ0,GMNIA = α/50. In both proposals, the varying influence of residual stresses from different cross‐section geometries and axes of bending is captured by the imperfection factor α, as defined by the buckling curves in EN 1993‐1‐1 for carbon steel and EN 1993‐1‐4 for stainless steel, respectively. [ABSTRACT FROM AUTHOR]

An experimental study into the flexural buckling response of wire arc additively manufactured (WAAM) columns is presented in this paper. A total of six square hollow section (SHS) columns were tested under axial compression with pin‐ended boundary conditions. The lengths of the members were varied to achieve a wide range of member slendernesses. Owing to the undulating as‐built profile introduced by WAAM, 3D laser scanning was adopted to capture the geometry and global imperfections of the specimens, while digital image correlation (DIC) was employed to monitor the surface deformation of the specimens during testing. The full load‐deformation histories and key experimental results are presented and discussed. The applicability of the column design provisions set out in EN 1993‐1‐4 to WAAM members is subsequently assessed using the obtained test results. [ABSTRACT FROM AUTHOR]

Design by GMNIA (Geometrically and Materially Nonlinear Analysis with Imperfections) allows the key behavioural features of structures to be directly captured in the analysis, dramatically reducing the need for subsequent design checks. Since the analysis of frames typically employs beam finite elements, which do not explicitly account for local buckling, cross‐section classification and capacity checks remain necessary. To resolve the step‐wise and overly conservative nature of traditional checks, the alternative use of strain limits, defined using the Continuous Strength Method, has been proposed. The framework allows cross‐sections of all classes to be treated in a consistent manner, and results in an accurate and consistent representation of the true behaviour of structures. To date, the accuracy of the design approach for stainless steel has been comprehensively demonstrated for isolated stainless steel members; the design method is extended to indeterminate stainless steel structural systems herein. The method is included in AISC 370 and prEN 1993‐1‐14; inclusion of this design framework in international codes of practice presents a step change for the future direction of efficient structural stainless steel design. [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]

Initial geometric imperfections have been identified as the main cause for the large discrepancies between experimental and theoretical buckling loads of thin-walled circular cylindrical shells under axial compression. The extreme sensitivity to imperfections has been previously addressed and mitigated through the introduction of stiffeners; however, sensitivity still remains. Optimized corrugated cylindrical shells are largely insensitive to imperfections and hence exhibit excellent load-bearing capacities, but their complex geometries make their construction difficult and costly using conventional manufacturing techniques. This was overcome in the present study through additive manufacturing (AM). Nine optimized corrugated shells with different diameter-to-thickness ratios, together with one reference circular cylindrical shell, were additively manufactured by means of powder bed fusion (PBF) from austenitic and martensitic precipitation hardening stainless steel. The structural behavior of the AM shells was then investigated experimentally with the testing program comprising tensile coupon tests, measurements of basic geometric properties, and axial compression tests. Numerical analyses were also conducted following completion of the physical experiments. The experimental and numerical results verified the effectiveness of optimized corrugated cylindrical shells in achieving improved local buckling capacity and reduced imperfection sensitivity. Initial recommendations for the structural design of the studied cross-sections are made. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is a metal three-dimensional (3D) printing method that enables large-scale structural elements with complex geometry to be built in a relatively efficient and cost-effective manner, offering revolutionary potential to the construction industry. However, fundamental experimental data on the structural performance of WAAM elements, especially at the member level, are lacking. Hence, an experimental study into the flexural buckling response of WAAM tubular columns has been conducted and is presented in this paper. A total of 18 stainless steel square and circular hollow section (SHS and CHS) columns were tested under axial compression with pin-ended boundary conditions. Regular SHS and CHS profiles were chosen to enable direct comparisons against equivalent, conventionally manufactured sections and, hence, to isolate the influence of the additive manufacturing process, whereas the cross-section sizes and column lengths were varied to achieve a broad spectrum of member slendernesses. Given the geometric undulations inherent to the WAAM process, 3D laser scanning was used to determine the as-built geometry and global geometric imperfections of the specimens; digital image correlation (DIC) was employed to monitor the surface deformations of the specimens during testing. Full details of the column testing program, together with a detailed discussion of the experimental results, are presented. The applicability of the current column design provisions in EN 1993-1-4 and AISC 370 to WAAM stainless steel members was assessed by comparing the test results with the codified strength predictions. The comparisons emphasized the need to allow for the weakening effect of the inherent geometric variability of WAAM elements to achieve safe-sided strength predictions. [ABSTRACT FROM AUTHOR]

Powder bed fusion (PBF) is an additive manufacturing method that enables complex metallic components to be manufactured with high precision. The microstructure, mechanical properties and cross‐sectional behaviour of PBF additively manufactured stainless steel circular hollow sections are investigated through experiments in this paper, with a view to applications in construction. The experimental programme included tensile coupon tests, microstructural characterisation, initial geometric imperfection measurements and compression tests on PBF 316L stainless steel cylindrical shells with large diameter‐to‐thickness (D/t) ratios. Advanced measurement methods – 3D laser scanning and digital image correlation, were employed to measure the specimen geometries prior to testing and deformation fields during testing, respectively. The possible anisotropy in mechanical properties was examined through tensile coupon tests and correlated with the underlying microstructural and textural features. Compression tests were performed to investigate the resistance against local buckling of thin‐walled cylindrical shells produced by PBF. All cylindrical shells buckled below their yield loads with a chequerboard failure mode and revealed the anticipated trend of reducing capacity relative to the yield load with increasing local slenderness, reflecting the increasing susceptibility to local buckling. [ABSTRACT FROM AUTHOR]

Cold‐working can occur during the production of flat sheet products and the fabrication of structural cross‐sections. In both cases, when the material is cold‐worked, plastic deformations result in material strength enhancements. These strength enhancements are particularly significant for materials such as stainless steel, which exhibit rounded stress‐strain behaviour and pronounced strain hardening, and for hollow cross‐sections, where the strength increases arise in both the corner and flat regions of the cross‐section. Numerous studies have shown the importance of utilising this strength enhancement in design, and expressions to predict the strength enhancements have been established. However, if cold‐worked material is welded, some enhanced strength can be lost due to partial annealing in the heat affected zone (HAZ). The extent of this strength loss is investigated experimentally herein. The experimental programme comprised ten tensile coupon tests, with central welds parallel and transverse to the direction of cold‐rolling, as well as twelve full cross‐section tensile tests. Digital imaging correlation was utilised to determine the local constitutive properties of the base metal, the HAZ, and the weld metal. The microhardness and microstructure of the welded coupons, along with the widths of the weld and HAZ, were also characterised. [ABSTRACT FROM AUTHOR]

In this paper, the flexural‐torsional buckling response of austenitic stainless steel I‐section beam‐columns is investigated. Finite element simulations are performed with the aim of analysing the parameters affecting the behaviour of the studied members. The accuracy and safety of the existing design provisions of the European structural stainless steel design standard EN 1993‐1‐4 (2015) are assessed. A new method providing more accurate ultimate resistance predictions for austenitic stainless steel I‐section beam‐columns undergoing flexural‐torsional buckling is put forward. The higher accuracy, safety and reliability of the proposed design rules relative to EN 1993‐1‐4 (2015) are demonstrated and the new proposals have now been included in the revised Eurocode – prEN 1993‐1‐4 (2021). [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 stability of compression members is typically assessed through buckling curves, which include the influence of initial geometric imperfections and residual stresses. Alternatively, the capacity can be obtained more directly by carrying out a second order analysis using equivalent bow imperfections that account for both geometric imperfections and residual stresses. For design by second order elastic analysis, following EN 1993‐1‐1 recommendations, the magnitudes of the equivalent bow imperfections can either be back‐calculated for a given member to provide the same result as would be obtained from the member buckling curves or taken more simply as a fixed proportion of the member length. In both cases, a subsequent linear axial + bending cross‐section check is required. For design by second order inelastic analysis, there are currently no suitable recommendations for the magnitudes of equivalent bow imperfections and, as demonstrated herein, it is not generally appropriate to use equivalent bow imperfections developed on the basis of elastic analysis. Equivalent bow imperfections suitable for use in design by second order inelastic analysis are therefore established in the present paper and shown to yield reliable results when compared to benchmark results and current design guidance. [ABSTRACT FROM AUTHOR]

Axially compressed circular cylindrical shells with large diameter‐to‐thickness ratios are known to be highly sensitive to initial geometric imperfections, which can drastically reduce their load‐carrying capacity. Their design typically involves the application of severe knock‐down factors on their theoretical buckling loads, which greatly impair their structural efficiency. In this paper, with the aim of reducing sensitivity to imperfections and enhancing load‐bearing resistance, optimised corrugated cylindrical shells are designed, additively manufactured, tested and analysed. Two corrugated shells with different equivalent diameter‐to‐thickness ratios, along with a reference circular cylindrical shell, were produced by powder bed fusion (PBF) additive manufacturing from martensitic precipitation hardening stainless steel powder. The structural performance of the PBF corrugated and circular shells was experimentally investigated, including tensile coupon tests, initial geometric measurements and compression tests. Numerical analyses were also carried out in parallel with the testing. The experimental and numerical results demonstrate that the optimised corrugated cross‐sections have lower imperfection sensitivity and higher axial resistances compared with their reference circular sections. [ABSTRACT FROM AUTHOR]

In contrast to conventional structural steel and stainless steel, wire and arc additively manufactured (WAAM) material can exhibit a strongly anisotropic response. To investigate the degree of anisotropy in WAAM sheet material, data obtained from tensile tests on machined and as‐built stainless steel coupons are utilised. The WAAM material was tested in three different loading directions relative to the deposition direction and the response was captured using digital image correlation; a summary of the key results is presented. In the elastic range, the observed mechanical response is characterised using an orthotropic plane stress material model, which requires the definition of two Young's moduli, the Poisson's ratio and the shear modulus. Good agreement between the test results and the theoretical predictions based on the orthotropic material model is demonstrated. In the inelastic range, to describe the anisotropic yielding of the material, the well‐known Hill's criterion utilising the 0.2% proof stresses is employed. Overall, the elastic and inelastic properties of the studied material are shown to vary significantly with the direction of loading. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing (WAAM) is a method of 3D printing that enables large structural elements to be built, with reasonable printing times and costs, making it well suited to applications in the construction industry. There is currently, however, limited information relating to the structural performance of WAAM material. Uncertainties include the basic mechanical properties, the degree of anisotropy and the influence of the as‐built geometry. Towards addressing this knowledge gap, a comprehensive series of tensile tests on coupons cut from WAAM stainless steel sheets was conducted and the results are presented and analysed herein. As‐built and machined coupons were tested to investigate the influence of the as‐built geometrical irregularity on the stress‐strain characteristics, while material anisotropy was explored by testing coupons produced at 0°, 45° and 90° to the printing layer orientation. Advanced non‐contact measurement techniques were employed to determine the geometric properties and deformation fields of the test specimens, while sophisticated analysis methods were used for post processing the resulting test data. The underlying material stress‐strain response, as determined from the tensile tests on the machined coupons, revealed a significant degree of anisotropy while the effective mechanical properties of the as‐built material were shown to be strongly dependent on the level of geometric variability arising from the printing process. [ABSTRACT FROM AUTHOR]

The Continuous Strength Method (CSM) provides accurate cross‐section resistance predictions since allowance is made for the partial spread of plasticity and the beneficial effects of strain hardening. Although CSM design provisions for different loading conditions are available, the method was limited to the determination of cross‐sectional resistance until recent research by Arrayago et al. (2020) proposed a consistent new approach to the design of stainless steel hollow section members subjected to compression. Extension of the CSM to the design of stainless steel members subjected to combined compression and bending moment is presented in this paper. The analysis is based on numerical results generated in the current study and existing results collected from the literature on stainless steel hollow section members. The results demonstrate that the adoption of the CSM design equations to predict column strength considerably improves the accuracy of the calculated beam‐column capacities. The reliability of the proposed approach is demonstrated through statistical analyses performed in accordance with EN 1990. [ABSTRACT FROM AUTHOR]

This paper presents the development of flexural buckling curves for austenitic and duplex stainless steel welded I‐sections and structural hollow sections, which are proposed for implementation in the new AISC stainless steel specification. The proposed buckling curves were developed following the same type of reliability analysis employed to develop the flexural buckling curve included in AISC 360 Specification for Structural Steel Buildings for carbon steel, considering all the experimental data available in the literature and a large number of numerical results. In order to facilitate their implementation, the proposed curves follow a similar form as the AISC‐type of curve included in AISC 360, with the only differences being the addition of a yield plateau and the values of selected coefficients used to adjust the shape of the curves. Three different buckling curves are proposed: one buckling curve for circular hollow section (CHS) columns and I‐section columns buckling about the major axis; one for rectangular hollow section (RHS) columns; and one for I‐section columns buckling about the minor axis. The proposed curves represent a significant improvement with respect to the currently available stainless steel flexural buckling curve included in AISC Design Guide 27, providing an increase in strength predictions of up to 55%. [ABSTRACT FROM AUTHOR]

A comprehensive investigation into the behaviour of structural stainless steel members under concentrated transverse loading is presented in this paper. A total of 34 member tests and over 500 finite element simulations have been performed covering three types of concentrated transverse loading – internal one‐flange, internal two‐flange and end one‐flange loading, three stainless steel grades – austenitic, duplex and ferritic and key influential parameters such as bearing length, web slenderness and beam span. The results have shown that existing design recommendations are conservative and that there is considerable scope for the development of more economical design guidance. New design equations are proposed that offer 10% to 20% improvements in capacity predictions over the current design formulae in EN 1993‐1‐4. These proposed design equations are to be included in the next revision of the European standards. An alternative design approach based on numerically generated reference loads – i.e. the plastic collapse and elastic buckling loads – in conjunction with strength curves, has also been proposed. This advanced FE‐based design approach allows the extension of the design scope to non‐standard cases, such as webs with partial depth stiffeners and members with web holes. The reliability of both design approaches has been successfully verified by statistical analysis. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study into the behaviour of concrete filled double skin tubular (CFDST) stub columns. A total of eight axial compression tests were carried out, half of which were filled with conventional concrete and the remainder had recycled aggregate concrete. The columns were circular in cross‐section and comprised an austenitic stainless steel outer tube and a carbon steel inner tube, of varying dimensions. Accordingly, hollow ratios of 0.67 and 0.55 were considered. The recycled coarse aggregate was made by crushing test specimens from a previous research project. A replacement ratio of 50% was adopted in these tests. Both the natural coarse aggregates and the recycled aggregates had a maximum diameter of 9.5 mm. During the tests, similar structural behaviour and failure modes were observed between the columns with conventional and recycled aggregate concrete, and the faiure modes were identical. The experimental results are compared with available design procedures and it is ultimately shown that using recycled aggregate concrete rather than regular concrete in CFDST stub columns does not have a significant effect on the performance. [ABSTRACT FROM AUTHOR]

With the growing use of stainless steel in the construction and offshore industries, there is an increasing interest and need to study the performance of stainless structures at elevated temperatures. The behavior and design of stainless steel I-section beam-columns in fire is investigated in this paper, addressing a scarcity of previous research on this topic. Finite element (FE) models of stainless steel beam-columns, able to replicate their response at elevated temperatures, are created and validated; the validated models are then used to perform parametric studies to generate extensive benchmark structural performance data. The design rules set out in the European structural steel fire design standard EN 1993-1-2 are assessed and shown to provide rather inaccurate and often unsafe ultimate strength predictions for stainless steel I-section beam-columns in fire. New fire design rules for stainless steel beam-columns are put forward. It is shown that the new proposals are able to offer improved accuracy and design efficiency relative to the EN 1993-1-2 beam-column design rules. The reliability of the proposed design rules is also verified on the basis of the fire design reliability criteria set out by Kruppa [Eurocodes–Fire parts: Proposal for a methodology to check the accuracy of assessment methods, CEN TC 250, Horizontal Group Fire, Document no: 99/130 (1999)], thereby demonstrating the suitability of the proposed design rules for inclusion in the upcoming revised version of EN 1993-1-2. [ABSTRACT FROM AUTHOR]

This paper provides a review of recent developments in research and design practice surrounding the structural use of stainless steel, with an emphasis on structural stability. The nonlinear stress-strain characteristics of stainless steel, which are discussed first, give rise to a structural response that differs somewhat from that of structural carbon steel. Depending on the type and proportions of the structural element or system, the nonlinear material response can lead to either a reduced or enhanced capacity relative to an equivalent component featuring an elastic, perfectly plastic material response. In general, in strength governed scenarios, such as the in-plane bending of stocky beams, the substantial strain hardening of stainless steel gives rise to capacity benefits, while in stability governed scenarios, the early onset of stiffness degradation results in reduced capacity. This behaviour is observed at all levels of structural response including at cross-sectional level, member level and frame level, as described in the paper. Current and emerging design approaches that capture this response are also reviewed and evaluated. Lastly, with a view to the future, the application of advanced analysis to the design of stainless steel structures and the use of 3D printing for the construction of stainless steel structures are explored. • Constitutive modelling of stainless steel reviewed. • Influence of material nonlinearity of structural stability explained. • Current and emerging structural stainless steel design methods described. • Future trends, including design by advanced analysis and 3D printing, explored. [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]

Steel-reinforced concrete-filled stainless steel tubular (SRCFSST) columns combine the advantages of concrete-filled stainless steel tubular (CFSST) columns and steel-reinforced concrete (SRC) columns, resulting in excellent corrosion resistance, good economy, good ductility, and excellent fire resistance. Thus, SRCFSST columns have many potential structural engineering applications, especially in offshore structures. The performance of SRCFSST columns at elevated temperatures is investigated by finite element (FE) analysis in this paper. Firstly, FE models capable of capturing the full load-deformation response of structural members at elevated temperatures are developed and validated against relevant published tests on CFSST and SRC columns under fire conditions. Based on the validated FE models, the behavioral mechanisms of the SRCFSST columns under fire are explained by analysis of the sectional temperature distribution, typical failure modes, axial deformation versus time response, and load redistribution. Finally, the fire resistance of SRCFSST columns is evaluated in comparison to CFSST columns with equivalent sectional load-bearing capacity at ambient temperature or equivalent steel ratios. The results lay the foundation for the development of fire resistance design rules for SRCFSST columns. [ABSTRACT FROM AUTHOR]

Abstract The current codified treatment of local buckling in stainless steel cross-sections is based on the traditional cross-section classification framework and a simplified elastic, perfectly-plastic material model, providing consistency with the corresponding carbon steel design rules. However, the cross-section classification framework treats the cross-section as an assemblage of isolated plate elements without considering the beneficial element interaction effect, and the elastic, perfect-plastic material model neglects the pronounced strain hardening exhibited by stainless steels. These limitations have been generally found to result in unduly conservative and scattered resistance predictions through comparisons against previous test data. To address these shortcomings, a deformation-based continuous strength method (CSM) has been developed, which relates the strength of a cross-section to its deformation capacity and employs a bi-linear (elastic, linear hardening) material model to account for strain hardening. The CSM has been established for the design of doubly symmetric plated sections and circular hollow sections, and shown to yield a high level of design accuracy and consistency. In this paper, the scope of application of the CSM is extended to cover the design of non-doubly symmetric cross-sections in bending. Global member buckling is not investigated. The developed design methodology and comparisons with existing test data and numerical results generated herein are described. Finally, reliability analysis is performed, which demonstrates the suitability of the proposals for inclusion in structural design codes. Highlights • Current design approaches for non-doubly symmetric stainless steel sections in bending were briefly reviewed. • The CSM has been extended to cover the design of non-doubly symmetric stainless steel sections in bending. • Assessment of the proposed CSM indicates a higher level of design accuracy and efficiency. • The reliability of the new proposal has been confirmed by means of statistical analyses. [ABSTRACT FROM AUTHOR]

• The Continuous Strength Method (CSM) is a strain based structural design approach. • The background and state of the art of the CSM is reviewed. • The CSM features in a number of European and US structural design standards. • The range of applicability and key advantages of the CSM are highlighted. • Aspects of the CSM that require further research are identified. The Continuous Strength Method (CSM) is a deformation-based approach to the design of structures that enables a continuous, rational and accurate allowance for material nonlinearity (i.e. the spread of plasticity and strain hardening). Central to the method is the application of strain limits, determined on the basis of the local slenderness of full cross-sections, to define the resistance of a structural member or system. The method can be applied to structures formed using different materials (e.g. steel, stainless steel or aluminium) and manufacturing processes (e.g. hot-rolled or cold-formed) through the assignment of suitable stress–strain relationships, and can be used for steel–concrete composite design and in fire scenarios. In composite construction, the CSM enables a more rigorous assessment to be made of the development of strength in the structural system taking due account of compatibility between the constituent materials. The design method enables enhancements in structural efficiency and, unlike traditional approaches, allows the assessment of both strength and ductility (which is particularly relevant for high strength steel) demands at the ultimate limit state. For hand calculations, a set of straightforward CSM design equations have been developed. Recognising the increasing importance and use of advanced analysis (i.e. GMNIA), recent research, summarised herein, has focussed on integration of the CSM strain limits into a framework of design by second order inelastic analysis, where the benefits of the method become even more substantial. This paper provides a review of the background and recent developments to the CSM, including incorporation into design standards. Current and ongoing research to expand the scope of the CSM is summarised and recommendations for future work are also set out. [ABSTRACT FROM AUTHOR]

Laser-welding is a high precision fabrication process suitable for joining a wide range of steels and stainless steels. Laser-welded structural stainless steel members, for which there are currently little experimental data owing to their recent introduction to the construction industry, are the focus of the present study. To address the lack of test data and to investigate their structural response, a total of 9 stub column tests and 22 flexural buckling tests (14 buckling about the minor axis and 8 about the major axis) have been performed on laser-welded austenitic stainless steel I-section members. Complementary tensile coupon tests, initial geometric imperfection measurements, and residual stress measurements have also been carried out and are reported herein. Based on the results obtained, a representative residual stress pattern is proposed, the design provisions of Eurocode 3 Part 1.4 and the continuous strength method are assessed, and column buckling curves for laser-welded stainless steel I-section members are recommended. [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]

A comprehensive experimental and numerical investigation into the structural performance of stainless steel circular hollow sections (CHS) under combined compression and bending moment has been performed and is fully reported in the present paper and its companion paper. The experimental programme employed four CHS sizes made of austenitic stainless steel, and included material tensile coupon tests, four stub column tests and twenty combined loading tests. The initial loading eccentricities for the combined loading tests were varied to provide a wide range of bending moment-to-axial load ratios. In conjunction with the testing programme, a numerical modelling programme was performed to simulate the experiments. The developed FE models were shown to be capable of replicating the key test results, full experimental curves including the post-ultimate range and deformed failure modes. Upon validation of the FE models, a series of parametric studies were conducted in the companion paper, aiming at extending the current test data pool over a range of cross-section sizes and combinations of loading. The experimental data, together with the generated parametric study results, were analysed and employed to evaluate the applicability of the codified provisions given in the European code, American specification and Australia/New Zealand standard for design of CHS under combined loading. Improved design rules were also sought through extension of the deformation-based continuous strength method (CSM) to the case of stainless steel CHS under combined loading. [ABSTRACT FROM AUTHOR]

Circular hollow sections (CHS) are widely used in a range of structural engineering applications. Their design is covered by all major design codes, which currently use elastic, perfectly-plastic material models and cross-section classification to determine cross-secti\on compressive and flexural resistances. Experimental data for stocky sections show that this can result in overly conservative estimates of cross-section capacity. The continuous strength method (CSM) has been developed to reflect better the observed behaviour of structural sections of different metallic materials. The method is deformation based and allows for the rational exploitation of strain hardening. In this paper, the CSM is extended to cover the design of non-slender and slender structural steel, stainless steel and aluminium CHS, underpinned by and validated against 342 stub column and bending test results. Comparisons with the test results show that, overall, the CSM on average offers more accurate and less scattered predictions of axial and flexural capacities than existing design methods. [ABSTRACT FROM AUTHOR]

An experimental and numerical study of ferritic stainless steel tubular cross sections under combined loading is presented in this paper. Two square hollow section (SHS) sizes--SHS 40 × 40 × 2 and SHS 50 × 50 × 2 made of Grade EN 1.4509 (AISI 441) stainless steel--were considered in the experimental program, which included 2 concentrically loaded stub column tests, 2 four-point bending tests, and 14 eccentrically loaded stub column tests. In parallel with the experimental investigation, a finite-element (FE) study was also conducted. Following validation of the FE models against the test results, parametric analyses were carried out to generate further structural performance data. The experimental and numerical results were analyzed and compared with the design strengths predicted by the current European stainless steel design code EN 1993-1-4 and American stainless steel design specification SEI/ASCE-8. The comparisons revealed that the codified capacity predictions for ferritic stainless steel cross sections under combined loading are unduly conservative. The deformation- based continuous strength method (CSM) has been extended to cover the case of combined loading. The applicability of CSM to the design of ferritic stainless steel cross sections under combined loading was also evaluated. The CSM was shown to offer substantial improvements in design efficiency over existing codified methods. Finally, the reliability of the proposals was confirmed by means of statistical analyses according to both the SEI/ASCE-8 requirements and those of EN 1990. [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]

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]

Abstract: The material properties of stainless steel are sensitive to plastic deformation which causes an increase in yield strength by a process termed cold working. The different strain paths experienced around cold-formed cross sections during manufacture create unique material strength distributions for sections from different forming routes and also influence residual stress patterns. The research program presented herein has examined experimentally the material and residual stress distributions found in two types of cold-formed sections–cold-rolled box sections and press-braked angles. Predictive tools to harness the observed strength enhancements have been proposed and incorporated into models. Subsequent comparisons have shown that these strength enhancements, in particular those observed for cold-rolled box sections, should be employed in structural design to avoid considerable underestimation of member resistance. [Copyright &y& Elsevier]

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

Abstract: A conceptually new structural design approach has recently been proposed by the authors to predict the resistance of stainless steel members subjected to various types of loading with cross-sections formed from thin flat plates including angles, channels, lipped channels, I-sections and rectangular hollow sections (RHS). The proposed method does not follow the traditional cross-section classification approach, which primarily relies on the assumption of a bilinear, elastic–perfectly-plastic material model. Instead, deformation capacity of a cross-section is determined directly from the local buckling characteristics of the constituent plate elements. This is then used to obtain the corresponding local buckling stress utilising an appropriate material model. This basic concept is extended herein to predict compression resistance of stainless steel columns with circular hollow sections (CHS). Available test and finite element (FE) results have been used to develop the basic design equation to predict the compression resistance of cross-sections and to propose column curves to determine flexural buckling resistances. The predicted resistances have been compared to those obtained using the current Eurocode; the predictions are significantly more accurate and more consistent than those given by the existing Eurocode. [Copyright &y& Elsevier]

Stainless steel structural sections possess several features that result in a significantly different response to that of equivalent carbon steel sections. To date these features have not been fully recognized in design codes, which have largely adapted rules devised for carbon steel in a rather simplistic fashion. Recently, a new approach for dealing with local buckling and the associated loss of effectiveness that does not utilize the concepts of either cross-sectional classification or effective cross-sectional properties has been developed for stainless steel and has also been applied to other nonlinear metallic materials. The method is based directly on the deformation capacities of cross sections and covers the behavior of stainless steel members subjected to flexural buckling and combined axial load plus bending. The proposed method has been verified using test results and its performance has been compared against the existing ASCE and Eurocode design guidance for structural stainless steel. Significantly improved and more consistent predictions have been obtained using the proposed method without any extra calculation effort. [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]

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]

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 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]

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]

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]

In current structural steel design specifications, the stability of members is typically assessed through the use of buckling curves which implicitly consider the influence of both initial geometric imperfections and residual stresses. An alternative and more direct approach is to perform a second order analysis of the member or structure with all imperfections included. For modelling convenience, i.e. to avoid the explicit modelling of residual stresses, so-called 'equivalent' geometric imperfections are typically utilised, which consider the combined influence of both geometric imperfections and residual stresses through an increased geometric imperfection amplitude. For columns and beams, equivalent geometric imperfections for use in design by geometrically and materially nonlinear analysis with imperfections (GMNIA) have recently been developed. However, for beam-columns, which are subjected to combined compression and bending, there are currently no specific provisions. Therefore, equivalent geometric imperfections for application in the stability design of steel and stainless steel beam-columns by GMNIA are developed herein. The proposals are calibrated against the results of benchmark finite element (FE) simulations performed on a large number of steel and stainless steel I-section or hollow section beam-columns, with or without intermediate lateral restraints, subjected to various ratios of axial compression and major and/or minor bending moments. Proposals for the shapes and amplitudes of equivalent geometric imperfections are developed for application with both eigenmode-affine imperfections e 0,mod and the direct modelling of sinusoidal bow imperfections e 0,bow. Relative to the traditional Eurocode design calculations, employing the developed equivalent geometric imperfections in GMNIA provides more accurate resistance predictions. The reliability analysis of the design provisions shows that partial safety factors of 1.0 for steel and 1.1 for stainless steel can be safely adopted. • Equivalent geometric imperfections consider the combined influence of both geometric imperfections and residual stresses. • Equivalent geometric imperfections for use in design of steel and stainless steel beam-columns by GMNIA have been developed. • Accuracy and reliability of the proposed equivalent geometric imperfections have been assessed against benchmark FE results. • Employing proposals in GMNIA provides more accurate resistance predictions relative to traditional Eurocode design provisions. • Proposed equivalent geometric imperfections are suitable for use in conjunction with recommended partial safety factors γ M1. [ABSTRACT FROM AUTHOR]

Modern structural design standards are based on the Limit State Design (LSD) philosophy, also known as Load and Resistance Factor Design (LRFD), which involves the use of resistance functions with accompanying safety factors that are based on a statistical evaluation of relevant experimental data, carried out within the framework of a probabilistic reliability theory. This paper presents the derivation of material factors for the yield strength and ultimate tensile strength of austenitic, duplex and ferritic stainless steels, and their associated coefficients of variation (COV) for use in evaluating the safety factors for the European design code EN 1993-1-4 and the American design codes Specification for Structural Stainless Steel Buildings (ANSI/AISC 370–21) and Specification for the Design of Cold-Formed Stainless Steel Structural Members (ASCE/SEI 8–22). Separate material factors and associated COV values are required for the U.S. and European design codes due to the different minimum specified strength values that are given in the respective product standards. The material factors were derived by analysing a large amount of material data provided by different stainless steel producers, which encompassed a wide range of stainless steels and material thicknesses. • Statistical analysis of the strength variability of stainless steels is presented. • Data from over 250,000 tensile coupons was collected and analysed. • Existing European material factors were found to be optimistic. • Stainless steel material factors are derived for European and U.S. standards. [ABSTRACT FROM AUTHOR]