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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]

An experimental investigation into the structural performance of wire arc additively manufactured (WAAM) steel single‐lap shear bolted connections is presented in this paper. Sixty specimens of different thicknesses, printing strategies and geometric features, including end distances and plate widths, were manufactured using steel wire of a nominal yield strength of 420 MPa and subjected to single shear lap tests. The test results are analysed while the observed failure modes, featuring shear‐out, net section tension fracture, end‐splitting, localised tearing and curl‐bearing failure, are discussed. Digital image correlation (DIC) was used for detailed monitoring and visualisation of the surface strain fields that developed during testing, providing valuable insight into the developed failure mechanisms. The experimental results, which generally followed the anticipated trends, were used to assess the applicability of current design specifications developed for conventional steel bolted connections to WAAM steel bolted connections. It was found that both the cold‐formed steel specifications (AISI S100 and AS/NZS 4600) and the structural steel specifications (AISC 360 and EN 1993‐1) yield considerable overestimations or underestimations of the test capacities, depending on the specimen geometry. Further research is underway to underpin the development of improved design provisions. [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]

An experimental study on sheathed cold‐formed steel C‐lipped columns (studs) with service holes in the web subjected to compression and major axis bending is presented in this paper. A total of 17 experiments was performed with both oriented strand board (OSB) and plasterboard used as the sheathing material and with varying connector spacing employed between the sheathing and the steel members. Material tests and geometric imperfection measurements were also undertaken. The tested specimens comprised a single 2.4 m long cold‐formed steel member sheathed on both sides and secured at its ends to top and bottom tracks. Eight pure compression tests with plasterboard and OSB sheathing and with the spacing of the connectors varying between 75 mm and 600 mm were initially performed. Specimens with OSB were then tested under pure bending and also under combined loading, by first applying a compressive load corresponding to the 75%, 50% or 25% of the predetermined axial resistance and then laterally loaded until failure. Reducing the spacing of the connectors from 600 mm to 75 mm resulted in up to 20% and 30% increases in capacity for the studs sheathed with OSB and plasterboard respectively. [ABSTRACT FROM AUTHOR]

The importance of allowing for the many different types of structural interaction that have an effect on the performance of light gauge members when used in practical situations is emphasized. A distinction is drawn between internal interactions involving the various plate elements of the steel profiles and external interactions involving the other components in the system. Although full-scale testing of representative systems can capture this behavior, the costs involved make this an impractical general basis for design; codified methods generally consider only isolated plates within members and isolated members within systems, thereby neglecting the potentially beneficial effects of both forms of interaction. Properly used, modern methods of numerical analysis offer the potential to systematically allow for both forms of interaction — provided the numerical models used have been adequately validated against suitable tests. The use of such an approach is explained and illustrated for three commonly used structural systems: roof purlins, floor beams, and columns in stud walls. In each case, it is shown that, provided sufficient care is taken, the numerical approach can yield accurate predictions of the observed test behavior. The subsequently generated large portfolio of numerical results can then provide clear insights into the exact nature of the various interactions and, thus, form the basis for more realistic design approaches that are both more accurate in their predictions and which lead to more economic designs. Building on this, modifying existing arrangements so as to yield superior performance through specific modifications is now possible. Two such examples, one in which improved interconnection between the components in a system is investigated and a second in which prestressing is shown to provide substantial enhancement for relatively small and simple changes, are presented. [ABSTRACT FROM AUTHOR]

The behavior and design of hot-rolled and cold-formed steel square and rectangular hollow section (SHS and RHS) columns, made of both normal- and high-strength material, are addressed in this paper. A series of experiments on hot-rolled high-strength steel SHS columns was first conducted—six tests on S690 SHS 100×100×4 columns and six tests on S770 SHS 120×120×6.3 columns were performed. Finite-element (FE) models were developed to replicate the experimental results and to carry out parametric studies to expand the column buckling data pool. The accuracy of the European and North American buckling design rules for normal- and high-strength steel SHS and RHS columns was evaluated through comparisons with the freshly generated test and FE results, as well as with existing test data collected from the literature. Finally, a modified approach was proposed and statistically verified in accordance with existing standards; the new approach features an imperfection factor that is a continuous function of yield strength, reflecting the reducing relative influence of residual stresses and global imperfections with increasing steel grades. Improved consistency in resistance predictions over the existing design provisions is demonstrated across a wide range of steel grades and relative slenderness values. [ABSTRACT FROM AUTHOR]

Structural design rules for prestressed cold-formed steel beams, considering both the prestressing and imposed vertical loading stages, are presented herein. In the proposed approach, the cold-formed steel member is designed as a beam-column using linear interaction equations in conjunction with the Direct Strength Method (DSM), while the prestressed cable is designed by ensuring that its tensile capacity is not violated during the two loading stages. In the present paper, the design approach and the failure criteria, which define the permissible design zone for the prestressed system, are first introduced. The suitability of the design recommendations is then assessed by comparing a set of parametric finite element (FE) results for several combinations of prestress levels, beam geometries and cable sizes, with the corresponding design predictions. Finally, following reliability analysis, the implementation of the design recommendations is illustrated through a practical worked example. • Design recommendations for prestressed cold-formed steel beams developed. • Linear interaction equations in conjunction with the Direct Strength Method utilised. • Capacities of cold-formed steel beam and cable to be checked for both loading stages. • Design rules assessment through comparisons with parametric finite element results. • Implementation of design rules illustrated through a practical worked example. [ABSTRACT FROM AUTHOR]

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

Graphical abstract Highlights • Review of existing stress-strain models and models for predicting the strength enhancements in cold-formed steel sections. • Collection of data from over 700 experimental stress-strain curves on cold-formed steels from the global literature. • Proposal of two-stage Ramberg-Osgood model to represent stress-strain curves of cold-formed steels. • Development of predictive expressions and numerical values for the key material parameters for cold-formed steels. • Evaluation of the accuracy of the proposed stress-strain curves through comparisons with experimental data. Abstract Cold-formed steels are generally characterized by a rounded stress-strain response with no sharply defined yield point. It is shown herein that this material behaviour can be accurately described by a two-stage Ramberg-Osgood model provided that the values of the key input parameters can be established. The focus of the present paper is to develop predictive expressions for these key parameters to enable the full engineering stress-strain response of cold-formed steels to be represented. The predictive expressions are based on the analysis of a comprehensive set of material stress-strain data collected from the literature. In total, more than 700 experimentally-derived stress-strain curves on cold-formed steel material have been collected from around the world, covering a range of steel grades, thicknesses and cross-section types. The strength enhancement in the corner regions of cold-formed sections has also been analysed and the applicability of existing predictive models has been evaluated. Finally, standardized values of strain-hardening exponents used in the Ramberg-Osgood model have been recommended for both flat and corner material in cold-formed steel sections. The proposed stress-strain curves are suitable for use in advanced numerical simulations and parametric studies on cold-formed steel elements. [ABSTRACT FROM AUTHOR]

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

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

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

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

An experimental study was conducted into the degree of composite action that can arise between cold-formed steel joists and wood-based flooring panels. A series of material, push-out and 4-point bending tests were carried out, and alternative means of shear connection, featuring fasteners and adhesives, were investigated. It was found that the spacing of the fasteners and the application of structural adhesive at the beam-board interface had a significant influence on the attained degree of shear connection and, hence, the moment capacity and flexural stiffness of the system. The highest degree of shear connection (up to approximately 60%) was obtained using the structural adhesive, bringing corresponding increases in capacity and stiffness of approximately 100 and 40%, respectively, over the bare steel. Smaller, but still very significant, increases in capacity and stiffness were achieved through the use of screws alone. On the basis of the results of the push-out tests, a load-slip relationship for screw fasteners in wood-based floorboards was proposed; this was designed for use in future analytical and numerical models. The findings of this research demonstrate, for the first time, the benefits that can be derived through the practical exploitation of composite action in cold-formed steel flooring systems in terms of enhanced structural performance and efficiency of material use. [ABSTRACT FROM AUTHOR]

The external envelope of steel framed industrial buildings normally involves the use of purlins and rails spanning between the main hot-rolled frames to support the roofing/cladding. These purlins are typically light-gauge cold-formed steel members of complex shape for which the thin-walled nature of the material means that local instabilities will significantly influence their structural behaviour. Economic design should be based on failure of the system, recognising the opportunity for redistribution of moments. This paper presents the findings from a numerical investigation of the degree of moment redistribution in continuous cold-formed steel beams subjected to a downward (gravity) uniformly distributed load (UDL). Three types of nonlinear finite element analysis were validated against previously reported physical tests: (i) continuous two-span beams subjected to a UDL, (ii) single span beams subjected to a central point load producing a moment gradient and (ii) single span beams subjected to two point loads producing a central region under pure bending. The interior support moments from the continuous beam models were compared against reference moment capacities from the three-point bending models. Based on various different section sizes, covering a range of cross-sectional slenderness, full moment redistribution with no drop-off in moment at the interior support was found to be possible only for stocky sections but not for slender sections. In the case of slender sections, local and distortional buckling caused a reduction in interior support moment prior to failure of the system. Hence a design formula is proposed to estimate the post-peak reduction of interior support moment from its initial peak, and this reduced moment capacity is then used in conjunction with the full span moment to determine the load-carrying capacity of the system. Comparisons show the proposed approach to offer accurate prediction of observed system failure loads. [ABSTRACT FROM AUTHOR]

An experimental investigation has been conducted into the degree of shear interaction between cold-formed steel floor joists and wood-based flooring panels and the resulting benefits derived in terms of composite action. A series of four-point bending tests have been carried out to evaluate the overall system behavior, while material tests have been performed to accurately define the material properties of each component of the examined system. Two different shear transfer mechanisms were examined: self-drilling screws with varying spacing and structural adhesive. The bare system was also tested to provide a reference response, against which the stiffness and capacity of the composite system could be bench-marked. The experiments showed that significant benefit could be derived as a result of composite action with as much as a 100% increase in bending capacity and 42% increase in stiffness. [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]

• 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]

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]

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]

The behaviour and design of pin-ended stainless steel equal-leg angle section members under compression and compression plus minor-axis bending are investigated herein. The studied members are cylindrically pinned about the minor axis. 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 and validated against the new experimental data. A numerical parametric study is then presented considering both hot-rolled and cold-formed stainless steel angle section columns alongside beam–columns with a wide range of slenderness values. Finally, new design proposals for pin-ended stainless steel equal-leg angle section members under compression and combined compression and minor-axis bending are developed and verified against the results of existing physical experiments, as well as the newly-generated test 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. 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 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]

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

The structural behaviour and design of cold-formed steel square and rectangular hollow section (SHS and RHS) beam–columns, made of both normal and high strength steels, are investigated in the present study through a comprehensive numerical modelling programme. Refined finite element (FE) models were first established and calibrated against a collection of existing cold-formed steel member test results from the literature. Following this, an extensive parametric study was undertaken to expand the cold-formed steel beam–column data pool, covering a wider range of steel grades, cross-section geometries, member slendernesses and loading combinations. Results from the parametric study were then used to examine the accuracy of the current codified beam–column design methods, provided in the European Standards EN 1993-1-1 (2005) and EN 1993-1-12 (2007) as well as the American Specification AISC 360-16 (2016). The comparisons revealed that the codified design rules provide varying levels of accuracy in predicting the ultimate resistances of cold-formed steel beam–columns depending on the steel grade. An improved design approach, compatible with current codified design rules in EN 1993-1-1 (2005), is proposed that features (1) recently developed column buckling curves that reflect the increasing normalised column buckling resistance with increasing steel yield strength; (2) bending moment resistances calculated using the Continuous Strength Method (CSM) and (3) new interaction curves for cold-formed steel beam–columns, which are anchored to these more accurate end points. The newly proposed design approach is shown to yield more accurate and consistent resistance predictions over current design provisions for cold-formed steel SHS and RHS beam–columns made of different steel grades, and its reliability has also been statistically verified in accordance with EN 1990. • Numerical study on cold-formed steel SHS and RHS beam–columns was conducted. • Modified EC3 column design approach was extended to columns in steel grades up to S1100. • Bending resistance predictions from CSM were adopted in beam–column design. • New beam–column design approach was developed to account for influence of steel grade. • Current EC3 partial safety factor was shown to be applicable to design proposal. [ABSTRACT FROM AUTHOR]

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

An experimental study of sheathed cold-formed steel C-lipped wall studs, with service holes, subjected to compression and major axis bending is presented in this paper. A total of 17 experiments were performed with both oriented strand board (OSB) and plasterboard used as sheathing and with varying connector spacing employed between the sheathing panels and the steel members. The tested specimens comprised a single 2.4 m long column sheathed on both sides and secured at the ends to top and bottom tracks. The member tests were complemented by material tests, stub column tests and initial geometric imperfection measurements. The specimens were tested in a dual-actuator rig where axial compression was applied by means of a vertical actuator through the top track, while bending was applied through the application of four lateral point loads. Eight pure compression tests with both plasterboard and OSB sheathing and with the spacing of the connectors varying between 75 mm and 600 mm were initially performed. Specimens with OSB sheathing were then tested under pure bending and combined loading. The full load–deformation responses and failure modes of the member test specimens are reported. The compressed studs connected to the plasterboard sheathing at wider spacings exhibited pull-through failure of the connectors, followed by flexural torsional buckling, while the specimens with denser connector spacings, failed by local buckling at the member ends. The OSB sheathed specimens under pure compression failed by local and distortional buckling, those under combined loading exhibited local failure at the service openings, while for those under pure bending, local buckling and stud-to-track connector failure occurred. Reducing the spacing of the connectors from 600 mm to 75 mm resulted in up to 20% and 30% increases in capacity for the studs sheathed with OSB and plasterboard respectively. • Seventeen full-scale tests on sheathed cold-formed steel members were conducted. • The tests included eight specimens under pure compression. • The tests included six specimens under combined compression and bending. • The tests included three specimens under pure bending. • The tested specimens were sheathed with either plasterboard or OSB. • Sheathing was connected on both sides of the member at various screw spacings. • Initial geometric imperfection measurements were carried out. • Reducing the screw spacing from 600 mm to 75 mm led up to 30% capacity increases. [ABSTRACT FROM AUTHOR]

• Bespoke shear connectors for cold-formed steel-timber structures. • Bespoke shear connectors designed to mobilise higher timber embedment forces. • Best performing connectors achieved double the shear resistance of ordinary screws. • Bespoke shear connectors achieved significant improvement in slip modulus. • Analytical model can accurately describe the ultimate load and the slip moduli. An experimental investigation into the behaviour of bespoke shear connectors designed to generate composite action in cold-formed steel-timber structures is presented. The response of the shear connectors was assessed through a comprehensive set of push-out tests, where the cold-formed steel thickness and the connector type and material were varied. Previous studies have shown that while the use of ordinary self-drilling screws as shear connectors enables the development of some composite action, their performance was inhibited by timber embedment. Hence, the main feature of the innovative shear connectors was the introduction of a fitting around the screw to mobilise higher timber embedment forces. The best performing shear connectors achieved about double the shear resistance, four times the initial slip modulus k s and seven times the mid-range slip modulus k s,m of ordinary self-drilling screws. An analytical model presented in previous research was extended to describe the response of the innovative shear connectors developed in this study. The model was validated against the push-out test results, and shown to be able to accurately predict the ultimate load, slip at ultimate load, and the two slip moduli k s and k s,m of the innovative connectors, with mean model-to-test ratios of 1.01, 1.15, 1.29 and 1.19 respectively. [ABSTRACT FROM AUTHOR]

• Tensile tests on WAAM steel sheet material performed. • Tests on WAAM steel double-lap shear bolted connections presented. • Non-contact measurement methods used to determine specimen geometry and deformations. • Observed failure modes discussed and a new failure mode identified. • Applicability of existing design provisions to WAAM connections assessed. An experimental study into the structural behaviour of Directed Energy Deposition-arc or wire arc additively manufactured (DED-arc AM and WAAM, respectively) steel double-lap shear bolted connections is presented. The mechanical properties of the material, which had a nominal yield stress of 420 MPa, were first determined by means of tensile coupon tests. Sixty connection specimens of two different nominal thicknesses and two print layer orientations were then tested to failure. The geometry of the test specimens was determined by 3D laser scanning, while the deformation and strain fields were measured during testing using digital image correlation. The observed failure modes included shear-out, net section tension, bearing and end-splitting, while a new hybrid mode of shear-out and net section tension was identified for the first time. The test results were compared against the predictions of current design specifications, namely AISI S100 and AS/NZS 4600 for cold-formed steel and AISC 360 and Eurocode 3 for structural steel, to evaluate their applicability to WAAM elements. Overall, the structural behaviour of the tested specimens followed the anticipated trends, and the predicted resistances determined from the current design specifications were generally reasonable. There were, however, a number of exceptions to this, highlighting the need for new design provisions, together with appropriate safety factors, that are specific to this form of manufacture. [ABSTRACT FROM AUTHOR]

An experimental investigation into the structural performance of wire arc additively manufactured (WAAM) steel single-lap shear bolted connections is presented in this paper. The steel wire had a nominal yield stress of 420 MPa. Sixty specimens of different thicknesses, printing strategies and geometric features including end distances and plate widths were tested and analysed. The shear-out, net section tension fracture, localised tearing and curl-bearing failure modes were observed and discussed, while end-splitting was also evident. Digital image correlation (DIC) was used for detailed monitoring and visualisation of the surface strain fields that developed during testing, providing valuable insight into the developed failure mechanisms. The experimental results, which generally followed the anticipated trends, were used to assess the applicability of current design specifications developed for conventional steel bolted connections to WAAM steel bolted connections. It was found that both the cold-formed steel specifications (AISI S100 and AS/NZS 4600) and the structural steel specifications (AISC 360 and EN 1993-1) devised for conventionally manufactured steel elements, could yield considerable overestimations and underestimations of the test capacities, depending on the geometry. The overestimations are caused by shortcomings in the existing design provisions for out-of-plane failure modes, which are particularly prevalent among WAAM steel connections due to their material ductility and surface undulations, which promote curling. The underestimations relate primarily to the conservatism of the shear-out provisions. Further research is underway to underpin the development of improved design provisions. • Tensile tests on WAAM steel sheet material performed. • Tests on single shear WAAM steel lap bolted connections presented. • Non-contact measurement methods used to determine geometry and deformations. • Observed failure modes discussed and a new failure mode identified. • Applicability of existing design provisions to WAAM connections assessed. [ABSTRACT FROM AUTHOR]

• 26 ferritic stainless steel beam-column tests undertaken. • Over 2000 numerical results generated for austenitic, duplex and ferritic stainless steel CHS beam-columns over a range of local and global slenderness values. • Existing Eurocode 3 design provisions are evaluated and new design proposals are determined and verified. • Reliability analyses are undertaken for existing and proposed stainless steel CHS beam-column design methods using the new experimental and numerical dataset. The present work was prompted by shortcomings identified in existing design provisions for stainless steel circular hollow section (CHS) beam-columns. First, addressing a lack of existing experimental data, a series of ferritic stainless steel CHS beam-column tests was undertaken at the cross-section and member levels. In total, 26 beam-column tests, including two section sizes (a non-slender class 3 and slender class 4 cross-section), two member slenderness values for each cross-section type and a wide range of loading eccentricities were carried out to investigate the interaction between local and global buckling. Following validation of finite element (FE) models, a numerical study was then undertaken to explore the buckling response of stainless steel CHS beam-columns, covering austenitic, duplex and ferritic grades with a wide range of local and global slendernesses and applied loading eccentricities. Over 2000 numerical results were generated and used to assess new design proposals for stainless steel beam-columns, featuring improved compression and bending end points and new interaction factors. The new proposals are more consistent and more accurate in their resistance predictions than the current EN 1993-1-4 (2015) design approach. The reliability of the new proposals has been verified by means of statistical analyses according to EN 1990 (2005). [ABSTRACT FROM AUTHOR]