Search

Wire arc additive manufacturing (WAAM) is a method of metal additive manufacturing (AM) that can be used to fabricate optimised large‐scale structural elements of complex form in a cost‐effective manner, opening up opportunities to unleash the true potential of structural optimisation. To demonstrate this potential, two optimised steel cantilever trusses were fabricated by means of WAAM and tested to investigate their structural performance. The tested specimens comprised members of tubular cross‐section of varying diameter and thickness. The geometric features of the tested specimens were determined using 3D laser scanning, while digital image correlation was employed to monitor the displacement and strain fields during testing. Full details of the experimental programme are provided; the obtained results are analysed and comparisons against equivalent conventional reference designs are made. The results of complementary numerical simulations, undertaken to gain further insight into particular features of the structural response of the examined specimens, are also presented. The structural efficiency of all optimised trusses, as measured by the capacity‐to‐mass ratio, was found to be at least 80% higher than that of the corresponding reference designs, underlining the benefits in terms of structural efficiency that can be achieved by the combination of WAAM with advanced optimisation methods. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation into the structural response of wire arc additively manufactured (WAAM) steel T‐stub connections subjected to tension. A total of fifty‐two T‐stub specimens of different printing strategies and geometric configurations were tested to failure. 3D laser scanning was employed to determine the specimen geometry, while digital image correlation was used to monitor the strain and displacement fields during testing. The structural response exhibited by the tested specimens was more complex than that reported in the literature for conventionally fabricated T‐stubs. Therefore, a new approach for the determination of the plastic resistance and failure modes of WAAM T‐stub connections was developed. Finally, the obtained results were used to evaluate the applicability of current design equations to WAAM T‐stub connections. [ABSTRACT FROM AUTHOR]

Portal frames are a common form of structural system used to create efficient wide‐span enclosures. Over the past few decades, the design of portal frames has evolved in the direction of longer, lighter and taller structures, while cladding systems have become more substantial. Although this allows larger spaces, it can also result in heightened structural challenges, such as increased frame flexibility, a greater portion of the load being borne by the cladding and greater differential thermal movement. This has led to general concerns related to the effects of scale. To investigate these concerns, with a particular focus on the contribution of the cladding to the global strength and stiffness of the structure (also referred to as the stressed skin effect), and the resulting demands placed on secondary components, this study presents the development of a numerical model for the accurate representation of the structural response of full single‐span portal frames. The model is validated herein in two ways; (i) through validation of each individual frame component against relevant physical experiments, and (ii) through validation of the full model against full scale frame tests. Finally, a preliminary parametric investigation is presented. [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 structural behavior and residual capacity of S700 high-strength steel circular hollow section (CHS) columns after exposure to elevated temperatures were studied through testing and numerical modeling. The testing program was conducted on 10 S700 high-strength steel CHS columns and comprised heating and cooling of the specimens as well as postfire material testing, measurements of initial geometric imperfections, and pin-ended column tests. Numerical simulations were subsequently performed, where finite element models were built and validated with reference to the experimental results and afterward used to conduct parametric studies to obtain further numerical data. Given that there are no specific provisions for the design of steel structures after exposure to elevated temperatures, the relevant room-temperature design buckling curves were evaluated, using postfire material properties, for their applicability to S700 high-strength steel CHS columns after exposure to elevated temperatures, based on the experimental and numerical data. The evaluation results indicated that the buckling curves prescribed in the American specification and Australian standard lead to accurate and consistent residual capacity predictions for S700 high-strength steel CHS columns after exposure to elevated temperatures, while the Eurocode buckling curve yields conservative predictions of residual capacity. A revised Eurocode buckling curve was then proposed, and resulted in a higher level of accuracy than its original counterpart. [ABSTRACT FROM AUTHOR]

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]

The mechanical behaviour and design of fixed‐ended steel equal‐leg angle section members subjected to axial compression are addressed in this study. First, the critical buckling behaviour is described. Experimental data on steel equal‐leg angle section columns collected from the literature are then used for the validation of numerical (shell finite element) models, developed within the commercial package ABAQUS. Validation is performed by means of comparisons between 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 steel angle section columns with a wide range of slenderness values. The behaviour and load‐carrying capacity of the columns is shown to be dependent on, not only the column slenderness, but also the ratio of the elastic torsional‐flexural buckling load to the elastic minor‐axis flexural buckling load. Finally, the collected experimental and generated numerical results are used to develop a new design approach for fixed‐ended steel equal‐leg angle section columns, reflecting the observations made. The proposed approach offers improved accuracy and consistency in strength predictions compared to the existing codified design rules. [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]

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]

The use of advanced analytical and numerical modelling in structural engineering has increased rapidly in recent years. A key feature of these models is an accurate description of the material stress-strain behaviour. Development of standardised constitutive equations for the full engineering stress-strain response of hot-rolled carbon steels is the subject of the present paper. The proposed models, which offer different options for the representation of the strain hardening region, feature an elastic response up to the yield point, followed by a yield plateau and strain hardening up to the ultimate tensile stress. The Young's modulus E , the yield stress f y and the ultimate stress f u are generally readily available to the engineer, but other key parameters, including the strains at the onset of strain hardening and at the ultimate stress, are not, and hence require predictive expressions. These expressions have been developed herein and calibrated against material stress-strain data collected from the literature. Unlike the widely used ECCS model, which has a constant strain hardening slope, the proposed models, reflecting the collected test data, have a yield plateau length and strain hardening characteristics which vary with the ratio of yield to ultimate stress (i.e. with material grade). The proposed models require three basic input parameters ( E , f y and f u ), are simple to implement in analytical or numerical models, and are shown herein to be more accurate than the widely employed ECCS model. The proposed models are based on and hence representative of modern hot-rolled steels from around the world. [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]

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

Prestressed steel trusses can offer efficient structural solutions for long span applications such as aircraft hangars, stadia and warehouses. In the current study, the tensile behaviour of prestressed steel elements, which comprise tubular steel members with internal prestressing cables, is investigated. The stability of the elements under prestress and the load–deformation response of the prestressed elements to the subsequent application of tensile loading are examined analytically, numerically and experimentally, with good correlation achieved between the three approaches. The benefits of prestressing, in terms of increased member strength and stiffness, are demonstrated, and optimal prestress levels are investigated. [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]

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

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

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

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]

An introduction is presented in which the editor discusses various reports within the issue on topics including buckling behaviour of cold-formed steel, influence of strain-hardening on structural response and steel capacity, and a numerical study of steel response under compression and bending.

In current structural stainless steel design codes, local buckling is accounted for through a cross-section classification framework, which is based on an elastic, perfectly-plastic material model, providing consistency with the corresponding treatment of carbon steel cross-sections. Hence, for non-slender cross-sections, the codified design stress is limited to the 0.2% proof stress without considering the pronounced strain hardening exhibited by stainless steels, while for slender cross-sections, the effective width method is employed without considering the beneficial effect of element interaction. Previous comparisons between test results and codified predictions have generally indicated over-conservatism and scatter. This has prompted the development of more efficient design rules, which can reflect better the actual local buckling behaviour and nonlinear material response of stainless steel cross-sections. A deformation-based design approach called the continuous strength method (CSM) has been proposed for the design of stocky cross-sections, 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. In this paper, the scope of the CSM is extended to cover the design of slender stainless steel cross-sections under compression, bending and combined loading, underpinned by and validated against 794 experimental and numerical results. The proposed approach allows for the beneficial effect of element interaction within the cross-section, and is shown to yield a higher level of accuracy and consistency, as well as design efficiency, in the capacity predictions of slender stainless steel cross-sections, compared to the effective width methods employed in the current international design standards. Non-doubly symmetric sections in bending, which may be slender, but still benefit from strain hardening, are also discussed. The reliability of the CSM proposal has been confirmed by means of statistical analyses according to EN 1990, demonstrating its suitability for incorporation into future revisions of international design codes for stainless steel structures. [ABSTRACT FROM AUTHOR]

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

The structural behaviour 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]

• Equivalent imperfections for use in out-of-plane stability design by GMNIA developed. • Accuracy and reliability of the proposals assessed against benchmark beam FE results. • Proposals provide more accurate resistance predictions compared to traditional method. • Proposals suitable for use with EC3 recommended values of partial safety factor γ M1. In current structural design specifications, such as EN 1993-1-1 for steel and EN 1993-1-4 for stainless steel, the stability of members is typically assessed through the use of buckling curves, which consider the influence of initial geometric imperfections and residual stresses. An alternative, more direct, approach is to perform either an elastic or inelastic second-order analysis of the member or structure with imperfections. For modelling convenience, so-called 'equivalent' imperfections are typically utilised, which consider the combined influence of both geometric imperfections and residual stresses. Equivalent imperfections for the design of columns and beams by second-order elastic analysis, also referred to as geometrically nonlinear analysis with imperfection (GNIA), are provided in the current design specifications. For columns, equivalent imperfections for design by second-order inelastic analysis, also referred to as geometrically and materially nonlinear analysis with imperfections (GMNIA), were recently developed, but for beams that are susceptible to lateral-torsional buckling (LTB), there are currently no appropriate provisions. The aim of this study is therefore to develop equivalent imperfections for use in out-of-plane stability design of steel and stainless steel members by GMNIA. The proposals are calibrated against the results of benchmark finite element (FE) simulations performed on a large number of steel and stainless steel members with geometric imperfections and residual stresses subjected to major axis bending. Two proposals for equivalent imperfection amplitudes are developed: (1) e 0,mod , for use with eigenmode-affine imperfections and (2) e 0,bow , for use with sinusoidal bow imperfections. The latter is applied solely in the lateral direction and as a summation of a half-sine wave and a full-sine wave. Relative to the traditional Eurocode design calculations, employing the proposed LTB imperfections in GMNIA provides generally more accurate member resistance predictions, while remaining safe-sided relative to the benchmark FE results. The reliability of the design provisions is demonstrated through statistical analysis, where it is shown that partial safety factors of 1.0 for steel and 1.1 for stainless steel can be safely adopted. [ABSTRACT FROM AUTHOR]

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

The structural behaviour of S960 ultra-high strength steel (UHSS) welded I-section beam–columns is studied in the present paper. Nonlinear finite element (FE) models were first created and validated against relevant test results collected from the literature; the models were then used to carry out parametric studies to obtain additional FE data over an extensive spectrum of cross-section dimensions, member lengths and loading combinations. Given the lack of existing design rules for S960 UHSS structures, the codified beam–column interaction curves prescribed in the current European (EC3) and American (AISC 360) design specifications for lower strength steel members, were assessed for their applicability to the studied S960 UHSS non-slender welded I-section members, utilizing the generated numerical data. It was found that EC3 yielded conservative failure load predictions for Class 1 and 2 S960 UHSS welded I-section beam–columns buckling about either principal axis; similar results were found for Class 3 members under combined compression and strong-axis bending, with the mean FE to predicted failure load ratio being 1.29, the corresponding COV being 0.12, but rather conservative strength predictions arose for Class 3 members under combined compression and weak-axis bending, with the mean FE to predicted failure load ratio being 1.50. AISC 360 led to overall accurate and consistent failure load predictions for S960 UHSS non-slender welded I-section beam–columns, but resulted in some unconservative strength predictions for members under combined compression and weak-axis bending. New design proposals, adopting the format of EC3 design interaction curve, but with more accurate compression and bending end points, interaction factors and buckling reduction factors determined from the continuous strength method (CSM), were proposed and shown to lead to improved design accuracy. • The structural behaviour of S960 UHSS non-slender welded I-section beam–columns is studied. • FE models are developed and validated against test results and then used to perform parametric studies. • The current design rules are assessed for their applicability to S960 UHSS non-slender welded I-section beam–columns. • A CSM-based design approach is proposed and shown to lead to improved design accuracy. [ABSTRACT FROM AUTHOR]

An accurate and consistent approach to the out-of-plane stability design of steel beams and structures utilising second-order inelastic analysis with strain limits is proposed. The method is implemented using computationally efficient beam elements, with the ultimate structural resistance defined either by (i) the ultimate load factor or (ii) the load factor at which a strain limit, determined on the basis of the continuous strength method (CSM), is attained, whichever occurs first. Thus far, the method has been established for the in-plane design of steel structures and structural components; in the present paper, its scope is extended, for the first time to the scenarios in which out-of-plane stability effects, with a focus on lateral–torsional buckling (LTB), govern. The accuracy and safety of the method are assessed against the results of nonlinear shell finite element (FE) modelling. It is shown that the proposed method consistently provides more accurate results than the traditional LTB design method of prEN 1993-1-1. In addition to its accuracy, the proposed approach also streamlines the design process by eliminating the need for cross-section classification and member design checks. [Display omitted] • Advanced out-of-plane stability design method for steel beams and structures proposed • Provisions for considering shear-torsion effects for different sections presented • Accuracy of proposed design method verified against shell finite element results • Proposed method consistently provides more accurate ultimate strength predictions [ABSTRACT FROM AUTHOR]

• A design method performed by second-order inelastic analysis with CSM strain limits is proposed. • CSM strain limits are adopted to account for local buckling and control the spread of plasticity. • Applied to 3680 members with various taper ratios, loading conditions and member slendernesses. • The accuracy is verified against benchmark shell FE results as well as a number of experiments. • The proposed design method is consistently more accurate than current EN 1993-1-1 design. A consistent design approach, performed by second-order inelastic analysis using beam finite elements with strain limits, is proposed for web-tapered steel members. In the proposed design approach, a geometrically and materially nonlinear analysis with imperfections (GMNIA) of the tapered steel member is carried out and the ultimate strength of the member is signified by reaching either the strain limit defined according to the Continuous Strength Method (CSM) or the peak load factor, whichever occurs first. To consider the beneficial effect of strain gradients along the lengths of the members on local cross-section resistances, the strains are averaged over the local buckling half-wavelength. The accuracy of the proposed design approach is verified against results from nonlinear shell finite element modelling as well as a number of experiments on tapered members considering various taper ratios, loading conditions and member slenderness values. The proposed method provides more accurate and consistent ultimate strength predictions than EN 1993-1-1 [1] , because the following aspects, which are ignored in traditional design methods, are captured: (1) the interaction between cross-section elements for the consideration of local buckling, (2) the influence of local moment gradients on cross-section resistance, (3) the partial plastification of cross-sections and (4) strain hardening. [ABSTRACT FROM AUTHOR]

The structural fire response of hot-rolled steel square and rectangular hollow sections (SHS and RHS) under combined compression and bending is investigated in this study through finite element (FE) modelling. The developed FE models were firstly validated against available test results on hot-rolled steel SHS/RHS subjected to combined compression and bending at elevated temperatures. Upon validation, an extensive parametric study was then carried out to examine the resistance of hot-rolled steel SHS/RHS under combined loading at elevated temperatures, covering a wide range of cross-section slendernesses, cross-section aspect ratios, combinations of loading and temperatures up to 800 °C. The numerical data, together with the experimental results, were compared with the strength predictions according to the current structural fire design rules in the European Standard EN 1993-1-2 (2002) and American Specification AISC 360–16 (2016) for hot-rolled steel SHS/RHS under combined loading. The comparisons generally indicated significant disparities in the prediction of resistance of hot-rolled steel SHS/RHS under combined loading at elevated temperatures, owing principally to inaccurate predictions of the end points of the design interaction curves. The deformation-based continuous strength method (CSM) has been shown to provide accurate strength predictions for these end points i.e. the resistances of hot-rolled steel SHS/RHS stub columns and beams at elevated temperatures. In this study, proposals are presented to extend the scope of the CSM to the structural fire design of hot-rolled steel SHS/RHS under combined compression and bending. The CSM proposals are shown to offer improved accuracy and reliability over current design methods and are therefore recommended for incorporation into future revisions of international structural fire design codes. • Numerical models validated against fire test results for SHS/RHS under combined loading. • Validated numerical models used to perform parametric studies considering key parameters. • Current design provisions in EN 1993-1-1 and AISC 360–16 assessed using the experimental and numerical data. • The Continuous Strength Method extended to cover the fire design of SHS/RHS under combined loading. • Reliability of the CSM proposals confirmed by means of statistical analyses. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation into the structural response of wire arc additively manufactured (WAAM) steel T-stub connections subjected to tension. A total of eighty T-stub specimens featuring different printing strategies, bolt arrangements and geometric configurations were tested to failure. 3D laser scanning was employed to determine the specimen geometry, while digital image correlation (DIC) was used to monitor the strain and displacement fields during testing. Utilising the DIC data, a new method was introduced for the determination of the failure mode and key points on the load-deformation response of T-stub connections. The structural response of the WAAM T-stubs generally followed the anticipated trends, though the geometric irregularities resulted in a delay in the development of prying action in some specimens and the printing strategy was shown to have a clear influence on the load-carrying capacity. Finally, comparisons between the test results and the capacity predictions yielded by existing design equations were made; overall, reasonable agreement was achieved, but further research is required to establish reliable design rules that are specific to this form of manufacture. • Tests on WAAM steel T-stub connections presented. • Non-contact measurement methods used to determine specimen geometry and deformations. • A new method for the determination of failure modes and T-stub collapse loads introduced. • Obtained load-displacement curves discussed and key points highlighted. • Applicability of existing design equations to WAAM T-stub connections assessed. [ABSTRACT FROM AUTHOR]

• Structural performance of S960 UHSS non-slender welded I-sections under combined loading is studied. • FE models are developed and validated against test results and then used to perform parametric studies. • Current design rules are assessed for their applicability to S960 UHSS welded I-sections under combined loading. • A CSM-based design approach is proposed and shown to offer improved design accuracy. The structural performance of S960 ultra-high strength steel non-slender welded I-sections subjected to combined loading is studied in the present paper. Nonlinear finite element (FE) models were first created and validated with reference to test results collected from the literature, and then used for conducting parametric studies to derive numerical data over an extensive spectrum of cross-sectional geometries, aspect ratios, as well as loading combinations. Given the lack of existing design rules for S960 ultra-high strength steel structures, the suitability of the current provisions for lower strength steels given in the European, Australian and American specifications to S960 ultra-high strength steel was assessed based on the generated numerical data. It was found that (i) the European code and Australian standard can accurately predict the strengths of Class 1 and 2 (i.e. compact) S960 ultra-high strength steel welded I-sections subjected to both strong- and weak-axis combined loading, but results generally in conservative strength predictions for Class 3 I-sections, and (ii) the American specification yields accurate strength predictions for S960 ultra-high strength steel welded I-sections subjected to strong-axis combined loading, but leads to conservative strength predictions for weak-axis combined loading. Finally, the continuous strength method (CSM) was applied to the studied S960 ultra-high strength steel non-slender welded I-sections subjected to combined loading and found to offer significantly improved design consistency and accuracy relative to the current codified provisions. The reliability of the latter design method was also confirmed by means of statistical analyses. [ABSTRACT FROM AUTHOR]

• Fatigue crack growth tests on 13 WAAM steel compact tension specimens presented. • Hardness and tensile strength of examined WAAM steels are approximately proportional. • Influence of deposition strategy on the fatigue crack growth (FCG) behaviour studied. • Test results compared against conventional steels and BS 7910 recommended FCG laws. • Fractography performed to analyse the mechanisms of crack growth. Combining welding technology with robotics, wire arc additive manufacturing (WAAM) is emerging as a viable method of construction. To facilitate its wider application, in particular with structural integrity in mind, an improved understanding of the fatigue properties of WAAM materials is needed. Hence, an experimental investigation into the fatigue crack growth (FCG) behaviour of WAAM plates made of normal- and high-strength steels has been conducted and is reported herein. Following material characterisation, FCG tests on 13 machined compact tension specimens were undertaken, extracted in different directions from WAAM plates built using a parallel deposition strategy. Fractography of the tested specimens was also performed to analyse the mechanisms of crack growth. The material testing demonstrated an approximately proportional relationship between the hardness and ultimate strength. From the FCG tests, Paris' law constants were derived for the WAAM normal- and high-strength steel specimens, revealing consistently lower material constants m for the latter. Similar FCG behaviour to that of equivalent, conventionally-produced steels, with no significant anisotropy, was found. The observed response was shown to be generally well captured by the FCG laws given in BS 7910, with the recommended curve for unwelded steels providing a close match to the experimental data and the recommended curve for welded steels providing conservative predictions. Additional FCG data on WAAM steels printed using the parallel and oscillatory deposition strategies were collected and analysed. It was shown that the two deposition strategies led to similar crack growth rates for WAAM normal-strength steels, but distinct FCG behavioural trends for WAAM high-strength steels. Finally, the fractographic analysis showed that the WAAM specimens exhibited principally brittle behaviour during FCG but somewhat ductile behaviour before fracture. [ABSTRACT FROM AUTHOR]

An experimental investigation into the structural response and slip resistance of aluminium alloy–stainless steel connections fastened by means of high-strength stainless steel swage-locking pins is presented herein. Thirty-seven friction tests on aluminium alloy–stainless steel shear connections featuring different surface treatments and material grades were carried out. Complementary material tests were also performed, while the roughness and hardness of the connected surfaces were measured. The failure modes, load–slip responses, friction coefficients and preloading behaviour of all specimens are fully reported, while the test setup, specimen dimensions, configurations of fasteners, and positions of displacement measurements, are explained. The slip factors corresponding to the different surface treatments are presented, while the key parameters affecting the preload losses of the swage-locking pins and the friction coefficients are described. Finally, the suitability of various surface treatments for aluminium alloy–stainless steel connections is evaluated, while design slip factors, as well as correction coefficients accounting for the influence of different material grades and preload levels on the response of the examined connections, are set out. • Friction tests on aluminium alloy–stainless steel shear connections fastened by swage-locking pins conducted. • Key parameters affecting the preload losses of the swage-locking pins and the friction coefficients described. • Suitability of various surface treatments for aluminium alloy–stainless steel connections evaluated. • Design slip factors, as well as correction coefficients, set out. [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]

[Display omitted] • Results of tensile tests on WAAM normal- and high-strength steel coupons are presented. • Influence of geometric variability and deposition strategy on the mechanical properties is investigated. • Non-contact measurement methods are used to determine the specimen geometries and deformations. • Slower cooling rates associated with the WAAM process result in lower mechanical strengths. • Microstructural analysis reveals a weak crystallographic texture, explaining the mechanical properties being almost isotropic. Wire arc additive manufacturing (WAAM) is a metal 3D printing method that allows the cost-effective and efficient production of large-scale elements, and has thus gained great interest from architects and structural engineers. Integration of this novel technology into the construction industry, however, requires the development of a clear understanding of the mechanical behaviour of WAAM materials. To this end, a comprehensive experimental study into the mechanical properties and microstructure of WAAM plates made of normal- and high-strength steels has been undertaken and is reported herein. A total of 137 as-built and machined tensile coupons were tested, extracted in various directions relative to the print layer orientation from WAAM plates of two nominal thicknesses, built using different deposition strategies. The influence of the geometric undulations inherent to the WAAM process and deposition strategy on the resulting mechanical properties was investigated. Microstructural characterisation was also performed by means of optical microscopy (OM) and electron backscatter diffraction (EBSD). The WAAM normal-strength steel plates exhibited a principally ferritic-pearlitic microstructure, while the WAAM high-strength steel plates displayed a mixed microstructure featuring ferrite, bainite and martensite. The EBSD analysis revealed a weak crystallographic texture, which explained the observed mechanical properties being almost isotropic. No significant differences in tensile properties were observed with the different deposition strategies, except for some variation in ductility. The geometric undulations of the as-built coupons resulted in some reduction in effective mechanical properties and a degree of anisotropy. Overall, the examined WAAM material exhibited consistent mechanical properties, a Young's modulus comparable to conventionally-produced steel plates, marginally lower strength, reflecting the slower cooling conditions than is customary, and good ductility. [ABSTRACT FROM AUTHOR]

Externally anchored prestressed cables can be employed to enhance the stability of steel truss compression elements significantly. To demonstrate this concept, a system comprising a tubular strut subjected to an external compressive load and a prestressed cable anchored independently of the strut is studied. Energy methods are utilized to define the elastic stability of the perfect and imperfect systems, after which the first yield and rigid–plastic responses are explored. The influence of the key controlling parameters, including the length of the strut, the axial stiffness of the cable and the initial prestressing force, on the elastic stability, the inelastic response and the ultimate strength of the system is demonstrated using analytical and finite element (FE) models. To illustrate the application of the studied structural concept, FE modelling is employed to simulate the structural response of a prestressed hangar roof truss. A nearly two-fold enhancement in the load-carrying capacity of the truss structure is shown to be achieved owing to the addition of the prestressed cable. • Analytical modelling of steel struts with externally anchored prestressed cables. • Post-buckling stability dependent on ratio of cable axial stiffness to strut bending stiffness. • Failure evaluated from Perry-Robertson type approach and a rigid-plastic analysis. • Ultimate strength predictions verified through FE modelling of a prestressed truss. • Two-fold enhancement in capacity demonstrated compared to system without cables. [ABSTRACT FROM AUTHOR]