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

The design and performance of optimised wire and arc additively manufactured (WAAM) rectangular hollow section (RHS) beams, with varying material strengths and thicknesses along their lengths, are investigated in this study. Simply‐supported beams under three‐point bending were considered. Size optimisation of the RHS beams was carried out by fixing the nominal outer profile and varying the local thicknesses and steel grades in discrete steps to accommodate the variation of the bending moment along the member length. Two optimised beam specimens were manufactured via WAAM and tested, and were shown to have excellent load‐carrying capacities at greatly reduced self‐weights compared with the conventionally manufactured beams, indicating a considerable increase in their structural efficiency. This study confirms the feasibility of combining materials with different thicknesses and steel grades using WAAM, which provides structural engineers with further design freedom and opportunities to minimise material use. [ABSTRACT FROM AUTHOR]

The primary aim of the present study is to explore the use, advantages and potential of two advanced data acquisition techniques – 3D scanning and digital image correlation (DIC), in the testing of metallic structures. 3D scanning is a novel method for capturing the full outer geometry of an object. It is being increasingly used in experimental studies for the determination of dimensional parameters and the characterisation of local and global imperfections, examples of which are given and discussed. Digital image correlation (DIC) is a rapidly evolving technology for the full‐field measurement of the displacements and strains over a surface. A brief introduction to DIC and its workflow is firstly provided. Example applications of DIC in various scales of experiments, including material tests, structural element tests and full‐scale structural system tests, are subsequently discussed. These new‐generation data acquisition techniques enable structural researchers to gain a deeper insight into the behaviour of metallic structures in experimental research. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study into the effect of moment gradients on the local buckling behaviour of hot‐rolled high strength steel square hollow section (SHS) beams. The influence of moment gradients was investigated by testing 20 beam specimens, ranging from Class 2 to Class 4 according to the cross‐section classification limits given in prEN 1993‐1‐1:2020. Both four‐ and three‐point bending loading configurations were considered with varying shear span lengths. The influence of intermediate stiffeners at the loading point was examined by employing two different loading configurations in the three‐point bending tests, achieving fully stiffened or unstiffened conditions. Local geometric imperfections were measured by means of 3D laser scanning, and the displacement and strain fields at critical regions were monitored by digital image correlation (DIC) during testing. It was shown from the tests that specimens subjected to moment gradients exhibited higher ultimate moment capacities than those subjected to uniform moments. [ABSTRACT FROM AUTHOR]

An experimental investigation into the structural behaviour of steel frames made up of hybrid steel welded I‐section members is presented in this paper. The tested hybrid steel welded I‐section profile had quenched and tempered S690 steel flanges and an S355 steel web. The experimental programme comprised four two‐dimensional, single storey, single bay frames subjected to different combinations of horizontal and vertical loading, thus enabling different beam, sway as well as combined beam and sway plastic collapse mechanisms to be examined. The frames were fully laterally restrained using a bespoke lateral bracing system to ensure that no out‐of‐plane instability phenomena were experienced during testing. The experimental setup, loading schemes, instrumentation and key experimental results are reported. The experimental results are fundamental to developing an understanding of the behaviour of hybrid steel welded I‐sections at the structural system level. Further research is underway to underpin the development of suitable design rules for steel frames made of such hybrid steel welded I‐section members. [ABSTRACT FROM AUTHOR]

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]

In this work, an experimental campaign was carried out to evaluate the post‐fire mechanical performance of high‐strength steel specimens (grade S700) when being subjected simultaneously to different combinations of tensile load and elevated temperature. To this end, transient‐state tests were firstly carried out to obtain the 'critical temperature', i.e., the temperature at which a specimen failed while being simultaneously subjected to tensile load and heated at a constant temperature rate. Secondly, post‐fire tests were performed on unloaded as well as loaded specimens. For that purpose, specimens were heated to temperatures below the critical temperature, cooled down in air and finally submitted to tensile testing. In order to investigate the influence of production route, specimens were extracted from cold‐formed circular hollow sections and hot‐rolled sheets. Moreover, coupons with five different thicknesses were tested to investigate the influence of section thickness on the post‐fire behaviour. Residual values of yield strength, ultimate strength, elastic modulus and ductility were determined from the tests and discussed. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is a method of metal 3D printing which, when strategically combined with traditional methods of manufacture, has the potential to make a significant impact on the construction sector. To illustrate this potential, an experimental investigation into the flexural buckling response of 13 hot‐rolled I‐section columns, strengthened by WAAM, has been undertaken and is presented herein. The WAAM material was added at the flange tips and distributed non‐uniformly along the member length. Complementary material tests on the conventional and WAAM steels were also carried out. 3D laser scanning was employed to determine the geometry and global geometric imperfections of all specimens, while digital image correlation measurements were taken to provide a detailed insight into the surface deformation characteristics of the specimens during testing. The beneficial effects of the WAAM stiffeners were an increased cross‐sectional area and second moment of area, enhanced local buckling capacity and a more favourable residual stress pattern. Increases in axial capacity of between 17% and 54% for increases of mass between 2% and 26% were achieved, highlighting the tremendous potential in terms of structural efficiency and material savings that can be realised by the combination of WAAM with traditional manufacturing 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]

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

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

The use of wire arc additive manufacturing (WAAM) in conjunction with topology optimisation enables the production of structural components with significantly higher strength‐to‐weight ratios than conventional structural components. However, owing to the additional production stages involved in WAAM (e.g. arc welding), a common question arises regarding the environmental impacts of using WAAM to produce structural components relative to conventional fabrication techniques (e.g. hot‐rolling.) A cradle‐to‐gate life cycle assessment is conducted herein to compare the environmental performance of a conventional hot‐rolled I‐section steel beam with that of a topologically optimised WAAM beam, the latter having 53% lower mass than the former. With regards to climate change, it is demonstrated that, for a typical deposition rate of 2 kg/h, WAAM can lead to lower CO2‐eq. emissions than conventional hot‐rolling if topology optimisation can offer mass reductions of at least ∼50%. The contribution of the individual processes in WAAM production is analysed, demonstrating that the use of shielding gas is the greatest contributor to the climate change impact of WAAM production. [ABSTRACT FROM AUTHOR]

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

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

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

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

This paper presents an experimental study into the effect of moment gradients on the local buckling behaviour of hot‐rolled high strength steel square hollow section (SHS) beams. The influence of moment gradients was investigated by testing 20 beam specimens, ranging from Class 2 to Class 4 according to the cross‐section classification limits given in prEN 1993‐1‐1:2020. Both four‐ and three‐point bending loading configurations were considered with varying shear span lengths. The influence of intermediate stiffeners at the loading point was examined by employing two different loading configurations in the three‐point bending tests, achieving fully stiffened or unstiffened conditions. Local geometric imperfections were measured by means of 3D laser scanning, and the displacement and strain fields at critical regions were monitored by digital image correlation (DIC) during testing. It was shown from the tests that specimens subjected to moment gradients exhibited higher ultimate moment capacities than those subjected to uniform moments. [ABSTRACT FROM AUTHOR]

The design and performance of optimised wire and arc additively manufactured (WAAM) rectangular hollow section (RHS) beams, with varying material strengths and thicknesses along their lengths, are investigated in this study. Simply‐supported beams under three‐point bending were considered. Size optimisation of the RHS beams was carried out by fixing the nominal outer profile and varying the local thicknesses and steel grades in discrete steps to accommodate the variation of the bending moment along the member length. Two optimised beam specimens were manufactured via WAAM and tested, and were shown to have excellent load‐carrying capacities at greatly reduced self‐weights compared with the conventionally manufactured beams, indicating a considerable increase in their structural efficiency. This study confirms the feasibility of combining materials with different thicknesses and steel grades using WAAM, which provides structural engineers with further design freedom and opportunities to minimise material use. [ABSTRACT FROM AUTHOR]

The primary aim of the present study is to explore the use, advantages and potential of two advanced data acquisition techniques – 3D scanning and digital image correlation (DIC), in the testing of metallic structures. 3D scanning is a novel method for capturing the full outer geometry of an object. It is being increasingly used in experimental studies for the determination of dimensional parameters and the characterisation of local and global imperfections, examples of which are given and discussed. Digital image correlation (DIC) is a rapidly evolving technology for the full‐field measurement of the displacements and strains over a surface. A brief introduction to DIC and its workflow is firstly provided. Example applications of DIC in various scales of experiments, including material tests, structural element tests and full‐scale structural system tests, are subsequently discussed. These new‐generation data acquisition techniques enable structural researchers to gain a deeper insight into the behaviour of metallic structures in experimental research. [ABSTRACT FROM AUTHOR]

An experimental investigation into the structural behaviour of steel frames made up of hybrid steel welded I‐section members is presented in this paper. The tested hybrid steel welded I‐section profile had quenched and tempered S690 steel flanges and an S355 steel web. The experimental programme comprised four two‐dimensional, single storey, single bay frames subjected to different combinations of horizontal and vertical loading, thus enabling different beam, sway as well as combined beam and sway plastic collapse mechanisms to be examined. The frames were fully laterally restrained using a bespoke lateral bracing system to ensure that no out‐of‐plane instability phenomena were experienced during testing. The experimental setup, loading schemes, instrumentation and key experimental results are reported. The experimental results are fundamental to developing an understanding of the behaviour of hybrid steel welded I‐sections at the structural system level. Further research is underway to underpin the development of suitable design rules for steel frames made of such hybrid steel welded I‐section members. [ABSTRACT FROM AUTHOR]

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]

In this work, an experimental campaign was carried out to evaluate the post‐fire mechanical performance of high‐strength steel specimens (grade S700) when being subjected simultaneously to different combinations of tensile load and elevated temperature. To this end, transient‐state tests were firstly carried out to obtain the ‘critical temperature’, i.e., the temperature at which a specimen failed while being simultaneously subjected to tensile load and heated at a constant temperature rate. Secondly, post‐fire tests were performed on unloaded as well as loaded specimens. For that purpose, specimens were heated to temperatures below the critical temperature, cooled down in air and finally submitted to tensile testing. In order to investigate the influence of production route, specimens were extracted from cold‐formed circular hollow sections and hot‐rolled sheets. Moreover, coupons with five different thicknesses were tested to investigate the influence of section thickness on the post‐fire behaviour. Residual values of yield strength, ultimate strength, elastic modulus and ductility were determined from the tests and discussed. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is a method of metal 3D printing which, when strategically combined with traditional methods of manufacture, has the potential to make a significant impact on the construction sector. To illustrate this potential, an experimental investigation into the flexural buckling response of 13 hot‐rolled I‐section columns, strengthened by WAAM, has been undertaken and is presented herein. The WAAM material was added at the flange tips and distributed non‐uniformly along the member length. Complementary material tests on the conventional and WAAM steels were also carried out. 3D laser scanning was employed to determine the geometry and global geometric imperfections of all specimens, while digital image correlation measurements were taken to provide a detailed insight into the surface deformation characteristics of the specimens during testing. The beneficial effects of the WAAM stiffeners were an increased cross‐sectional area and second moment of area, enhanced local buckling capacity and a more favourable residual stress pattern. Increases in axial capacity of between 17% and 54% for increases of mass between 2% and 26% were achieved, highlighting the tremendous potential in terms of structural efficiency and material savings that can be realised by the combination of WAAM with traditional manufacturing 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]

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

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

The use of wire arc additive manufacturing (WAAM) in conjunction with topology optimisation enables the production of structural components with significantly higher strength‐to‐weight ratios than conventional structural components. However, owing to the additional production stages involved in WAAM (e.g. arc welding), a common question arises regarding the environmental impacts of using WAAM to produce structural components relative to conventional fabrication techniques (e.g. hot‐rolling.) A cradle‐to‐gate life cycle assessment is conducted herein to compare the environmental performance of a conventional hot‐rolled I‐section steel beam with that of a topologically optimised WAAM beam, the latter having 53% lower mass than the former. With regards to climate change, it is demonstrated that, for a typical deposition rate of 2 kg/h, WAAM can lead to lower CO2‐eq. emissions than conventional hot‐rolling if topology optimisation can offer mass reductions of at least ∼50%. The contribution of the individual processes in WAAM production is analysed, demonstrating that the use of shielding gas is the greatest contributor to the climate change impact of WAAM production. [ABSTRACT FROM AUTHOR]

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

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

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

A comprehensive numerical investigation into the cross-sectional behaviour and ultimate capacity of non-slender welded I-sections, made of both normal and high strength steels (NSS and HSS), under combined compression and uniaxial bending is presented. Finite element (FE) models were initially established and validated against test results collected from the literature. Subsequently, parametric studies were conducted using the validated FE models to generate extensive numerical data considering different steel grades, cross-section geometries and loading combinations. The obtained numerical data, together with the test results collected from the literature, were utilised to assess the accuracy of the traditional European (EC3) and North American (AISC) design provisions, as well as the Continuous Strength Method (CSM), for NSS and HSS welded I-sections under combined loading. The assessment indicated that the CSM was able to provide more accurate and consistent resistance predictions than the current EC3 and AISC design provisions owing to its ability to capture the spread of plasticity and strain hardening in a systematic, mechanics-based manner. Finally, the reliability levels of the different design methods were statistically evaluated in accordance with EN 1990:2002. [ABSTRACT FROM AUTHOR]

Prestressed stayed columns (PSCs) are structural systems whose compressive load-carrying capacity is enhanced through pre-tensioned cable stays. Much research has demonstrated that PSCs buckle subcritically when their prestressing levels maximize the critical buckling load of the theoretically perfect arrangement. Erosion of the pre-tensioned cables' effectiveness (e.g. through creep or corrosion) can thus lead to sudden collapse. The present goal is to develop a structural health monitoring (SHM) technique for in-service PSCs that returns the current structural utilization factor based on selected probing measurements. Hence, PSCs with different cable erosion and varying compression levels are probed in the pre-buckling range within the numerical setting through a nonlinear finite element (FE) model. In contrast to the previous work, it is found presently that the initial lateral stiffness from probing a PSC provides a suitable health index for in-service structures. A machine learning-based surrogate is trained on simulated data of the loading factor, cable erosion and probing indices; it is then used as a predictive tool to return the current utilization factor for PSCs alongside the level of cable erosion given probing measurements, showing excellent accuracy and thus provides confidence that an SHM technique based on probing is indeed feasible. This article is part of the theme issue 'Probing and dynamics of shock sensitive shells'. [ABSTRACT FROM AUTHOR]

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

Although additive manufacturing (AM) continues to gain widespread adoption, the overhang problem remains a critical issue affecting printing quality. The design of self-supporting structures via topology optimisation approaches has been extensively studied. However, current optimisation research predominantly focuses on 3-axis AM machines, overlooking the more recently developed multi-axis machines. Moreover, the performance sacrifice due to overhang constraints in 3-axis AM can be significant, especially in structures with small volume fractions. To address this, we propose a two-step approach considering overhang constraints for multiaxis AM. This approach begins with a structure optimised using traditional topology optimisation. In the first step, a new optimisation problem determines printing surfaces for the given structure. If the proportion of unprintable elements isn't satisfactory, a second reoptimisation step is carried out to further reduce the unprintable proportion. Several examples demonstrate the effectiveness of the proposed approach. Notably, the significant performance sacrifice associated with the 3-axis AM approach becomes negligible when applying our multiaxis AM-based method. [ABSTRACT FROM AUTHOR]

In the framework of the revision of Eurocode 3, Part 1–1, several amendments have been proposed and accepted in order to improve the rules for the resistance to member buckling. For clarification, a flow chart connecting the global analysis (first or second order), the imperfections and the type of verification has been implemented for ease of use. Since the publication of the standard in 2005, many research projects have been conducted across Europe on this topic and their results have contributed to provide appropriate answers to problems identified in practice. Therefore, the revised code provides new design rules for stability. Important works of calibration have been performed in these different projects to derive appropriate values of the partial factor on the resistance side. For example, a new formulation for lateral–torsional buckling has been introduced for the calculation of the reduction factor. The consequence is a reduction of the discrepancy between the results obtained by these new methods and those from experimental or numerical tests. In order to extend the scope of Eurocode 3, Part 1–1, additional methods have been implemented in an annex to cover the stability of members with mono‐symmetric cross‐section under compression axial force, biaxial bending, with or without torsion. The format of the resistance criteria remains similar to the format of the current interaction formulae so that the designers can easily identify the evolution of the rules. This article presents in a systematic way the new implementations in the formal vote version FprEN 1993‐1‐1 of the code. [ABSTRACT FROM AUTHOR]

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

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]

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

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

In the framework of the revision of Eurocode 3 Part 1‐1, several amendments have been proposed and accepted in order to improve the rules for the resistance to member buckling. For clarification, a flow‐chart connecting the global analysis (1st or 2nd order), the imperfections and the type of verification has been implemented for ease of use. Since the publication of the standard in 2005, many research projects have been carried out across Europe on this topic and their results have contributed to provide appropriate answers to problems identified in practice. Therefore, the revised code provides new design rules for stability. Important works of calibration have been performed in these different projects to derive appropriate values of the partial factor on the resistance side. For example, a new formulation for lateral torsional buckling has been introduced for the calculation of the reduction factor. The consequence is a reduction of the discrepancy between the results obtained by these new methods and those from experimental or numerical tests. In order to extend the scope of Eurocode 3 Part 1‐1, additional methods have been implemented in an annex to cover the stability of members with mono‐symmetric cross‐section under compression axial force, biaxial bending, with or without torsion. The format of the resistance criteria remains similar to the format of the current interaction formulae so that the designers can easily identify the evolution of the rules. This paper presents in a systematic way the new implementations in prEN 1993‐1‐1. [ABSTRACT FROM AUTHOR]

In this paper, the flexural‐torsional buckling response of austenitic stainless steel I‐section beam‐columns is investigated. Finite element simulations are performed with the aim of analysing the parameters affecting the behaviour of the studied members. The accuracy and safety of the existing design provisions of the European structural stainless steel design standard EN 1993‐1‐4 (2015) are assessed. A new method providing more accurate ultimate resistance predictions for austenitic stainless steel I‐section beam‐columns undergoing flexural‐torsional buckling is put forward. The higher accuracy, safety and reliability of the proposed design rules relative to EN 1993‐1‐4 (2015) are demonstrated and the new proposals have now been included in the revised Eurocode – prEN 1993‐1‐4 (2021). [ABSTRACT FROM AUTHOR]

An accurate and consistent approach to the out‐of‐plane stability design of steel beams and structures utilising geometrically and materially nonlinear analysis with imperfections (GMNIA) and 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. In the present paper, the scope of this method is extended from the in‐plane design of steel structures and structural components to scenarios in which out‐of‐plane stability effects, with a focus on lateral‐torsional buckling (LTB), govern. First, two shapes and corresponding amplitudes of equivalent imperfections, which consider the combined influence of both geometric imperfections and residual stresses, for the out‐of‐stability design of steel and stainless steel members by GMNIA are established. The existing CSM strain limits for in‐plane design are then extended to allow for the influence of shear, torsion and warping, to enable their general applicability to three‐dimensional buckling problems. It is shown that employing the proposed design method together with the proposed equivalent imperfections generally provides more accurate and consistent ultimate strength predictions than traditional Eurocode design calculations and also streamlines the design process by eliminating the need for cross‐section classification and individual member design checks. [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]

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

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

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

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

In the framework of the RFCS project HOLLOSSTAB, a new design method for determining the resistance of hollow section members has been developed. This method links a generalized slenderness, calculated under the effect of the combined loading, to the resistance of the cross‐section and of the member. This so‐called "Generalized Slenderness‐based Resistance Method" (GSRM) has been shown to provide accurate predictions of experimentally and numerically determined resistances of hollow sections. Nonetheless, the real benefit of this new design method could only be evaluated after a conscientiously performed reliability analysis that is presented in this paper. First, the statistical data of the input variables (cross‐section dimensions, material law) obtained through measurements are presented and compared to the assumptions of Annex E of EN 1993‐1‐1:2020. Then, the reliability analysis is outlined. In particular, attention is given to specific problems resulting from the fact that several basic parameters of GSRM have to be determined numerically (for example the critical loads under combined loading). In addition, the sensitivity of the resulting partial factors to assumptions concerning the statistical distribution of the input variables is studied and discussed. [ABSTRACT FROM AUTHOR]

The stability of compression members is typically assessed through buckling curves, which include the influence of initial geometric imperfections and residual stresses. Alternatively, the capacity can be obtained more directly by carrying out a second order analysis using equivalent bow imperfections that account for both geometric imperfections and residual stresses. For design by second order elastic analysis, following EN 1993‐1‐1 recommendations, the magnitudes of the equivalent bow imperfections can either be back‐calculated for a given member to provide the same result as would be obtained from the member buckling curves or taken more simply as a fixed proportion of the member length. In both cases, a subsequent linear axial + bending cross‐section check is required. For design by second order inelastic analysis, there are currently no suitable recommendations for the magnitudes of equivalent bow imperfections and, as demonstrated herein, it is not generally appropriate to use equivalent bow imperfections developed on the basis of elastic analysis. Equivalent bow imperfections suitable for use in design by second order inelastic analysis are therefore established in the present paper and shown to yield reliable results when compared to benchmark results and current design guidance. [ABSTRACT FROM AUTHOR]

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