555 results found
Behzadi-Sofiani B, Wadee MA, Gardner L, 2023, Testing, FE modelling and design of pin-ended stainless steel equal-leg angle section columns and beam-columns, Journal of Constructional Steel Research, Vol: 208, Pages: 1-19, ISSN: 0143-974X
The behaviour and design of pin-ended stainless steel equal-leg angle section members under compression and compression plus minor-axis bending are investigated herein. The studied members are cylindrically pinned about the minor axis. An experimental investigation, including material testing, initial geometric imperfection measurements and physical tests on hot-rolled stainless steel equal-leg angle section members is first presented. Numerical models are developed and validated against the new experimental data. A numerical parametric study is then presented considering both hot-rolled and cold-formed stainless steel angle section columns alongside beam–columns with a wide range of slenderness values. Finally, new design proposals for pin-ended stainless steel equal-leg angle section members under compression and combined compression and minor-axis bending are developed and verified against the results of existing physical experiments, as well as the newly-generated test and numerical results. The proposed design rules are shown to offer substantially more accurate and consistent resistance predictions compared to existing codified design rules. The reliability of the new design provisions, with a recommended partial safety factor γM1 = 1.1, is verified following the EN 1990 procedure.
Huang C, Zheng Y, Chen T, et al., 2023, Fatigue crack growth behaviour of wire arc additively manufactured steels, International Journal of Fatigue, Vol: 173, Pages: 1-12, ISSN: 0142-1123
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.
Vella N, Kyvelou P, Buhagiar S, et al., 2023, Innovative shear connectors for composite cold-formed steel-timber structures: an experimental investigation, Engineering Structures, Vol: 287, Pages: 1-18, ISSN: 0141-0296
An experimental investigation into the behaviour of bespoke shear connectors designed to generate composite action in cold-formed steel-timber structures is presented. The response of the shear connectors was assessed through a comprehensive set of push-out tests, where the cold-formed steel thickness and the connector type and material were varied. Previous studies have shown that while the use of ordinary self-drilling screws as shear connectors enables the development of some composite action, their performance was inhibited by timber embedment. Hence, the main feature of the innovative shear connectors was the introduction of a fitting around the screw to mobilise higher timber embedment forces. The best performing shear connectors achieved about double the shear resistance, four times the initial slip modulus ks and seven times the mid-range slip modulus ks,m of ordinary self-drilling screws. An analytical model presented in previous research was extended to describe the response of the innovative shear connectors developed in this study. The model was validated against the push-out test results, and shown to be able to accurately predict the ultimate load, slip at ultimate load, and the two slip moduli ks and ks,m of the innovative connectors, with mean model-to-test ratios of 1.01, 1.15, 1.29 and 1.19 respectively.
Zhu Y, Gardner L, Yang H, 2023, Experimental investigation into the transverse impact performance of high-strength circular CFST members, Thin Walled Structures, ISSN: 0263-8231
Meng X, Weber B, Nitawaki M, et al., 2023, Optimisation and testing of wire arc additively manufactured steel stub columns, Thin Walled Structures, ISSN: 0263-8231
Yun X, Zhu Y, Meng X, et al., 2023, Welded steel I-section columns: residual stresses, testing, simulation and design, Engineering Structures, Vol: 282, Pages: 1-19, ISSN: 0141-0296
The flexural buckling behaviour and design of homogeneous and hybrid welded I-section columns, considering a wide range of steel grades, are investigated in the present study. Residual stresses are first examined through the statistical analysis of 71 existing experimental results collected from the literature; on the basis of the findings, a new residual stress model for S235 to S960 steel welded I-sections is proposed. Experiments on a total of five pin-ended homogeneous (S690) and hybrid (S355 web and S690 flanges) welded I-section columns buckling about the major axis are then presented. In parallel with the experimental programme, finite element (FE) models were created and validated against the experimental results obtained from the present study, as well as those collected from the literature. The developed FE models were shown to be capable of accurately replicating the key experimental responses, and were then utilised to carry out extensive parametric studies, through which additional 6000 numerical column buckling data covering a wide range of steel grades, cross-section geometries and member slendernesses were generated. The combined experimental and numerical data were used to evaluate the accuracy of the flexural buckling design rules for welded I-section columns set out in the current European and North American design standards, where shortcomings relating to the consideration of steel grade were identified. A modified Eurocode 3 (EC3) method was devised to reflect the influence of yield strength on the buckling resistances of welded I-section columns more systematically and shown to provide substantially improved resistance predictions in terms of accuracy and consistency; the reliability of the modified approach was statistically verified following the procedure set out in Annex D of EN 1990 and is considered to be suitable for incorporation into future revisions of Eurocode 3.
Zhu Y, Yun X, Gardner L, 2023, Numerical modelling and design of normal and high strength steel non-slender welded I-section beam–columns, Thin-Walled Structures, Vol: 186, Pages: 1-14, ISSN: 0263-8231
This paper presents a comprehensive numerical study into the in-plane member stability and design of normal and high strength steel (NSS and HSS) non-slender welded I-section beam–columns subjected to compression plus uniaxial bending. Finite element (FE) models were firstly developed to replicate the structural performance of welded I-section beam–columns made of different steel grades, as observed in existing tests collected from the literature. The validated FE models were then employed in a comprehensive parametric study to generate extensive numerical data covering a wide range of cross-section geometries, steel grades, member slendernesses and loading combinations. The numerically obtained data were utilised to evaluate the accuracy of the current design methods set out in the European Standards EN 1993-1-1:2005 and EN 1993-1-12:2007 as well as the American Specification AISC 360-16 for both NSS and HSS non-slender welded I-section beam–columns. The comparisons revealed that the codified design methods yield varying levels of accuracy in predicting the ultimate capacities of welded I-section beam–columns depending on the steel grade. To address this issue, new design proposals that are compatible with the European beam–column design framework have been developed, featuring more accurate yield strength-dependent interaction curves anchored to improved resistance predictions for members subjected to isolated loading scenarios (i.e. the compression and bending end points of the interaction curves). The new design proposals have been found to provide more accurate and consistent resistance predictions than the existing codified design provisions for NSS and HSS non-slender welded I-section members under compression plus uniaxial bending. The reliability of the new proposals has been confirmed through statistical analyses according to EN 1990: 2002.
Zhang Y, Kyvelou P, Wang Y, et al., 2023, Experimental investigation and design of slip resistant aluminium alloy-stainless steel connections, Thin Walled Structures, Vol: 186, Pages: 1-15, ISSN: 0263-8231
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.
Shen J, Lapira L, Wadee MA, et al., 2023, Probing in-situ capacities of prestressed stayed columns: Towards a novel structural health monitoring technique, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 381, ISSN: 1364-503X
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 maximise 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 utilisation 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 model. In contrast with 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 utilisation 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.
Zhang R, Gardner L, Amraei M, et al., 2023, Testing and analysis of additively manufactured stainless steel corrugated cylindrical shells in compression, Journal of Engineering Mechanics, Vol: 149, ISSN: 0733-9399
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.
Guo X, Kyvelou P, Ye J, et al., 2023, Experimental study of DED-arc additively manufactured steel double-lap shear bolted connections, Engineering Structures, Vol: 281, Pages: 1-16, ISSN: 0141-0296
An experimental study into the structural behaviour of Directed Energy Deposition-arc or wire arc additively manufactured (DED-arc AM and WAAM, respectively) steel double-lap shear bolted connections is presented. The mechanical properties of the material, which had a nominal yield stress of 420 MPa, were first determined by means of tensile coupon tests. Sixty connection specimens of two different nominal thicknesses and two print layer orientations were then tested to failure. The geometry of the test specimens was determined by 3D laser scanning, while the deformation and strain fields were measured during testing using digital image correlation. The observed failure modes included shear-out, net section tension, bearing and end-splitting, while a new hybrid mode of shear-out and net section tension was identified for the first time. The test results were compared against the predictions of current design specifications, namely AISI S100 and AS/NZS 4600 for cold-formed steel and AISC 360 and Eurocode 3 for structural steel, to evaluate their applicability to WAAM elements. Overall, the structural behaviour of the tested specimens followed the anticipated trends, and the predicted resistances determined from the current design specifications were generally reasonable. There were, however, a number of exceptions to this, highlighting the need for new design provisions, together with appropriate safety factors, that are specific to this form of manufacture.
Huang C, Kyvelou P, Gardner L, 2023, Stress-strain curves for wire arc additively manufactured steels, Engineering Structures, Vol: 279, Pages: 1-19, ISSN: 0141-0296
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.
Zhu Y, Yun X, Gardner L, 2023, Cross-sectional behaviour and design of normal and high strength steel welded I-sections under compression and uniaxial bending, Advances in Structural Engineering, ISSN: 1369-4332
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.
Walport F, Chan HU, Nethercot D, et al., 2023, Design of stainless steel structural systems by GMNIA with strain limits, Engineering Structures, Vol: 276, ISSN: 0141-0296
Design by GMNIA (Geometrically and Materially Nonlinear Analysis with Imperfections) allows the key behavioural features of structures to be directly captured in the analysis, improving accuracy and dramatically reducing the need for subsequent design checks. Since the analysis of frames typically employs beam elements, in which local buckling of cross-sections cannot be explicitly simulated, cross-section classification and capacity checks remain necessary. However, the step-wise and overly conservative nature of these traditional checks restricts accuracy. To resolve this, the use of strain limits, defined using the Continuous Strength Method, in place of these cross-section checks has been proposed. This design method is extended to indeterminate stainless steel structural systems herein. Ultimate load-carrying capacity predictions from the proposed design approach are compared against results obtained from benchmark shell finite element models as well as predictions using traditional stainless steel design methods. The new design framework allows for element interaction at the cross-section level, the influence of local moment gradients, the partial spread of plasticity, moment redistribution, strain hardening and the visualisation of the structural failure mechanism, resulting in more accurate and consistent resistance predictions. The method is included in AISC 370 and prEN 1993-1-14 offering a step change in efficiency for the future direction of structural stainless steel design.
Kyprianou C, Kyvelou P, Gardner L, et al., 2023, Finite element modelling of sheathed cold-formed steel beam-columns, Thin Walled Structures, Vol: 183, ISSN: 0263-8231
The structural behaviour of sheathed cold-formed steel lipped channel section columns (studs) subjected to combined compression and major axis bending is investigated herein by means of numerical modelling. Finite element (FE) models of single studs, set in tracks and connected to oriented strand board (OSB) and gypsum plasterboard sheathing under varying combinations of axial compression and horizontal loading were developed in ABAQUS and validated against experimental results reported in the literature. The developed numerical models incorporated cross-sectional and global geometric imperfections, while geometrical and material nonlinearities for both the steel and the sheathing were considered in the analyses. Particular emphasis was given to replicating the “as-built” boundary conditions at the ends of the columns, controlled by the screws connecting the column to the track and by the column–track contact interaction. The interaction between the sheathing and the column, as well as the behaviour of the fasteners connecting the two components, were also explicitly modelled. Both the shear and pull-through characteristics of the fasteners were considered and simulated based on experimental findings. Following successful validation of the finite element models, parametric studies were conducted. The results showed that substantial structural performance benefits can be achieved by the addition of sheathing to cold-formed steel members and that the spacing of the connectors has a strong influence on the member response. For a typical system, decreasing the connector spacing from 300 mm to 75 mm was found to increase stud capacity and stiffness by up to 12% and 10% respectively when in pure compression and up to 26% and 22% respectively when in pure bending; under combined loading, capacity increases of up to 29% were found.
Afkhami S, Amraei M, Poutiainen I, et al., 2023, Data related to the manufacturing and mechanical performance of 3D-printed metal honeycombs, Data in Brief, Vol: 46, Pages: 1-15, ISSN: 2352-3409
The data available in this article include 3D mechanical designs used for the computer-aided fabrication of metal honeycombs produced by additive manufacturing and studied in . In addition, the force-displacement data utilized to evaluate the mechanical performance of the metal used in this study are available via the digital image correlation technique. Further, the surface features obtained using 3D scanning microscopy of the fabricated parts are available as raw files and processed data. Finally, the impact test data are presented as high-frame-rate videos showing the time-displacement numerical values. This information has been provided in this data article to complement the related research, serve as a guide for future studies, and ensure the data's repeatability and reliability of the related research paper. The research article  investigates the mechanical performance and failure mechanism of additively manufactured metallic honeycombs under various scenarios, from quasi-static to dynamic loading. It also investigates the design optimization of these energy-absorbing hollow structures by comparing hollow structures made of three distinct novel cell designs (triangular, diamond-shaped, and diamond-shaped with curved walls) with traditional honeycombs made of hexagonal cells.
Shah IH, Hadjipantelis N, Walter L, et al., 2023, Environmental life cycle assessment of wire arc additively manufactured steel structural components, Journal of Cleaner Production, Vol: 389, Pages: 1-14, ISSN: 0959-6526
Wire arc additive manufacturing (WAAM) enables the production of structural components with topologically optimised geometries thus leading to significant self-weight reductions for a given load-carrying capacity. A common question arises regarding the environmental performance of WAAM structural components in comparison with conventional steel structural components. Thus, a comparative cradle-to-gate life cycle assessment has been conducted where the environmental impact of producing a topologically optimised WAAM steel beam is compared with that of producing a conventional hot-rolled steel I-beam. The beams are 2 m long, simply-supported and loaded vertically at midspan. The impact of using either carbon steel or stainless steel is investigated. The results demonstrate that the carbon steel and stainless steel WAAM beams have 7% and 24%, respectively, lower climate change impact than the corresponding I-beams. It is concluded that WAAM can lead to lower CO2-eq. emissions than conventional hot-rolling, provided that mass reductions of the order of 50% (which are readily attainable) can be achieved by employing WAAM in conjunction with, for instance, topology optimisation. Furthermore, it is shown that the shielding gas contributes greatly to the environmental impact of WAAM, and that, by using higher deposition rates or by utilising renewable energy sources, the impact of WAAM can be reduced by more than 30%.
Zhu Y, Yun X, Gardner L, 2023, Behaviour and design of high strength steel homogeneous and hybrid welded I-section beams, Engineering Structures, Vol: 275, ISSN: 0141-0296
The behaviour and design of high strength steel (HSS) beams are addressed in the present study. Six in-plane three-point bending tests on three different welded I-sections − two homogeneous S690 steel welded I-sections and one hybrid welded I-section with S690 steel flanges and an S355 steel web, were first conducted. The beam tests were carried out in major axis bending and a bespoke restraint system was designed and employed in the test programme to prevent lateral-torsional buckling. Following the experimental investigation, a thorough 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. The test results obtained in the present study and collected from the literature, together with the generated FE data from the parametric study, were used to evaluate the suitability of the current Eurocode 3 cross-section slenderness limits for HSS homogeneous and hybrid welded I-sections in bending. 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 from the present study indicate that plastic design can be used for HSS structures, provided the proposed stricter Class 1 slenderness limits are employed.
Gardner L, 2023, Metal additive manufacturing in structural engineering: Review, opportunities and outlook, Pages: 3-8
Although still in its infancy, metal additive manufacturing (AM) has arrived at construction scale. In this paper, a review of recent developments in metal AM in structural engineering is presented, including the latest research advances, lessons learned from other sectors and applications in practice. Emphasis is placed on wire-arc additive manufacturing (WAAM) since this is deemed to be the most promising technique for the requirements of the construction sector. A description of the observed material response of both steel and stainless steel WAAM thin-walled elements, as well as the structural behaviour of crosssections, members, connections and systems, is provided. The challenges surrounding the inherent geometric variability of as-built WAAM material, as well as the implications of possible anisotropy, are discussed. Optimization and additive manufacturing go hand in hand, with the latter now enabling the former to be more readily realised in practice. Recent examples of optimized, additively manufactured structural components are presented. The economics and sustainability of WAAM are then discussed. Finally, with a view to the future, the opportunities and outlook for metal additive manufacturing, including the production and design of new structural elements, as well as its potential use in the strengthening and repair of structures, are presented.
Behzadi-Sofiani B, Gardner L, Wadee MA, 2023, Numerical simulation and design of steel equal-leg angle section beams, Pages: 937-943
The stability and design of steel equal-leg angle section members subjected to uniaxial bending are studied herein. Numerical models are developed and validated against existing experimental data on steel equal-leg angle section beams. A numerical parametric study is then presented considering both hot-rolled and cold-formed steel angle section beams. Under major-axis bending, both lateral-torsional and local buckling are observed, with the former characterised by lateral deflection and twist of the cross-section along the member length but no cross-section deformation, while the latter by relative twist and transverse bending of the outstands. Under minor-axis bending, lateral-torsional buckling and Brazier flattening are observed, with the latter characterised by splaying of the outstands. 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 are achieved when account is taken both of lateral-torsional buckling and Brazier flattening in the design of equal-leg angle section beams under minor-axis bending using a normalised slenderness. Finally, new design proposals for steel equal-leg angle section beams are developed and verified against both physical experiments and numerical simulations. The proposed design rules are shown to offer substantially more accurate resistance predictions compared to existing codified design rules.
Gardner L, 2023, Metal additive manufacturing in structural engineering – review, advances, opportunities and outlook, Structures, Vol: 47, Pages: 2178-2193, ISSN: 2352-0124
Although still in its infancy, metal additive manufacturing (AM) or 3D printing has now arrived at a scale suitable for use in construction. The new technology offers the potential for improved economy, sustainability, safety and productivity through greater automation, enhanced customisation, reduced material usage and reduced wastage. In this paper, a review of recent developments in metal AM in structural engineering is presented, including the latest research advances, current trends and applications in practice. Emphasis is placed on Directed Energy Deposition-arc (DED-arc) AM or wire arc AM (WAAM) since this is deemed to be the most promising technique for the requirements of the construction sector. A description of the observed material response of both steel and stainless steel WAAM elements, as well as the structural behaviour of cross-sections, members, connections and systems, is provided. The challenges surrounding the inherent geometric variability of as-built WAAM material, as well as the implications of possible anisotropy, are discussed.
Lapira L, Gardner L, Wadee MA, 2023, Elastic local buckling formulae for thin-walled I-sections subjected to shear and direct stresses, Thin Walled Structures, Vol: 182, ISSN: 0263-8231
Formulae for calculating the elastic local buckling stresses of doubly-symmetric thin-walled I-section girders subjected to combined shear and direct stresses, accounting for the interaction between the plate elements are presented. The interaction between the plate elements (i.e. the flanges and web) is bounded by a theoretical lower-bound, where there is no interaction and the critical plate is considered to be simply-supported, and a theoretical upper-bound where interaction is strongest and the critical plate is considered to have rotationally fixed edges. The interaction is accounted for by introducing an interaction coefficient ζ that quantifies the relative level of fixity between the aforementioned lower and upper bounds. Expressions to calculate ζ are calibrated using results from finite element analyses generated in Abaqus. Doubly-symmetric I-sections of varying geometric proportions loaded in shear, major axis bending, compression and a full range of combinations thereof are considered. Using the developed formulae, the elastic local buckling stresses of the studied cross-sections are accurately predicted, typically within 5% of the values obtained from FE models; this is a significant improvement over the results determined in the traditional manner in which plate element interaction effects are ignored, where the full cross-section buckling stress is shown to be underestimated by as much as 40%.
Behzadi-Sofiani B, Gardner L, Wadee MA, 2023, Behaviour, finite element modelling and design of cruciform section steel columns, Thin Walled Structures, Vol: 182, Pages: 1-13, ISSN: 0263-8231
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.
Huang C, Meng X, Gardner L, 2023, Flexural behavior of wire arc additively manufactured tubular sections
Wire arc additive manufacturing (WAAM) is a promising metal 3D printing technique in the construction industry for its ability to produce large and complex-shaped elements, with reasonable printing accuracy, time and costs. There is currently, however, a lack of fundamental test data on the structural performance of WAAM elements. To address this, an experimental study into the cross-sectional behavior of WAAM tubular beams has been conducted and is presented herein. A total of 14 stainless steel square, rectangular and irregular hollow sections, spanning over all cross-section classes of EN 1993-1-4 and AISC 370, were tested in four-point bending. 3D laser scanning, silicone casting and Archimedes’ measurements were employed to collectively determine the as-built geometry and local geometric imperfections of the test specimens, while digital image correlation (DIC) was used to monitor the deformation responses of the specimens during testing. The full moment-curvature histories and key experimental results are presented and discussed. Similar cross-sectional behavior to that of equivalent, conventionally manufactured sections was observed, with the more slender cross-sections showing increased susceptibility to local buckling. However, owing to the inherent geometric variability of WAAM, the tested 3D printed beams exhibited more variable flexural capacities between the repeat specimens than is generally displayed by conventionally produced stainless steel sections. Finally, the test results were used to assess the applicability of current cross-section design provisions in the European (EN 1993-1-4) and American (AISC 370) structural design specifications, as well as the continuous strength method (CSM), to WAAM stainless steel tubular beams.
Gardner L, Yun X, Walport F, 2023, The continuous strength method – review and outlook, Engineering Structures, Vol: 275, Pages: 1-16, ISSN: 0141-0296
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 isparticularly 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, recent research, summarised herein, has focussed on integration of the CSM strain limits into a framework of design by secondorder 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.
Wynne Z, Buchanan C, Kyvelou P, et al., 2022, Dynamic testing and analysis of the world’s first metal 3D printed bridge, Case Studies in Construction Materials, Vol: 17, ISSN: 2214-5095
The MX3D Bridge is the world’s first additively manufactured metal bridge. It is a 10.5 m-span footbridge, and its dynamic response is a key serviceability consideration. The bridge has a flowing, sculptural form and its response to footfall was initially studied using a 3D finite element (FE) model featuring the designed geometry and material properties obtained from coupon tests. The bridge was tested using experimental modal analysis (EMA) and operational modal analysis (OMA) during commissioning prior to installation. The results have shown that the measured vibration response of the bridge under footfall excitation is 200% greater than predictions based on the FE model and contemporary design guidance. The difference between predicted and measured behaviour is attributed to the complexity of the structure, underestimation of the modal mass in the FE model, and the time-variant modal behaviour of the structure under pedestrian footfall. Both OMA and EMA give a dominant natural frequency for the bridge of between 5.19 Hz and 5.32 Hz, higher than the FE model prediction of 4.31 Hz, and average damping estimates across all modes of vibration below 15 Hz of 0.61% and 0.74% respectively, higher than the 0.5% assumed within the design guidance, slightly reducing the peak response factor predicted for the bridge.
Huang C, Meng X, Gardner L, 2022, Cross-sectional behaviour of wire arc additively manufactured tubular beams, Engineering Structures, Vol: 272, Pages: 1-17, ISSN: 0141-0296
Wire arc additive manufacturing (WAAM) is a promising metal 3D printing technique in the construction industry for its ability to produce large and complex-shaped elements, with reasonable printing accuracy, time and costs. There is currently, however, a lack of fundamental test data onthe structural performance of WAAM elements. To address this, an experimental study into the cross-sectional behaviour of WAAM tubular beams has been conducted and is presented herein. A total of 14 stainless steel square, rectangular and irregular hollow sections, spanning over all cross-section classes of EN 1993-1-4 and AISC 370, were tested in four-point bending. 3D laser scanning, silicone casting and Archimedes’ measurements were employed to collectively determine the as-built geometry and local geometric imperfections of the test specimens, while digital imagecorrelation (DIC) was used to monitor the deformation responses of the specimens during testing. The full moment-curvature histories and key experimental results are presented and discussed. Similar cross-sectional behaviour to that of equivalent, conventionally manufactured sections wasobserved, with the more slender cross-sections showing increased susceptibility to local buckling. However, owing to the inherent geometric variability of WAAM, the tested 3D printed beams exhibited more variable flexural capacities between the repeat specimens than is generallydisplayed by conventionally produced stainless steel sections. Finally, the test results were used to assess the applicability of current cross-section design provisions in the European (EN 1993-1-4) and American (AISC 370) structural design specifications, as well as the continuous strength method (CSM), to WAAM stainless steel tubular beams.
Guo X, Kyvelou P, Ye J, et al., 2022, Experimental investigation of wire arc additively manufactured steel single-lap shear bolted connections, Thin Walled Structures, Vol: 181, Pages: 1-21, ISSN: 0263-8231
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, wereused 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.
Bureau A, Snijder B, Knobloch M, et al., 2022, Revision of EN 1993-1-1 – Design rules for structural analysis, cross-sectional resistance and member buckling, Steel Construction, Vol: 15, Pages: 202-212, ISSN: 1867-0520
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.
Zhang R, Meng X, Gardner L, 2022, Shape optimisation of stainless steel corrugated cylindrical shells for additive manufacturing, Engineering Structures, Vol: 270, Pages: 1-14, ISSN: 0141-0296
Axially compressed circular cylindrical shells with large diameter-to-thickness ratios are highly susceptible to local buckling, and their load-carrying capacities are known to be very sensitive to initial geometric imperfections. Hence, severe knock-down factors on their theoretical buckling loads are typically prescribed in design specifications, which greatly impair their structural efficiency. With the aim of enhancing load-bearing resistance and reducing sensitivity to imperfections, the shape optimisation and assessment of compressed free-form wavy cylindrical shells, the realisation of which is now viable through additive manufacturing, are the subject of the present study. The adopted optimisation framework employs the Particle Swarm Optimisation (PSO) algorithm, integrating computer-aided geometric design, nonlinear numerical simulations and imperfection sensitivity analyses. The structural performance of the optimised free-form wavy shells is analysed and compared to that of reference circular shells, as well as other types of non circular shell profiles, including sinusoidally corrugated shells, Aster shells and stringer-stiffenedshells. The optimised free-form wavy shell profiles are shown to exhibit increases in ultimate stress of up to 136% compared with the reference circular shell profiles; in general, greater benefits are achieved for more slender cross-sections. In future work, the proposed optimised shells will be manufactured in stainless steel by means of powder bed fusion (PBF), and their structural performance will be further verified through physical experiments. Keywords: Additive manufacturing; Axial compression; Corrugated cylindrical shells; Imperfection sensitivity; Particle Swarm Optimisation (PSO); Shell buckling; Stainless steel; 3D printing.
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