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Journal articleSpinasa A, Meng X, Weber B, et al., 2026, , Thin-Walled Structures, Vol: 224, ISSN: 0263-8231
Wire-arc directed energy deposition (DED-Arc), is a metal 3D printing technology that enables the production of large, intricate steel components with significant potential in structural engineering. The cyclic thermal history inherent to the DED-Arc process induces residual stresses, which can influence the structural performance of fabricated components. This study experimentally investigates residual stress distributions in seven DED-Arc steel tubular specimens fabricated using ER90S-D2 welding wire. These include three square hollow section (SHS) tubes with nominal thicknesses of 3.5 mm, 4.5 mm, and 5.5 mm, two 3.5 mm-thick circular hollow section (CHS) tubes with interpass temperatures of 150 °C and 350 °C and two 8 mm-thick oval sections with active and passive cooling. The sectioning method was used to measure residual stresses in both longitudinal and transverse directions. Released strains were recorded using a Demec gauge and, as an alternative, using digital image correlation (DIC); the results showed generally good agreement, but the accuracy of the DIC results was compromised in the case of large out-of-plane deformations. For the SHS tubes, tensile stresses appeared in the corners and compressive stresses in the middle of the faces in the longitudinal direction, while the transverse direction showed peak tensile stresses at the top and bottom. Similar distributions were observed across the SHS thicknesses, except in the thinnest tube, where local buckling altered the pattern. The CHS tubes exhibited high through-thickness bending stresses linked to interpass temperature, while membrane stresses were negligible. In the oval tubes, active cooling led to slightly higher residual membrane stresses. The presented results and findings offer key insights into the residual stress distributions in DED-Arc tubular parts, serving as a sound basis for model validation and the evaluation of structural performance.
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Journal articleZuo W, Chen M-T, Zhao O, et al., 2026, , Engineering Structures, Vol: 353, ISSN: 0141-0296
The integration of topology optimization (TO) and metal 3D printing offers transformative opportunities for the design and fabrication of steel joints in spatial structures. This study develops a parametric joint TO-based design workflow, incorporating subdivision surface technology, the Bi-directional Evolutionary Structural Optimization (BESO) algorithm and advanced re-engineering techniques. Four X-joints for connecting circular tubes were optimized and then fabricated using Selective Laser Melting (SLM) with 316 L austenitic stainless steel powder. To characterize the mechanical properties of the printed material, uniaxial tensile coupon tests were conducted in five loading orientations. The 3D printed steel optimized X-joints were tested under axial compression, with the deformations and the strains captured using 3D Digital Image Correlation. The structural response was assessed in terms of strain distribution, load-deformation behavior, joint strength and ductility, as well as failure mode. The results demonstrate that the 3D printed TO designed X-joints exhibit a more uniform distribution of stress, superior ductility and more efficient load transfer compared to conventional tubular joints. This excellent structural performance is due to the inherent high ductility of SLM-fabricated 316 L stainless steel, the smooth geometric transitions achieved by means of subdivision surface technology, and the optimized material layout from BESO-based TO. The findings validate the feasibility of 3D printing TO designed joints for next-generation structural systems, with potential benefits in structural performance, fabrication efficiency and design flexibility.
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Journal articleZhang M, Meng X, Hong W, et al., 2026, , Thin-Walled Structures, Vol: 223, ISSN: 0263-8231
Relative to conventional formative or subtractive manufacturing techniques, additive manufacturing (AM) offers increased geometric freedom, and the potential for enhanced structural efficiency and greater automation. Hybrid construction, which combines conventionally produced structural components with AM parts, is considered the most practical way to deploy metal AM in construction. This study aims to develop an optimisation methodology for hybrid tubular joints, incorporating topology optimisation and printability considerations. The studied tubular joints have an X-shaped configuration, comprising conventionally produced circular hollow section (CHS) members and wire-arc directed energy deposited (DED-Arc) nodes. The DED-Arc nodes were topology optimised, with performance and printability enhanced by imposing stress and overhang constraints, preventing the formation of overly slender elements and excessive overhang angles. The printability was further improved by manual adjustments to satisfy manufacturing requirements. The structural performance of the hybrid joints, including the initial stiffness, ultimate load-bearing capacity, ductility and material efficiency, was assessed through geometrically and materially nonlinear numerical analyses and physical experiments on nine printed joints; five conventional X-joints were also fabricated and tested to provide benchmark results. Overall, the hybrid joints exhibited up to about 80 % higher initial stiffness, 20 % higher load-bearing capacity and 100 % higher capacity-to-mass ratios under biaxial compression compared with the conventionally produced joints, indicating markedly enhanced structural efficiency.
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Journal articleQuan C, Walport F, Kucukler M, et al., 2026, , Engineering Structures, Vol: 351, ISSN: 0141-0296
To address the limitations of existing design specifications for laterally unrestrained stainless steel I-section beam-columns, new design rules are proposed in this study. A comprehensive parametric study was conducted using finite element modelling to investigate the member behaviour and generate benchmark member resistances, covering Class 1–3 cross-sections and considering a range of material grades, member geometries and combined loading conditions. It was observed that the numerically derived compression-bending interaction factor for out-of-plane buckling checks decreases with more pronounced bending moment gradients, indicating their beneficial influence on member resistances. Thus, calibrated against the numerical results, a new formulation of the interaction factor is proposed, covering combined compression and uniform or non-uniform bending and ensuring alignment between member buckling and cross-section resistance checks. The new proposals are shown to provide accurate and consistent member resistance predictions for all load cases, and can be applied with the partial safety factor of 1.1 as specified in EN 1993–1–4:2025. These proposals have been included in the new version of the European structural stainless steel design standard EN 1993–1–4:2025.
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Journal articleDai X, Xing W, Ye J, et al., 2026, , Engineering Structures, Vol: 350, ISSN: 0141-0296
Wire arc additive manufacturing (WAAM) technology is becoming increasingly widely used in the fabrication of large-scale metal components in engineering structures. By combining WAAM with conventionally manufactured structural elements, more efficient, cost-effective and customized structures can be produced. To explore the potential of this hybrid construction concept further, steel endplate connections, formed through the deposition of WAAM steel material onto conventional cold-formed steel hollow sections, are studied herein. A total of 4 groups of hybrid endplate connections, designed with various thicknesses, shapes and deposition strategies, were manufactured through CMT-WAAM. Material tests were conducted on both the deposited material and the substrate hollow steel sections. The geometrical dimensions of the specimens were measured via 3D laser scanning. Tests were then carried out to determine the failure modes, moment-rotation responses and capacities of the hybrid endplate connections. Digital Image Correlation (DIC) was used to record the structural responses of the specimens throughout testing. All the examined hybrid endplate connection specimens failed in the endplates and demonstrated excellent bending and rotation capacities. The printing strategy and layer orientations were found to have limited impact on the material and connection behaviour. The results of the connection tests were compared against the predictions from existing design methods in terms of the failure modes, yield capacity and ultimate capacity. Traditional yield line and T-stub analysis methods captured the performance and failure modes of the hybrid endplate connection accurately, with the average ratios of predicted-to-test yield and ultimate capacities being 0.97 and 0.91, respectively. The results demonstrate the potential and efficiency of using WAAM to produce hybrid bolted connections in the construction industry.
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Journal articleHorisawa E, Meng X, Gardner L, et al., 2026, , Journal of Constructional Steel Research, Vol: 238, ISSN: 0143-974X
Wire arc additive manufacturing (WAAM) is a metal 3D printing technique with the potential to produce structural steel elements in a cost-effective fashion. However, there is currently a paucity of data concerning the mechanical behaviour of WAAM steel under uniaxial and multiaxial cyclic loading. This study aims to address this gap via a comprehensive experimental investigation and constitutive modelling of the multiaxial cyclic behaviour of WAAM steel. Cyclic testing featuring axial and torsional loading was conducted on WAAM Grade ER70S-6 steel, and a constitutive model to describe the multiaxial cyclic behaviour of the examined material is proposed. First, radial loading in the biaxial stress plane was conducted to identify the shape of the initial yield surface and the strain development paths of the material. Uniaxial and biaxial cyclic loading tests were performed to investigate the hardening of the material. The experimental results show that WAAM steel exhibits a von Mises isotropic yield surface, with plastic strain developing in the direction normal to the yield surface. The proposed modified two-surface plasticity model accurately reproduces both the uniaxial and multiaxial cyclic stress-strain responses, while offering improved accuracy for the multiaxial ratcheting behaviour compared with the conventional model. The results of this study show that the classical plasticity theory used for conventional steel is also applicable to WAAM steel.
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Journal articleZhang R, Zhu Y, Gardner L, 2026, , Construction and Building Materials, Vol: 512, ISSN: 0950-0618
A strain rate-dependent constitutive model for stainless steels, calibrated against 184 coupon test results assembled from the literature on austenitic, ferritic, duplex and martensitic alloys, is presented. The rate-dependent material behaviour of two austenitic stainless steels, EN 1.4307 and EN 1.4678, was first examined experimentally. A total of 46 coupon tests were conducted, at different strain rates ranging from 0.00018 s–1 to 2000 s–1. The effect of strain rate on the strength and ductility of the tested stainless steels was analysed. The test results indicated that both the yield strength and ultimate strength of the two stainless steels are strain rate-dependent, though each exhibited distinct trends. As the strain rate increased, the yield strength exhibited an increasing trend, whereas the ultimate strength initially decreased at strain rates below 0.1 s–1 and then increased at higher strain rates. Compared to the normal-strength EN 1.4307 stainless steel, the high-strength EN 1.4678 stainless steel exhibited lower sensitivity to strain rates, as reflected by lower dynamic increase factors. The Johnson–Cook model was calibrated to match the observed response of the studied grades. Based on both the newly obtained test results, as well as additional experimental data collected from previous studies, a continuous dynamic constitutive model applicable to all stainless steels — expressed as a function of strain rate and yield strength — was developed by combining a modified Cowper–Symonds formulation for the strain rate effect with the two‑stage Ramberg–Osgood model for describing the stress-strain curve. The developed formulations are suitable for inclusion in advanced analytical models and numerical simulations of stainless steel elements under high strain rate loading scenarios.
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Journal articleHong W, Zhang R, Hadjipantelis N, et al., 2026, , Thin-Walled Structures, Vol: 219, ISSN: 0263-8231
Wire-Arc Directed Energy Deposition (DED-Arc) or Wire Arc Additive Manufacturing (WAAM) is a metal 3D printing method offering the ability to produce large-scale structural components with complex geometries in an efficient and cost-effective manner. To date, only a limited number of experimental studies on the structural behaviour of slender DED-Arc hollow sections have been conducted. To fill this gap, new experimental evidence on the behaviour of DED-Arc shell structures is thus reported. A comprehensive experimental programme investigating the local buckling response of DED-Arc high strength steel circular hollow sections (CHS) over a wide range of cross-sectional slendernesses has been conducted. In total, twelve DED-Arc CHS stub columns with a series of diameter-to-thickness ratios were produced using ER120S-G wire. The undulating as-built geometry and the initial geometric imperfections of the stub columns were captured using 3D laser scanning. During the stub column tests, the deformation fields were captured by means of digital image correlation. In the present paper, following the description of the specimen production, the experimental programme is described, the test results are analysed and the applicability of the current Eurocode 3 rules to the design of DED-Arc CHS is assessed by comparing the test results with the EN 1993-1-1 and EN 1993-1-6 design provisions. The test results show that the structural behaviour of DED-Arc CHS is similar to that of conventionally-produced (i.e. cold-formed and hot-rolled) steel CHS. Both EN 1993-1-1 and EN 1993-1-6 yield safe-sided resistance predictions, with the latter being more accurate since it incorporates the influences of both the fabrication quality and of the initial geometric imperfections.
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Journal articleEl Khoury K, Vollum R, Izzuddin B, et al., 2026, , ENGINEERING STRUCTURES, Vol: 347, ISSN: 0141-0296
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Journal articleWeber B, Meng X, Gardner L, 2026, , Automation in Construction, Vol: 181, ISSN: 0926-5805
Wire-arc directed energy deposition (DED-Arc), or wire arc additive manufacturing (WAAM), enables large-scale, intricate metallic components to be created in an automated manner, with great promise in construction. This paper presents the design, manufacture and experimental verification of a 4 m-span, East Asian garden bridge-inspired and structurally optimised DED-Arc steel pedestrian bridge. The bridge consists of optimised DED-Arc steel tubular components as the main load-carrying structure, and wooden boards on top as the decking. The structural performance of the bridge was examined through non-destructive testing of the fully assembled bridge up to the design load and destructive testing to failure of a duplicate of the main arch, which confirmed the load-carrying capacity of the bridge and showed generally good correlation with the prior numerical simulations. This study successfully demonstrates the feasibility of integrating DED-Arc with structural optimisation at scale, and its significant role in construction automation and decarbonisation.
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