Nominated for Eurosteel 2021 Best Paper Award
Additive manufacturing (AM) is playing an increasing role in the production of complex steel structures. Robot- or machine-guided gas-shielded metal arc welding (GMAW), known as wire and arc additive manufacturing (WAAM), is suitable for this purpose. A small footbridge was designed in shell form at TU Darmstadt. It was completely additively manufactured over a stream on site using a welding robot. The work called for cantilevered manufacturing without support structures, which poses special challenges in manufacturing. This paper describes selected aspects of this project: the preliminary strength studies, the manufacturing strategy to ensure homogeneous manufacturing and the findings from on-site manufacturing. In addition, investigations were carried out which led to a notable increase in the deposition rate with the right choice of gas and wire.

As part of the ongoing revision of the Eurocodes, design provisions in EN 1999-1-1 on the buckling of longitudinally welded aluminium compression members have been subjected to a critical review. The numerical investigations described in part 1 of the paper were conducted because a need for improvement was identified. In part 2 the main observations were presented qualitatively. Part 3, the final part of the paper, presents the statistical evaluation of the numerical investigations and the determination of the buckling curves. Two different approaches are conceivable for these buckling curves: conventional buckling curves with explicitly specified imperfection factor and plateau length parameters, and a modified Ayrton-Perry approach with interpolated parameters. Both approaches are compared with the results of the numerical investigations and with test results.

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Vertical web stiffeners partially restrain the warping of the simply supported beam when lateral buckling occurs. The restraint increases the critical moment of the beam. This increase can be shown through the decrease of the warping effective length factor in the general formula determining the critical moment. An approximative expression to determine the warping effective length factor is proposed and verified by numerical analysis. Simply supported beams stiffened by vertical stiffeners, including end plates, which are subjected respectively to uniform bending, uniformly distributed loads, two concentrated loads and one concentrated load are numerically analyzed using COMSOL finite element software. The reliability of the proposed expression is assured by small coefficients of variation and very high coefficients of determination. It can provide a solution to improve the critical moment in the design of the beam without using an intermediate lateral bracing system.

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With the completion of the Peljeac Bridge, the northern and southern Croatian territories ended their long period of geographical isolation since their independence from Yugoslavia in June 1991. Under the severe influence of the global epidemic, the main contractor, China Road and Bridge Corporation (CRBC), has struggled diligently for more than three years to realize the Croatian people's long-cherished aspiration. The steel structure of this bridge is purchased from raw materials, steel box girders are fabricated in the workshop, long-distance transportation, and on-site erection are all performed under EU specifications by Chinese companies. Mr. Bicheng Tang and Mr. Xuefeng Wang, the contractors' steel structure expert and construction chief manager of this project respectively, authored this technical article and described the entire manufacturing procedure of such a huge number of steel structures (s. p. 26).

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The clearance between the core plate and the restraining part of the buckling-restrained brace using steel mortar planks (BRBSM) considerably affects the failure mode and hysteretic characteristics of the brace. A clearance adjustment construction is proposed for the BRBSM which can control the clearance through partially pasting clearance adjustment materials and polishing the mortar plank surface. First, the clearance adjustment construction workflow and quality control are demonstrated, and it is verified that the clearance can be assured by fabricating specimens. Further, the effects of the difference in clearance between the core plate and restraining part on the structural performance of the BRBSM in terms of failure behaviour, increase strength ratio, buckling mode and cumulative plastic strain energy ratio are evaluated by conducting a cyclic axial loading test.

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Increasing loads on the connections of tubular towers that support wind turbines are making the traditional bolted L-flange more challenging to design, while the large mass of components and tools make installation challenging from a safety perspective. The C1 Wedge Connection is a symmetrical connection between tubular sections. The connection consists of a cylindrical lower flange and a fork-shaped upper flange that slides over the lower flange. Both flanges have radial elongated holes distributed along the perimeter allowing the C1 fasteners to pull the two flanges together. The fastener assembly of the C1 Wedge Connection uses a small, horizontally placed bolt to pull two wedges together. The wedges transform and magnify the horizontal bolt force into a larger preload between the flanges by pulling them together. The orientation of the bolt in the fastener prevents significant load fluctuations under external loading. As a result, unlike a bolted L-flange, the C1 Wedge Connection is less susceptible to preload loss, thereby eliminating the need for regular maintenance and inspection. The scalability of the C1 Wedge Connection makes it suitable for larger loads. These larger loads are expected with increasing size of wind turbines and when connections are used in more demanding locations such as hurricane and seismic conditions or where connections are subjected to high dynamic loads caused by extreme wave conditions or on floating foundations.

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The new Peljeac Bridge and access road project, which links Mainland Croatia to the Peljeac Peninsula, is the most significant social infrastructure project in Croatia under construction at present. The bridge site lies in the highly active seismic region with ground acceleration ag = 0.34g and a maximum average ten-minute wind speed above 33.7 m/s. As a result, the execution class for the steel structure was judged to be EXC4 based on the recommended matrix in standard EN 1090-2, which defines execution classes according to consequence class, service category, and production category. The correspondingly determined quality level was class B+, which equates to quality class B under ISO 5817 with supplementary requirements for bridge decks from EN 1090-2. This article describes the whole fabrication process in the workshop, the long-distance transportation and the installation on the bridge site. To satisfy such high-quality technical requirements, the heavy steel structures were fabricated using a wide variety of mechanized equipment and automatic welding techniques. This helped to ensure a more efficient fabrication process and more consistent product quality. The length of the large side span segments was designed to suit the capabilities of the floating cranes and transit barges, thereby making on-site installation more efficient. Against the backdrop of the global Covid-19 pandemic, the contractor CRBC overcame seemingly unsurmountable obstacles beyond their control to successfully complete this challenging assignment in two years.

As part of the ongoing revision of the Eurocodes, design provisions in EN 1999-1-1 on the buckling of longitudinally welded aluminium compression members have been subjected to a critical review. The numerical investigations described in part 1 of the paper were conducted because a need for improvement was identified. In part 2 of the paper, the main observations are presented in qualitative terms. Those observations are: the influence of the allocation of the materials to buckling classes, the influence of the imperfections plus the cross-section geometry including the position and size of the HAZ within the cross-section. Part 3 will conclude this paper by discussing the proposed design approaches in detail.

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Nominated for Eurosteel 2021 Best Paper Award
The paper addresses the instability of large angle columns in high-strength steel subjected to compression loads. It presents a number of compression tests on such columns with different eccentricities and slenderness and the resulting different buckling failure modes observed. The experimental campaign is intended to widen our understanding of the behaviour of high-strength steel columns with large angle sections in compression and bending and so to complement previous experimental studies. The tests were accompanied by numerical analyses and calculations of the load carrying capacities based on current Eurocode 3 design recommendations. The numerical simulations were conducted using the FEM software FINELG, which takes into account the influence of geometrical and material non-linearities. The numerical and analytical results are compared with the corresponding experimental ones. The experimental campaign and the numerical simulations were conducted as part of the ANGELHY project funded by the European Commission's Research Fund for Coal and Steel (RFCS).

Nominated for the Eurosteel 2021 Best Paper Award
This short report has been prepared in the context of the Eurosteel 2021 Best Paper Award. It summarizes developments completed and in progress at the University of Liège designed to characterize the complete shear behaviour of the panel zone in steel beam-to-column joints in terms of stiffness, resistance and ductility. This work is part of a larger research project which aims to predict the complete rotational response of the joint to failure.

Welding is by far the most widely used metal joining method. High-Frequency Mechanical Impact (HFMI) treatment and Tungsten Inert Gas (TIG) remelting are two post-weld treatment methods that aim to enhance the strength of the steel. In this paper, the improvement in residual stress and material characteristic obtained with these methods are studied by conducting several experimental investigations such as hole drilling, hardness testing and microscopy. Hole drilling shows that HFMI treatment improves the status of residual stress at the weld toe in the first 1 mm from the surface. Furthermore, Vickers testing shows a remarkable improvement in the hardness values at the weld toe in the first 2 mm. This can be attributed to the reduction in grain size after treatment. Moreover, acicular ferrite and tempered bainite are found to be the main constituents in the fusion and heat-affected zones after TIG-remelting.

Double-I sections are widely used as columns in moment-resisting frames. The conventional welded moment connection between I-beam and double-I built-up column behaves in a partially restrained manner and does not provide the strength and ductility required in special moment frames. In this paper, a modification method is proposed to improve the behavioural characteristics of conventional moment connections. The modification involves replacing the continuous cover plate with two alternative plates having increased width and thickness at the location of the beam flange-plates. The behaviour of the proposed connection was investigated in detail both experimentally, by means of two full-scale specimens, and analytically, by means of eight finite element models. Based on the results obtained, in beams with a modified connection most of the plasticity develops remote from the column cover plate, and the panel zone remains in an elastic state. Accordingly, the deformation of the modified connection is reduced significantly and its stiffness is increased to the level required for a fully restrained connection. The hysteresis curves of the modified connection are also stable during large inelastic deformations with no substantial pinching. The modified connection provides the strength and ductility required in special moment frames.

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Steel and composite bridges offer economic advantages, even for short and medium spans. To simplify and speed up the design process, ArcelorMittal now offers Advance Bridge Expert, a free preliminary design software that includes complex geometries and innovative solutions. The software is suitable for the pre-dimensioning of curved and/or skewed composite road, railway and pedestrian bridges according to the Eurocodes and several National Annexes. It supports the predesign of steel composite bridges, filler beam bridges and PreCoBeam/composite dowel strips using the hot-rolled section and modern steel grades libraries of ArcelorMittal up to S460, including HISTAR® grades and weathering steel (Arcorox®) according to EN 10025-5:2019.
The free version of Advance Bridge Expert can be downloaded from the following website:
https://sections.arcelormittal.com/design_aid/design_software/EN (© ArcelorMittal)
(Photo: Wirkowice composite bridge in Poland: Europe's first road bridge in Arcorox 460® weathering steel.
© MOSTY ZAMO Tomasz Czy)

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