A 2 stories, 15 m cantilever, called the “Effet Wow” being erected in the 8th floor in Issy-Les-Moulineaux near Paris. An exceptional space is created to accommodate 700 m2 of restaurant and bar amenities on the new Orange's Headquarters (Foto: Bouygues Bâtiment Îles de France. S. paper pp. 264 ff).

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This article presents new equations for the design shear resistance of headed studs in solid concrete slabs and new reduction factors that consider the influence of profiled steel sheeting with ribs transverse to the supporting beam. Comparisons with push-out test results show that the current reduction factor kt in Eurocode 4 does not take sufficiently into account parameters such as geometry or position of the headed stud in the rib. Therefore, the mean shear test results are overestimated by the current equations. When introducing the new approach for the design resistance of headed studs, the main focus is on the description of the basic procedure for the development of the new approach and on the comparison with values in the existing code. Comparisons with push-out test results from a recent European project have shown the good quality of the new approach.

Nominated for the Professor Eduardo de Arantes e Oliveira Award at XII Conference on Steel and Composite
Construction in Coimbra 2019
Orange's new headquarters, Bridge, is under construction in suburban Paris. This is a project designed to centralize the company's services and its 3000 employees, who are currently scattered throughout the city. The architectural concept is unique and comprise complex forms that are highly dependent on the structural design. The building is mostly precast concrete, with several steel structures used to support the most structurally challenging areas. One of these is a two-level roof cantilever. This article examines some of the technical challenges faced by the project team as well as the peculiarities inherent in this composite steel structure.

This article presents Polish experience with the design and construction of net-arch bridges using cold-bent HD sections in the arch. So far, four road bridges have been built, and they are currently in service. The experience gained and the positive economical footprint is leading to a growth in the popularity of this solution, together with much better recognition of the technology on the market. One of the first net-arch bridges using cold-bent HD beams was built in Poland in 2011. The arch has a span of 75 m. The composite deck is constructed from HE sections, which are suspended from the arches. One bridge built recently has a span of 120 m. Several other bridges are at the design or erection phase, in particular, the first railway net-arch bridge with nine independent decks and a maximum span of 116 m. The aim of this paper is to familiarize the reader with the technical solution developed and present the economic background and, specifically, to focus on the fabrication of cold-bent HD-section steel arch structures as a new task in engineering.

This paper addresses the assessment of fatigue details according to EN 1993-1-9, which form the basis of the most important fatigue verification, the nominal stress approach. First of all, a suitable statistical methodology had to be defined for consistent detail classification. A structured database on the MySQL platform serves as a basis for the evaluation of the detail categories. In addition to fatigue test data documented in the background document to EN 1993-1-9, this database also includes new test data provided by the authors. After selecting the most meaningful test data, important details, such as longitudinal welds, were reassessed. In addition, the authors carried out fatigue tests in connection with numerical simulations in order to be able to evaluate the fatigue strength with better accuracy. The results so far show that the details analysed often prove to have a higher fatigue strength than currently documented in EN 1993-1-9.

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Cold-formed steel (CFS) members have been used significantly in light-gauge steel buildings due to their inherent advantages. Optimizing these CFS members in order to gain enhanced loadbearing capacities will result in economical and efficient building solutions. This research presents the investigation and results of the optimization of CFS members for flexural capacity. The optimization procedure was performed using the particle swarm optimization (PSO) method, while the section moment capacity was determined based on the effective width method adopted in EN 1993-1-3 (EC3). Theoretical and manufacturing constraints were incorporated while optimizing the CFS cross-sections. In total, four CFS sections - lipped channel beam (LCB), optimized LCB, folded-flange and super-sigma - were considered in the optimization process, including new sections. The section moment capacities of these sections were also obtained through non-linear finite element (FE) analysis and compared with the EC3-based, optimized section moment capacities. The results show that, compared with a commercially available LCB with the same amount of material, the new CFS sections possess the highest section moment capacity enhancements (up to 65 %). In addition, the performance of these CFS sections when subjected to shear and web-crippling actions was also investigated using non-linear FE analysis.

This study focuses on a study of cold-formed steel wall framing installed with hold-down anchors and subjected to lateral loads. The steel framing wall specimens were assembled with sheathing on one or both sides. Two different thicknesses of calcium silicate board were used as the sheathing material. The wall specimens were tested under both monotonic and cyclic loads. All wall specimens were fixed at both ends with hold-down anchors. In addition to structural strength, the energy absorption, ductility ratio, overstrength factor and response modification factor were studied for all wall specimens. Previous studies in which the specimens were tested without a hold-down anchor are discussed for comparison. The test results show that the ultimate strengths are similar for the specimens with the same configuration tested under either monotonic or cyclic loads. The wall specimen installed with hold-down anchors has a higher ultimate strength but lower ductility ratio compared with the same configuration's wall specimen without hold-down anchor. The response modification factor given in the AISI standard was found to be conservative for the wall framing with sheathing of calcium silicate board tested in the present study.

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The 277 m high Baku Tower in Baku, the capital of Azerbaijan, is the tallest building in the Caucasus ever built. The tower is constantly subjected to enormous wind loads, that gave the city's name it's meaning “city of wind”. To cope with these wind loads a 400 t pendulum damper was installed on the tower's uppermost platform. Its special feature: in case of strong wind and earthquake, the 400 t mass block moves horizontally by up to 1.3 m in all directions in a controlled manner. This pendulum damper reduces the strain on the structure, thus it ensures the building's living and working comfort. The mass block consists of a massive steel box that was filled with concrete on site. MAURER not only manufactured the steel construction but also supervised the entire assembly and put the vibration damper into operation. (© Maurer SE)

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Extended keynote paper of Eurosteel 2021
Automated production is finding its way into the fabrication of structural steel. One robot holds attachments (stiffeners, end plates, etc.) on a steel beam or column and another robot produces weld seams. However, welding robots can also be used for Additive Manufacturing (Wire and Arc Additive Manufacturing, WAAM). The wire electrode serves as a printing material. The Institute of Steel Construction and Materials Mechanics in Darmstadt is investigating how typical connecting elements for steel structures can be printed directly on steel beams using Additive Manufacturing with arc welding and robots. Furthermore, structural elements such as nodes for space frames can be printed and even complete structures, e.g. columns and a little bridge, have already been manufactured additively. The main focus is on determining suitable welding and process parameters. In addition, topology optimization is necessary in order to achieve good structures using a small amount of material. This is possible due to the free design prospects of WAAM, which opens up new design and production strategies.

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Extended keynote paper of Eurosteel 2021
The robustness of steel structures during severe earthquakes is largely based on the calibration of stiffness, strength and ductility. Such a robust system dissipates the energy by plastic deformations in the plastic members (fuses) made from mild carbon steel (MCS), while the other members remain elastic. In the case of concentrically braced frames (CBF), the fuses can be in the form of buckling-restrained braces (BRB), while for eccentrically braced frames (EBF), the short links could take on this role. In the case of shear walls (SW), slender steel plates can be used. To avoid oversized elastic members, they can be made of high-strength steel (HSS). Structures made from HSS and MCS are called dual steel (DS) structures. In order to ease the post-earthquake intervention, the fuses can be detachable. Furthermore, their replacement is less costly if the structure is re-centred using moment-resisting frames (MRF) connected to the main dissipative system, i.e. a dual frame (DF) structure. This paper presents the concept of DS DF structures and some examples.

Extended keynote paper of Eurosteel 2021
This two-part paper provides a state-of-art report on the most recent findings concerning the behaviour, strength and Direct Strength Method (DSM) design of cold-formed steel (CFS) columns and beams affected by mode coupling phenomena not adequately covered by the current specifications for CFS members, namely local-distortional (L-D), local-distortional-global (L-D-G), distortional-global (D-G) and global-global (flexural-torsional/flexural - FT-F) interaction. The paper addresses experimental tests, numerical simulations and DSM-based design approaches that are intended to i) acquire in-depth knowledge on the non-linear behaviour (elastic and elastic-plastic), load-carrying capacity and failure mode nature of the members under consideration, and ii) make use of that knowledge to develop, propose and assess the merit of efficient DSM-based design approaches to estimate their failure loads/moments. Initially, illustrative column results are briefly presented to help grasp some fundamental concepts, namely the characterisation of i) the aforementioned mode coupling phenomena, ii) different sources of mode interaction that may lead to failure load/moment erosion, and iii) the most detrimental initial geometrical imperfections. The DSM design curves currently codified and two strength curves recently developed for column flexural-torsional and beam distortional failures are presented next. The two-part paper then addresses separately each mode coupling phenomenon dealt with, for columns, but only L-D and D-G interaction for beams - while L-D interaction (in columns and beams) appears in Part 1, the remaining column and beam coupling phenomena (all involving global buckling) are dealt with in Part 2 [1]. For columns undergoing L-D and L-D-G interaction, beams experiencing L-D interaction and angle columns susceptible to FT-F interaction, the work reported includes experimental studies, numerical simulations and DSM-based design considerations and/or guidelines. For the remaining coupling phenomena, only numerical results are reported, but they unveil interesting (and unexpected) behavioural features that will help plan future test campaigns and achieve efficient design approaches. Finally, the two-part paper closes with a few concluding remarks and an outlook regarding future developments in this field.

Extended keynote paper of Eurosteel 2021
This is Part 2 of a two-part paper providing a state-of-art report of the most recent findings concerning the behaviour, strength and Direct Strength Method (DSM) design of cold-formed steel (CFS) columns and beams affected by mode coupling phenomena not adequately covered by the current specifications for CFS members. This second paper covers interactions involving global buckling modes, namely local-distortional-global (L-D-G), distortional-global (D-G) and global-global (flexural-torsional/flexural - FT-F) interaction - note that local-global (L-G) interaction, already well mastered by the technical/scientific community, is not dealt with. Like Part 1 [1], this paper also addresses experimental tests, numerical simulations and DSM-based design approaches, intended to i) acquire in-depth knowledge on the non-linear behaviour (elastic and elastic-plastic), load-carrying capacity and failure mode nature of the members under consideration, and ii) make use of the above knowledge to develop, propose and assess the merits of efficient DSM-based design approaches to estimate their failure loads/moments. Taking into account the fundamental concepts and DSM design curves presented in Part 1 [1], the paper addresses separately each mode coupling phenomenon dealt with, for columns, and only D-G interaction for beams - recall that L-D interaction (columns and beams) was covered in Part 1 [1]. For columns undergoing L-D-G interaction and angle columns susceptible to FT-F interaction, the work reported includes experimental studies, numerical simulations and DSM-based design considerations and/or guidelines. For columns and beams experiencing D-G interaction and channel columns prone to FT-F coupling, only numerical results are reported - they reveal surprising behavioural features that will be very useful in planning future test campaigns and achieving efficient design approaches. Finally, the two-part paper closes with a few concluding remarks and a perspective about future developments in this field.

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This two-part article gives an overview of the developments of the structural member verification in prEN 1993-1-1:2020 “Eurocode 3: Design of steel structures - part 1-1: General rules and rules for buildings”, one of the second generation of Eurocodes. These developments were undertaken by Working Group 1 (WG1) of Subcommittee CEN/TC250/SC3 and by Project Team 1 (SC3.PT1) responsible for drafting the new version of EN 1993-1-1. In the past, WG1 collected many topics needing improvement, and the systematic review conducted every five years also yielded topics needing further development. Based on this, the current version of EN 1993-1-1 has been developed into a new draft version prEN 1993-1-1:2020 enhancing “ease of use”. The technical content of this new draft was laid down at the end of 2019. Many improvements to design rules have been established with respect to structural analysis, resistance of cross-sections and stability of members. This two-part article focuses on member stability design rules and deals with the basis for the calibration of partial factors, the introduction of more economic design rules for semi-compact sections, methods for structural analysis in relation to the appropriate member stability design rules, new design rules for lateral torsional buckling plus other developments and innovations. This second part of the article is dedicated to illustrating the most relevant changes to member buckling design rules.

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Many mechanical joints in steel structures use conventional bolts. Nevertheless, this proven joining technology has some significant disadvantages. These basically include the high levels of scatter during application of the assembly preload using the torque-controlled tightening process, the risk of loosening during cyclic loads due to transverse displacement of the components and the low fatigue resistance under axial loading. Lockbolt technology was invented as long ago as the 1930s and mainly used for the aviation and space industry because of its evident advantages. This joining technology has been constantly further developed in response to the most diverse demands from sectors such as aviation, commercial vehicles, rail vehicles, agricultural machinery, defence technology and steel structures. The application of lockbolt technology, which is primarily used in mechanical engineering, was in most cases based on individual studies, since no consistent rules and guidelines were available for the design and execution of lockbolt connections in steel structures. Within the scope of several public research projects funded by the AiF (German Federation of Industrial Research Associations) and conducted by the iGF (Industrial Collective Research) organization as well as through approval investigations, the Fraunhofer Institute for Large Structures in Production Engineering (IGP) has successively developed the necessary design rules according to the EN 1993 standard (Eurocode 3) for use in structural connections. These design rules will be presented within the context of this article in order to make the benefits of this joining technology available to other users. In addition, insights into the use of technical approvals will be presented together with some current applications.

Nominated for the Professor Eduardo de Arantes e Oliveira Award at XII Conference on Steel and Composite Construction in Coimbra 2019
This paper presents the results of a numerical parametric study that investigated the M-V interaction behaviour of box-girder bridge deck specimens. The study made use of an advanced numerical model that was previously verified against the experimental results. Based on the numerical results and the current rules for trapezoidal box girders, new design models are proposed for predicting the bending and shear resistance of cross-sections with a curved bottom flange. Additionally, the force-based M-V interaction equation proposed by Jáger et al. [1], adopted in the new version of EN 1993-1-5 [2], was verified and slightly modified to fit this type of cross-section.