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. Numerical investigations were conducted because a need for improvement was identified. This part 1 of the paper describes the individual steps of the revision and the modifications discussed, which include the introduction of longitudinally welded members. Before going into the numerical investigations in more detail, previous observations are presented regarding buckling classes and plateau lengths. In part 1 of the paper, explanations of the numerical investigations are limited to presenting the modelling of the geometry, the mechanical properties and the imperfections as well as their respective variation in the context of the parametric studies. The results of the numerical investigations and the proposed design approaches will be presented in detail in parts 2 and 3.

This paper investigates the effects of stiffeners on the compressive and flexural capacities of cold-formed steel channel members. Stiffeners are added on the web of the channel section to form a new section called SupaCee. This new section is shown to be more innovative and stable than the traditional channel section. The structural advantages of this new section are investigated by comparing the capacities of SupaCee and channel members under compression and bending. The capacities are determined by using the direct strength method (DSM) according to AS/NZS 4600:2018 with the support of THIN-WALL-2, a buckling analysis program. It was found that the stiffeners are effective for small section dimensions and thicknesses, but become ineffective for large section dimensions.

This paper describes an investigation into the cross-sectional behaviour of elliptical hollow section (EHS) columns made from ferritic and duplex stainless steel. The EHS is a relatively new structural shape with a number of favourable attributes including aesthetic appeal, high strength-to-weight ratio, good torsional resistance and excellent flexural strength. In recent years there have been significant developments in the analysis and understanding of these shapes, although most studies have focused on carbon steel EHS. The work so far is taken a step further here by considering some of the newer grades of stainless steel that are used in structural applications. A numerical model is developed and validated against test data from the literature and is then employed to generate structural performance data. Subsequently, parametric studies are performed to investigate the influence of individual parameters such as the material properties, aspect ratio and local slenderness of cross-sectional elements. The accuracy of existing design procedures is assessed by comparing the numerical data with the resistances obtained using Eurocode 3. It is shown that the cross-sectional slenderness limits given in Eurocode 3 for EHS members made from carbon steel can also be safely used for sections made from ferritic and duplex stainless steel.

In the AiF-FOSTA research project P1020 [1], a new design model for welded joints was developed. In this context, a small scale test on flat tensile specimens was designed, with the help of which various influences on the strength and ductility of the welds were investigated. Furthermore, extensive tests were carried out on overlap joints, cruciform joints with double fillet welds as well as partially and fully penetrated butt joints. This was done to calibrate the weld construction factor &agr;w, which takes into account the influence of the type of joint on the load-bearing capacity. In the following article, after a short summary of the current state of research, the design model, and the results from the parameter studies on flat tensile tests are described in more detail in [2-4]. Subsequently, the test program on welded joints and the calibration of the weld construction factor &agr;w are presented. Finally, the results of the design model and the tests carried out are compared with test results from other research projects and the design model of prEN 1993-1-8 [5].

Resilience has many components, but two are of importance when structural systems are envisaged, i.e. the capacity to resist the hazard, or robustness, and the ability to recover from the hazard. So, the structure may sustain structural damage, but collapse should be avoided. Moreover, the damages are repairable, such that the initial functionality is recovered.
In terms of structural mechanics, a robust structure is associated with a good balance between stiffness, strength, and plastic deformation capacity. As a result, it is expected that alternative routes are available for redistributing the loads and prevent the progressive collapse in case of a local damage. The seismic design codes in force today aim at these objectives by applying the capacity design method and using relevant admissibility criteria. However, there are exceptional situations when the earthquakes are more powerful than expected, and even the structures correctly designed can be at risk. The situation can be worsened by cascading hazards, like fire or explosion. When safety margins are exceeded, partial or global collapse can be initiated. The reliability demands of building structures at high seismic risk need to be considered to increase the resilience. One such approach is based on the so-called Dual Steel-Dual Frame concept, which combines steel grades and structural systems to increase the capacity of response and reduce the consequences of extreme hazards.

In this study, an experimental program on welded hollow section joints fabricated from high-strength steel is presented. The experimental program tested a total of six T or Y cold-formed circular hollow section (CHS) joints under brace axial compression. One mild steel with a nominal yield stress of 355 MPa and two high-strength steels with nominal yield stresses of 460 and 650 MPa were included. The test results and existing test database were used to evaluate the relevant design provisions for high-strength steel joints. The material factor - used in the current standards to reduce the design resistance of high-strength steel tubular joints - was found to be adequate for CHS T/Y-joints with steel grades up to 700 MPa. The chord stress effect resulting from a particular test setup needs to be considered when evaluating the experimental joint strength. The experimental load-indentation relationships were analysed to appraise the behaviour of high-strength steel CHS T/Y-joints from the perspectives of ductility and serviceability. The ductility of high-strength steel T/Y-joints is slightly lower than that of mild steel joints. T/Y-joints show relatively lower ductility and serviceability performance compared to CHS X-joint counterparts that comprise identical members. Local strain distributions in tested T/Y-joints of different steel grades were analysed to identify the location and intensity of strain concentration. The possibility of fracture failure near the weld seam of the cold-formed chord member is discussed.

Many steel rope systems are subjected to fluctuating tensile loads and therefore can fail due to fatigue. Available fatigue test data indicate that rope diameter, mean stress, socket type, lay angle and rope length influence the fatigue resistance. Most of the tests were terminated before full failure of the ropes. This paper shows that the test termination criterion, such as fracture of the first wire, fracture of 5 % of the wires or full rope fracture, has a large influence on the resulting fatigue resistance. A probabilistic analysis is carried out for a rope system in a bridge, demonstrating that the required structural reliability levels are met when considering full failure as the end-of-life criterion for ropes.

Many steel rope systems are subjected to fluctuating tensile loads and therefore can fail due to fatigue. There are indications that the fatigue resistance of full-locked coil ropes is somewhat lower than that of other types of rope. Fatigue test data on full-locked coil ropes have been collected, but they terminate at different conditions. A semi-empirical model is employed to extrapolate the test results to full failure of the rope. The resulting S-N curve is being adopted for the revision of European standard prEN 1993-1-11.

This article provides an overview of the various support structures for offshore wind turbines and addresses the challenges that arise for the different design variants. First of all, the existing types of support structures are explained and their benefits and shortcomings discussed. Following that, the focus is on material fatigue and its analysis, which is of great importance due to the cyclic loading on the structures. A central topic of this article is the experimental evaluation of fatigue strength using large-scale test setups and state-of-the-art measurement methods. Critical and complex design details such as welds for extremely thick plates, tubular joints, grouted connections, large HV bolts and ring flanges are investigated to improve methods of analysis. Further, the new series of German standards (DIN 18088) for support structures for wind energy turbines and platforms is addressed. Finally, these topics are summarized and the importance of offshore wind energy for the transition to cleaner energy is emphasized.

The research into an innovative steel-concrete-steel composite (SCSC) plate presented here is being carried out in the Steel Structures Research Unit of the Institute of Structural Engineering at TU Wien. The aim of the research is to use the SCSC plate for single-track, short-span railway bridges in Austria. The SCSC plate is designed to be a loadbearing structure in the transverse direction, transferring the loads to the main steel girders of the bridge cross-section. An engineering model will be presented in this paper to reproduce the results of the ABAQUS finite element analysis software [1]. Using this simple framework model, which includes springs, it is possible to consider cyclic loading and inelastic slip, too. This results in an increase in the global vertical displacements and a change to the internal forces, which are discussed in the paper.

Different post-weld treatment methods have been developed to enhance the fatigue strength of welded steel structures and extend the service lives of their components. High-frequency mechanical impact (HFMI) treatment and tungsten inert gas (TIG) remelting are two methods that have attracted considerable interest in recent decades. This paper presents the results of a study of fatigue life extension for pre-fatigued welded steel details which can be achieved using HFMI treatment and TIG remelting. More than 250 fatigue test results were collected - including different details such as butt welds, longitudinal attachments, transverse attachments and cover plate attachments. HFMI treatment was found to extend the life considerably when the specimens treated were free from cracks or when existing cracks were < 2.25 mm deep. TIG remelting could extend fatigue lives even with cracks > 4 mm deep. In comparison to TIG remelting, HFMI treatment results in a longer fatigue life extension for pre-fatigued details, provided existing cracks are < 2.25 mm deep. Regarding TIG remelting, the depth of possible remaining cracks was found to be a substantial parameter when assessing the degree of life extension.

This study presents a numerical investigation into the cyclic performance of skewed special moment frame (SMF) connections that include composite concrete slabs. The study uses advanced finite element simulations to investigate the behaviour of shallow (W14×), medium (W24×) and deep (W33×) steel column sections with three levels of beam skew (10, 20 and 30 degrees) for both bare-steel and composite (steel-concrete) construction. To account for complex torsional boundary conditions that may affect the skewed connection response, prequalification-type analyses were conducted considering the middle storey of a three-storey, two-way moment frame configuration. In the analyses, all skewed configurations achieved at least 0.04 rad of connection rotation during the cyclic loading protocol prior to a 20 % reduction in moment capacity. When a composite concrete slab was added, column twisting and column flange yielding increased at large skew angles (30 degrees) during positive moment cycles.

This article presents a comprehensive review of the state of the art in composite cold-formed steel flooring research over the past couple of years. The most relevant and significant literature references were reviewed to provide some insights into trends and developments in composite cold-formed steel floors. Advantages of this type of composite flooring system are also highlighted. A broad description of mainly two types of composite floor - mainly consisting of cold-formed steel and concrete, and cold-formed steel and timber-based floorboards - are outlined in this study. The experimental and numerical investigations that have been carried out worldwide are likewise discussed in the paper. The most important aspects covered are shear connection behaviour and the flexural and dynamic behaviour of the floors. There is also a brief description of fire testing.

This paper investigates the design of steel-concrete composite beams, with an emphasis on the shear connectors as specified in Eurocode 4-1. A structural safety inaccuracy is identified and analysed. Improvements for the future design code are proposed.

Extended keynote paper of Eurosteel 2021
This paper provides an overview of recent work regarding the revision of Eurocode 3 on the European level. Selected scientific and technical issues are described and there is a summary of the activities executed within European Standardization Committee CEN/TC250/SC3 “Design of Steel Structures” chaired by Prof. Dr.-Ing. Ulrike Kuhlmann. This includes the description of current normative developments for the 2nd Generation of Eurocodes, which aim at evolution through improvements and harmonization of the existing codes. In addition, a technical review of selected rules is given for several issues, which support the code revision and reflect well the recent tendencies in steel structures.

This paper presents the analytical results of six steel bolted T-connection models and four steel bolted beam-to-column connection models with top and seat angles. This study was undertaken to analyse the influence of bolted T-connections instead of welded connections and the influence of angles with and without stiffeners on the behaviour of the beam-to-column connections under hysteretic loading. The aim was to compare the energy dissipation of different connections with each other. The energy dissipation characteristics are obtained from the main characteristics of moment-rotation hysteresis curves. This study shows that the energy dissipation decreased by about 2-29 % and 2-13 % for bolted T-connection and top-and-seat-angle connection models respectively after switching from one cycle to another in five hysteretic loadings.

Steel plate shear walls (SPSW) are being increasingly used in steel or concrete structures as lateral load-resisting systems. Shear buckling is one of the major shortcomings of the SPSW and so to address this issue, buckling-restrained steel plate shear walls (BRSPSW) have started to appear. Owing to the novel concept of this structural system, this paper aims to investigate the effect of factors influencing the response of BRSPSWs. For this purpose, a parametric study was conducted using ABAQUS software. Based on the results acquired from the hysteretic curves, an increase in the concrete compressive strength does not markedly affect the ductility and energy dissipation capacity. Moreover, it was observed that as the width of the gap between concrete panel and steel plate grows, the energy dissipation and response modification factor are reduced. Besides, the results indicate that as steel strength increases, so energy dissipation increases from 0.7 to 11.7 %. Accordingly, based on a comparison between the rate of improvement in shear capacity arising from an increase in the strength of the concrete panels, frame and steel plate, it is concluded that it would be much more rational to increase the concrete strength so that a high shear capacity can be achieved for the BRSPSW. Lastly, in all models, as the gap width increases from 0 to 20 mm and 20 to 35 mm, ductility decreases by 41 and 30 % respectively.

This paper describes how a wavelet model comprised of a linear combination of sine terms is capable of representing the cross-section inertia variation along the length of cellular beams. This allows the efficient computation of deflections of cellular beams when these are deployed as a part of steel-concrete composite flooring systems. This method does not involve purely statistical approaches or piece-wise integration of moment-curvature relationships that lead to cumbersome matrix approaches and complicate the assessment of deflections. Despite its simplicity, the proposed approach is found to be reliable as it successfully predicts displacements obtained through finite element model representations of more than 260 cases with errors smaller than ±5 %. Furthermore, the proposed analytical description of cross-section inertia along the beam length is defined by only three parameters that can be inferred through linear expressions considering the geometrical characteristics of a perforated beam, namely, the ratio of flange to web thickness, the second moment of inertia of the steel beam and the ratio between beam length and depth, making it easy for widespread application by practitioners.

The Committee on the Design, Construction and Production of Aesthetic Architecture, established by the Japanese Society of Steel Construction (JSSC), has for a long time stood for the promotion of appealing architecture - particularly in steel-glass structures. Such aesthetic architecture, despite being very modern, often expresses the tradition of the particular location and its culture. The choice of structural configuration is one of the tools for achieving relevant architecture. This paper, introducing attractive and innovative steel structures combined with glass, shows several examples typical of this trend in Japan.

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.

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.