Current design equations given in EN 1993-1-3 for calculating the web-crippling resistance of cross-sections with one web were copied from the AISI's Specification for the design of cold-formed steel structural members, taking into account the different safety concepts: load and resistance factor design (LRFD), with resistance factors&phgr;w applied to nominal values, and limit state design, with partial factors &ggr;M applied to characteristic values as defined in EN 1990. Furthermore, the web-crippling equations of subsequent editions of the AISI specification (then designated AISI S100) were completely revised based on the web-crippling data collected and evaluated by Beshara and Schuster [5].
This paper presents the results of a calibration of a generalized web-crippling equation to be used for cross-sections with one web (i.e. C- and Z-sections). The coefficients of the generalized web-crippling equation were calibrated to comply with the safety concept described in EN 1990, taking into account EN 1990, Annex D, and a partial factor &ggr;M1 = 1.1. This paper therefore provides an introduction to as well as background information on proposed changes and amendments to EN 1993-1-3.

Shear stresses can be transferred via bond at the steel-concrete interface without having to consider any mechanical shear connectors. The research conducted shows that the use of anti-adhesive products, such as grease, reduce the bond at the steel-concrete interface in push-out tests (POTs). However, the effect is still significant, especially for fully encased steel profiles. The results of an experimental POT campaign with nine small-scale cube specimens and two composite column specimens are presented here. Three different surface conditions were examined: a) an untreated surface, b) a surface treated with anti-adhesive agent (formwork release oil) and c) a surface treated with PTFE spray. The resulting ultimate shear stresses were compared with the experimental results available in the literature [1-10]. How the different geometries of the specimens, the concrete age and the surface treatment conditions influence the bond strength are compared and summarized.

Current design codes do not consider distortional buckling failure modes, which can occur in the chord member of a tubular X-joint loaded axially by brace members. In this study the critical load for distortional buckling is established based on the energy method and a beam on elastic foundation (BEF) approach. In the theoretical model the capacity is created by elastic bending of the chord faces in their own planes and elastic bending of the cross-section as a frame structure. The theoretical capacity of an X-joint is compared with numerical results obtained from finite element analyses (FEAs). Some discrepancy was found between theoretical model and numerical analysis, with the theoretical model slightly underestimating the load-carrying capacity. Experimental tests show that an X-joint can be prone to distortional buckling failure mode. However, detailed scrutiny of distortional buckling failure in X-joints is only legitimate for joints made of high-strength steel (HSS), because other failure mechanisms are more critical when conventional steels are used. Nevertheless, designers of X-joints with rectangular hollow section (RHS) members should be aware of this potential failure mode.

In Memoriam of Prof. Dr. Bernt Johansson
The use of high-strength steels (HSS, 460 < fy ≤ 700 MPa) and particularly very high-strength steels (VHSS, fy > 700 MPa) is limited in steel structures in civil and offshore engineering. This is due to a lack of experience in structures made of these materials and a lack of understanding of the structural performance of HSS and VHSS. The main questions that are unanswered concern the topics of static strength, fracture toughness, fatigue, material (in)homogeneity and manufacturing. With regard to the static strength, it is unclear as to whether requirements currently stated in the Eurocodes for the yield-to-tensile strength ratio (fy/fu) as well as the Von Mises yield criterion are applicable to structural designs in HSS and VHSS. With regard to fracture toughness, it is unclear as to whether the crack arrest capability of HSS and VHSS is currently sufficiently covered in Eurocode requirements. Furthermore, Eurocode requirements for maximum plate thickness are quite restrictive if they are extrapolated to HSS and VHSS. Other questions relate to the homogeneity of the material. Are HSS and VHSS sufficiently resistant to lamellar tearing and is material testing in different orientations necessary? This study gives an overview of the relevant questions, outlines the requirements in the current Eurocode system, presents answers to these questions where possible and provides a recommended research focus for the coming years.

In Memoriam of Prof. Dr. Bernt Johansson
It is a general question as to whether the established rules for predicting ultimate resistance under global tension can also be applied to structures made from HSS, i.e. up to fy = 960 MPa. Apart from the welding issue, for the base material, this question refers to several items, e.g. the plastic flow curve, the yield stress level, the yield ratio, the upper-shelf ductility and strainability and the lower-shelf toughness. It reveals that predicting the ductile fracture of steel components can only be an approximation, and neither allows for a deeper understanding of the real ductile crack development up to ultimate load nor leads to a realistic extrapolation if high-strength steels are used. The research work presented in this paper therefore suggests an innovative extension of the FEM analysis by implementing appropriate GTN ductile damage approaches. After a short introduction to the principles of this methodology, possibilities for its use in structural steel research and design as well as further insights into the structural behaviour of steel components, especially HSS up to S960, are presented - insights that are not possible by traditional testing or simulation.

In Memoriam of Prof. Dr. Bernt Johansson
The influence of the cooling time t8/5 has been examined as part of the ongoing AiF-FOSTA P1020 research project for the development of a new design approach for welded joints on high-strength steels. Four thermomechanically rolled and quenched steel grades were investigated. The temperature-time course of a MAG welding process was thermo-physically simulated in a quenching and deformation dilatometer to evaluate the material behaviour. Subsequently, the influence of the cooling time on the mechanical properties of welds was examined using a flat tensile test specimen with a centric hole. The results of the examinations form the scientific basis for a significant improvement of the current execution rules for welded joints between high-strength steels taking into account mismatching of base material and filler metal.

In Memoriam of Prof. Dr. Bernt Johansson
In addition to the common mild steels, nowadays, high-performance steels with good weldability and high ductility are available for the construction industry. By using steels with higher resistance and better weight of material ratios, savings can be achieved, especially in the case of heavy structures such as bridges, long-span roofs and high-rise buildings. However, for the particular situation of joining high-strength steel (HSS) by fillet welds, in many cases the rules in the design codes such as EN 1993-1-8 [1] are inadequate because recent rules and safety margins have traditionally been developed for standard steels and then transferred to high-strength steels.

In Memoriam of Prof. Dr. Bernt Johansson
Representative steel design standards have limited the use of high-strength steels to tubular joints, partly because of concerns about their unique material characteristics. However, the mechanical background behind the limitations is unclear, and its validity needs to be re-evaluated. In this study, a set of CHS (circular hollow section) X-joints fabricated from cold-formed tubes was tested under static axial compression. Then, as supplemental work, extensive test-validated numerical analyses were carried out to investigate further the behaviour of high-strength steel CHS X-joints. In both the testing and the analyses, where three steel grades covering ordinary to very high-strength steels were considered, the high-strength steel joints showed satisfactory structural performance comparable with that of ordinary steel joints in terms of strength and ductility.

In Memoriam of Prof. Dr. Bernt Johansson
Owing to the advantages in economy, environmental protection and energy efficiency, high-strength steel (HSS) has represented an important trend in the development of steel structures and has been adopted in numerous building and bridge structures. This article summarizes engineering applications for HSS structures and comprehensively reviews the recent research advances in HSS structures at Tsinghua University. Investigations were conducted into the behaviour and performance of HSS materials, sections, members, connections and structural systems. Based on the research results, the mechanical behaviour of HSS structures could be improved compared with ordinary strength steel structures. In order to update the current design codes so that they are applicable for HSS structures, a new specification in China, the “Standard for Design of High-Strength Steel Structures”, is undergoing codification, with Tsinghua University as the chief editorial institute. The outline of the specification, as well as the new design methods included in it, is introduced in this paper.

In Memoriam of Prof. Dr. Bernt Johansson
European standard EN 1993 does not permit the design of joints made from steel with a yield stress > 460 MPa using the principles of semi-continuous/partially restrained construction, and will remain forbidden in its current revision within the scope of the CEN/2014-02 programme for the evolution of the structural Eurocodes. The findings of a comprehensive research programme on the non-linear behaviour of moment-resisting joints with components made from high-strength steel grades (yield stresses of 690 and 960 MPa) carried out at Delft University of Technology are summarized in this paper and used to reappraise these restrictions.

In Memoriam of Prof. Dr. Bernt Johansson
The current design codes for steel reinforced concrete (SRC) columns are, in general, only applicable to normal-strength materials. In Eurocode 4, concrete grades C20/25 to C50/60 and steel grades S235 to S460 are allowed to be used in composite columns, whereas it is possible to use higher-strength concrete (up to C90/105) in Eurocode 2 and S690 steel in Eurocode 3. In this paper, an analytical method is proposed to predict the ultimate strength of SRC columns, taking into account the effect of strain compatibility and lateral confinement. A finite element model is developed to analyse the behaviour of SRC columns under axial loading using ABAQUS. The parametric studies are conducted by varying the diameter, spacing and volumetric ratio of the lateral reinforcement and the column length. It was found that the full plastic method given in EC4 overestimated the strength of SRC columns with high-strength steel. Nevertheless, the proposed method can predict the strength of SRC columns with concrete strengths up to 90 N/mm2 and steel strengths up to 690 N/mm2.

Bridges are of vital importance for the European infrastructure network. Due to their significance in the political economy, the requirement for sustainable, meaning highly advanced, cost-effective, environmentally friendly and long-lived structures is outstanding. Therefore steel composite road bridges were analysed in the Sustainable Steel-Composite Bridges in Built Environment RFCS project (SBRI) by means of a holistic approach combining Lifecycle Assessment, Lifecycle Costs and Lifecycle Performance analyses to promote steel in the bridge construction. The partners of the project were the Institute of Structural Design Universität Stuttgart, Universidade Coimbra, Institut français des sciences et technologies des transports, de l'aménagement et des réseaux, BRISA Engenharia e Gestão SA and ArcelorMittal.
The paper presents a holistic approach to steel and concrete composite bridges by combining analyses of their environmental, economic and functional qualities. The idea of sustainable design is implemented by the project SBRI+ to increase the acceptance of this new way of sustainable thinking, especially among bridge owners and planners. The project includes the SBRI tool which provides designers and authorities with a tool for the evaluation and comparison of the sustainability of different bridge types in the early stages of design, implementing a holistic lifecycle analysis methodology. This helps to select the best option by considering the pros and cons of each alternative in the entire lifespan of the bridge (i.e. construction, operation and end-of-life stages) as opposed to the simple comparison of initial construction costs.

The era of globalization enables the design, fabrication and erection of steel structures to take place in different locations far away from each other. Therefore, a widely acceptable steel design standard is required, and designers should be familiar with alternative specifications that may be considerably different from one another. This study deals with single-span unbraced steel portal frames and makes a comparison between the design methodologies adopted by the Australian and American design provisions, in particular, the effective length method (ELM) and direct analysis method (DAM). A brief discussion on the main features of both standards is also presented. Furthermore, the results of the parametric study are portrayed, highlighting the differences between these two design standards regarding stress interaction. Finally, of the two aforementioned methods, the most applicable optimization method for the design and development of cost-effective industrial portal frame buildings is proposed with respect to the structure geometry.

In many European countries, both road and railway infrastructure needs intensive investment to keep up with the growing demands of mobility [1] and goods traffic. Steel or steel-concrete composite bridges offer viable and very sustainable solutions in this context [2]. Owing to its unlimited recyclability, steel can generally be regarded as the ideal material for such sustainable structures. In particular, when designers or fabricators exploit the possibilities of the steel industry available nowadays, very cost-efficient and remarkable structures are feasible. This paper will highlight some of the newest developments in heavy plates for bridge-building. For example, the so-called thick-plate trough bridges have proved to be a favourable concept for small-span railway bridges [3]. Very heavy plates with single plate weights of up to 42 t allow these bridges to be built very efficiently from just one or very few single plates. Another interesting development is the so-called longitudinally profiled plate, which allows the plate thickness to be varied along the actual loading profile. Finally, the benefits of high-thickness thermomechanically rolled plates (TM steel) will be discussed; these offer an ideal solution as the use of higher-strength steels in bridge-building gains more and more ground.

Growing problems in terms of damage to bridges correlated with - in some cases huge - long-term impacts on road traffic have shown how essential it is to ensure the durability of the infrastructure and thus the mobility of people as well as the exchange of goods. Corrosion damage can be sustainably avoided in future by employing alternative protection systems for steel and composite bridges. Both hot-dip galvanizing with a coating thickness of at least 200 &mgr;m and weathering steel offer crucial advantages over traditional coating systems when considering the whole life cycle of a bridge: They require no maintenance, and so traffic disruption can be avoided. When using these systems in combination with hot-rolled sections, there are further significant advantages as they render composite bridges more economical and durable, particularly when it comes to short and medium spans. Standard higher strengths with steel grade S460 allow for more economical cross-sections, with weight- and cost-savings of often 20-30 % compared with welded built-up sections in grade S355. Sophisticated designs employing rolled sections can achieve not only small and medium spans, but also longer ones, e.g. arch bridges with spans > 100 m. This article describes new trends in Europe using hot-rolled sections in steel and composite bridges.

Portal frames and portal truss structures are two of the most cost-effective and sustainable structural forms for the design and construction of long-span industrial buildings. Although the use of both structure types as steel-clad structures is widely accepted, due to frame complexity and variation of frame types for use in single-storey buildings with spans > 30 m, literature providing a comprehensive investigation of the concepts of portal trusses and portal frames is scarce. This study compares the behaviour of a portal truss configuration with pitched portal frames for use in industrial buildings with spans > 30 m, focusing on weight, costs and construction time. Furthermore, this study entails a numerical investigation that utilizes the SAP2000 computer program to model and structurally optimize the member properties for both portal frame and portal truss configurations. Based on the results obtained from the investigation, it has become apparent that, due to the smaller sections used, the portal truss configurations are lighter and cheaper to fabricate and construct in comparison to the pitched portal frames, which, however, require a shorter construction time.

All over the world the amusement ride industry is growing steady and all manufactures deliver their products all over the world. This requires a harmonized philosophy of the standards. Today most of the rides are designed to the American Standards of ASTM (F2291-2017) or the European Standard EN 13814. The new revision of EN 13814 passed the formal vote of European members in April 2018. Both committees work close together and the new EN 13814 is in the most important parts harmonized with ASTM F2291.
This article covers the ongoing discussion of passenger weights, wind loads and partial safety factors. Portable rides especially, set up at various locations; need a clear guideline for the design for in-service and out-of-service winds. The study gives proposal wind assumptions, but is necessary to draft guidelines defining when the operator should stop the ride. In mountainous and coastal areas especially, the wind may build up faster than in urban agglomerations, and the ride must be stopped earlier.
Use of the fatigue calculation along with the Eurocode and ASTM philosophy with FKM is already common practice and is now defined as an applicable design basis in both standards.

Dedicated to our speaker, Prof. Werner Sobek, in honour of his 65th birthday
In 2017, the University of Stuttgart started a Collaborative Research Centre with the title Adaptive Skins and Structures for the Built Environment of Tomorrow. The goal of this research project is to find an answer to today's most urgent social and ecological questions as the global population continuously increases and the available resources remain limited. As the central approach to the solution of this problem, adaptive elements will be included in the structure, the interior and the façade of an experimental 37 m tall building. This paper introduces the topic of adaptivity in building structures and provides an overview of the research topics applied in this globally unique adaptive high-rise building. Due to the complexity of research topics of this Collaborative Research Centre, this paper only covers the research concerning the experimental high-rise building.

Dedicated to Prof. Werner Sobek on the occasion of his 65th birthday
In 1864, James Clerk Maxwell wrote the remarkable paper “On Reciprocal Figures and Diagrams of Forces.” Maxwell observed that for a frame (what today would be called a truss or a net) to be in equilibrium, it must be the projection of a plane-faced polyhedron. It is now known that this observation is correct, provided the bars of the truss or net and the lines of the external applied forces can be represented by a planar graph. We also know that the plane-faced polyhedron is the Airy stress function.
This information can greatly assist a structural designer in creating, adjusting, and analysing structural nets. These nets can be planar structures or the planar projections of three dimensional nets (including spider webs). Simple visual techniques can be used to evaluate how many independent states of self-stress exist and how to adjust the design to achieve goals such as targeted geometries, redundancies or forces. Combined with force-density form finding, this process creates a powerful design tool. This paper will review the theoretical background and applications of the design process.

Dedicated to Prof. Werner Sobek on the occasion of his 65th birthday
On 16 May 2018, Prof. Werner Sobek turned 65. A few months earlier, the group of companies he founded, with more than 300 employees worldwide, celebrated its 25th anniversary. We would like to use Werner Sobek's birthday as an opportunity to reflect on some of the steel structures inspired by him. Out of the many projects that would have been eligible, the authors have focused on those that seem of primary importance or have not been written about yet.

Dedicated to Prof. Werner Sobek on the occasion of his 65th birthday

Dedicated to Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Werner Sobek on his 65th birthday.

Dedicated to Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Werner Sobek on the occasion of his 65th birthday

This paper deals with revised, simplified, consistent equations for plate-to-Circular Hollow Section (CHS) joints for inclusion in codes. After a short review of the background to these resistance equations in the current consolidated version of EN 1993-1-8 and those in ISO 14346, the background to these simplified new equations is discussed. The equations for Plate-to-Circular Hollow Section T and X joints (called TP and XP joints respectively) in the current EN 1993-1-8 are based on experimental data available up to 1991. They are further related to the equations for CHS T and X joints. Most of the data used are based on the ultimate joint resistance. A similar approach is used for the TP and XP equations in ISO 14346, but these are related to the updated equations for CHS T and X joints.
Since the drafting of ISO 14346, new consistent numerical data from Voth became available where the resistance is not only based on the ultimate resistance but also takes the 3 %d0 joint deformation limit into account.
The new equations in prEN 1993-1-8 are based on the Voth data, the de Winkel data and the Voth-Packer equations, but use a simplified uniform presentation which permits one to relate joints with an I, H and RHS brace-to-CHS chord to these basic equations. Furthermore, the presented equations are based on the case of axial compression load in the plate, which is the lower bound of the compression and tension load cases.

The authors have studied the buckling-restrained brace providing a stable hysteretic characteristic even under high-strain conditions. The structural performance of the buckling-restrained brace is represented by the evaluation formula that is the lower limit of the cumulative plastic strain energy ratio. However, as earthquakes are becoming much longer, so it is necessary to research and develop a new buckling-restrained brace with a higher energy dissipation capacity. In this paper, our past studies are reviewed and the conditions of high-performance of buckling-restrained braces extracted. The buckling-restrained brace considered was tested. As a result, a buckling-restrained brace with a larger cumulative plastic strain energy ratio is proposed.