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.

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PhD thesis: Load-bearing capacity of sandwich panels under bending and transverse compression
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Torre Diamante in the heart of Milano is with 130 m the tallest steel building in Italy. The use of high strength steel sections enables a low total weight, advantageous costs, less transport, slender columns and a preferred raft foundation. With long span composite floor beams flexible column-free offices and integrated building services can be realised. For the LEED certification the recycling-material steel played a major role. (Foto: Bernhard Hauke)

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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.

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3rd Annual conference on Steel and Structural Engineering
CASP2019 - Corrosion and Surface Protection for Steel
Congress on Numerical Methods in Engineering
SEMEC 2019 - Seventh International Conference on Structural Engineering, Mechanics and Computation
The international Colloquium on Stability and Ductility of Steel Structures SDSS2019
17th International Probabilistic Workshop
Nordic Steel Construction Conference 2019
Green Engineering for Infrastructure and Safety against Hazards. 7th International Conference of Euro Asia Civil Engineering Forum

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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.

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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.