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Publication Type: search.filters.UBSTyp.ZeitschriftenartikelAuthor: search.filters.author.Pourostad, Vahid

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    Update on the revision of Eurocode 3 : evolution by improvement and harmonization
    (2021) Kuhlmann, Ulrike; Schmidt‐Rasche, Christina; Jörg, Fabian; Pourostad, Vahid; Spiegler, Jennifer; Euler, Mathias
    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.
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    Buckling resistance of longitudinally stiffened panels with closed stiffeners under direct longitudinal stresses
    (2022) Pourostad, Vahid; Kuhlmann, Ulrike
    The buckling behaviour of panels may be determined according to EN 1993‐1‐5 [1]. Most of the design rules relating to stiffened panels in EN 1993‐1‐5 were derived on the basis of open‐section stiffeners. Several recent investigations have shown that the application of the design rules according to EN 1993‐1‐5 considering the torsional stiffness of the stiffeners may overestimate the resistance of the panels. Therefore, the recent Amendment A2 to EN 1993‐1‐5 states that the torsional stiffness of stiffeners should generally be neglected in determining critical plate buckling stresses. In addition, prEN 1993‐1‐5 [2] provides rules for considering the torsional stiffness of stiffeners. However, in this article it is shown that even the rules of prEN 1993‐1‐5 are not sufficient to overcome the safety deficiencies. The article focuses on the investigation of the buckling behaviour of stiffened panels with closed‐section stiffeners subjected to constant longitudinal compression stresses. Improved rules have been developed that allow to consider the torsional stiffness of the stiffeners. Based on an extensive numerical parametric study, a new interpolation equation between column‐ and plate‐like behaviour is proposed. In comparison to [3], the investigations have been extended to the effective width method. They show that the proposal provides a safe and economic solution for the reduced stress method and the effective width method when considering the torsional stiffness of stiffeners by calculating the critical plate buckling stresses.
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    Buckling resistance of stiffened panels subjected to constant transverse compression stresses
    (2023) Pourostad, Vahid; Kuhlmann, Ulrike
    In a box girder cross-section with inclined web panel, transverse compression may be introduced into the bottom panel from both sides in addition to constant longitudinal compressive stresses. In EN 1993-1-5, the only analytical method for determining the resistance of panels to biaxial compression is the Reduced Stress Method (RSM). However, the current rules were mainly derived for longitudinal stresses. Due to missing rules, in practice the longitudinal stiffeners need being verified according to flexural member buckling considering the transverse updrift forces. Therefore, in order to assess the real behaviour, a large parametric study of stiffened panels with closed longitudinal stiffeners under transverse compressive stresses was carried out using a verified numerical model. LBA and GMNIA are performed for each case. To apply the RSM, all critical buckling stresses were determined considering the torsional stiffness of stiffeners. According to EN 1993-1-5, the support of the edges of the panels parallel to the load direction should be set free when determining the critical stress for column-like behaviour. In the case of a longitudinally stiffened panel under transverse stresses, it is not clear whether the support of the plate and the stiffeners or only the plate should be released. In this paper, these interpretations are discussed and results are compared. Finally, a simplified procedure to determine the global reduction factor of plate buckling for transverse stresses in a single step is proposed.
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    Steel and composite bridges : enabling sustainable solutions
    (2024) Kuhlmann, Ulrike; Arnim, Mareike von; Gölz, Lisa‐Marie; Hofmann, Gloria; Knecht, Wigand; Mönch, Simon; Pourostad, Vahid; Stempniewski, Lena
    Sustainable bridges are characterised by three main aspects: saving resources by an efficient construction, allowing for a lifelong use of bridges by optimal detailing in view of fatigue and flexible design concepts for strengthening and adapting to changed user requirements. After a short introduction in the assessment of sustainability for bridges, an overview on recent bridge research in view of sustainability is given. The key point of efficient construction in future is the use of high strength steel (HSS): basic research and adaptation of rules are needed for welding of matching and mismatching connections. Joints and their relevant failure modes are to be investigated before hollow sections of HSS can be used in a wider range. And for steel and composite bridges, optimised plate buckling rules may serve for more efficiency in construction. Bridges are designed for a service life of 100 years. This can easily be achieved and even exceeded if the detailing is realised in view of fatigue. Research on welded details such as butt welds or joints of tubular bracings will be presented. Welds can be improved by post‐weld treatment such as high‐frequency mechanical impact (HFMI) treatment. Fatigue is also a key issue when steel and concrete or timber and concrete are combined for composite bridges. Reinforced composite slabs without prestressing require a fatigue verification for the transverse shear also in areas with cracked concrete. The notch forms an efficient connection in timber‐concrete composite (TCC) bridges, where, however, little has been known up to now on the fatigue behaviour.