02 Fakultät Bau- und Umweltingenieurwissenschaften

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3

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Publication Type: search.filters.UBSTyp.ZeitschriftenartikelAuthor: search.filters.author.Kuhlmann, Ulrike

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    Guidelines for a finite element based design of timber structures and their exemplary application on modelling of beech LVL
    (2023) Töpler, Janusch; Buchholz, Lea; Lukas, Julian; Kuhlmann, Ulrike
    Design verifications of buildings are usually carried out supported by a finite element analysis (FEA), for which, however, there are only a few and almost exclusively non-binding application rules. Within the Cluster of Excellence Integrative Computational Design and Construction for Architecture (IntCDC) at the University of Stuttgart, Guidelines for a Finite Element-Based Design of Timber Structures have been developed. The scope of the guidelines is daily engineering practice, expert engineering applications and product development and certification. Essential parts of the guidelines are design procedures, modelling (including geometrical, material and imperfection modelling), analysis, model verification and validation and design. The content and application of the guidelines are described and illustrated in this paper using two benchmarks. These two benchmarks, which are based on experimental investigations, deal with the elastic material modelling of glulam made of beech laminated veneer lumber (beech LVL) and dowel-type connections for beech LVL members. The experimental basis of the benchmarks is described. With the experiments for the benchmarks, all Poisson’s ratios and the complete elastic material stiffness matrix of beech LVL are determined by means of an optical measuring system. The experimentally determined stiffnesses of the investigated dowel-type connections in beech LVL are compared with normative values. Based on the experiments, a numerical model is developed in RFEM (Dlubal).
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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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    Structural member stability verification in the new part 1‐1 of the second generation of Eurocode 3 : part 1: evolution of Eurocodes, background to partial factors, cross‐section classification and structural analysis
    (2020) Knobloch, Markus; Bureau, Alain; Kuhlmann, Ulrike; da Silva, Luís Simões; Snijder, Hubertus. H.; Taras, Andreas; Bours, Anna‐Lena; Jörg, Fabian
    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 first part of the article primarily serves to explain the general background to the European Commission Mandate M/515 that led to the further evolution of the Eurocodes and to illustrate the developments in prEN1993‐1‐1:2020 that pertain to new material grades, partial factors, cross‐sectional classification and structural analysis. These form the necessary background to the changes to member buckling design rules, which are treated more specifically in the second part.
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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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    A statistical assessment of the fatigue strength improvement of butt-welded joints by flush grinding
    (2023) Braun, Moritz; Baumgartner, Jörg; Hofmann, Gloria; Drebenstedt, Karl; Bauer, Niklas Michael; Bakhschi, Hadi; Kuhlmann, Ulrike
    All major rules and guidelines include fatigue design (FAT) classes for flush ground butt-welded joints. These FAT classes vary between FAT110 and FAT155; however, in the majority of cases, the underlying database and specimen-related details are unclear or unknown. This study evaluates 1003 fatigue test results gathered from various literature sources and tries to relate the fatigue strength improvement to typical specimen types and test conditions. To this goal, statistical methods based on correlation analysis are employed. Next, proposals for updates of rules and guidelines for flush ground butt-welded joints made of steel are established by determining new FAT classes and a suitable slope exponent. In addition, an overview of design standards and recommendations is given and main influencing factors are discussed.
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    Influence of the geometric properties, the timber-concrete interface, and the load protocol on the mechanical properties of timber-concrete composite connections
    (2024) Mönch, Simon; Campos, Joana A. A.; Dias, Alfredo M. P. G.; Kuhlmann, Ulrike
    Timber-concrete composite (TCC) structural systems are characterized by the combination of timber and concrete, which are connected to transmit shear forces between the two elements. In addition, to achieve an efficient connection, the slip between the two materials should be limited. Therefore, the load-carrying capacity, the stiffness, and the failure mode of TCC connections are important for the behavior of the composite element. This work aims to investigate the influence of test conditions on TCC connections using shear tests to determine the mechanical properties of connections. Therefore, it is essential to understand the influence of the configuration of the specimens (symmetric as push-out tests or asymmetric as inclined tests), the type of interface between the timber and concrete, and the test procedure (static or cyclic load protocol) on the resulting load-carrying capacity, stiffness, and failure modes. This paper reviews experimental tests conducted on TCC shear connection specimens, using various configurations to assess the influence of the test specimen configuration, material interface, and testing protocol on the determination of the mechanical properties.
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    Structural member stability verification in the new part 1‐1 of the second generation of Eurocode 3 : part 2: member buckling design rules and further innovations
    (2020) Knobloch, Markus; Bureau, Alain; Kuhlmann, Ulrike; Simões da Silva, Luís; Snijder, Hubertus. H.; Taras, Andreas; Bours, Anna‐Lena; Jörg, Fabian
    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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    Heat management and tensile strength of 3 mm mixed and matched connections of butt joints of S355J2+N, S460MC and S700MC
    (2023) Eichler, Stefan; Arnim, Mareike von; Brätz, Oliver; Hildebrand, Jörg; Gericke, Andreas; Bergmann, Jean Pierre; Kuhlmann, Ulrike; Henkel, Knuth‐Michael
    High-strength structural steels are beneficial in terms of the sustainability of constructions due to the possible reduction of weight and overall material needs. Nevertheless, high-strength steels have a smaller processing parameter range in regarding the specific heat input and resulting cooling rate. Especially the cooling time t8/5 characterizing the time span to cool down from 800 to 500 °C is an important indicator. Single layer butt-welded gas metal arc welding (GMAW) connections of 3 mm plates between normal strength (S355J2+N, S460MC) and high-strength steels (S700MC) as well as matched connections (S460MC, S700MC) are carried out. Hereby, the influence of the energy input, melting rate, joint preparation, filler metal (matching and undermatching) and backing methods are observed. Spatially resolved IR-thermal observation shows variations within the welds of up to 50 % in the cooling time t8/5 depending on those parameters. These fluctuations lead to significant changes of the microstructure within the melting and heat-affected zone. UCI hardness mappings show the softening and microstructural change within these zones. Those soft zones can be the region of failure for butt welded connections as shown by transverse tensile tests with spatially resolved optical strain measurements. The results obtained can be used to define more precise welding procedures of these types of connections and also are used to develop design rules for mixed connections made of normal strength and high-strength steel.
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    Load‐carrying capacity of MAG butt and fillet welded joints on high‐strength structural steels of grade S960QL and S960MC
    (2023) Brätz, Oliver; Arnim, Mareike von; Eichler, Stefan; Gericke, Andreas; Henkel, Knuth‐Michael; Hildebrand, Jörg; Bergmann, Jean Pierre; Kuhlmann, Ulrike
    The use of high-strength structural steels brings great advantages in constructions regarding material requirements, weight reduction and productivity. Different steel grades within the S960 range are commercially available but not yet represented in Eurocode 3. The weldability of these steels is limited to smaller process windows to ensure the high material properties. In contrast to steels with moderate strength, there is a considerable risk of softening in the heat-affected zone causing a strength reduction of the connection. By now, the current EN 1993-1-12 only extends the design rules to cover steel grades up to S700. Therefore, the potential of these high-strength steels cannot be used to its full extent in structural engineering. This study, made within a steel application research project (FOSTA P 1507), deals with the weldability and load-carrying capacity of butt and fillet welded joints of S960QL and S960MC produced by gas-shielded metal arc welding. The influence of different bevel geometry, filler metal, and plate thicknesses was investigated. To extend the design rules up to S960, a need of an amendment was found for some combinations.
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    Composite bridges with cracked concrete deck spanning between transverse beams under fatigue shear loading
    (2023) Stempniewski, Lena; Kuhlmann, Ulrike
    For concrete deck of large steel-concrete composite road bridges cracking occurs due to tension because of negative bending moments at the support area, at the same time traffic load with high wheel loads passes the deck spanning between transverse beams. They induce cyclic shear loading in the cracked concrete deck. In composite bridges the application of prefabricated concrete elements has led to economical designs with a benefit in construction time. In this case, the prefabricated concrete elements are supported by the transverse beams when the on-site concrete is poured. For this construction, the concrete is subjected to tension forces resulting from the global load-carrying effect, which needs to be superimposed with local effects as wheel loads acting as shear fatigue loading. In this paper, the fatigue strength of cracked concrete deck under tension and shear fatigue loading is discussed.