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TY - THES AU - Bartsch, Helen TI - Zum Einfluss von Schweißnahtimperfektionen auf die Ermüdungsfestigkeit von Stahlbauteilen; 1. Auflage VL - 95 PB - RWTH Aachen University VL - Dissertation CY - Aachen M1 - RWTH-2023-11029 SN - 978-3-95886-512-9 T2 - Schriftenreihe Stahlbau - RWTH Aachen University SP - ix, 174, XV Seiten : Illustrationen PY - 2023 N1 - Druckausgabe: 2023. - Zweitveröffentlicht auf dem Publikationsserver der RWTH Aachen University N1 - Dissertation, RWTH Aachen University, 2023 AB - In every weld, manufacturing-related weld imperfections occur, which play a greater role in fatigue-loaded steel structures than in predominantly statically loaded steel structures. This is because the imperfections typically have an influence on the fatigue strength of the welded joint. However, the fatigue strength values of welded structural steel details in terms of fatigue-classes (FAT-classes) are insufficiently well linked to the quality level of the welded joints. Although the background of the detail classification in the design standard for sufficient safety against fatigue failure, EN 1993-1-9, hardly provides any information on the size and extent of weld imperfections to be taken into account, the design standard for steel structures, EN 1090-2, generally restricts the sizes of tolerable weld imperfections for fatigue-stressed structures in accordance with quality standard EN ISO 5817, quality level B. In a simplified way, it is assumed that this size limitation of the weld imperfections harmonizes with the effects of the FAT-classes of EN 1993-1-9. However, the limit values of the quality levels have been determined without scientific background, so that the actual limit values are unknown. It turns out that the quantitative influence of weld imperfections on the fatigue strength of structural steel details has been insufficiently researched so far. This is the reason for this dissertation to develop a methodology to determine FAT-classes as a function of weld imperfection size. After a brief introduction to reliability methods in civil engineering, an overview of the normative situation with regard to the consideration of weld imperfections in fatigue-stressed structures is given. Together with the review of previous research activities, it is shown that the influence of weld imperfections on the fatigue strength of steel components is sparsely known and, consequently, is insufficiently considered in the design. For this reason, experimental investigations on the fatigue strength of welded details were conducted first. The fatigue tests include 30 cruciform specimens and 15 transverse stiffener specimens with external and internal weld imperfections. Detailed 3D laser scans and ultrasonic testing methods are utilised to accurately measure weld imperfections in the steel members. Numerical investigations using the effective notch stress concept serve to extend the experimentally considered investigation scope. With validated finite-element (FE) models, geometry influences on the fatigue strength of the details of the cruciform joint and the transverse stiffener can first be determined. By means of a comprehensive fatigue test database, which represents the basis of the current fatigue detail classification of EN 1993-1-9, it is then possible to check numerically determined geometry influences. Furthermore, the validated FE models serve to determine the influence of weld imperfections on the fatigue strength of the various details using the effective notch stress concept. In doing so, influences resulting from lack of penetration, lack of root fusion, incorrect root gap for fillet welds, undercut, excessive convexity, incorrect weld toe, excessive asymmetry of fillet welds and linear misalignment were considered individually. To efficiently consider multiple imperfections in the FAT-class, the Fatigue Class Combination Model (FCCM) has been developed. Starting from the basic FAT-class of a detail, which is reduced by a leading imperfection influence, a second imperfection influence can be considered. Its fatigue reducing effect, however, is not fully applied, but reduced by a combination coefficient ψImp smaller than one. The combination coefficient ψImp for the accompanying imperfection size is derived from safety theory. It is based on statistical distributions of the measured imperfections and considers the comparatively low probability of the occurrence of two imperfection extremes at one location. The required safety level of the presented approach is confirmed by numerous random examples. Thus, not only can a relationship be established between FAT-classes and weld imperfection sizes, but a methodology is provided for determining Imperfection-FAT-classes for arbitrary geometries and imperfections, provided that the influence of the imperfection is known. Since time-consuming reworking of welds with specific imperfection sizes can be omitted in the future, the verification for sufficient safety against fatigue failure can be optimized in terms of cost and resource efficiency. LB - PUB:(DE-HGF)11 ; PUB:(DE-HGF)3 DO - DOI:10.18154/RWTH-2023-11029 UR - https://publications.rwth-aachen.de/record/973853 ER -