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@PHDTHESIS{Bartsch:973853,
author = {Bartsch, Helen},
othercontributors = {Feldmann, Markus and Ummenhofer, Thomas},
title = {{Z}um {E}influss von {S}chweißnahtimperfektionen auf die
{E}rmüdungsfestigkeit von {S}tahlbauteilen; 1. {A}uflage},
volume = {95},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {Verlag Mainz},
reportid = {RWTH-2023-11029},
isbn = {978-3-95886-512-9},
series = {Schriftenreihe Stahlbau - RWTH Aachen University},
pages = {ix, 174, XV Seiten : Illustrationen},
year = {2023},
note = {Druckausgabe: 2023. - Zweitveröffentlicht auf dem
Publikationsserver der RWTH Aachen University; Dissertation,
RWTH Aachen University, 2023},
abstract = {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.},
cin = {311710},
ddc = {624},
cid = {$I:(DE-82)311710_20140620$},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.18154/RWTH-2023-11029},
url = {https://publications.rwth-aachen.de/record/973853},
}
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