Equivalent imperfections for the out-of-plane stability design of steel beams by second-order inelastic analysis
Author(s)
Quan, Chunyna
Walport, Fiona
Gardner, Leroy
Type
Journal Article
Abstract
In current structural design specifications, such as EN 1993-1-1 for steel and EN 1993-1-4 for
stainless steel, the stability of members is typically assessed through the use of buckling curves,
which consider the influence of initial geometric imperfections and residual stresses. An
alternative, more direct, approach is to perform either an elastic or inelastic second-order
analysis of the member or structure with imperfections. For modelling convenience, so-called
‘equivalent’ imperfections are typically utilised, which consider the combined influence of
both geometric imperfections and residual stresses. Equivalent imperfections for the design of
columns and beams by second-order elastic analysis, also referred to as geometrically nonlinear
analysis with imperfection (GNIA), are provided in the current design specifications. For
columns, equivalent imperfections for design by second-order inelastic analysis, also referred
to as geometrically and materially nonlinear analysis with imperfections (GMNIA), were
recently developed, but for beams that are susceptible to lateral-torsional buckling (LTB), there
are currently no appropriate provisions. The aim of this study is therefore to develop equivalent
imperfections for use in out-of-plane stability design of steel and stainless steel members by
GMNIA. The proposals are calibrated against the results of benchmark finite element (FE)
simulations performed on a large number of steel and stainless steel members with geometric
imperfections and residual stresses subjected to major axis bending. Two proposals for
equivalent imperfection amplitudes are developed: (1) e0,mod, for use with eigenmode-affine
2
imperfections and (2) e0,bow, for use with sinusoidal bow imperfections. The latter is applied
solely in the lateral direction and as a summation of a half-sine wave and a full sine wave.
Relative to the traditional Eurocode design calculations, employing the proposed LTB
imperfections in GMNIA provides generally more accurate member resistance predictions,
while remaining safe-sided relative to the benchmark FE results. The reliability of the design
provisions is demonstrated through statistical analysis, where it is shown that partial safety
factors of 1.0 for steel and 1.1 for stainless steel can be safely adopted.
stainless steel, the stability of members is typically assessed through the use of buckling curves,
which consider the influence of initial geometric imperfections and residual stresses. An
alternative, more direct, approach is to perform either an elastic or inelastic second-order
analysis of the member or structure with imperfections. For modelling convenience, so-called
‘equivalent’ imperfections are typically utilised, which consider the combined influence of
both geometric imperfections and residual stresses. Equivalent imperfections for the design of
columns and beams by second-order elastic analysis, also referred to as geometrically nonlinear
analysis with imperfection (GNIA), are provided in the current design specifications. For
columns, equivalent imperfections for design by second-order inelastic analysis, also referred
to as geometrically and materially nonlinear analysis with imperfections (GMNIA), were
recently developed, but for beams that are susceptible to lateral-torsional buckling (LTB), there
are currently no appropriate provisions. The aim of this study is therefore to develop equivalent
imperfections for use in out-of-plane stability design of steel and stainless steel members by
GMNIA. The proposals are calibrated against the results of benchmark finite element (FE)
simulations performed on a large number of steel and stainless steel members with geometric
imperfections and residual stresses subjected to major axis bending. Two proposals for
equivalent imperfection amplitudes are developed: (1) e0,mod, for use with eigenmode-affine
2
imperfections and (2) e0,bow, for use with sinusoidal bow imperfections. The latter is applied
solely in the lateral direction and as a summation of a half-sine wave and a full sine wave.
Relative to the traditional Eurocode design calculations, employing the proposed LTB
imperfections in GMNIA provides generally more accurate member resistance predictions,
while remaining safe-sided relative to the benchmark FE results. The reliability of the design
provisions is demonstrated through statistical analysis, where it is shown that partial safety
factors of 1.0 for steel and 1.1 for stainless steel can be safely adopted.
Date Issued
2022-01-15
Date Acceptance
2021-10-20
Citation
Engineering Structures, 2022, 251 (Part B), pp.1-24
ISSN
0141-0296
Publisher
Elsevier
Start Page
1
End Page
24
Journal / Book Title
Engineering Structures
Volume
251
Issue
Part B
Copyright Statement
© Elsevier Ltd. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence http://creativecommons.org/licenses/by-nc-nd/4.0/
Identifier
https://www.sciencedirect.com/science/article/abs/pii/S0141029621015844?via%3Dihub
Subjects
Science & Technology
Technology
Engineering, Civil
Engineering
Advanced analysis
Equivalent imperfections
Finite element modelling
Inelastic analysis
Lateral-torsional buckling
Plastic design
Stainless steel
Steel
STRESS-STRAIN CURVES
3 PART 1-1
BOW IMPERFECTIONS
STRENGTH
VERIFICATION
RELIABILITY
SECTIONS
Civil Engineering
0905 Civil Engineering
0912 Materials Engineering
0915 Interdisciplinary Engineering
Publication Status
Published online
Date Publish Online
2021-11-26