Practical rules for defining initial geometric imperfections for in-plane stability design of steel frames
File(s)
Published version
Author(s)
Chan, HU
Walport, F
Slack, H
Wadee, MA
Gardner, L
Type
Journal Article
Abstract
The appropriate modelling of initial imperfections, in terms of both amplitude and shape/direction, is a key challenge in the design of structures by geometrically and materially nonlinear analysis with imperfections (GMNIA). While recent research has addressed the amplitude aspect of imperfection modelling, there remains a lack of clear guidance for determining the appropriate imperfection shape. This is tackled herein through the establishment of comprehensive rules for introducing global sway and member bow imperfections in the in-plane stability design of steel frames. The proposed rules cover the two most commonly used imperfection definition approaches – the direct definition (DD) method and the elastic buckling mode (EBM) method. In the DD method recommended herein, the directions of global sway and member bow imperfections are introduced following a set of prescribed rules. Two EBM methods are recommended. In the first EBM method, the ultimate capacity is taken as the lowest among n values obtained by considering the first n buckling modes as imperfection shapes individually, with n = 6 recommended. In the second EBM method, the bow and sway components of the imperfection shape are determined separately from different LBA in which loads are applied on the key load paths. The bow components are established by combining the first buckling mode for each key vertical and horizontal load path, while the sway component is based on the first mode – provided it is a sway mode – obtained from an LBA considering the maximum gravity load case. The consequences of using no imperfections are also explored. The accuracy of the proposed methods is verified based on a series of moment frames and braced frames considering both regular and irregular configurations.
Date Issued
2025-12-01
Date Acceptance
2025-11-05
Citation
Structures, 2025, 82
ISSN
2352-0124
Publisher
Elsevier
Journal / Book Title
Structures
Volume
82
Copyright Statement
© 2025 The Author(s). Published by Elsevier Ltd on behalf of Institution of Structural Engineers. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
License URL
Subjects
Advanced analysis
BEAMS
BEHAVIOR
BOW IMPERFECTIONS
Engineering
Engineering, Civil
GMNIA
Imperfection shape
Initial geometric imperfections
Linear buckling analysis
MEMBER
PART 1-1
Science & Technology
Steel frames
STRENGTH
Technology
VERIFICATION
Publication Status
Published
Article Number
110643
Date Publish Online
2025-12-02