Design and Optimization of Cold-Formed Steel Sections in Bolted Moment Connections Considering Bimoment
Publication: Journal of Structural Engineering
Volume 146, Issue 8
Abstract
The load transfer mechanism in cold-formed steel (CFS) bolted moment connections is mainly through the bolt group in the web of beam elements, which may lead to relatively large bimoment and warping deformations. While the bimoment effects can be considered in the Direct Strength Method (DSM), ignoring the fact that the bolt-group length in the conventional design process can lead to nonconservative solutions. This paper presents an alternative analytical design approach using Eurocode 3 (EC3) effective width method to determine the ultimate flexural strength of CFS bolted moment connections by considering bimoment effects. The results compare very well with previously published experimental test data as well as detailed finite-element models developed in this study. It is shown that a short bolt-group length may lead to up to 25% reduction in the flexural strength of the CFS bolted connections. However, a longer bolt-group length generally results in a moment capacity almost equal to the flexural strength of the CFS channel section. Shape optimization is then conducted using a genetic algorithm (GA) to improve the flexural capacity of the connections by taking into account the bimoment effects. The main design variables are considered to be the relative CFS beam cross-sectional dimensions, while the plate slenderness and dimension limits suggested by EC3 as well as a number of manufacturing and practical end-use constraints are incorporated as design constraints. It is found that, compared with standard cross-sectional dimensions, the optimized sections can improve the flexural strength by as much as 36% for a bolt-group length equal to the depth of beam element.
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Data Availability Statement
Some or all data, models, or code generated or used during the study are available from the corresponding author by request. This data includes material properties, geometric imperfections, connector behavior, and optimization.
Acknowledgments
This research was supported by the Engineering and Physical Sciences Research Council (EPSRC) Grants EP/L019116/1. The second author was also supported by EPSRC Doctoral Scholarship Grant 1625179.
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©2020 American Society of Civil Engineers.
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Received: Oct 14, 2019
Accepted: Feb 25, 2020
Published online: May 25, 2020
Published in print: Aug 1, 2020
Discussion open until: Oct 25, 2020
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