Evaluation of Methods of Design for Strongback Braced Frames
Publication: Journal of Structural Engineering
Volume 150, Issue 11
Abstract
Strongback braced frames (SBFs) are a relatively new structural system intended to reduce structural damage during seismic events and improve resilience. SBFs combine buckling-restrained braces, which provide the primary lateral resistance and energy dissipation, with a stiff elastic spine to distribute demands across the height of the structure and prevent the formation of weak- and soft-story mechanisms. Designing the spine is challenging, as higher mode effects and partial nonlinear mechanisms have been shown to be significant. These effects, and their interaction, are not fully accounted for by standardized design methods. It is also unclear how stiff and strong the spine must be in order to achieve the desired behaviors. There are proposed procedures for designing SBFs; however, they have not been broadly evaluated, and they have not been compared. This work evaluates two proposed design procedures, the simplified modal pushover analysis (SMPA) and generalized modified modal superposition (GMMS), with a “control” procedure based on current standardized capacity design procedures. A total of nine frames were designed for three buildings using the three procedures. Nonlinear response history analyses were performed to evaluate the differences in behavior resulting from the different design methods. To determine the effect of the strength and stiffness of the strongback, the yield strength and elastic modulus of the strongback members were varied and the analyses repeated. The results of this work show that the GMMS and SMPA design procedures are generally well-calibrated and provide benefits over current standardized procedures in several ways: collapse performance is improved, and yielding in the strongback and residual drifts is reduced. The GMMS procedure results in larger members, but provides similar outcomes to the more-complicated-to-implement SMPA. The insights from this work will assist engineers when implementing these design methods and support the codification of strongback braced frames in design standards.
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Data Availability Statement
All data, models, and code generated or used during the study are available in a repository online at Talley et al. (2024) in accordance with funder data retention policies.
Acknowledgments
This material is based upon work supported by the National Science Foundation under Grant No. 1940197. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. The computation for this work was performed on the University of Tennessee Infrastructure for Scientific Applications and Advanced Computing (ISAAC) computational resources.
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Published In
Journal of Structural Engineering
Volume 150 • Issue 11 • November 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: Oct 31, 2023
Accepted: May 17, 2024
Published online: Aug 24, 2024
Published in print: Nov 1, 2024
Discussion open until: Jan 24, 2025
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