Full-Scale Cyclic Testing of Low-Ductility Concentrically Braced Frames
Publication: Journal of Structural Engineering
Volume 143, Issue 6
Abstract
Two full-scale, two-story, low-ductility steel concentrically braced frame (CBF) systems were tested to evaluate failure mechanisms, postelastic frame behavior, reserve capacity, and overall collapse performance. These frames were designed for a moderate seismic region, where reserve capacity is emerging as a parameter that can be employed instead of primary system ductility to economically prevent seismic collapse. One test unit used a split-x bracing configuration and satisfied seismic detailing and proportioning requirements in the AISC Seismic Provisions for an ordinary concentrically braced frame (OCBF) with . The other test unit used a chevron CBF configuration with and included no seismic detailing. Each test unit was subjected to a quasistatic cyclic loading protocol and was cycled to total frame drifts in excess of 3.0%. The split-x OCBF exhibited ductile brace buckling behavior up to 1.5% total frame drift, but possessed little reserve capacity after two weld fractures. The chevron CBF exhibited brittle brace buckling and subsequently developed several distinct reserve capacity mechanisms. These tests demonstrate overall hysteretic behaviors that are highly dependent on two underlying design parameters: system type and system configuration. OCBF brace local slenderness and connection capacity design requirements are effective for providing ductile brace-buckling behavior. The split-x configuration appears more vulnerable to developing multistory mechanisms that possess limited reserve capacity, but this can be improved with strategically placed, enhanced beam-column connections. The chevron configuration is more prone to single-story mechanisms that possess significant reserve capacity developed through beam and column flexure.
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Acknowledgments
This study is supported by the National Science Foundation (Grant No. CMMI-1207976) and the American Institute of Steel Construction. All steel was donated by the American Institute of Steel Construction. The fourth author was partially supported by a National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144245. The authors gratefully recognize the support of the faculty and lab staff in the NEES at Lehigh facility including Dr. Richard Sause, Dr. James Ricles, Peter Bryan, Gary Novak, Tommy Marullo, Darrick Fritchman, Jeffrey Sampson, Todd Anthony, and Carl Bowman. The opinions, findings, and conclusions in this paper are those of the authors and do not necessarily reflect the views of those acknowledged here.
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Published In
Journal of Structural Engineering
Volume 143 • Issue 6 • June 2017
Copyright
©2017 American Society of Civil Engineers.
History
Received: Jul 13, 2016
Accepted: Nov 18, 2016
Published online: Feb 17, 2017
Published in print: Jun 1, 2017
Discussion open until: Jul 17, 2017
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