Experimental Evaluation of the Seismic Vulnerability of Braces and Connections in Older Concentrically Braced Frames
Publication: Journal of Structural Engineering
Volume 142, Issue 9
Abstract
Concentrically braced frames (CBFs) have been used as seismic force resisting systems in steel structures for many decades. CBFs designed prior to about 1988 were not capacity designed for the expected brace strength, and many are therefore prone to undesirable failure modes when subjected to large earthquakes. The consequences of other factors, such as weld toughness, gusset plate clearance to permit brace end rotation, and local slenderness of the brace, were also not fully understood, so older CBFs may also exhibit premature failure relative to modern, special CBFs (SCBFs). Thus, these older CBFs are expected to exhibit low inelastic deformation capacity and are termed nonductile CBFs (NCBFs) here. An infrastructure review showed that many NCBFs are deficient by SCBF standards and an experimental program was undertaken to explore the impact of brace and connection deficiencies in particular. Brace local slenderness and brace-to-gusset plate weld deficiencies were found to be highly detrimental to drift capacity. Beyond these concerns, welds joining the gusset plate to the frame were found to be vulnerable to fracture even if they had sufficient strength based upon the yield capacity of the brace. Bolted connections were found to be generally more robust, especially if bolt bearing and fracture resistances were similar. The findings presented here will aid engineers in determining need and type of retrofit for NCBFs.
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Acknowledgments
The writers gratefully acknowledge the support of the National Science Foundation (Grant No. CMMI-1208002). Dr. Joy Pauschke is the Program Officer. AISC, with Tom Schlafly providing oversight, provided independent funding for some of the specimens and material donations. The tests were performed at the Structural Research Laboratory at the University of Washington and the authors gratefully acknowledge the students and staff who conducted these tests. This work was also supported by the National Science Foundation Graduate Research Fellowship (DGE-1256082). The authors are grateful to all of the above-mentioned agencies for their support. The opinions and findings expressed here are those of the authors alone and do not necessarily reflect the views of the sponsoring agencies.
References
AISC. (2010a). Steel construction manual, Chicago.
AISC. (2010b). “Seismic provisions for structural steel buildings.” ANSI/AISC 341-10, Chicago.
AISC. (2010c). “Specification for structural steel buildings.” ANSI/AISC 360-10, Chicago.
ASCE. (2013). “Seismic evaluation and retrofit of existing buildings.”, Reston, VA.
ATC (Applied Technology Council). (1992). “Guidelines for cyclic seismic testing of components of steel structures for buildings.”, Redwood City, CA.
Ballard, R. (2015). “Impact of connection type on system performance of non-seismic concentrically braced frames.” M.S. thesis, Univ. of Washington, Seattle.
Goel, S. C. (1992). “Cyclic post buckling behavior of steel bracing members.” Stability and ductility of steel structures under cyclic loading, CRC Press, Boca Raton, FL.
Hsiao, P. C., Lehman, D. E., Berman, J. W., Roeder, C. W., and Powell, J. (2014). “Seismic vulnerability of older braced frames.” J. Perform. Constr. Facil., 108–120.
Hsiao, P. C., Lehman, D. E., and Roeder, C. W. (2013). “A model to simulate special concentrically braced frames beyond brace fracture.” Earthquake Eng. Struct. Dyn., 42(2), 183–200.
ICBO (International Conference of Building Officials). (1988). “Uniform building code.” Whittier, CA.
Johnson, M. M. (2014). “Seismic evaluation of bolted connection in non-seismic concentrically braced frames.” M.S. thesis, Univ. of Washington, Seattle.
Johnson, S. M. (2005). “Improved seismic performance of special concentrically braced frames.” M.S. thesis, Univ. of Washington, Seattle.
Lehman, D. E., Roeder, C. W., Herman, D., Johnson, S., and Kotulka, B. (2008). “Improved seismic performance of gusset plate connections.” J. Struct. Eng., 890–901.
Powell, J. A. (2010). “Evaluation of special concentrically braced frames for improved seismic performance and constructability.” M.S. thesis, Univ. of Washington, Seattle.
Roeder, C. W., Lumpkin, E. J., and Lehman, D. E. (2011). “A balanced design procedure for special concentrically braced frame connections.” J. Constr. Steel Res., 67(11), 1760–1772.
Sen, A. D., et al. (2016). “Experimental investigation of chevron concentrically braced frames with yielding beams.” J. Struct. Eng., in press.
Sloat, D. A. (2014). “Evaluation and retrofit of non-capacity designed braced frames.” M.S. thesis, Univ. of Washington, Seattle.
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© 2016 American Society of Civil Engineers.
History
Received: Sep 16, 2015
Accepted: Jan 4, 2016
Published online: Mar 29, 2016
Discussion open until: Aug 29, 2016
Published in print: Sep 1, 2016
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