Experimental Seismic Collapse Study of a Full-Scale, 4-Story, Soft-Story, Wood-Frame Building
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Volume 21, Issue 2
Abstract
In the San Francisco Bay Area and throughout much of California, there are a large number of wood-frame buildings with garage space at ground level, resulting in open fronts on one or two sides. This type of geometry results in a soft and weak first story, and buildings of this archetype are generally referred to as soft-story buildings. During an earthquake, these buildings are susceptible to severe damage and collapse and have been recognized as a disaster-preparedness problem. The five-university Network for Earthquake Engineering Simulation (NEES)-Soft project culminated in a series of full-scale soft-story wood-frame building tests to validate two different retrofit philosophies and included a 2-month test program encompassing four different retrofits. The building had of living space and was designed to be generally representative of older San Francisco Marina and Mission District construction, circa 1950s. Following the retrofit testing, which only moderately damaged the test building, retrofits were removed, repairs were conducted, and the building was nominally instrumented for testing without retrofits in place. A series of unidirectional shake table tests was conducted, beginning with the Cape Mendocino acceleration record scaled to 0.4g spectral acceleration up to two successive shakes with the Superstition Hills acceleration record scaled to 1.8g spectral acceleration. Little residual lateral displacement was observed until the last two earthquakes. The objectives of the collapse testing phase of the NEES-Soft project were to (1) observe and document the nature of the soft-story collapse mechanism and (2) quantify the collapse drift for these types of soft-story wood-frame buildings. The building collapsed at approximately 19% interstory drift of the soft story (ground floor).
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Acknowledgments
This material is based on work supported by National Science Foundation Grant Nos. CMMI-1041631 and 1314957 (NEES Research) and NEES Operations. The authors thank Simpson Strong-Tie for financial, personnel, and product support throughout the project, including the engineering support for the steel moment frames in San Diego. The authors kindly acknowledge the other senior personnel of the NEES-Soft project: David V. Rosowsky at University of Vermont, Andre Filiatrault at University at Buffalo, Shiling Pei at South Dakota State University, David Mar at Tipping Mar, and Charles Chadwell at Cal-Poly; the other graduate students participating on the project: Ph.D. student Jingjing Tian (Rensselaer Polytechnic Institute), M.Sc. student Jason Au (Cal-Poly Pomona); and the practitioner advisory committee: Laurence Kornfield, Tom Van Dorpe, Doug Thompson, Kelly Cobeen, Janiele Maffei, Douglas Taylor, and Rose Grant. A special thank you to all of the Research Experience for Undergraduate (REU) students (Sandra Gutierrez, Faith Silva, Gabriel Banuelos, Rocky Chen, and Connie Tsui). Others that have helped include Asif Iqbal, Vaishak Gopi, Ed Santos, Tim Ellis, and Russell Ek. Finally, the authors thank NEES and all site staff and site principal investigators, Jose Restrepo, Enrique Luco, and Joel Conte at NEES at UCSD for their help and support getting the tests ready. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the investigators and do not necessarily reflect the views of the National Science Foundation.
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Journal of Architectural Engineering
Volume 21 • Issue 2 • June 2015
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Mar 20, 2014
Accepted: Oct 20, 2014
Published online: Nov 14, 2014
Published in print: Jun 1, 2015
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