15th Triennial International Conference
Decommissioning of SR520 Floating Bridge, Seattle, WA
Publication: Ports 2019: Port Engineering
ABSTRACT
The original Evergreen Point Floating Bridge consisted of 31 individual pontoons, interconnected and anchored with cables to the bottom of the lake. Even with the retrofits, the aging bridge was deemed to be vulnerable to severe windstorms. Hence the bridge was eventually replaced with a modern floating bridge that could remain operational after larger storms. Decommissioning the original bridge was a challenging operation which was complicated by the various retrofits, ballast modifications, and recent external post-tensioning along the entire length of the bridge. Detailed ballast and separation plans were developed to protect the new replacement bridge which was built in close vicinity. Any accidents with the removal work would potentially damage the new floating bridge and its anchor cables and could result in unmeasurable consequences. A multi-stage dynamic structural analyses was performed to ensure that the original floating bridge could be safely disassembled. The bridge was successfully decommissioned, and the pontoons were recycled as docks and artificial reefs.
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ACKNOWLEDGEMENTS
The Washington Department of Transportation (WSDOT) was the owner of the SR-520 Bridge. Kiewit-General-Manson Joint Venture (KGM JV) was the general contractor for the bridge decommissioning. Simpson Gumpertz & Heger was the lead structural marine engineer for the demolition and removal of the old SR-520 Floating Bridge. The authors would like to express their appreciation and gratitude to WSDOT and KGM JV for significant contribution to the engineering of the bridge demolition.
REFERENCES
Associated Press. “Old Interstate 90 Span Cuts Anchor Cables for New Bridge as It Sinks.” The Spokesman-Review (Spokane, Washington), November 26, 1990.
HistoryLink, Hood Canal Bridge Sinks during a Severe Storm on February 13, 1979. August 05, 2003. Accessed January 15, 2019. https://www.historylink.org/File/5501.
WSDOT, and Historylink.org. “SR520 History - 1956 - Present - Building the New SR 520 Bridge” 520 History. Accessed January 14, 2019. http://www.520history.org/1956-present/EvergreenPtBridge/BridgeConstruction.htm.
WSDOT. SR 520: 2016 Floating Bridge Construction. October 11, 2016. Accessed January 15, 2019. https://www.flickr.com/photos/wsdot/30146531752/in/album-72157681081411414/.
Information & Authors
Information
Published In
Ports 2019: Port Engineering
Pages: 78 - 89
Editors: Pooja Jain, Moffatt & Nichol and William S. Stahlman III, America's Central Port
ISBN (Online): 978-0-7844-8261-2
Copyright
© 2019 American Society of Civil Engineers.
History
Published online: Sep 12, 2019
Published in print: Sep 12, 2019
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