Decommissioning of SR520 Floating Bridge, Seattle, WA: Fid-Bau Portal

Decommissioning of SR520 Floating Bridge, Seattle, WA

Naeem, M. A. / Iversen, R. / Yao, S. X.

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.