Failure of Lacey V. Murrow Floating Bridge, Seattle, Washington

Abstract

In November of 1990, approximately 850 m (2,800 ft) of the 2020 m (6,620 ft) long Lacey V. Murrow Bridge (LVMB), a 50-year-old floating concrete bridge over Lake Washington near Seattle, sank after a major storm. The bridge had been closed for renovations for several months when it sank; there were many structural changes and interim conditions which affected the performance of the bridge. The investigation described herein identifies the most probable causes of the failure. The primary cause of the sinking of the LVMB was water that accumulated in the bridge during renovation. Hydrodemolition, rain, and wave splash water entered through construction openings and severed roadway drains. The cause of the failure was unrelated to strength reductions caused by the openings, and the age and condition of the bridge were of minor significance.