I-90 Floating Bridge By: Gyan Sinha Darton Riely-Gibbons Betsy Pickrell
Bridge Information • Also known as Lacey V. Murrow Memorial Bridge • The bridge was the brainchild of George Lightfoot • The second longest floating bridge at 6,620 ft. • Crosses lake Washington from Seattle to Mercer Island. • Made of reconstructed concrete and floats on Pontoons. • Bridge sank on Nov 25, 1990; over Thanksgiving Break. • Designed by the engineer Homer Hadley in 1940 • At the time, The Seattle Times called it "the biggest thing afloat”
What is floating bridge? • A bridge which floats on pontoons on the surface of the water rather than resting on columns or suspended from cables • Supported by barge-or-boat-like pontoons to support the bridge deck and its dynamic loads • While pontoon bridges are usually temporary structures, some are used for long periods of time • Permanent floating bridges are useful for sheltered water-crossings where it is not considered economically feasible to suspend a bridge from anchored piers.
Clip of Bridge Collapse I-90 Collapse Video
Reasons of Collapse • The bridge needed resurfacing and was to be widened. • Construction done on the old bridge • Cut six-foot-high holes into the hollow concrete pontoons, but the wholes were not closed over the weekend. • Storm water was able to enter the pontoons which couldn’t handle the load. • by the time the construction workers realized the bridge was sinking, it was too late to pump out all the water.
Reason Of Collapse • one pontoon filled and dragged other down • the pontoons were temporarily used to store contaminated water from the construction. • the contaminated water was released in Lake Washington
Reason of Collapse • The state faulted the contractor for not responding adequately to the accumulation of water in the pontoons. • Ben C. Gerwick, Inc hired by Traylor bros to find cause of failure. • The failure of the bridge was primarily the result of structural weaknesses that accrued over many years prior to the sinking and as a result of the storm immediately preceding. • Bond slip had progressively occurred in the bottom slab of many of the pontoons, leading to cracks which did not close.
Results of Collapse • The public was simply told that A large storm on the Thanksgiving holiday weekend 1990 filled some of the pontoons with rain and lake water causing it to sink. This wasn’t necessarily true. • WSDOT (WA state department of transportation), filed a $69 million lawsuit against Traylor Brothers, the contractors hired to repair Lacey bridge. • The dispute was resolved in August 1993, through a mediated settlement in which Traylor agreed to pay the state $20 million
In the End • No one was hurt or killed, since the bridge was closed for renovation and the sinking took some time.
Work Cited Enlow, Clair. "Architecture & Engineering." DJC.Com. 1 Dec. 2007 <http://www.djc.com/news/ae/05003121.html>. Vallone, Christine. "Pontoon Bridge-Building Pitfalls Cited." Bnet Research Center. 1 Dec. 2007 <http://findarticles.com/p/articles/mi_hb5249/is_199604/ai_n20045882> “I-90 Bridge Sinks." Youtube. 1 Dec. 2007 <http://www.youtube.com/watch?v=gm0YQ3vuyyY>. "Lacey V. Murrow Bridge." Gerwick Inc. 1 Dec. 2007 <http://www.gerwick.net/pdf/inland_waterways/033e_lacey_murrows.pdf>.