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1. I-90 Floating Bridge By: Gyan Sinha
2. 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
3. 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.
4. Clip of Bridge Collapse
I-90 Collapse Video
5. 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 couldnt handle the load.
by the time the construction workers realized the bridge was sinking, it was too late to pump out all the water.
6. 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
7. 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.
8. 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 wasnt 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
9. In the End No one was hurt or killed, since the bridge was closed for renovation and the sinking took some time.
10. 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>.