I-90 Floating Bridge

By: Gyan Sinha Darton Riely-GibbonsBetsy 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>.