New Highway 520 Pontoon Bridge

[msquared48]

I have been trying to follow the recent controversy here with the leaking concrete pontoons and I am in a quandry.

For those who are unfamiliar with the situation, this bridge, a concrete "floating" bridge, is the sixth in the state of Washington of its kind, two on Hood Canal, and the fourth for Lake Washington, considering additions and replacements.

The pontoons are being fabricated in Aberdeen on the coast of Washigton, and being floated to the site on Lake Washington between Seattle and Bellevue. Apparently, the pontoons have developed cracks and leaking, both in the casting yard, and on site. The bridge is now delayed 6 months in it's completion until the summer of 2015. Lawsuits have been filed at this point to discover how the rep[airs are to be paid for and by whom.

What I cannot understand, is with the four previous bridges over the last 50 to 60 years of history with the original floating bridge for I-90 over Lake Washington, why is this a problem now? If details that worked were changed, why re-invent the wheel?

I have heard allegations regarding the contractor, state inspectors, and ths like, but I don't know what to believe here. Any additional insight Bridgebuilder?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[MiketheEngineer]

Bad concrete, not enough rebar, cured too quickly, not sealead??? And it goes on and on...

 

[bridgebuster]

Is this the same bridge that was discussed in this thread?

http://www.eng-tips.com/viewthread.cfm?qid=334389

 

[msquared48]

Yes, BB, it is.

My question still stands. After all that experience with success with the other bridges, why so many problems with this one? Something is fishy.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[bridgebuster]

Hard to say Mike. I tend to agree with your thinking. On the one hand "if it ain't broke, don't fix it"; on the other hand, a lot of engineers believe in N-I-H. Or maybe it comes down to good old fashioned corruption.

 

[yakpol]

Well, it did happen before, in 1990 just a few miles south of 520 bridge. Watch this video:

http://www.youtube.com/watch?v=gm0YQ3vuyyY

 

[msquared48]

This was due to the demolition of the old portion of the bridge, not service conditions.

A large portion of the Hood Canal bridge sank back in the 80's too during a storm, but not because of cracks in the concrete structure. Instead, it sank because a maintenance worker did not properly re-install the accessway cover plates in the bridge deck, and the compartments flooded leading to the sinking.

I am only referring to the inherent cracking of the sidewalls, intersections and bottom of the pontoons. That should not happen in my opinion, pumps provided or otherwise.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[msquared48]

Well, it turns oiut that Kewitt apparently did not use the same mix design as the test original design, plus used Chinese cement in the mix.

I will not comment any further.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

According to this article, the design by the state DOT engineers has been found to be the problem.

http://seattletimes.com/html/localnews/2020439320_520pontoonscostsxml.html

 

[hokie66]

Some light reading for anyone who wants to study the "Expert Panel Report".

http://www.wsdot.wa.gov/NR/rdonlyre...3464/0/2013_0200_WSDOTPontoons_ERPReport2.pdf