A worker inspects a reaction frame inside a pontoon. Credit: Sound Transit

Sound Transit announced on Wednesday that construction crews are nearly done with their work retrofitting the I-90 bridge for East Link. Crews have worked for more than a year to post-tension the bridge’s pontoons.

ST reinforced the bridge to help it carry the load of Link’s tracks, overhead lines, and vehicles. The retrofit also improves the integrity of the bridge in heavy wind and an attendant storm surge, the likes of which sank the eastbound span in 1990.

All the Lake Washington floating bridges use a system of tensioned steel cables to hold the span in place. Construction crews installed additional cables in the pontoons of the I-90 span. The cables, which crews stressed and winched, pull the pontoons closer together, which creates greater load bearing capacity. Altogether, according to Sound Transit’s Zach Ambrose, “crews installed and stressed 1,080,000 feet of steel strand and applied 41,000 pounds of pressure.”

Steel cable and the frame that anchors it. Credit: Sound Transit

Giant steel structures, called reaction frames, anchor the new cables at both ends. They absorb the force from winching the steel cables, and whatever event that might stress the structure. Each of the ten reaction frames weigh about 17,500 pounds.

The structural work is finished. Crews are removing equipment from the pontoons and grouting the housing of the cables, to prevent water corrosion. After that work is done, construction of the guideway can start.

A diagram of the retrofit. Credit: Sound Transit

6 Replies to “I-90 bridge’s Link retrofit almost finished”

  1. “crews installed and stressed 1,080,000 feet of steel strand and applied 41,000 pounds of pressure”

    pounds is not a unit of pressure

    1. Maybe they meant pounds per square inch (PSI)? Since yes pounds is not a measurement of pressure.

    2. lol, given all the recent infrastructure failures in the news lately, I really hope it wasn’t one of the bridge engineers that relayed that tidbit to the blogger 0_o

    3. They likely meant “pounds of force”, which is generally how tension is measured (or Newtons in metric). In layman terms, force and pressure can mean the same thing.

  2. Many thanks for this one, Peter. At this point in the building of our regional transit system, should be at least three postings a week on structures and machinery, and their operations, and the training required.

    So everybody discussing, and advocating for transit can start seeing of every statistic as a gauge-reading on a control-board.We need to be able to identify and trace a burning statistic before the smoke gets in the window at The Seattle Times.

    Mark Dublin

  3. https://www.youtube.com/watch?v=o-z3Pp0QiPo

    Wonder if the Seattle Room- archives, Downtown library tenth floor, has any of the reports on what happened here. And also, legal defense.

    Good thing about floating bridges, though…try to float in and reattach The Golden Gate. Especially if it had East Link attached to it. Bay Bridge was hard enough.


    But interesting article from BART after same ‘quake…The Loma Prieta. Stakeholders’ meetings on this part of public transit will de-fang a lot of both superstition and complacence without a single fake-
    Austrian accent- if somebody with an ST hard-hat chairs the event.


    Thanks again, Peter


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