The Platform

Your express stop for the latest news and behind-the-scenes Sound Transit information.

The Platform Blog - We dig deep, so you don't have to. Subscribe today.

    

Making the I-90 floating bridge stronger, longer lasting for trains by Rachelle Cunningham July 12, 2018

Upcoming bridge work requires full overnight closures of westbound I-90 bridge

(NOTE: This post has changed to reflect updated overnight closure dates now scheduled for 7/28 - 7/30.)

Inside the pontoons of the I-90 floating bridge, mostly out of sight, crews have been working for the past year to prepare the bridge for post-tensioning, an important milestone that is set to happen this month.

This work is part of the East Link light rail project to connect Seattle, Mercer Island, Bellevue and Redmond with a new rail line opening in 2023.  

I-90-strength-for-trains.jpg

Crews have been hard at work inside the I-90 floating bridge since June 2016. The bridge is made up of several floating pontoons with passageways between each one as seen above. 

During the East Link design process, engineers determined through wind and wave analyses that the pontoons of the Homer M. Hadley Bridge are susceptible to damage during strong north wind events. Post-tensioning, a method of reinforcing concrete with high-strength tensioned steel strands, will enable the bridge to withstand stronger winds and higher waves, as well as strengthen it to carry light rail tracks and vehicles.

Since last June, crews have placed 10 steel “reaction frames,” each weighing 17,500 pounds, into the pontoons at either end of the floating bridge. These frames serve as the anchor points for about 3,600 feet of high-strength steel strands that now stretch from one end of the bridge to the other inside the pontoons.

I-90-strength-for-trains.jpg

Inspecting the "reaction frames" inside one of the floating bridge pontoons. 

Here's one of the plan diagrams showing where the anchor frames have been installed at either end of the bridge. The new steel cables run through all of the pontoons between the anchors and will be tightened to make the bridge stronger for running trains across. 

I-90-strength-for-trains.jpg

Starting July 20, crews will begin tightening these strands to strengthen the bridge pontoons. To complete this work safely, westbound I-90 is planned to be closed for several nights.

I-90 westbound will be closed overnight on:

  • Saturday, July 28 – Sunday, July 29 (11 p.m. – 7 a.m.)
  • Sunday, July 29 – Monday, July 30 (10:30 p.m. – 4:30 a.m.)

Throughout the rest of this year’s work season, crews will continue to perform additional retrofitting work on the floating bridge. With the retrofits complete, crews will be able to begin installing track in the coming months.

Check out previous stories from The Platform for an overview of the I-90 work and dive into the engineering details about how we'll run trains across the floating bridge.

Back to The Platform >>

Listed in :
Related stories
Rendering of track bridge on I-90 floating bridge
Publish Date: 
Thursday, Jul 12, 2018 - 1:30 pm