UPDATE: Bearings on 1st Ave South bridge need replacement; Overnight closures start next month as work begins
The Washington State Department of Transportation has announced that work to replace and repair the bridge bearings on the 1st Ave South Bridge will begin in February but the exact date is not yet certain. They posted the news on their blog:
"The current estimate is early February; once we have a specific date we'll share it on our website and Twitter.
Massana Construction Inc. of Gig Harbor had the lowest bid among the five contractors who submitted proposals. Their bid of roughly $380,000 was actually about 18 percent below our engineer's estimate. The savings will be available for us to use on other projects.
With the West Seattle Bridge closed, we understand how important the SR 99 Duwamish River Bridge is to people who travel to or from West Seattle. We are working closely with the Seattle Department of Transportation as we plan for and schedule repairs.
When this work begins it will only affect southbound SR 99; the northbound lanes will remain open at all times. While we're working, several alternative routes are available.
Our contract allows for up to 15 nights of work. At the start of the project we will need to close all lanes of southbound SR 99 between 10 p.m. and 5 a.m. for one night so our contractor can set up their equipment. Travelers can expect about three weeks with the southbound bridge reduced to two lanes. We'll also need a full overnight southbound closure at the end of the project to remove equipment.
During the work, Massana's crews will replace bearing pads, which allow the structure to flex and move with weather and traffic conditions. They'll also do some steel repair and concrete bridge deck repairs. To accommodate this, crews will shift traffic to one side of the bridge first, then move traffic to the other side to finish.
Why we're working now
The bearing pads – masonry pads that the girder rests on – were part of the initial construction when the southbound SR 99 Duwamish River Bridge opened in 1996. These pads are worn out and need to be replaced. The pads allow us to precisely set the elevation of the bridge's superstructure.
During a regular inspection in October 2020, our bridge maintenance crews noted the bridge was moving on the bearing pads more than it should, so we did temporary repairs to keep the bridge stable while we planned the permanent fix.
There's never a good time to reduce capacity on a major highway. However, scheduling this work allows people to plan ahead and consider alternate routes. It also helps us avoid the need for emergency repairs that require unscheduled closures.
Original Post Oct. 28, 2020
Traffic into and out of West Seattle is going to struggle even more starting in January as repairs are made on one of the primary detour routes now in use.
The Washington State Department of Transportation shared earlier this month that the bearings of two piers on the SR99 Duwamish River Bridge (also known as the 1st Ave South Bridge) showed they must be replaced. This was shown during a regular inspection of the bridge. These bearings are critical as they allow the bridge deck to move up and down a little when traffic goes over the pier. Similar in some ways to the damaged bearing at Pier 18 on closed West Seattle Bridge, they must be replaced.
As WSDOT stated in a blog post, "In this case, the bridge bearings have worn to the point that the bridge settles a little when heavy loads go over it... In immediate terms, this isn't too big a deal, but it should be fixed as soon as possible. Left as it is, eventually it will become a big deal."
WSDOT, working with SDOT has done some brief daytime closures (roughly the same length of time as a closure for marine traffic), which have allowed crews to put in shims, shaped pieces of metal to close the gap that has formed between the bearing and top of the bridge piers. These temporary repairs only last a few months and while the bridge remains safe to travel over, a more permanent fix is needed.
WSDOT said that work will likely take place early in 2021, "Right now we're looking at a project that will require us to reduce the bridge to two lanes for about four weeks to replace cement and grout. This will eliminate the settlement on that side of the bridge. When one side is finished, it will take another roughly two weeks to do the same thing on the other side." The specific design of that work is being developed now.
50,000 cars a day use the southbound lanes so the impact on travel times will be significant.
Work on the bridge deck panels will continue through the winter.
A little known fact - the northbound span of the 1st Avenue South Bridge is technically a floating bridge. A series of chambers make up the bridge piers at either end of the span and there is a long horizontal, encased walkway-like structure under the water and mud of the Duwamish River that connects the bridge piers. Water is pumped in and out of the chambers to help keep the bridge steady and level. When lower areas need to be inspected, water is pumped into the higher chambers so the lower chambers and enclosed walkway are accessible. A person can actually walk from one end of the bridge to the other underwater.
The article doesn't make it totally clear, but this is just for the older southbound bridge, correct? I'm assuming that the floating nature of the newer northbound bridge (as described at the end of the article) obviates the need for these types of bearings. Does that make sense?