Bearings on 1st Ave South bridge need replacement; 24 hour closures coming next year
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?