Tuesday, October 29, 2019

Repair for damaged SR 99 Aurora bridge begins Thursday night

By Thomas Charlson

Repairs to Seattle's damaged SR 99 Aurora bridge will begin at 9 p.m. Thursday, Oct. 31. During the repair work, the bridge will be reduced to two lanes in each direction for about 10 days as crews repair a damaged support beam section below the bridge.

The walkway on the west side of the bridge will also close.

We've coordinated the closure with our partners at the city of Seattle and King County Metro to try to keep traffic moving as well as possible through the area. The bridge is safe for traffic but there will be a new lane configuration and delays are expected, especially during peak travel times. If possible, consider using alternate routes, carpooling or public transit.

The lane closures are needed to create room for the contractor to stage equipment. Temporary lane markings will shift a single lane of southbound traffic into the northbound lanes, allowing two lanes of travel in each direction.

We typically try to give the public as much notice as possible for significant lane closures. But sometimes, it just isn't possible. In this case, a right-lane closure on the southbound side was put in place quickly, and without much warning on Sunday, Oct. 27 when bridge inspectors discovered advanced deterioration of a steel support beam during an in-depth inspection. We immediately began developing a repair plan and hired Guy F. Atkinson Construction to make the repairs.

We have more than 3,300 bridges that we maintain statewide and they each get regular inspections to ensure they're in good working order and to identify any issues that need attention.

This past September was time for the SR 99 Aurora bridge to get its regular checkup. Structural engineers found a few areas of concern so we did a much closer inspection this past weekend, Oct. 26-27. During this time, they discovered the damage to the support beam (known as a stringer), leading to added pressure on the next beam, which is now carrying twice the weight it was designed for.
This diagram shows the exact location of the problem area under the right southbound lane of the SR 99 Aurora bridge.

What is a stringer?
Stringers are long steel beams that run length-wise under the bridge, parallel to the lanes of traffic. The stringer under the far-right southbound lane is losing strength due to corrosion, and a support plate has separated half of an inch from the stringer itself.
The stringer beam's support plate separated half of an inch from the stringer beam.

It will be important to plan for added travel time if you're headed south into downtown. Be sure to check our app, Twitter account and webpage to help navigate the lane closures.
The area that needs to be repaired is over water, so our repair plan will have to safely access the underside of the bridge.

It's never convenient to close lanes, especially on short notice, and especially on a highway as heavily traveled as SR 99. We'll work as quickly as we safely can to get the bridge repaired and traffic fully reopened, and we appreciate everyone's patience as we get this work done.