The Aurora Bridge seismic retrofit project reaches a milestone that measures less than an inch this week.  Crews will close both directions of SR 99 overnight Tuesday to jack up the structure ¾ of an inch and install new one ton bearings that will allow the bridge to gently sway during an earthquake.

This sets the stage for the final phases of work on a $5.7 million project that will help the 80-year old historic bridge better withstand seismic shaking.

Construction:

Since April 2011, crews have been under the bridge reinforcing the steel and concrete on the north and south ends. Work includes adding steel to the skeleton, thickening concrete girders and covering existing columns with fiber designed for shaking. Crews also are digging deep into the ground to create stronger foundations. Work scheduled in the final phase includes new bearings and a new expansion joint.

“An earthquake twists and turns a structure. These materials allow the bridge to move but not entirely fail,” said John Chi, WSDOT project engineer in a press release.  “As we saw in Japan after the tsunami, a bridge that’s bruised is better than a bridge that’s broken when it comes to restoring the transportation infrastructure.”

Work under the north end of the bridge near the Fremont Troll is nearly complete; work under the south end is on schedule to be done by August. Work on the bridge deck itself takes place this week and again in late June and July as crews replace the bearings, lower the bridge into place and then replace the thick metal expansion joint that runs across all six lanes of traffic.

“Working on this bridge is a challenge because it’s so beautiful,” said Chi. “We need to make improvements while maintaining the look and feel of this iconic gem.”

Seismic retrofit program:

Earthquakes pose a substantial risk to transportation infrastructure in Washington state. 
The purpose of the seismic retrofit program is to minimize and avoid catastrophic bridge failures by strengthening bridges and structures.

An estimated 900 bridges are on the retrofit program list including the Alaskan Way Viaduct, the SR 520 floating bridge. Of those 900, 268 have been repaired, 134 partially repaired, 487 are in need of repair and 12 are under repair right now. By 2015, funding for the seismic retrofit program will be depleted.

This project is paid for with federal transportation and state highway gas tax funds, and is scheduled to be complete by October 2012.

This week’s closures:

Crews will close the southbound lanes at 10 p.m., and northbound lanes will close at 11:59 p.m. Tuesday, May 29 through 5 a.m. Wednesday, May 30. Northbound drivers will detour off SR 99 at Denny Way and onto Dexter Avenue and/or I-5. Southbound drivers will be detoured off at 39th and onto Fremont Avenue.

Residents on the north face of Queen Anne may hear the noisy work between midnight and 5 a.m. 

Free earplugs are available by contacting Jamie Holter at 206-440-4698 or holterj@wsdot.wa.gov.

Queen Anne drivers should plan for closures on 6th Avenue North between Raye and Halladay streets.

Crews will close one lane Monday through Friday between 9 a.m. and 3 p.m. until the end of August. Flaggers at both ends of the closure will allow local access.

During the daytime closure, crews will work on 6th Avenue North underneath the Aurora Avenue Bridge. They are building a skeletal system for the extra steel that will be attached to the existing girders.

For more information, please visit the project website at http://www.wsdot.wa.gov/projects/sr99/aurorabridgeseismicretrofit/