(2012 WSB photo by Christopher Boffoli, from original pad-replacement work beneath the bridge)

As we first reported back in January, dozens of nighttime closures are ahead for the Fauntleroy Expressway end of the West Seattle Bridge, as SDOT begins the year-delayed re-replacement of 600+ earthquake-safety bearing pads.

This afternoon, the city announced that the first closure is expected to be the night of April 25th. Read on for the rest of the announcement:

Construction crews will be replacing the 674 bearing pads on the West Seattle Freeway (Fauntleroy Expressway) from just west of the Delridge Way on/off ramp westward to where the road turns south (where the road is no longer a bridge). Bearing pads provide a cushion between the bridge girders and the horizontal support for the girders, and are important to preserving and protecting the long term integrity of the bridge.

The work is complex, requiring each bridge segment to be jacked up in order to remove the old bearing pads and install the new ones. Crews will set up the jacks on the underside of the bridge during the day, with the actual jacking and bearing pad replacement work done at night while the bridge is closed (impacting the fewest number of motorists). The work will move from east to west, one horizontal support at a time.

The West Seattle Freeway will be closed 40-50 weeknights to complete the work, with closures running from Sunday evenings through Friday mornings. The bridge would be closed from 9 p.m. until 5 a.m. the following morning. The West Seattle Freeway will NOT be closed on Friday or Saturday nights. West Seattle Freeway traffic will be detoured around the closure. On nights with well attended Mariners or Sounders games, the closure will be delayed until 11 p.m.

Nighttime closures are currently scheduled to begin on the evening of April 25, although preparatory work underneath the bridge will begin a week earlier. This will include pressure washing debris from the underside of the bridge during the day. This will require closure of the parking underneath the structure. Once the actual jacking and replacement work begins, those parking areas immediately below the work area will be closed to parking.

The West Seattle Freeway was built in 1963, spans 2,527 feet, and carries more than 60,000 vehicles per day. An initial seismic retrofit of the structure was completed in 1994, when column jackets were erected around select columns, and post tensioning was added to the supports. Longitudinal restrainers were also included to interconnect the roadway over each support.

A second phase seismic retrofit began in 2011, when SDOT updated the structure by strengthening 33 columns with steel jackets, strengthening pile caps, and adding longitudinal restrainers. At the time, it was decided to take advantage of the seismic work by also replacing the original bearing pads which were reaching the end of their service life.

SDOT engineers discovered a problem after the bearing pad replacement had been completed. The outside design consultant had ordered the wrong pad. Instead of replacing the existing pads with stiffer ones, they mistakenly ordered a less stiff pad. The design consultant has acknowledged their error, and will be paying the $1.9 million cost of replacing the pads.

New standards for bearing pads have since been established, so the bearing pads being installed this spring will have steel shims imbedded within them, which is expected to give them a longer service life than the originals.

The exact dates and times of the Expressway closures will be announced as they are determined. This information will also be posted on the project website, located at: http://www.seattle.gov/transportation/fauntleroyexpressway.htm.