As part of the Levy to Move Seattle, 16 bridges were selected for seismic retrofits, including the West Howe Street Bridge. The West Howe Street Bridge was constructed in 1946 prior to the modernization of the seismic design code. The bridge provides a more direct connection across 32nd Ave W to the neighborhood located along the southwest edge of the Magnolia community.
Shimmick’s work addresses seismic deficiencies of the bridge structure. The retrofit includes clearing and grubbing, steel column strengthening, steel bracing strengthening, column base strengthening, gusset plates, replacing existing rocker bearings with elastomeric bearings, seat extension and a catcher block at the west and east abutment, and stop block at each side of the stringer at the east abutment.
The original contract drawings outlined the steps to replace the existing rocker bearings with elastomeric bearings during the span of two weekend bridge closures. Shimmick developed and engineered a jacking plan that would allow us to replace all five bearings in one weekend. The plan included using high early concrete and grout mixes to ensure the required strength was met during one weekend to allow traffic back on the bridge. We also developed a contingency plan that would allow traffic back onto the bridge if we were not able to complete the bearing replacement in one weekend that allowed traffic back onto the bridge. By creating this detailed plan, we were able to remove and replace the bearings in one weekend instead of two, which was a substantial cost saving for the project.