The nearly two yearlong project to seismically retrofit the 1.8 mile long Antioch Bridge has been completed. The bridge, opened in 1978 using the current earthquake safety technology, was originally thought to be adequately protected from earthquake damage. Upon further review Caltrans and the Bay Area Toll Authority (BATA) evaluated the seismic safety of the bridge and determined it required seismic retrofit work to make the bridge safe during a major earthquake. The $47 million project was paid for by the BATA using your bridge toll dollars.
On Tuesday I had the opportunity to tour what had been done. For the first part of the tour we climbed up the scaffolding to view the seismic isolation bearings that were installed at each of the 41 piers. These bearings use a sliding mechanism to control the bridge’s seismic response and to dissipate earthquake energy and will allow for up 26 inches of movement in any direction. The bearings were installed using jacks to separate the bridge from the pier and then sliding in the bearing. A total of 82 bearings were installed without affecting the nearly 15,000 vehicles that cross the bridge each day.
You’ll notice that 21 pier columns have been strengthened by the addition of cross braces and strengthening hinges. Additionally 116 columns supporting the nearly 800-foot-long concrete slap approach on Sherman Island were enhanced with steel casing jackets.