The state Toll Bridge Seismic Retrofit Program (TBSRP) reached another milestone this week as construction crews completed a 21-month, $47 million project to bring the 1.8-mile Antioch Bridge up to contemporary seismic safety standards.
The Antioch Bridge project involved the installation of cross-braces and steel hinges to strengthen the piers that support the bridge deck. Work crews also installed 82 separate bearings to allow the bridge deck to move independently of its supports in the event of an earthquake. In all, crews added more than 3 million pounds of structural steel, 280,000 pounds of reinforcing steel, and 800 cubic yards of structural concrete to strengthen the bridge, which carries some 15,000 vehicles daily between Contra Costa and Sacramento counties.
Completion of work on the Antioch Bridge brings to eight the number of TBSRP projects on which seismic safety has been achieved and leaves just two more such projects outstanding: retrofit of the 1.6-mile Dumbarton Bridge and replacement of the nearly three-mile-long eastern span of the East Span of the San Francisco-Oakland Bay Bridge. Both projects are slated for completion in 2013.
Previously completed toll bridge retrofits include the Vincent Thomas Bridge in Los Angeles (2000), the San Mateo-Hayward Bridge (2000), the San Diego-Coronado Bridge (2002), the 1958 Carquinez Bridge (2002), the 1962 Benicia-Martinez Bridge (2003), the West Span of the Bay Bridge (2004), the Richmond-San Rafael Bridge (2005), and the West Approach to the Bay Bridge in San Francisco (2008).
Because the Antioch Bridge (built in 1978) and the Dumbarton Bridge (1982) met seismic standards established after the 1971 Sylmar earthquake in Southern California and were comparatively new when the TBSRP was established, neither was included in the original program. However, due to findings from subsequent quakes, seismic standards are now much higher. A two-year evaluation completed in 2008 by BATA and Caltrans revealed that both bridges need significant strengthening to protect public safety.
The state Legislature in 2009 passed Assembly Bill 1175 to expand the TBSRP to include the Antioch and Dumbarton spans, and authorized BATA to increase tolls to finance the work. The new toll schedule went into effect in July 2010.
Pleasanton-based California Engineering Contractors is the prime contractor for the Antioch Bridge retrofit. Remaining project tasks, such as removal of a fence and an access road, and the installation of an earthquake monitor, are scheduled for completion by late July.