The Viable Alternative

by Wen David Liu, P.E., Tech. Dir. and Vice Pres.; Imbsen & Assocs., Inc., Sacramento, CA,
Farid S. Nobari, P.E., Proj. Engr.; Imbsen & Assocs., Inc., Sacramento, CA,
Moe Amini, P.E., Sr. Engr.; Ofc. of Struct. Contract Mgmt., California Dept. of Transp.,


Serial Information: Civil Engineering—ASCE, 2000, Vol. 70, Issue 11, Pg. 42-47


Document Type: Feature article

Abstract:

The Benicia-Martinez Bridge is a high-level, welded deck truss bridge that carries Interstate 680 over the eastern end of the Carquinez Strait near San Francisco. To bring the bridge into compliance with the latest seismic design criteria, designers considered additional strengthening as well as more traditional approaches. If the bridge were strengthened, using fixed rocker bearings, the full seismic force would be developed and transferred from the deck, through the truss system and bearings, down to the substructure piers and foundations, thus affecting an already vulnerable substructure. Instead, the engineers chose to decouple the dynamic responses of the superstructure and substructure by installing the largest frictional pendulum bearings ever made. In addition, a retrofit of the substructure included adding new caissons, installing pipe tie-downs within the existing caissons, and strengthening the footing boxes to distribute seismic forces to all caissons.

Subject Headings: Bridge decks | Substructures | Truss bridges | Structural strength | Seismic tests | Seismic design | Caissons

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