The east spans of the San Francisco-Oakland Bay Bridge are vulnerable to collapse during earthquakes that are possible and predicted in the Bay Area of California. It has been determined that a replacement structure would be of better value than a retrofit, if the replacement structure is in place before a predicted large earthquake occurs. This $1.4-billion bridge replacement project features a single-tower self anchored suspended span. Most of the 2.2-mile replacement will consist of viaducts on friction piles.

Modjeski and Masters, as a subconsultant to the joint venture of T. Y. Lin/Moffatt Nichol, was contracted to perform a 30% design of the east approach steel skyway alternative. This approach consisted of 17 spans ranging in length from 86 to 160 m. The continuous span lengths investigated were up to 525 feet long, and carried five lanes of traffic in each direction. Twin rectangular and trapezoidal shaped steel box girders were analyzed, and both steel orthotropic deck plates and reinforced concrete decks were considered for the design. Modjeski and Masters also completed an independent check of the main suspension bridge superstructure, which consists of dual trapezoidal shaped steel orthotropic box girders.

Specific design activities included:

Develop Design & Seismic Performance Criteria
   Review all relevant design codes, standards, and guidelines
   Recommend design loads for long span bridges

Develop 30% Structure Plans for the Skyway Steel Alternative
   Evaluate superstructure types and determine economic spans
   Develop alternative structure arrangement
   Provide preliminary superstructure calculations
   Develop typical and unique superstructure details
   Provide preliminary substructure calculations
   Prepare 30% plans

Develop a 30% Report