San Francisco-Oakland Bay Bridge

Opportunity

In 1989, an earthquake with a magnitude of 7.1 shifted the east span of the San Francisco–Oakland Bay Bridge by seven inches (18 cm). It was enough to cause a 50-foot (15-meter) section of the bridge’s upper deck to collapse. One person was killed.

To replace the east span, a 2.2-mile (3.5-kilometer) series of low trusses supported by piers, the city wanted a structure that was visually striking and capable of withstanding tremors in a location between the San Andreas and Hayward faults. Mission accomplished!

Solution

The new east span includes the world’s first single-tower Self-Anchored Suspension bridge, which hangs 1,860 feet (567 meters) of a roadway from a single central tower. Linked to this bridge is the equally important and innovative Skyway.

The decks of the 1.3-mile (2.1-kilometer) Skyway are built from 452 precast, post-tensioned concrete segments. Each one three stories high, they are the largest segments of their kind ever cast. Together, they consumed about 130,000 cubic yards of concrete and 31 million pounds (14 million kilograms) of steel.

Hinge pipe beams between the deck segments were designed to slide in response to thermal expansion. Collapsible steel “fuses” in the hinge pipe beams are intended to absorb the energy of an earthquake and protect the deck segments from damage.

Piles to support the Skyway were driven into the soil at an angle, a method used to create foundations for oil rigs. The piles, each about 365 tons, were driven by one of the world’s largest hydraulic hammers, generating 1.2 million pounds (0.5 million kilograms) of force. Dense curtains of air bubbles were created around the piles to dissipate the shock waves and help protect fish and other wildlife.

The Bay Area Toll Authority retained Mott MacDonald as part of a joint venture to provide program management services for the construction of the Skyway. We provided construction management tasks related to quality assurance, advised on technical documents, and produced monthly reports for the BATA Policy Board and California state legislature.

Mott MacDonald's contribution included the following:

• Provided value engineering and technical expertise to help manage projects and resolve engineering challenges
• Recommended construction packaging approaches to reduce the risk of the project
• Advocated early-completion incentives to accelerate project schedules
• Assisted with inspection of the hinge pipe beams
• Provided structure protection from seismic events and resolved subsequent change in contract
• Developed specification language to increase price competition and reduce risk
• Developed change order language for contracts to implement technical best practices
• Performed due diligence on commercial negotiations and helped negotiate independent cost estimates

We identified “workarounds” to solve unforeseen issues that had resulted in “earned value” schedule slowdowns. Mott MacDonald provided the following services:

• Supported the “hold point” QA parts process for fabrication of steel orthogonal box girders (OBGs)
• Provided technical assistance for load transfer on the Self-Anchored Suspension bridge
• Recommended speeding the schedule by allowing the steel contractor for the SAS span to complete the 30-foot concrete hinge structure between the SAS and the Yerba Buena Transition Structures
• Created the concept for the Oakland Touchdown detour, allowing the bridge to open in both directions at the same time
• Recommended painting main cable in an enclosed environment to maximize quality

Outcome

Our participation helped manage risk, control costs, and accelerate the construction timetable for this ambitious and iconic bridge project.

In addition to Mott MacDonald's work on the Skyway, we helped identify $400 million in savings for the state of California by reviewing bridge bid documents and other technical documents for the Self-Anchored Suspension bridge.

See time-lapse video of the bridge's construction.