Following the destructive 1989 Loma Prieta earthquake, California needed a replacement for the eastern span of the San Francisco–Oakland Bay Bridge that could withstand the powerful seismic activity of the Hayward and San Andreas faults. Engineers chose a Self-Anchored Suspension (SAS) design, creating the longest single-tower SAS bridge in the world. Traditional suspension bridges rely on massive concrete anchorages embedded deep into geology on either side to hold the tension of the main cables.
However, the soft bay mud at the eastern end made conventional anchorages structurally impractical. In an SAS bridge, the main cable loops around the western end of the bridge deck, travels up over the 525-foot single tower, loops around the eastern end, and attaches back to the deck itself. This compresses the deck longitudinally, making the structure self-contained.
To endure extreme earthquakes, the bridge incorporates key seismic innovations: a single single-loop cable made of 137 wire strands, load-bearing shear link beams in the tower designed to deform and absorb energy during a quake, and heavy-duty hydraulic hinges. This allows the tower to sway and flex without causing catastrophic collapse to the primary load-bearing members.