Bay Bridge Info

The design, engineering and construction teams have met the challenge of making the Bay Bridge seismically resilient with cutting-edge seismic innovations and enhancements - some never before used in bridge building – that are transforming the bridge into a state-of-the-art engineering icon.

 

The first section crews completed was the Skyway, which also includes some of the most amazing seismic innovations. To build the Skyway’s foundations, 160 rebar and concrete-filled steel piles were driven up to 300 feet below the water’s surface to anchor into stable soils. The piles were driven into the soil at an angle, through a process called “battering” to create greater stability. This method has been used to create secure foundations for oil rigs for more than two decades, but has not been used for bridge construction of this scale.

 

Hinge-pipe beams, which look like massive metal dowels, are another amazing state-of-the-art innovation, as they are designed to move within their sleeves during expansion or contraction of the decks during minor events, such as changes in temperature. Twenty of these 60-foot-long devices were placed between deck sections, as well as where the Skyway and SAS will meet. The beams are designed to absorb the energy of an earthquake by deforming in their middle or “fuse” section. This will minimize the damage to the bridge’s main structure. The damaged fuses can then be removed and replaced. Hinge pipe beams are also found at the western piers where the SAS connects to the YBITS.

 

Hinge pipe beams are not the only innovation in the SAS. The single, 525-foot tall tower is made up of four separate steel legs connected by shear link beams, which allow the legs to move independently. The beams are designed to absorb most of the seismic energy during an earthquake and protect the tower from catastrophic damage. The damaged beams can later be removed and replaced.

Two massive marine foundations provide solid support for the tower and eastern end of the SAS, while a land-based foundation on Yerba Buena Island supports the western end. The tower’s foundation includes 13 drilled shafts that extend 196 feet below water to anchor into bedrock. The 16 piles in the eastern support reach down nearly 340 feet to reach bedrock, while the western support’s foundations extend down 80 feet through the island’s solid rock.

At the other end of the East Span is the Oakland Touchdown, where much of the seismic innovations can be found in its foundations. Columns are pinned at the top to reduce severe motion from being dispersed to the foundations and to the road-decks. The foundations utilize flexible vertical piles to absorb seismic forces more effectively. The OTD also features hinge pipe beams where it connects to the Skyway.

The existing East Span’s seismic upgrade began with an interim retrofit of the original span that echoes much of the permanent work on the West Span. Original rivets were replaced with high-strength bolts, and viscous dampers, steel plates and steel lateral braces were added. At the section that collapsed, during the 1989 earthquake, expanded hinge seats were added to allow greater movement in that area.