The Self-Anchored Suspension Span (SAS) TOWER
AN ELEGANT TOWER
The SAS's single, elegant tower is composed of four separate pentagonal legs, each of which is made up of four vertical sections or lifts, connected by shear link beams. The faceted forms of the tower legs are tapered and slender to enhance their appearance and to allow light to permeate through the interior of the tower and between the legs.
The leg sections are floated on barges to the construction site and erected one at a time. The barge, equipped with rails, positions itself on the open east side of the erection tower. Strand jacks positioned atop the erection tower lift the top of the tower segment, while a winch-assisted tipping cart stabilizes the bottom as it moves down the rails, pivoting from a horizontal to a vertical position. The strand jacks then lift the segment off the barge and into position inside the erection tower. To keep the barge steady while accommodating the shifting weight of the tower leg, thousands of gallons of ballast water are pumped from one side of the barge to the other through interior bulkheads.
Once the tower leg is vertical, crews detach the pin assembly connecting it to the barge; at that point it is only suspended by the strand jacks, which can hoist 1,455 tons/2.9 million pounds. The first sections are placed onto the tower’s massive marine foundation. These initial segments are slipped onto 150 steel dowels sticking out of the foundation, and fastened with 424 large anchor rods. When sections are stacked on top of each other, they are bolted together using splice plates. The 456 ton cable saddle at the top of the tower is the largest for a suspension bridge.
As sections are placed, workers attach cross bracings and shear link beams. Shear link beams, which connect the tower’s four independent legs, are designed to absorb seismic energy during an earthquake and to protect the tower from catastrophic damage. The damaged beams can be removed and replaced.
The single tower is taller than numerous other Bay Area landmarks, including San Francisco’s Coit Tower (210 feet), the Campanile at U.C. Berkeley (307 feet) and the Tribune Tower (310 feet) in Oakland.
- Weight of grillage: 500 tons (1 million pounds)
- Length of grillage:30ftWidth of grillage: 30ft
- Height of grillage: 15ftLength of each leg in Lift 4: 105.6ft
- Weight of each leg of Lift 4: 490.5 tons (981,957 pounds)
- Lifting capacity of strand jacks: 1,455ft (2.9 million pounds)
- Elevation of the operator cab on the tower crane: 560ft
- Elevation of the gantry on the erection tower: 538ft
- Height of tower after fourth lift is in place: 480ft
- Final height of tower when complete: 525ft
- Dimensions of tower’s footing box (marine foundation): 85ft X 73ft
- Thickness of footing box: 21ft
- Number of concrete-filled steel piles supporting footing box: 13
- Depth of piles anchored into bedrock: 196ft