Second Set of Bay Bridge Tower Sections in Place

While the Bay Area’s attention was focused on the San Francisco Giants and the World Series, another high stakes event was going on over the Bay last week. Crews on the new East Span of the San Francisco-Oakland Bay Bridge hit their own home run with the successful installation of four 617-ton tower legs that make up the second “lift” of the span’s signature tower, which now stands 272 feet tall, a little more than halfway to its ultimate height.

 “The tower segments are fitting together seamlessly,” said American Bridge/Fluor Operations Manager Brian Petersen on Thursday, as the third of the four legs was set in place. The 107-foot-tall steel shaft – fabricated in Shanghai, China, along with the massive steel deck sections of the new suspension span – landed silently and within millimeters of plumb. “Every time we do this, it shows the incredible accomplishment of what was fabricated in China and what we’re installing here.”

Made up of four independent legs, each of which is composed of five vertical sections, the tower will eventually rise to 525 feet and will help give the bridge its unique design, which calls for a single cable to anchor into one side of the span’s eastern end, drape over the tower, wrap around the west end, and go back over the tower to anchor back into the eastern end.

Two crews of a dozen workers each manned alternate 12-hour shifts for the five days – Monday, October 25 through Friday, October 29 – of the operation. The painstaking process involved tilting each leg from horizontal to vertical on a specially-designed barge positioned at the tower’s base, and then hoisting the legs 300 feet into the air before lowering them into place and bolting them to the splice plates.

Eight ironworkers toiled at the plates, where the second tier of the tower attaches to the first, and four more operated the lifting system, a powerful overhead strand jack (see image at right) which raised the tower sections at 45 vertical feet per hour. “It may seem slow to you,” said Petersen, “but it’s fast for a strand jack!” The movement was perceivable on each upstroke, when the colossal column crept 16 inches upward over two minutes.

Once the tower leg reached its vertical apex and was moved into place, ironworkers swarmed the scene and, using cables and winches, swivelled each shaft into place before lowering them on to their mate.

The arrival of the third “lift” of tower sections is expected in December 2010, when this entire process will begin again, even higher above the Bay.

The East Span project is being overseen by the Toll Bridge Program Oversight Committee (TBPOC), made up of MTC’s Bay Area Toll Authority (BATA), Caltrans and the California Transportation Commission (CTC).

— Karin Betts