Construction starts at San Francisco-Oakland Bay Bridge's towers

The California Department of Transportation (Caltrans) has started moving the huge steel and concrete sections of the San Francisco-Oakland Bay Bridge's new eastern span tower.

Construction crews will lift the second set of sections of the Self-Anchored Suspension Span's single 525- ft (160 m) tall tower into place this week.

These latest sections will rise over 10 stories above the Bay Bridge's deck, which will give motorists an "up-close" view of this "herculean endeavour" to replace the existing East Span, said a Caltrans spokesman, who urged the public "to focus on driving safely and to not be distracted by the construction."

The second set of four tower sections arrived in the Bay Area on October 9. The tower is made up of four independent legs, each of which is composed of five vertical sections.

The second set of four sections are 107 ft tall (32.6 m), each weighing 617 tons (561 tonnes). With the placement of these sections, the tower will be 272 ft-tall (82.9 m), a little more than halfway toward its ultimate height.

Two strand jacks will hoist each section about 30 stories into the air, so that each segment can be moved into the erection tower just above the first sections of the tower. Once the second section is lowered onto the first, crews will bolt them together using splice plates.

Crews will work around the clock, using two 12-hour shifts, to erect all four tower sections; it takes approximately 16 hours to lift, place and bolt each section. The work is expected to be completed by this weekend.

Crews placed the first tower sections onto the foundation in July 2010. The arrival of the third group of tower sections is expected in December 2010.

The entire eastern span will be complete in late 2013. The cost of the project so far is about US$ 5.4 billion.