Posted Mar 1, 2011, 6:20 PM
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Droppin' Loads
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Join Date: Nov 2010
Location: Ventura, Santa Rosa, California
Posts: 288
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Quote:
Bay Bridge suspension tower's 4th piece of 5 rising
Michael Cabanatuan, Chronicle Staff Writer
Just before dawn on Monday, ironworkers laboring more than 40 stories above the bay began hoisting the fourth section of the sleek new tower of the Bay Bridge into place.
The piece is just one of four massive white sticks of steel that will dangle above the bay this week as the penultimate pieces of the new tower are lifted and bolted into place.
Despite its slow pace, it's amazing work to watch. But bridge officials hope drivers won't succumb to the temptation.
"Our advice is, please, keep your eyes on the road while driving across the bridge," said Bart Ney, a Caltrans spokesman.
The work Monday involved using strand jacks mounted on a 500-foot steel frame. Crews carefully lifted and then lowered the 105.6-foot-long, 500-ton tower leg into place about 6:30 p.m. and began bolting it to the third level. All told, it takes about 30 hours to install each leg.
When all four are bolted in place, by Friday, if weather cooperates, the tower will stand at 480 feet of its ultimate 525 feet.
"We expect to go around the clock until this entire segment is done," Ney said.
After this week, all that remains to complete the tower is to place the final piece, known as the grillage, which includes the saddle from which the span's suspension cable will be draped, and some decorative flourishes. That work is expected to be done in early April.
The self-anchored suspension bridge, the signature piece of the $6.3 billion new eastern span, is an unusual structure that will feature the lone tower just east of Yerba Buena Island. It will hold up a single suspension cable that will support the bridge deck.
"It's the only suspension bridge in the country that has just one cable," Ney said. "You think of a traditional suspension bridge as a hammock. This is more like a sling."
The latest delivery of tower pieces, along with more sections of the bridge deck, arrived in the Bay Area from Shanghai on Feb. 14. The tower is made of four independent legs joined together with horizontal connection bars that act as fuses, breaking apart to provide flexibility in the event of a major earthquake.
Workers installed the first level of the tower, atop a 21-foot thick foundation anchored by 13 piles reaching 196 feet into the bay floor, in July. The second section was installed in October, and the third in December.
Once the tower is completed, construction crews will drape temporary footbridges along the path the cable will follow, and the cable will be strung along that route - not spun, as most suspension cables are - and compacted. Suspender cables, reaching from the main cable to the bridge deck, will be installed, and the weight of the bridge deck, now supported by a temporary steel trestle, will be shifted to the main cable. That's expected to occur sometime near the end of 2012.
The bridge is scheduled to open to traffic in both directions by the end of 2013. To make that possible, construction crews in May will detour traffic coming off of the existing Bay Bridge, shifting it slightly to the south, as part of a plan to allow construction of the eastbound Oakland landing of the new span.
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http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/03/01/MNMG1I0F1D.DTL
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