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from the how-long-will-it-take-to-dry? dept.
WHEN FINISHED, SALESFORCE Tower will be the tallest building in San Francisco. For now, it's a big hole in the ground. And at the bottom of that hole is a new, massive concrete slab—14 feet thick, spread nearly an acre in breadth, and ready to support 1,070 feet of glass, steel ... and a lot more concrete.
Pouring it all took more than 18 hours on a cloudy San Francisco Sunday. An armada of trucks delivered nearly 49 million pounds of concrete and brontosaurine pumps vomited it into the hole while a small army of rubber-booted workers scurried about, directing the flow. It was one of the biggest, longest concrete pours in history.
And it's all to keep the building upright. "Skyscrapers are basically big sticks coming out of the ground, so obviously one concern is the whole thing toppling over," says Leonard Joseph, structural engineer at Thornton Tomasetti, a firm in Los Angeles. High wind or quaking earth can make buildings bend and wriggle, and if the wriggling takes the upper mass too far off center, the bottom of the building will begin to lift. This is called hinging, and it is very, very, bad: Buildings that hinge tend to collapse.
Holding back the hinge means attaching the structure to something big, solid, and subterranean. In places like Manhattan, developers can drill down and affix buildings directly to the island's shallow bedrock. But San Francisco's bedrock is below 300 feet of mud and clay, which is why the engineers for Salesforce Tower had to build a big, shallow, fake rock using concrete and metal.
As an aside, the longest continuous concrete pour took 49 hours.
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(Score: 1, Interesting) by Anonymous Coward on Sunday November 15 2015, @08:27AM
Slip-cast concrete elevator testing tower.
https://www.youtube.com/watch?v=43xflCG2xac [youtube.com]
Much bigger project. Grand Coulee Dam, 11,975,521 cubic yards.
http://users.owt.com/chubbard/gcdam/html/photos/construction.html [owt.com]
Forms on one part of the dam, http://www.usbr.gov/pn/grandcoulee/history/construction/gallery/8.html [usbr.gov]
First pour in 1935, last work done in 1943. Effectively non-stop pouring the whole time.
Until the third powerplant was built between 1967 and 1974.
More facts: https://en.wikipedia.org/wiki/Grand_Coulee_Dam [wikipedia.org]
A 24 hour record of 21960 cubic yards was placed in May 1939. That was the peak rate, and without fancy pumper cranes.
September 1939, they placed 400,000 cubic yards of concrete. 13333 cu.yds every day the whole month.
Two on-site concrete mix plants running continuously 24/7.
The article's project poured 21200 cu.yd. in 18 hours. And then they went home.
Their pro-rated 24 hour rate would have been 28267 cu.yd. Not bad, but on Grand Coulee, that's just an average Tuesday and Wednesday.
(Score: 1) by khallow on Sunday November 15 2015, @03:22PM
A 24 hour record of 21960 cubic yards was placed in May 1939. That was the peak rate, and without fancy pumper cranes.
They did have fancy cranes [pbs.org] (see 0:37 for an example), they just didn't have pumps.