SoylentNews is people
SoylentNews
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.
-- submitted from IRC
(Score: 2, Informative) by Francis on Sunday November 15 2015, @01:26PM
Why not? People have been building high rise buildings in earthquake zones for decades. The problems are well understood and the main complication is that actual design.
The building needs to be on top of good soil, have a heavy foundation to help keep the center of mass low and the building itself needs to have structural supports that are tuned to bend properly rather than break. The skyscrapers around here are designed for 8.4 magnitude quakes, IIRC, and I'm sure the can do better if need be.