How is concrete googie made?
May 7, 2021 1:51 PM   Subscribe

How are concrete structures like these made? Are they poured in place with towering forms or are they built from discrete pieces?
posted by donpardo to Grab Bag (8 answers total) 6 users marked this as a favorite
Back in the day, they were mostly poured in place. And some of them didn't hold up.
posted by mumimor at 2:21 PM on May 7, 2021

Best answer: I used to work in the office of a company that made large concrete tanks. They were "cast-in-place" by building a form that used a wood frame with a lot of rebar for strength. The concrete was poured into the wood mold, around the rebar. This gas station pic looks similar to the domes rood of the tanks.
posted by Ochre,Hugh at 2:46 PM on May 7, 2021 [1 favorite]

Best answer: Now, they may be made in several ways (including drones and 3D printing), but yes traditionally a huge amount of formwork.

Inflatable formwork has been a thing for at least 50 years. No system is low cost though - there's always a lot of work somewhere in the production pipeline. I have costed, but not built, a large complex structure that would have used an inflatable form to create the underside of a spiral stair., system needs multiple backups for power to keep pressurized until set up complete, which could be a couple of weeks.

Polystyrene blocks have been used for bridge and overhanging structures for decades, but again quite a cost on forming the blocks if you only need a few. I've costed a 75m² undulating poly surface form, I found a factory that had a 400m² bed with a router and they would set 1m³ blocks across the surfaces and then cut the form from them, it's very cost-effective; at the time it was $100/m² and would have saver a lot of money, and especially a lot of time as it would have turned a 5 day formwork job into a half-day one

This from ETH/ Zaha Hadid is a new method, suspending a woven form and then basically using shotcrete "team poured five tons of fiber-reinforced concrete over the original 120-pound polyester-and-cable framework". But even this needs a lot of structure to support the 5+tonnes of concrete until it has set.
posted by unearthed at 3:14 PM on May 7, 2021 [6 favorites]

Best answer: This is just like pouring the second floor of an apartment building-- the steel structure reinforcements are added, then the forms (which aren't themselves towering-- they're just sitting a top a temporary scaffolding structure), and then concrete is poured using a hose from a truck that pumps it high into the air so it's accessible. You can bet there was some additional scaffolding all over so people could access the upper portion, but yes, totally in-situ.
posted by Sunburnt at 5:50 PM on May 7, 2021 [1 favorite]

Best answer: Formwork. More details here.
posted by many more sunsets at 6:26 PM on May 7, 2021 [10 favorites]

Furthermore, a structure like this would almost certainly use tensioned cables across the top in addition to the rebar.
posted by sjswitzer at 9:38 AM on May 8, 2021

Oops, no. The previous excellent article describes it using some kind of wire mesh. Amazed at what a detailed and specific document many more sunsets found!
posted by sjswitzer at 9:47 AM on May 8, 2021

Response by poster: Formwork. More details here.

many more sunsets, how did you find that!? That answers all my questions and more!
posted by donpardo at 9:58 AM on May 8, 2021

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