Take for example the Taipei 101 Tower:
– 508.2 meters high
– Weighs 700,000 tons
– Ground floor is 57×63.5 meters, which is 3619.5 m²
– That means an area of 3619.5m² has to hold up 700.000 tons, which is ~193 tons per m² which is 193.000 kilograms per m²
I don’t know but 193.000 kilograms feels like an unbearable crushing all-pulverizing weight to me.
Obviously it works since the Taipei 101 tower and other huge buildings exist, but intuitively I don’t understand how the bases of large and tall buildings don’t instantly pulverize under the weight of everything above it.
In: 1790
There are several types of stress that can be put on a material (like compression, tension, shearing and torsion).
Compression is when something is being pressed together (like for example if there is 700.000 tons of weight pushing down), and commercial concrete* has a compressive strength of more than 28 Megapascals (up to a theoretical strength of 51 MPa. 41 MPa is considered standard for megaprojects like bridges and supertall buildings). That’s at least 285 kilos per square centimeter, or 2850 tons per m^(2)
In short. If they used the shittiest commercial quality concrete (and they probably didn’t), the base of Taipei tower needs to use 6% of its base surface as concrete pillars to hold up the weight.
In theory, because you need safety marginals, there are other forces involved (like tension, shearing and torsion). That’s why you use steel as well, because steel is good at absorbing those forces. But when you’re building tall the weight of the building pressing down is the least of their worries compared to for example “what about the wind pressure on a building that tall”.
*Commercial quality is in this case “the types of concrete used for commercial buildings”. Residential quality concrete can have a compressive strenght as low as 17 MPa.
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