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
Steel and concrete are ***really*** strong. Also, a square meter is a LOT of concrete and/or steel.
It’s actually not even an area of 3619.5 m² holding up the weight. It’s actually much less because buildings are mostly open floor space. Let’s assume that 5% of the ground floor is structural area. That’s 181 m^(2), or 1,810,000 cm^(2). That’s 0.3867 tons per cm^(2), a.k.a. 37.9 MPa. The theoretical ultimate strength of structural steel ***starts*** at about 400 MPa, or about 10 times that much. Even low-quality concrete is usually at least 30 MPa. If you’re building Taipei 101, you’re looking at closer to 100 MPa.
Of course, the dead weight of the building is not usually the driving consideration. Materials are rarely configured to reach their theoretical maximum capacities, and buildings have to hold STUFF in them while also surviving heavy winds and earthquakes. Tall things that stick far up into the air do not like wind and earthquakes.
Then you have the foundations, which have to spread this weight out due to the lower strength of the rock or soil under the building, but even the area of the foundation is usually less than the area of the floor space. There’s also a trick where long, skinny foudndtion elements (e.g. “piles”) can hold on to the ground kind of like tree roots instead of just pressing down flat into the ground like a foot does.
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