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
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Because they design them that way. Its literally the job of engineers to do the math and figure out how much weight the foundation and ground can support, then use materials and designs that work. If they do a bad job, the building would collapse.
193.000 kilograms per m²
is 19 kg per cm²
now if your weight is about 80 kg, find something that is 4 cm² (so 2×2 cm cube) and try to stand on it
will look easier now i think
200 tons may sound like a lot. That is more then two fully loaded semi-trucks. But concrete and steel are similarly strong so the weight itself is not the big issue. For a simple demonstration you can look at [https://www.youtube.com/watch?v=2Spj8_ED0TA](https://www.youtube.com/watch?v=2Spj8_ED0TA) . That shows 150 tons on a single concrete brick without cracking it, only when they turned it on its weaker side did it fail. So as long as you have more then two of these bricks every square meter you can hold up the Taipei 101. Obviously it is a bit more complex as the load can shift around as things move, and you have lateral forces from wind and the building swaying.
In addition to the other answers, I’ll give you an interesting fact.
>The Eiffel Tower weights 7300 tons. But, the pressure it applies on the ground is only equivalent to the pressure of a chair with a man seated on it.
https://www.parisdigest.com/monument/eiffel-tower-facts.htm
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The concrete has excellent load bearing capacity. They have used high performance concrete with 68 MPa strength in construction of load bearing parts of Taipei 101 tower.
68 MPa is significantly stronger than everyday concrete (which is usually in the 20-40 MPa range) but it is still quite achievable with standard cement types and carefully selected, but not exotic aggregates.
68 MPa is more than 7000 tons/m2 so in theory they could get away with using only 100 meter square of the 3620 meterquare ground floor for support. Obviously they are various other loads (most notably wind and earthquakes) and safety factors, so they should use a lot more than 100 m2.
Concrete is essentially aggregates glued with cement paste. Both aggregates and cement paste itself can achieve about 400 MPa strength separately. But concrete can only be as strong as its weakest link (aggregates, cement, or the interface between them) and the weakest link is the binding force between cement and aggregates. In practice 110-120 MPa is the limit.
It’s not “tons” but rather “tonnes”. They are different things: 1 imperial ton is around 1020kg, whereas 1 metric tonne is 1000kg. And it gets worse: 1 US ton is around 980kg.
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.
Your question mostly regarding “compression strength”. Concrete used in large buildings is likely “high strength” concrete, which has a compression strength of 6,000 psi or higher. Sometimes as high as 12,000 psi.
So, a 1 meter x 1 meter column of concrete (39″x39″) would have a compression strength of 18,252,000 pounds (9,126 tons = 9,126,000 kg).
Compression strength of steel, depending on alloy, shape, etc, can also be in the tens of thousands of psi.
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