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
A single empty soda can weighing 15 g and with a diameter of less than 7 cm can support over 75 kg of weight.
A full soda can can support over 320 kg of weight.
It all depends on the material and the form it takes.
There are two things to understand.
The first is that most materials are very strong when under balanced compression. You can think about how the head of a nail when struck perfectly flat will drive straight into wood without bending, but if you hit it off-center or at an angle, the head will deform and the shaft will bend.
The second is that skyscrapers are not a stack of floors each pressing down on the one below them. Each floor puts all of its weight on the steel beams that extend straight down from top to bottom. The ceiling on the bottom floor is not bearing any weight from the floors above it. Only the steel beams experience that force. To visualize this, if you removed every other floor so that each one was floating in the air except for steel stilts, the structure would stand without a problem.
The ground is actually much weaker than the steel beams that support the tower, so a LOT of engineering goes into anchoring the building so the ground beneath won’t fail, depending on the local geology.
Many good answers.
I am a geotechnical engineer. Buildings transfer their weight (load) to the ground with a foundation. The type of foundation depends on how strong the ground is and how heavy the building is. Tall skyscrapers (and bridges) typically use some kind of deep foundation. These can either transfer the weight past weak stuff down to strong stuff (this is like Manhattan as another comment stated) or use friction on the sides to transfer the weight to the material (think about holding a rope in your hand).
A great EILI5 is the Practical Engineering YouTube channel.
Lots of videos which are easy to understand.
[Why buildings need foundation](https://youtu.be/0_KhihMIOG8?si=qfogeeRL9gy0WB4o)
whats the end game here? Taipei 101 just pulverizes all the way to the center of the earth
Because the final destination of the load transfers would not be on the “ground floor” as if you visualize the very wide ground floor slab at the lowest floor holding all of the loads from above. But most of the load will be transfered to the very deep foundation piles (from what I can gather, there are 380 piles in total, each with 1,5 meter IN DIAMETER, with around 80 METER LONG EACH, inside the ground until they all hit the sandstone layer of earth/”the rigid layer”). Then, the piles will transfer those loads into the earth. All of those 380 piles, each of them can hold 1100-1450 tons of load.
https://structures-explained.com/wp-content/uploads/2021/06/Slide7-1-1024×576.jpg
https://image.slidesharecdn.com/projecttaipae101-140828105356-phpapp01/85/project-taipei-101-11-320.jpg?cb=1667418037
Tall buildings are actually really light, at least comparatively speaking. They have a steel frame on the inside that is hollow, and then they kind of “hang” the concrete on the outside like curtains. Again, the inside is totally hollow. Then they add things like floors, etc., but its all light weight. They’re designed to move, and bend to an extent. They aren’t built like you’d expect in ancient buildings where each floor is a “base” and it just goes up higher and higher.
Because they’re specifically engineered to be able to handle it, basically
This is also the exact literal reason we don’t use bricks to build sky scrapers. Tall buildings by brick standards had bases with walls 6 feet thick and were limited to 16 floors as a ceiling just because any higher and the base would be crushed by the weight of it all, but Steel is a fucking champ and so was able to allow for much taller buildings.
Sometimes they do. take a look at this example https://www.youtube.com/watch?v=OOWn-HMd5Co&t=0s
To answer the question, I think that the base doesn’t pulverise because it is strong.
But I mostly want to say that this has been the most enjoyable Reddit thread I’ve found so far.
ELI5 is intended to mean make the answer simple. Much of this thread is like 5 year olds discussing advanced physics, and it’s hilarious. 😂. “Kids say the darndest things.”
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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