Comment by socalgal2

Comment by socalgal2 a day ago

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I don't know the physics involved nor do I have any knowledge of architecture or building construction but when I look at tall buildings it's really hard for me to imagine how they remain standing.

The bottom floor of a 100 story building is holding up 99 floors of weight. The base of a 100 story building it really thin relative to it's height. If I built anything out of legos to the same dimensions it would not be structurally sound. Well, the legos at the bottom would easily hold the weight). Yea I know reinforced steel and concrete is not legos. Other examples though, every piece of furinture I own has some degree of wobbliness. It's easy to see how the pyramids hold up. It's not so easy to see how the Vancouver House Building stays up (https://en.wikipedia.org/wiki/Vancouver_House). The one in the article as well just looks, at the bottom, like it has to tip over eventually. (not saying it will, only that it looks like it)

I'm not in any way denying science. I'm only in awe that more builings don't fall down. Bridges too. I'm surprised to some degree an 93 year old steel bridge being sprayed with salt water for the entire time hasn't had its cables snap.

Maybe a need a physics simulation game like 3d world of goo that lets me see how such structures hold togehter.

userbinator a day ago

If you're not familiar with it, steel is actually surprisingly strong for its size. Look up "ultimate tensile strength" and "compressive yield strength". They are many tens of thousands of pounds per square inch for structural steel. Even the tensile strength of small fasteners like bolts is very high in "human" terms:

https://www.engineeringtoolbox.com/us-bolts-tensile-proof-lo...

The bottom floor of a 100 story building is holding up 99 floors of weight.

That's not how it works. All the load of the floors above is held by the columns, which go into the foundation.

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  • Terr_ 18 hours ago

    Kind of like a stand of bamboo, and we're just critters weaving little platforms at different heights.

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adgjlsfhk1 a day ago

I think a lot of the answer here is in the foundation. a 100 story building isn't sitting on top of the ground. it has several stories of foundation below the ground, and likely has concrete piles that go hundreds of feet further down.

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  • EGreg a day ago

    This. It is like roots of a tree for instance. The trunk by itself is actually much smaller than the branches — like the opposite of a pyramid.

    I guess most of the stress is distributed throughout the building frame going into the foundation - like they drive those pylons into the ground before building a large building.

    But still, it could snap from all that stress, like a tree that’s been felled by the wind…

    That is why the other part is that skyscrapers are designed to sway in the wind and have the entire structure above the ground absorb the kinetic energy and sorta cancel it out before it reaches the base.

    Some buildings use tuned mass dampers (like the giant pendulum in Taipei 101) to counteract swaying by moving in opposition to the wind-induced motion.

    In fact, a lot of the time the majority of the building’s outer shell (glass etc) can be blown out by the wind, if it is too strong, and the steel structure will then have a lot of holes in it for the wind to pass through.

    They test these structures for how the wind and water will flow around them. Look at the base of the Burj Al Arab, and how they built it to withstand the 100-year storm.

    https://theskydeck.com/do-skyscrapers-sway/

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i_am_jl a day ago

>Maybe a need a physics simulation game like 3d world of goo that lets me see how such structures hold together.

Bridge Designer, formerly West Point Bridge Designer is a physics simulation that does almost that, though is more a learning tool than a game.

https://bridgedesigner.org/

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II2II a day ago

Don't worry, engineers can imagine (or, more accurately, analyze) how these buildings will remain standing. A good chunk of it is understanding how to distribute forces throughout a structure. The other chunk of it is understanding the properties of materials. While I didn't read the article in question, I did see the Veritasium video a while back. They have a decent overview of how it works, and how they figured out that there was a problem before the building collapsed. (Specifically, how the change from the original concept to the constructed building posed a problem.)

By the way, trust engineers and never trust physicist with these things. Physicists do have the theoretical tools to handle such problems, but they rarely have the practical knowledge to successfully implement them. :)

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DiggyJohnson a day ago

What you think of as a “floor” is more accurately described as hanging off the support structure.

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  • AnimalMuppet a day ago

    OK, but at the bottom floor, the support structure is carrying the weight of the 99 higher floors. It's not the ceiling, but it's still a subset of the cross section of that floor.

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    • IAmBroom 10 hours ago

      No.

      The support structure that is carrying the weight of the building is not a floor.

      It's bedrock, a/o concrete pylons. Force doesn't ever take a 90-degree turn. Floors are only structural to carpet, furniture, and meatbags (tensioning members aren't part of the floor, even though they run parallel to them).

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      • AnimalMuppet 10 hours ago

        Fine, call it the "vertical supports" instead of the "support structure".

        The vertical supports that carry the weight of a floor run vertically through that floor. They also carry the weight of all the higher floors. So there are vertical structures that pass through the bottom floor that support the weight of the bottom floor, plus the weight of every floor above it.

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ilinx a day ago

I know virtually nothing about architecture or structural engineering, but I imagine all the weight isn’t necessarily going down from floor to floor, but a lot of the weight is attached to support columns, and the floors are built out from that.

All the weight is still on those support columns though, and I also have a hard time wrapping my head around how something like that is possible. Engineering is amazing.

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  • antod a day ago

    I think what they meant was not literally the bottom floor, but the columns at the bottom floor.

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  • foobarian 21 hours ago

    I'm somewhat familiar with the engineering but I still marvel that this kind of building is possible. I think we are damn lucky to have a material such as steel to build with - all the engineering in the world wouldn't help without it.

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