5 ms·

If the earthquake were large enough, could the Millenium Tower completely fall over? Or is it only destined to keep leaning?

gibsonf1 8y ago
High rises in general are designed to sway in an earthquake - that sway absorbs the horizontal forces being applied - similar to a tree. If an earthquake gets sufficiently large, say larger than any known measured earthquake to date, that sway differential would increase enough that buildings would either hit each other, or the building would sway beyond the ability of the structure to recover and fall over. A standard approach for tall buildings is to incorporate either a dynamic weight high in the tower to counterbalance the sway so it doesn't go critical, or incorporate dynamic elements in the foundation system. In general, if a modern high rise is falling over, all buildings without the benefit of this level of modern engineering have already fallen over.
- malnourish 8y ago
  Would you be able to provide an explanation of what a dynamic element in the foundation is, for example?
  - toufka 8y ago
    See how a dampened dynamic build vs a regular dynamic build react to movement (and you can imagine the static build): https://youtube.com/watch?v=xp2pGxFzrzI https://youtube.com/watch?v=xp2pGxFzrzI
  - drharby 8y ago
    What is your background?
    - deleted 8y ago
      [deleted]
  - JshWright 8y ago
    >Apologies for the complaint, but could someone please let me know why I'm being downvoted for this question? It's likely because you're implying "dynamic" is a "buzzword" in a discussion about structural engineering and seismic movements (which is, by definition, a dynamic system).
    - malnourish 8y ago
      But I'm not, I was saying that due to my background, I can't help but think dynamic is a buzzword. Therefor I was asking someone who was clearly knowledgeable on the subject to set me straight.
      - JshWright 8y ago
        I don't think linking it to a buzzword adds anything to the conversation. The question didn't need a justification.
        malnourish 8y ago
        All right. I've removed it. Such is life
      - always_good 8y ago
        The "why"s (your prejudices) are irrelevant. Also I don't really think there's a background you can have where you don't understand, or cannot lookup, the difference between dynamic and static if you really cared to understand. Seems more like self-important rhetoric than anything.
  - CGamesPlay 8y ago
    In mechanical fields, dynamic means "moving". The weight literally moves, so it's dynamic. Another YouTube video that explains it a bit better: https://www.youtube.com/watch?v=f1U4SAgy60c https://www.youtube.com/watch?v=f1U4SAgy60c
- ggcdn 8y ago
  > A standard approach for tall buildings is to incorporate either a dynamic weight high in the tower to counterbalance the sway so it doesn't go critical, or incorporate dynamic elements in the foundation system. As a structural engineer on the west coast, I can say that neither of these are standard. Tuned mass dampers (TMDs) are commonly used for reducing wind-induced vibration, but not for seismic applications. Nor have I ever designed, seen, or heard of 'dynamic elements in the foundation' The reason you can't rely on TMDs is because they are tuned to a structure's elastic period of vibration. That is to say, the materials are still in their elastic range. When a ductile structure is subjected to a sufficiently large earthquake, elements of the seismic force resisting system (SFRS) will yield. Hence the period will elongate. Hence the damper will be detuned and may not provide any benefit at all.
  - abduhl 8y ago
    I think he is referring to base isolation which, I agree, is non-standard.
    - gibsonf1 8y ago
      I meant standard for the really big buildings under the highest stress. For lesser challenges, agreed, non-standard.
      - ggcdn 8y ago
        They don't base isolate tall buildings, they isolate short ones. The whole point of base isolation is period elongation. In a tall building, you're already flexible, and your column loads are tremendous. It makes no sense.
  - gibsonf1 8y ago
    A link to the next generation TMD's to handle earthquakes: tuned mass blocks, orthogonal poles, and torsional pendulums (TMDPP) : https://www.hindawi.com/journals/sv/2017/5834760/ https://www.hindawi.com/journals/sv/2017/5834760/

gibsonf1 8y ago

High rises in general are designed to sway in an earthquake - that sway absorbs the horizontal forces being applied - similar to a tree. If an earthquake gets sufficiently large, say larger than any known measured earthquake to date, that sway differential would increase enough that buildings would either hit each other, or the building would sway beyond the ability of the structure to recover and fall over. A standard approach for tall buildings is to incorporate either a dynamic weight high in the tower to counterbalance the sway so it doesn't go critical, or incorporate dynamic elements in the foundation system. In general, if a modern high rise is falling over, all buildings without the benefit of this level of modern engineering have already fallen over.

malnourish 8y ago
Would you be able to provide an explanation of what a dynamic element in the foundation is, for example?
- toufka 8y ago
  See how a dampened dynamic build vs a regular dynamic build react to movement (and you can imagine the static build): https://youtube.com/watch?v=xp2pGxFzrzI https://youtube.com/watch?v=xp2pGxFzrzI
- drharby 8y ago
  What is your background?
  - deleted 8y ago
    [deleted]
- JshWright 8y ago
  >Apologies for the complaint, but could someone please let me know why I'm being downvoted for this question? It's likely because you're implying "dynamic" is a "buzzword" in a discussion about structural engineering and seismic movements (which is, by definition, a dynamic system).
  - malnourish 8y ago
    But I'm not, I was saying that due to my background, I can't help but think dynamic is a buzzword. Therefor I was asking someone who was clearly knowledgeable on the subject to set me straight.
    - JshWright 8y ago
      I don't think linking it to a buzzword adds anything to the conversation. The question didn't need a justification.
      - malnourish 8y ago
        All right. I've removed it. Such is life
    - always_good 8y ago
      The "why"s (your prejudices) are irrelevant. Also I don't really think there's a background you can have where you don't understand, or cannot lookup, the difference between dynamic and static if you really cared to understand. Seems more like self-important rhetoric than anything.
- CGamesPlay 8y ago
  In mechanical fields, dynamic means "moving". The weight literally moves, so it's dynamic. Another YouTube video that explains it a bit better: https://www.youtube.com/watch?v=f1U4SAgy60c https://www.youtube.com/watch?v=f1U4SAgy60c
ggcdn 8y ago
> A standard approach for tall buildings is to incorporate either a dynamic weight high in the tower to counterbalance the sway so it doesn't go critical, or incorporate dynamic elements in the foundation system. As a structural engineer on the west coast, I can say that neither of these are standard. Tuned mass dampers (TMDs) are commonly used for reducing wind-induced vibration, but not for seismic applications. Nor have I ever designed, seen, or heard of 'dynamic elements in the foundation' The reason you can't rely on TMDs is because they are tuned to a structure's elastic period of vibration. That is to say, the materials are still in their elastic range. When a ductile structure is subjected to a sufficiently large earthquake, elements of the seismic force resisting system (SFRS) will yield. Hence the period will elongate. Hence the damper will be detuned and may not provide any benefit at all.
- abduhl 8y ago
  I think he is referring to base isolation which, I agree, is non-standard.
  - gibsonf1 8y ago
    I meant standard for the really big buildings under the highest stress. For lesser challenges, agreed, non-standard.
    - ggcdn 8y ago
      They don't base isolate tall buildings, they isolate short ones. The whole point of base isolation is period elongation. In a tall building, you're already flexible, and your column loads are tremendous. It makes no sense.
- gibsonf1 8y ago
  A link to the next generation TMD's to handle earthquakes: tuned mass blocks, orthogonal poles, and torsional pendulums (TMDPP) : https://www.hindawi.com/journals/sv/2017/5834760/ https://www.hindawi.com/journals/sv/2017/5834760/