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.
> 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.
1) I'm not saying there aren't novel solutions - there's a whole category of devices that use active control. I'm saying its not common place.
2) From what I understand, China has a completely different design philosophy. They design structures to remain elastic, under certain earthquakes, which would then allow for TMDs.
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.
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
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
>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).
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.
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.
