> 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.
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.