Vibration control

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In earthquake engineering, vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures. All vibration control devices may be classified as passive, active or hybrid [1].

When ground seismic waves reach up and start to penetrate a base of a building, their energy flow density, due to reflections, reduces dramatically: usually, up to 90%. However, the remaining portions of the incident waves during a major earthquake still bear a huge devastating potential.

After the seismic waves enter a superstructure, there is a number of ways to control them in order to sooth their damaging effect and improve the building's seismic performance, for instance:

• to dissipate the wave energy inside a superstructure with properly engineered dampers;

• to disperse the wave energy between a wider range of frequencies by adequately configuring a building elevation [2];

• to absorb the resonant portions of the whole wave frequencies band with the help of so called mass dampers [3].

Devices of the last kind, abbreviated correspondingly as TMD for the tuned (passive), as AMD for the active, and as HMD for the hybrid mass dampers, have been studied and installed in high-rise buildings, predominantly in Japan, for a quarter of a century [4].

To increase the shielded range of forcing frequencies, the concept of Multi-Frequency Quieting Building System (MFQBS) was developed in U.S. [5].

However, there is quite another approach: partial suppression of the seismic energy flow into the superstructure known as seismic or base isolation. For this, some pads are inserted into all major load-carrying elements in the base of the building which should substantially decouple a superstructure from its substructure resting on a shaking ground. It also requires creating a rigidity diaphragm and a moat around the building, as well as making provisions against overturning and P-delta effect.