Vibration control

In earthquake engineering, vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures [http://www.ecs.csun.edu/~shustov/Seismic_Control_Directory.html] . All seismic vibration control devices may be classified as "passive", "active" or "hybrid" [http://physics-animations.com/Physics/English/spri_txt.htm] where:

* "passive control devices" have no feedback capability between them, structural elements and the ground;
* "active control devices" are force delivery devices integrated with real-time processing sensors and evaluators/controllers within the structure and on the ground;
* "hybrid control devices" have combined features of active and passive control systems.cite book|title= Active, Hybrid and Semi-Active Structural Control|author=Chu, S.Y.; Soong, T.T.; Reinhorn, A.M.|date=2005|publisher= John Wiley & Sons |isbn=0470013524]

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.

, 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" [http://www.ecs.csun.edu/~shustov/Topic5.htm] ;

* to reflect, diffract, and dissipate seismic waves in a process of their vertical propagation with the help of "elevated building foundation" (EBF) [https://central.nees.org/data/get/NEES-2006-0283/Public/EBF%20and%20EP.pdf] ;

* to absorb the resonant portions of the whole wave frequencies band with the help of so called "mass dampers" [http://ffden-2.phys.uaf.edu/211_fall2002.web.dir/Eva_Burk/Eva's%201st%20page.htm] .

[
San Francisco City Hall] 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 [http://www.takenaka.co.jp/takenaka_e/quake_e/seishin/seishin.htm] . To increase the shielded range of forcing frequencies, the concept of "Multi-Frequency Quieting Building System" (MFQBS) was developed in U.S. [http://www.ecs.csun.edu/~shustov/Topic9.htm] .

However, there is quite another approach: partial suppression of the seismic energy flow into the superstructure known as "seismic" or "base isolation" which was implemented in a number of historical buildings all over the world.

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.

ee also

*Earthquake engineering structures

Notes