Vibration control
In earthquake engineering, vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures.
All seismic vibration control devices may be classified as passive, active or hybrid where:- passive control devices have no feedback capability between them, structural elements and the ground;
- active control devices incorporate real-time recording instrumentation on the ground integrated with earthquake input processing equipment and actuators within the structure;
- hybrid control devices have combined features of active and passive control systems.[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;
- to absorb the resonant portions of the whole wave frequencies band with the help of so-called mass dampers 's%201st%20page.htm.
However, there is quite another approach: partial suppression of the seismic energy flow into the superstructure known as seismic or base isolation which has been implemented in a number of historical buildings all over the world and remains in the focus of earthquake engineering research for years.
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.
In refineries or plants snubbers are often used for vibration control. Snubbers come in two different variations: hydraulic snubber and a mechanical snubber.
- Hydraulic snubbers are used on piping systems when restrained thermal movement is allowed.[2]
- Mechanical snubbers operate on the standards of restricting acceleration of any pipe movements to a threshold of 0.2 g's, which is the maximum acceleration that the snubber will permit the piping to see.[3]
See also
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- Active vibration control
- Earthquake resistant structures
- Metallic roller bearing
- Tuned mass damper
- Dynamic Vibration Absorber
- Cushioning
- Vibration isolation
References
- ↑ Chu, S.Y.; Soong, T.T.; Reinhorn, A.M. (2005). Active, Hybrid and Semi-Active Structural Control. John Wiley & Sons. ISBN 0-470-01352-4.
- ↑ Hydraulic Snubbers Piping Technology and Products, (retrieved 2012)
- ↑ Mechanical Snubbers Piping Technology and Products, (retrieved March 2012)