Vibration control
Encyclopedia
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 http://physics-animations.com/Physics/English/spri_txt.htm where:
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:
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.
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
.
Earthquake engineering
Earthquake engineering is the scientific field concerned with protecting society, the natural and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels...
, vibration control is a set of technical means aimed to mitigate seismic impacts in building
Building
In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...
and non-building structures.
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 feedbackFeedbackFeedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...
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 actuatorActuatorAn actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which...
s within the structure; - hybrid control devices have combined features of active and passive control systems.
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
Superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships...
, 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 superstructureSuperstructureA superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships...
with properly engineered damperDamperA damper is a device that deadens, restrains, or depresses.Damper may refer to:* Dashpot, a type of hydraulic or mechanical damper,* Shock absorber , a mechanical device designed to dissipate kinetic energy...
s;
- to disperseDisperseDisperse is a Christian Rock band from Southern Indiana. The band was formerly known, with an adjusted roster, as "Stuff."-Members :...
the wave energy between a wider range of frequencies;
- to absorbAbsorption (acoustics)Acoustic absorption is that property of any material that changes the acoustic energy of sound waves into another form, often heat, which it to some extent retains, as opposed to that sound energy that material reflects or conducts. Acoustic absorption is represented by the symbol A in calculations...
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.
However, there is quite another approach: partial suppression
Suppression
The term suppression may refer to:* Oppression, the exercise of authority or power in a burdensome, cruel, or unjust manner, also an act or instance of oppressing...
of the seismic energy flow into the superstructure
Superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships...
known as seismic or base isolation
Base isolation
Base isolation, also known as seismic base isolation or base isolation system, is one of the most popular means of protecting a structure against earthquake forces...
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
Superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships...
from its substructure
Substructure
In mathematical logic, an substructure or subalgebra is a structure whose domain is a subset of that of a bigger structure, and whose functions and relations are the traces of the functions and relations of the bigger structure...
resting on a shaking ground. It also requires creating a rigidity diaphragm
Diaphragm (structural system)
In structural engineering, a diaphragm is a structural system used to transfer lateral loads to shear walls or frames primarily through in-plane shear stress...
and a moat
Moat
A moat is a deep, broad ditch, either dry or filled with water, that surrounds a castle, other building or town, historically to provide it with a preliminary line of defence. In some places moats evolved into more extensive water defences, including natural or artificial lakes, dams and sluices...
around the building, as well as making provisions against overturning and P-delta effect
P-Delta Effect
In structural engineering, the P-Δ or P-Delta effect refers to the abrupt changes in ground shear, overturning moment, and/or the axial force distribution at the base of a sufficiently tall structure or structural component when it is subject to a critical lateral displacement.The P-Delta effect is...
.
See also
- Earthquake engineering structuresEarthquake engineering structuresEarthquake-resistant structures are designed and constructed to withstand various types of hazardous earthquake exposures at the sites of their particular location....
- Elevated building foundation
- Earthquake-Protective Building Buffer
- Tuned mass damperTuned mass damperA tuned mass damper, also known as an active mass damper or harmonic absorber, is a device mounted in structures to reduce the amplitude of mechanical vibrations. Their application can prevent discomfort, damage, or outright structural failure...
- Dynamic Vibration AbsorberDynamic Vibration AbsorberIn vibration analysis, a dynamic vibration absorber, or vibration neutralizer, is a tuned spring-mass system which reduces or eliminates the vibration of a harmonically excited system. Rotating machines such as engines, motors, and pumps often incite vibration due to rotational imbalances...