In
earthquake engineering, vibration control is a set of technical means aimed to mitigate
seismic impacts in
building
A building or edifice is an enclosed Structure#Load-bearing, structure with a roof, walls and window, windows, usually standing permanently in one place, such as a house or factory. Buildings come in a variety of sizes, shapes, and functions, a ...
and
non-building structures.
All seismic vibration control devices may be classified as ''passive'', ''active'' or ''hybrid'' where:

* ''passive control devices'' have no
feedback
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause and effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handle ...
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
actuator
An actuator is a machine element, component of a machine that produces force, torque, or Displacement (geometry), displacement, when an electrical, Pneumatics, pneumatic or Hydraulic fluid, hydraulic input is supplied to it in a system (called an ...
s within the structure;
* ''hybrid control devices'' have combined features of active and passive control systems.
When ground
seismic waves
A seismic wave is a mechanical wave of acoustic wave, acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake (natural phenomenon), quake), types of volcanic eruptions ...
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
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.
Aboard ships and large boats
On water craft, the superstruct ...
, there is a number of ways to control them in order to soothe their damaging effect and improve the building's
seismic performance
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quake (natural phenomenon), quakes) and the generation a ...
, 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 damper
A tuned mass damper (TMD), also known as a harmonic absorber or seismic damper, is a device mounted in structures to reduce mechanical vibrations, consisting of a mass mounted on one or more Damping ratio, damped springs. Its oscillation fre ...
s''.

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 building
A tower block, high-rise, apartment tower, residential tower, apartment block, block of flats, or office tower is a tall building, as opposed to a low-rise building and is defined differently in terms of height depending on the jurisdiction ...
s, predominantly in Japan, for a quarter of a century.
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
A moat is a deep, broad ditch dug around a castle, fortification, building, or town, historically to provide it with a preliminary line of defence. Moats can be dry or filled with water. In some places, moats evolved into more extensive water d ...
around the building, as well as making provisions against overturning and
P-delta effect.
In refineries or plants
snubber
A snubber is a device used to suppress ("wiktionary:snub, snub") a phenomenon such as voltage transients in electronics, electrical systems, pressure transients in fluid systems (caused by for example water hammer) or excess force or rapid moveme ...
s 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.
* 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.
Mechanical Snubbers
Piping Technology and Products, (retrieved March 2012)
Vibration Control of Mechanical, Electrical, Plumbing, and & HVAC
Standards and guidelines for testing, installation, and performance of mechanical equipment have been created in order to provide attachment methods for
equipment located in noise sensitive areas. One manual that provides such specifications is:
* 412 Manual: Installing Seismic Restraints for Mechanical Equipment (VISCMA / Vibration Isolation and Seismic Control Manufacturers Association)
See also
* Active vibration control
* Anti-vibration compound
* Cushioning
* Earthquake-resistant structures
* Metallic roller bearing
* Tuned mass damper
*Vibration isolation
''Vibration isolation'' is the prevention of transmission of vibration from one component of a system to others parts of the same system, as in Building, buildings or mechanical systems. Vibration is undesirable in many domains, primarily engineere ...
References
{{reflist, 2
Building
Earthquake engineering
Seismic vibration control