In
earthquake engineering
Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earth ...
, vibration control is a set of technical means aimed to mitigate
seismic
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
impacts in
building
A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). Buildings come in a variety of sizes, shapes, and fun ...
and
non-building structures.
All seismic vibration control devices may be classified as ''passive'', ''active'' or ''hybrid'' where:
![LRBtest](https://upload.wikimedia.org/wikipedia/commons/b/bc/LRBtest.jpg)
* ''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 handled ...
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 component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover".
An actuator requires a control device (controlled by control signal) a ...
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 wave of acoustic energy that travels through the Earth. It can result from an earthquake, volcanic eruption, magma movement, a large landslide, and a large man-made explosion that produces low-frequency acoustic energy. S ...
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
Seismic analysis is a subset of structural analysis and is the calculation of the response of a building (or nonbuilding) structure to earthquakes. It is part of the process of structural design, earthquake engineering or structural assessment ...
, for instance:
* to
dissipate
In thermodynamics, dissipation is the result of an irreversible process that takes place in homogeneous thermodynamic systems. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to ...
the wave energy inside a superstructure with properly engineered
damper
A damper is a device that deadens, restrains, or depresses. It may refer to:
Music
* Damper pedal, a device that mutes musical tones, particularly in stringed instruments
* A mute for various brass instruments
Structure
* Damper (flow), a mechan ...
s;
* to disperse the wave energy between a wider range of frequencies;
* to
absorb the
resonant
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
portions of the whole wave frequencies band with the help of so-called ''
mass dampers''.
![SFCityHall](https://upload.wikimedia.org/wikipedia/commons/1/18/SFCityHall.png)
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 jurisdictio ...
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
Seismic base isolation, also known as base isolation, or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially decoupl ...
'' which has been implemented in a number of historical buildings all over the world and remains in the focus of
earthquake engineering
Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earth ...
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, either dry or filled with water, that is dug and surrounds a castle, fortification, building or town, historically to provide it with a preliminary line of defence. In some places moats evolved into more extensive ...
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 ("snub") a phenomenon such as voltage transients in electrical systems, pressure transients in fluid systems (caused by for example water hammer) or excess force or rapid movement in mechanical systems.
Ele ...
s are often used for vibration control. Snubbers come in two different variations: hydraulic snubber and a
mechanical snubber
A mechanical snubber is a mechanical device designed to protect components from excess shock or sway caused by seismic disturbances or other transient forces. During normal operating conditions, the snubber allows for movement in tension and compre ...
.
* 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
Active vibration control is the active application of force in an equal and opposite fashion to the forces imposed by external vibration. With this application, a precision industrial process can be maintained on a platform essentially vibration- ...
*Anti-vibration compound
An anti-vibration compound is a temperature-resistant mixture of a liquid with fine particles, which is used to reduce oscillations in calender rolls
and to dampen vibrations in fabricated structures like machine beds and housings.
Use
Vibration ...
*Cushioning
Package cushioning is used to protect items during shipment. Vibration and impact shock during shipment and loading/unloading are controlled by cushioning to reduce the chance of product damage.
Cushioning is usually inside a shipping container s ...
*Earthquake-resistant structures
Earthquake-resistant or aseismic structures are designed to protect buildings to some or greater extent from earthquakes. While no structure can be entirely immune to damage from earthquakes, the goal of earthquake-resistant construction is to ...
*Metallic roller bearing
A metallic roller bearing is a base isolation device which is intended for protection of various building and non-building structures against potentially damaging lateral impacts of strong earthquakes.
This bearing support may be adapted, with ce ...
*Tuned 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 damped springs. Its oscillation frequency is tuned ...
*Vibration isolation Vibration isolation is the process of isolating an object, such as a piece of equipment, from the source of vibrations.
Vibration is undesirable in many domains, primarily engineered systems and habitable spaces, and methods have been developed to p ...
References
External links
* {{curlie, Science/Technology/Structural_Engineering/Earthquake_Engineering/Control
Building
Earthquake engineering
Seismic vibration control