Earthquake
Resistant Designs:
- Design is nothing but calculation of loads on to structure and to make structure to resist them.
- If such design is to make such that it resists Earthquake, then such design is called Earthquake Resistant Designs.
- The most popular Earthquake resistant Designs are :
- Base Isolation Devices
- Seismic Dampers.
Base
isolation techniques
Earthquakes mainly happen in surface of
Earth, so if we separate the structure from surface, then we can build
Earthquake resistant Designs.
The main thought behind Base Isolation
Devices is to separate buildings from surface of Earth.
The above
diagram shows the Base Isolation Devices in a diagrammatic manner.
The above diagram shows the movement of
buildings separated by Base isolation device, during an Earthquake.
If the ground
motion is in left horizontal direction, the buildings separated by bearings
moves in backward direction, which resists earthquakes.
In above cases, the foundation is in
Earth, but the structure is separated by Bearings.
Dis-advantage:-
High-rise buildings or
buildings rested on soft soil are not suitable for base-isolation.
Spherical Sliding Base Isolation
In this case, the foundation pier of
entire is structure is separated by means of Spherical Sliding Isolation Bearing.
The building is supported by bearing pads
that have a curved surface and low friction. During an earthquake the building
is free to slide on the bearings. Since the bearings have a curved surface, the
building slides both horizontally and vertically. The forces needed to move the
building upwards limits the horizontal or lateral forces which would otherwise
cause building deformations.
Seismic Dampers
Another
approach for controlling seismic damage in buildings and improving their
seismic performance is by installing Seismic Dampers in place of structural
elements, such as diagonal braces. These dampers act like the hydraulic shock
absorbers in cars – much of the sudden jerks are absorbed in the hydraulic
fluids and only little is transmitted above to the chassis of the car. When
seismic energy is transmitted through them, dampers absorb part of it, and thus
damp the motion of the building.
Types of dampers
1. Viscous
Dampers 2.Friction
Dampers
3. Yielding
Dampers 4.Viscoelastic Dampers
Viscous Dampers (energy is absorbed by silicone-based fluid passing
between piston cylinder arrangement),
Friction Dampers (energy is absorbed by surfaces with friction between
them rubbing against each other),
Yielding Dampers (energy is absorbed by metallic components that
yield).
Viscoelastic Dampers (energy is absorbed by utilizing the controlled
shearing of solids).
Thus
by equipping a building with additional devices which have high damping
capacity, we can greatly decrease the seismic energy entering the building.
How
Dampers Work
Fluid dampers may be designed to behave
as a pure energy dissipater or a spring or as a combination of the two. A fluid
viscous damper resembles the common shock absorber such as those found in
automobiles. The piston transmits energy entering the system to the fluid in
the damper, causing it to move within the damper. The movement of the fluid
within the damper fluid absorbs this kinetic energy by converting it into heat.
In buildings this can mean that the building columns protected by dampers will
undergo considerably less horizontal movement and damage during an earthquake.
Active Control Devices for Earthquake
Resistance
After development of passive devices
such as base isolation and TMD. The next logical steps is to control the action
of these devices in an optimal manner by an external energy source the
resulting system is known as active control device system. Active control has
been very widely used in aerospace structures. In recent years significant
progress has been made on the analytical side of active control for civil
engineering structures. Also a few models explains as shown that there is great
promise in the technology and that one may expect to see in the foreseeable
future several dynamic “Dynamic Intelligent Buildings” the term itself seems to
have been joined by the Kajima Corporation in Japan. In one of their pamphlet
the concept of Active control had been explained in every simple manner and it
is worth quoting here.
People standing in swaying train or bus
try to maintain balance by unintentionally bracing their legs or by relaying on
the mussels of their spine and stomach. By providing a similar function to a
building it can dampen immensely the vibrations when confronted with an
earthquake. This is the concept of Dynamic Intelligent Building (DIB).
Other
Methods
The liquid sloshing during earthquakes
has assumed significance importance in view of over flow of petroleum products
from storage tank in post earthquakes. One of the important consideration with
sloshing is that is associated with a very low damping. The wave height was
controlled through force applied to the side wall by a hydraulic actuator. The
active control successfully reduced wave heights to the level of 6% of those
without control, for harmonic excitations at sloshing frequency. For earthquake
type excitation the wave heights were reduced to 19% level.
CONCLUSION
We can’t stop the natural calamities,
but we can reduce the damage to human life and property.
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