Kinematic Base Isolation: The Foundation of
Innovation
by Charlo Abogada
From the past few years, kinematic base isolation has become
one of the most popular tool for earthquake resistant design of structure. The
concept of decoupling of building, with the help of base isolation, was
invented from our past centuries of infrastructure. Many researchers have been
worked on base isolation system which become acceptable as a whole in
engineering field. However, several types of isolation systems were invented,
but only few of them were accepted thoroughly. Nowadays, full scale testing is
being performed on shake table to test the various characteristics of different
isolators. Filipino should actually acquire this great concept since we are in
distress of many calamities, such as earthquake, one of the most problem of
every infrastructures facing.
Kinematic Base
Isolation is one of the passive energy dissipation technique for earthquake
resistant design of structure. It is useful to control the energy which is
passed from foundation or ground to the upper stories. To achieve this, a
flexible layer of isolator is fix up between the superstructure and
substructure. This will shift the fundamental natural time period of structure
and the frequency of vibration ultimately reduces. This will avoid the
resonance condition between the ground acceleration and structural vibration.
The main use of isolation system is to reduce the displacements, base reactions
and member forces in structure. This technology can use two systems:
Elastomeric isolation and the sliding system. Though these two can use
different parts both still lessen the impact of earthquakes to buildings, for
these are designed to reduce the motion of buildings during earthquakes. In
elastomeric isolations, from the root word elastic, it uses the power of
elasticity with natural rubbers, lead cores, and high-damping rubber. Sliding
systems uses flat sliders and friction pendulum devices.
Elastomeric
isolation is better used for large buildings because these have large axial
loads. In this system, rubbers are used because of its ability to deform and
revert back to its original shape. Lead though made of plastic, it can deform
in multiple times but it will remain its shape and strength. Seismic dampers or
high-damping rubber, are used similarly to shock absorbers in cars. This
component can absorb the energy made by earthquakes so the building will take
less of the blow.
As for sliding systems, these are great for both small and
large buildings. The changes that base isolation brings can exponentially
decrease chances of building destruction compared to ordinary buildings. The components
of the system, which are flat/spherical sliders, and friction pendulum devices,
are used for the system to provide movement and avoid destruction. The sliders
itself makes it possible for the building to gain motion and maintain its
shape. The friction pendulum devices are what make this system stay together
even when in motion.
According to the research article: Analysis,
Design, and Construction of a Base-Isolated Multiple Building Structure,
Friction Pendulum Bearings, either with single, double, or triple, sliding
surfaces, are currently the most widely used isolation system worldwide. In
fact, thousands of bearings are in service in several earthquake-prone
countries, including Italy, where about 5000 single and about 2500 double
friction pendulum devices have been installed in new apartment blocks built in
L’ Aquila after the severe earthquake that struck the city in 2009. However,
most of these buildings are relatively small and regular in plan and elevation.
So, how this thing really works on real life?
During an
earthquake, the ground beneath the building will start to move. According to
the law of inertia, an object at rest will remain at rest and an object in
motion will remain in motion with the same speed and same direction unless
acted upon by an unbalanced forced.
Effect
of Inertia in a Building when shaken at its base
Because of this,
if the ground moves, so will the building. If the ground moves fast, the
building will also follow. Once the building moves, it will become unbalanced,
changing its form from rectangle to parallelogram.
With the base-isolated
buildings, it will help the building to retain its original rectangular form.
The base-isolated building, itself, will escape the deformation and
damages-which implies that the inertial forces acting on the base-isolated
buildings have been reduced. The base isolation system will decreased the
acceleration and lengthens the vibration of the building, the time it takes for
the building to rock back and forth and then back again. And in general,
structures with longer periods of vibration tend to reduce acceleration while
those with shorter periods tend to increase or amplify acceleration.
With the help of the kinematic base
isolation, the building is built away from the ground, resting on flexible
bearings or pads known as base isolators, it will only move a little or not at
all during an earthquake. A structure won't be having severe damages that were
brought by an earthquake. As the ground moves and shakes, the building will
just follow the rhythm and will still retain its original form. It will be
helpful for the society and will lessen accidents or any dangerous events.
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