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1
EARTHQUAKE AND POSSIBLE SOLUTIONS USING DAMPERS
TECHNOLOGY
Mahdi hosseini1, Mohammad Yousef Dastajani Farahani2 ,Prof.N.V.Ramana Rao3
1
Post Graduate Student, Dept. of Civil Engineering, Jawaharlal Nehru Technological University Hyderabad
(JNTUH), Hyderabad, Andhra Pradesh, India
Email: [email protected]
2
Post Graduate Student, Dept. of Civil Engineering, Jawaharlal Nehru Technological University Hyderabad
(JNTUH), Hyderabad, Andhra Pradesh, India
Email: [email protected]
3
Professor, Dept. of Civil Engineering, Jawaharlal Nehru Technological University Hyderabad (JNTUH),
Hyderabad, Andhra Pradesh, India
Email: [email protected]
with the blocks moving away from each other. Faults
ABSTRACT
occur from both tensional and compressional forces.
Earthquake is a natural phenomenon occurs due to the
disturbance in tectonic plates. Tectonic plates are the
pieces of the earth’s crust and the upper most mantles.
Dampers can be installed in the structural frame of a
The thickness of the plates is of around 100km and
building to absorb some of the energy going into the
consist principles materials like oceanic Crust and
building from the shaking ground during an earthquake.
continental crust. Earthquakes occur on faults. A fault is
The dampers reduce the energy available for shaking the
a thin zone of crushed rock separating blocks of the
building.
earth's crust. When an earthquake occurs on one of
Key words: Earthquake, Tectonic Plates, Fault, Crust,
these faults, the rock on one side of the fault slips with
Dampers
respect to the other. Faults can be centimeters to
I. BACKGROUND
thousands of kilometers long. The fault surface can be
vertical, horizontal, or at some angle to the surface of the
HISTORY'S 10 WORST EARTHQUAKES
earth. Faults can extend deep into the earth and may or
The
may not extend up to the earth's surface. A fault can be
p o we r f u l , d e a d l i e s t e a r t h q u a k e s e v e r . The death
defined as the displacement of once connected blocks of
toll continues to climb as Japan recovers from the most
rock along a fault plane. This can occur in any direction
powerful quake in its recorded history and the towering
Daily
Beast’s
r u n d o wn
of
the
most
tsunami that followed. Japan’s Kyodo News agency said
between 200 and 300 bodies have been found on a beach in
Sendai, the population center nearest the quake’s epicenter,
2
and another 110 people have been confirmed dead
127,000 in surrounding areas. The 7.8-magnitude quake—
elsewhere. But the agency said the death toll will likely
reported as 8.5 magnitudes by Chinese news sources—
surpass 1,000. Read more and view photos of the
caused nearly all of the houses to collapse in Longde and
devastation plus view shocking video from Japan's disaster
Huining, with damages in seven provinces and regions,
zone. Here The Daily Beast’s rundown of the most
including dammed rivers, landslides, and severe cracks in
powerful, deadliest earthquakes ever.
the ground. Seiches were even observed in various lakes and
SHAANXI EARTHQUAKE
fjords in Norway. Aftershocks from the earthquake occurred
The Shaanxi earthquake—also known as the Hua County
as long as three years later, but the effects did not come
earthquake—is the deadliest Quake to date, resulting in
close to the severity of the first.
approximately 830,000 deaths. On the morning of Jan. 23,
ALEPPO EARTHQUAKE
1556, it destroyed a 520-mile-wide area in China, killing 60
percent of the population in Some of the 97 affected
counties. One witness writes, “Mountains and rivers changed
places and roads were destroyed. In some places, the ground
suddenly rose up and formed new hills, or it sank abruptly
and became new valleys.” Because a majority of civilians
were living in yaodongs, or artificial caves in loess cliffs,
fatalities reached an all-time high as the caves collapsed,
killing those inside. Modern estimates predict the magnitude
was around 8.0, not a record high, but the earthquake still
Set in a nest of fault lines in northern Syria, Aleppo—now
known as Halab—was hit with an 8.5-magnitude earthquake
in 1138, jolting areas as far as 200 miles away from the city.
The most damage was seen in Harem, where crusaders had
built a large citadel that was crumbled below the castle,
killing 600 castle guards at the time. Although residents of
Aleppo were warned by foreshocks and some fled to the
countryside, the quake was much Larger than anticipated,
and the city and all homes surrounding it were brought to the
ground.
ranks third on the list of deadliest natural disasters in
history.
TANGSHAN EARTHQUAKE
INDIAN OCEAN EARTHQUAKE
Underwater earthquakes are believed to be the most
dangerous because they can create tsunamis and tidal waves,
Although some say there were early warnings of the
Tangshan earthquake, it hit Chinese civilians unexpectedly
at 3:42 a.m. on July 28, 1976, shaking people from their
beds and leveling the entire city in a matter of seconds. The
7.8-magnitude quake killed more than 240,000 people,
leaving survivors without access to water, food, or
electricity. Relief workers also caused an accidental traffic
jam on the only drivable road, and although 80 percent of
those stuck under the rubble were saved, a 7.1-magnitude
aftershock struck the afternoon of the 28th, killing many
which is exactly what happened on Dec. 26, 2004, when the
Indian Ocean earthquake wreaked havoc on India,
Indonesia, Sri Lanka, and Thailand—and beyond. With a
magnitude of between 9.1 and 9.3, this earthquake is the
second largest ever recorded, and it also had the longest
duration, lasting between eight and 10 minutes. Devastating
tsunamis hit land masses bordering the ocean, prompting a
widespread humanitarian response. Initially, reports said the
quake killed approximately 100,000, but later calculations
showed it resulted in more than 230,000 deaths.
more and cutting off access to those trying to provide aid,
making it one of the deadliest quakes of the 20th century.
HAIYUAN EARTHQUAKE
DAMGHAN EARTHQUAKE
In 856, in the area we now know as Iran, an earthquake of
8.0 magnitudes hit the capital city of Damghan, destroying
The Haiyuan earthquake hit Dec. 16, 1920, killing more than
73,000 in China’s Haiyuan County and approximately
the city, countryside, and nearly every village within 200
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miles of the epicenter. Situated between two major tectonic
businesses and poisoning wells led to the deaths of an
plates, Iran is an area of frequent earthquake activity, but
estimated 2,500 non-Japanese immigrants. The Japanese
residents of Damghan were unprepared for a temblor of this
government has heavily funded disaster preparation ever
magnitude. The quake resulted in approximately 200,000
since, holding “Disaster Prevention Day” on Sept. 1, the
deaths.
Kanto quake’s anniversary.
ARDABIL EARTHQUAKE
Another Iranian earthquake hit Feb. 28, 1997, when the 15-
II. INTRODUCTION
STRUCTURE OF THE EARTH
second quake rippled through northern Iran, with deaths
tallying up to 150,000. There was severe damage to roads
The Earth is an oblate spheroid. It is composed of a number
and electrical power lines, and all communications and
of different layers as determined by deep drilling and
water distribution became near impossible, leaving the city
seismic evidence (Figure 3.1). These layers are:
of Ardabil in a state of desperation. Hospitals overflowed

The core which is approximately 7000 kilometers
with patients, and even as it tried to recover, the area was hit
in diameter (3500kilometers in radius) and is
with nearly 350 aftershocks, the highest recorded at 5.2 on
located at the Earth's center.
the Richter scale.
HOKKAIDO EARTHQUAKE

The mantle which surrounds the core and has a
thickness of 2900 kilometers.
In 1730, an 8.3-magnitude earthquake hit Japan’s second
largest island, Hokkaido, causing landslides, power outages,

road damage, and a tsunami causing 137,000 fatalities. The
composed of basalt rich oceanic crust and granitic
island was struck by a similar, though not as intense,
rich continental crust.
The crust floats on top of the mantle. It is
earthquake in 2003.
ASHGABAT EARTHQUAKE
The 7.3-magnitude earthquake that hit Turkmenistan’s
capital, Ashgabat, in 1948 tore much of the city down,
collapsing almost all of its brick buildings, heavily
damaging concrete structures, and derailing freight trains
with effects felt across the border in the Darreh Gaz region
of Iran. The Turkmen government has upwardly revised the
official death toll from 110,000 to 176,000; the quake also
Fig 3.1 Layers beneath the Earth's surface
killed the mother of future dictator Saparmurat Niyazov and
resulted in his placement in a Soviet orphanage, an
important component of the former leader’s self-mythology.
The core is a layer rich in iron and nickel that is composed
of two layers: the inner and outer cores. The inner core is
theorized to be solid with a density of about 13 grams per
GREAT KANTO EARTHQUAKE
cubic centimeter and a radius of about 1220 kilometers. The
The Great Kanto Earthquake of 1923 devastated Tokyo and
outer core is liquid and has a density of about 11 grams per
Yokohama, causing huge fires and resulting in as many as
cubic centimeter. It surrounds the inner core and has an
142,000 deaths, but it may be best remembered for its
average thickness of about 2250 kilometers.
horrific aftermath, when rumors that Koreans were looting
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The mantle is almost 2900 kilometers thick and comprises
in an area known as the Basin and Range Province in the
about 83% of the Earth's volume. It is composed of several
western United States (centered in Nevada this area is about
different layers. The upper mantle exists from the base of the
1500 kilometers wide and runs about 4000 kilometers
crust downward to a depth of about 670 kilometers. This
North/South). Continental crust is thickest beneath mountain
region of the Earth's interior is thought to be composed of
ranges and extends into the mantle. Both of these crust types
peridotite, an ultramafic rock made up of the minerals
are composed of numerous tectonic plates that float on top
olivine and pyroxene. The top layer of the upper mantle, 100
of the mantle. Convection currents within the mantle cause
to 200 kilometers below surface, is called the asthenosphere.
these plates to move slowly across the asthenosphere.
Scientific studies suggest that this layer has physical
properties that are different from the rest of the upper
mantle. The rocks in this upper portion of the mantle are
more rigid and brittle because of cooler temperatures and
lower pressures. Below the upper mantle is the lower mantle
that extends from 670 to 2900 kilometers below the Earth's
surface. This layer is hot and plastic. The higher pressure in
this layer causes the formation of minerals that are different
from those of the upper mantle.
Fig 3.2 Structure of the Earth's crust and top most layer
of the upper mantle
The lithosphere is a layer that includes the crust and the
upper most portion of the mantle (Figure 3.2). This layer is
TECTONIC PLATES
about 100 kilometers thick and has the ability to glide over
PRIMARY PLATES
the rest of the upper mantle. Because of increasing
These seven plates comprise the bulk of the continents and
temperature and pressure, deeper portions of the lithosphere
the Pacific Ocean.
are capable of plastic flow over geologic time. The
lithosphere is also the zone of earthquakes, building,
(i) African Plate
(ii) Antarctic Plate (iii)Eurasian Plate
(iv)Pacific Plate
volcanoes, and continental drift.
(v)Indo-Australian Plate
The topmost part of the lithosphere consists of crust. This
material is cool, rigid, and brittle. Two types of crust can be
(vi)North American Plate
(vii)South American Plate
SECONDARY PLATES
identified: oceanic crust and continental crust (Figure 3.2).
Both of these types of crust are less dense than the rock
found in the underlying upper mantle layer. Ocean crust is
thin and measures between 5 to 10 kilometers thick. It is
These are generally not shown in the map as these propagate
only for lesser areas when compared with the major tectonic
plates.
also composed of basalt and has a density of about 3.0
(i)Arabian Plate
grams per cubic centimeter.
Plate
The continental crust is 20 to 70 kilometers thick and
composed mainly of lighter granite (Figure 3.2). The density
(ii)Caribbean Plate
(iii) Cocos
(iv)Indian Plate
(v)Juan de Fuca Plate (vi)Nazca Plate (vii)Philippine Sea
Plate
(viii)Scotia Plate
of continental crust is about 2.7 grams per cubic centimeter.
Major no of tectonic plates are located fortunately under
It is thinnest in areas like the Rift Valleys of East Africa and
Japan so often Japan is effected by earthquakes.
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PROPAGATION OF AN EARTHQUAKE
where seismographs cannot detect an earthquake after
Due to the disturbances caused in the lithosphere i.e. in the
its seismic waves have passed through the Earth. When an
movement of tectonic plates large amount of energy is
earthquake occurs, seismic waves radiate out spherically
released in the earth crust which turns into Seismic waves.
from the earthquake's focus. The primary seismic
The seismic activity refers to the type, magnitude and the
waves are refracted by the liquid outer core of the Earth and
size of the earthquake Earthquakes are measured using
are not detected between 104° and 140° (between
observations from seismometers. The moment magnitude is
approximately 11,570 and 15,570 km or 7,190 and
the most common scale on which earthquakes larger than
9,670 mi) from the epicenter
approximately 5 are reported for the entire globe. The more
numerous earthquakes smaller than magnitude 5 reported by
national seismological observatories are measured mostly on
the
local
magnitude
scale,
also
referred
to
as
the Richter scale. These two scales are numerically similar
over their range of validity. To sum it up briefly an
earthquake phenomenon can be explained as follows Due to
the uneven disturbances caused in the tectonic plates large
Fig 1.1 Earthquake
amount of energy is emerged into the earth’s surface and its
interior parts thus this energy is completely transferred into
SEISMIC WAVES
nearest areas from the focus with appropriate deviation.
Seismic waves consist of S-waves and P-waves.
Earthquakes that happen in one place can be detected by
PRIMARY WAVES (P-waves)
seismographs in other. The waves from the epicenter of a
major earthquake propagate outward as surface waves. In
Primary
the case of compression waves, the energy released in this
are longitudinal in nature. P waves are pressure waves that
fashion radiates from the focus under the epicenter and
travel faster than other waves through the earth to arrive at
travels all the way through the globe. Seismologists, who
seismograph stations first, hence the name "Primary". These
study the distribution of these waves, can map such
waves can travel through any type of material, including
propagation. The further away a point is on Earth from the
fluids, and can travel at nearly twice the speed of S waves.
focus of a quake, the longer the time it will take for a
In air, they take the form of sound waves; hence they travel
seismograph station at that point to detect the far-away
at the speed of sound. Typical speeds are 330 m/s in air,
quake. Compression waves are also named "P-waves" or
1450 m/s in water and about 5000 m/s in granite.
"pressure waves." Due to the nature of Earth's interior, "P-
SECONDARY WAVES (S-waves)
waves" can be refracted and reflected as they encounter
differing density layers between the core and the mantle. As
a result, seismographs in some areas on the other side of the
world opposite the epicenter of a major earthquake would
record nothing. Such an area on the Earth's surface is called
a "shadow zone."
A seismic shadow zone is an area of the Earth's surface
waves
are
compression
waves
that
Secondary waves are shear waves that are transverse in
nature. Following an earthquake event, S-waves arrive at
seismograph stations after the faster-moving P-waves and
displace the ground perpendicular to the direction of
propagation. Depending on the preoperational direction, the
wave can take on different surface characteristics; for
example, in the case of horizontally polarized S waves, the
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ground moves alternately to one side and then the other. Swaves can travel only through solids, as fluids (liquids and
gases) do not support shear stresses. S-waves are slower
than P-waves, and speeds are typically around 60% of that
of P-waves in any given material.
There are also some other waves which important in
measuring the intensity of earthquake but not so dangerous
compared to s and p waves, They are as follows:
SURFACE WAVES
Seismic surface waves travel along the Earth's surface. They
are called surface waves, as they diminish as they get further
from the surface. Their velocity is lower than those of
seismic body waves (P and S).
FIG 1.2 WAVES
THE MOMENT MAGNITUDE SCALE
Unfortunately, many scales, such as the Richter scale, do not
RAYLEIGH WAVES
provide accurate estimates for large magnitude earthquakes.
Rayleigh waves, also called ground roll, are surface waves
Today the moment magnitude scale, abbreviated MW, is
that travel as ripples with motions that are similar to those of
preferred because it works over a wider range of earthquake
waves on the surface of water.
sizes and is applicable globally. The moment magnitude
scale is based on the total moment release of the earthquake.
LOVE WAVES
Moment is a product of the distance a fault moved and the
Love waves are horizontally polarized shear waves (SH
force required to move it. It is derived from modeling
waves), existing only in the presence of a semi-infinite
recordings of the earthquake at multiple stations. Moment
medium overlain by an upper layer of finite thickness. They
magnitude estimates are about the same as Richter
usually travel slightly faster than Rayleigh waves, about
magnitudes for small to large earthquakes. But only the
90% of the S wave velocity, and have the largest amplitude.
moment magnitude scale is capable of measuring M8 (read
STONELEY WAVES
‘magnitude 8’) and greater events accurately. Magnitudes
A Stoneley wave is a type of large amplitude Rayleigh wave
that propagates along a solid-fluid boundary or under
specific conditions also along solid-solid boundary. They
can be generated along the walls of a fluid-filled borehole.
are based on a logarithmic scale (base 10). What this means
is that for each whole number you go up on the magnitude
scale, the amplitude of the ground motion recorded by a
seismograph goes up ten times. Using this scale, magnitude
5 earthquakes would result in ten times the level of ground
shaking as a Magnitude 4 earthquakes (and 32 times as
much as energy would be released). To give you an idea
how these numbers can add up, think of it in terms of the
energy released by Explosives: a magnitude 1 seismic wave
releases as much energy as blowing up 6 ounces of TNT. A
magnitude 8 earthquake releases as much energy as
detonating 6 million tons of TNT. Fortunately, most of the
earthquakes that occur each year are magnitude 2.5 or less,
7
too small to be felt by most people. Magnitude scales can be
used to describe earthquakes so small that they are
expressed in negative numbers. The scale also has no upper
limit, so it can describe earthquakes of unimaginable and (so
far) un-experienced intensity, such as magnitude 10.0 and
beyond.
DAMAGES CAUSED BY EARHTQUAKES
The effects of an earthquake are strongest in a broad zone
surrounding
the
epicenter.
Surface
ground
cracking
associated with faults that reach the surface often occurs,
with horizontal and vertical displacements of several yards
common. Such movement does not have to occur during a
major earthquake; slight periodic movements called fault
creep can be accompanied by micro earthquakes too small to
be felt. The extent of earthquake vibration and subsequent
damage to a region is partly dependent on characteristics of
the ground. For example, earthquake vibrations last longer
and are of greater wave amplitudes in unconsolidated
surface material, such as poorly compacted fill or river
deposits; bedrock areas receive fewer effects. The worst
Fig 1.6 Damage of earthquake
GLOBAL DISTRIBUTION OF EARTHQUAKES
According to a moderate estimate about 30,000 earthquakes
occur every year. But most of these are so slight that we
cannot feel them. There is no visible damage from them. But
every year there are some earthquakes of great intensity and
magnitude. If one of these occurs in a densely populated
region, there is damage and destruction enough to draw
people's attention all the world over. Every year hundreds of
earthquakes pass unnoticed because they occur in areas
where there is no possibility of any loss of human life and
damage to property.
damage occurs in densely populated urban areas where
structures are not built to withstand intense shaking. There,
L waves can produce destructive vibrations in buildings and
Earthquakes have a definite distribution pattern. There
break water and gas lines, starting uncontrollable fires.
are three major belts in the world which are frequented by
Damage and loss of life sustained during an earthquake
earthquakes of varying intensities. These belts are as under:
result from falling structures and flying glass and objects.
1. The Circum-Pacific Belt
Flexible structures built on bedrock are generally more
resistant to earthquake damage than rigid structures built on
loose soil. In certain areas, an earthquake can trigger
2. The Mid-Atlantic Belt
3. The Mid-Continental Belt
mudslides, which slip down mountain slopes and can bury
habitations below. A submarine earthquake can cause a
1. THE CIRCUM-PACIFIC BELT
tsunami, a series of damaging waves that ripple outward
from the earthquake epicenter and inundate Coastal cities
This belt is located around the coast of the Pacific Ocean. In
this belt the earthquakes originate mostly beneath the ocean
floor near the coast. The Circum- Pacific Belt represents the
convergent plate boundaries where the most widespread and
intense earthquakes occur. This belt runs from Alaska to
Kurile, Japan, Mariana and the Philippine trenches. Beyond
this, it bifurcates into two branches, one branch going
8
towards the Indonesian trench and the other towards the
by experiencing about 20 per cent of the earthquakes in the
Kermac-Tonga trench to the northwest of Newzealand
world. This belt records earthquakes of shallow and
spreading completely over the belt.This belt is located on
intermediate origin. However, it is true that sometimes
the western side of the Pacific Ocean. On the eastern side of
earthquakes of great violence occur in this belt. This belt
the Pacific Ocean, the earthquake belt runs parallel to the
forms a great circle approximately east and west around the
west coast of North America and moves on towards the
earth, through the Mediterranean, Southern Asia, Indonesia
South along the Peru and Chile trench lying on the west
and the East Indies, where the great majority of recorded
coast of South America. This belt has about 66 percent of
shocks occur. It may be pointed out that more than 50
the total earthquake that are recorded in the world. Most of
percent of all earthquakes are associated with the young
the earthquakes occurring in this belt are shallow ones with
folded mountains which are said to be still growing. The
their focus about 25 km deep. It may be pointed out that
Andes, Himalayas and Coast Ranges of the United States are
these belts being the zones of convergent plate boundaries
the specific examples. It is worthwhile to remember that this
(the subduction zones) are is statically very unstable, Japan
girdle of young fold mountains has no correspondence with
alone experience about 1500 earthquakes per year.
the line of active volcanoes like the Circum-Pacific
2. THE MID-ATLANTIC BELT
earthquake zone. There are some regions on the earth's
surface which are relatively immune from violent and
This belt is characterized by the sea floor spreading which is
the main cause of the occurrence of earthquakes in it. This
earthquake belt runs along the mid- oceanic ridges and the
other ridges in the Atlantic Ocean. In this belt most of the
earthquakes are of moderate to mild intensity. Their foci are
generally less than 70 km deep. Since the divergent plates in
this belt move in opposite directions and there is splitting as
well, transform faults and fractures are created. All this
becomes the causative factor for the occurrence of shallow
focus earthquakes of moderate intensity. The sea floor
spreading is the main cause for the occurrence of
earthquakes in this belt.
vigorous earthquakes. This is so because diastrophism and
volcanism are either absent or only moderately active. But
the infrequent occurrence of minor shocks in such regions is
not ruled out. Such shocks may occur due to local causes
like the subterranean Movement of imprisoned gases or
liquids. The most glaring example of the occurrence of
minor earthquakes in quite unexpected Places are the Koyna
earthquake which shook Koynanagar on September 13 and
14, 1967.It is believed that the earthquake in this stable area
was caused due to the building of a 103 m-high concrete
dam across the Koyna River which impounded a huge
volume of water to form an artificial lake. The magnitude of
3. THE MID-CONTINENTAL BELT
the earthquake was 6.5 on the Richter scale. Then again on
This belt extends along the young folded Alpine mountain
December 11, 1967, the most disastrous earthquake
system of Europe, North Africa, through Asia Minor,
occurred in the same area which affected the whole of
Caucasia, Iran, Afghanistan and Pakistan to the Himalayan
western Maharashtra. The zone of maximum intensity of the
mountain system. This belt continues further to include
shock
Tibet, the Pamir’s and the mountains of Tine Shan etc. The
Koynanagar.The death toll rose to 1000 people, and a large
young folded mountain systems of Myanmar, China and
number of people were injured. Its impact was felt as far
eastern Siberia fall in this belt. This belt happens to be the
north as Ujjain and as far South as Bangalore. Other towns
subduction zone of continental plates. It is in this belt that
like Surat, Ahmadabad, Broach and Hyderabad also felt the
the African as well as Indian plates sub-duct below the
shock. Since there was no record of earthquakes in this
Eurasian plate. This mid- Continental belt is characterized
particular region before 1962, it was thought that Koyna
and
its
epicenter
was
in
the
vicinity
of
9
earthquake was caused due to the hydrostatic pressure
Fig 3.5 graben fault
exerted by the reservoir. But the recent investigation does
not support this view. Now, the geologists are of the opinion
that the shock in this region was the result of tectonic
A horst fault is the development of two reverse faults
causing a block of rock to be pushed(Figure 3.6)
movement along a north-south axis of weakness in the
.
underlying rocks buried below the Deccan trap.
There are several different kinds of faults. These faults are
named according to the type of stress that acts on the rock
and by the nature of the movement of the rock blocks either
side of the fault plane. Normal faults occur when tensional
Fig 3.6 horst fault
forces act in opposite directions and cause one slab of the
rock to be displaced up and the other slab down (Figure
3.3).
Fig 3.3 Normal faults
Reverse faults develop when compressional forces exist
(Figure 3.4). Compression causes one block to be pushed up
Figure 10l-8: Location of some of the major faults on the
Earth.
and over the other block.
III. POSSIBLE SOLUTIONS
HOW TO REDUCE EARTHQUAKE EFFECTS ON
BUILDINGS?
ADDING DAMPERS
Fig 3.4 Reverse faults
Dampers can be installed in the structural frame of a
A graben fault is produced when tensional stresses result in
building to absorb some of the energy going into the
the subsidence of a block of rock. On a large scale these
building from the shaking ground during an earthquake. The
features are known as Rift Valleys (Figure 3.5).
dampers reduce the energy available for shaking the
building. This means that the building deforms less, so the
chance of damage is reduced.
Why Earthquake Effects are to be Reduced?
Conventional seismic design attempts to make buildings that
10
do not collapse under strong earthquake shaking, but may
introduces flexibility in the structure. As a result, a robust
sustain damage to non-structural elements (like glass
medium-rise masonry or reinforced concrete building
facades) and to some structural members in the building.
becomes extremely flexible. The isolators are often designed
This may render the building non-functional after the
to absorb energy and thus add damping to the system. This
earthquake, which may be problematic in some structures,
helps in further reducing the seismic response of the
like hospitals, which need to remain functional in the
building. Several commercial brands of base isolators are
aftermath of the earthquake. Special techniques are required
available in the market, and many of them look like large
to design buildings such that they remain practically
rubber pads, although there are other types that are based on
undamaged even in a severe earthquake. Buildings with such
sliding of one part of the building relative to the other. A
improved seismic performance usually cost more than
careful study is required to identify the most suitable type of
normal buildings do. However, this cost is justified through
device for a particular building. Also, base isolation is not
improved earthquake performance. Two basic technologies
suitable for all buildings. Most suitable candidates for base-
are used to protect buildings from damaging earthquake
isolation are low to medium-rise buildings rested on hard
effects. These are Base Isolation Devices and Seismic
soil underneath; high-rise buildings or buildings rested on
Dampers. The idea behind base isolation is to detach
soft soil are not suitable for base isolation.
(isolate) the building from the ground in such a way that
earthquake motions are not transmitted up through the
building, or at least greatly reduced. Seismic dampers are
special devices introduced in the building to absorb the
energy provided by the ground motion to the building(much
like the way shock absorbers in motor vehicles absorb the
impacts due to undulations of the road).
BASE ISOLATION
The concept of base isolation is explained through an
example building resting on frictionless rollers(Figure 3.
7a). When the ground shakes, the rollers freely roll, but the
building above does not move. Thus, no force is transferred
to the building due to shaking of the ground; simply, the
building does not experience the earthquake. Now, if the
same building is rested on flexible pads that offer resistance
against lateral movements (Figure 3. 7b), then some effect of
Fig 3.7 Building on flexible supports shakes lesser – this
technique is called Base Isolation.
the ground shaking will be transferred to the building above.
If the flexible pads are properly chosen, the forces induced
by ground shaking can be a few times smaller than that
experienced by the building built directly on ground, namely
a fixed base building(Figure 3. 7c). The flexible pads are
called base-isolators, whereas the structures protected by
means of these devices are called base-isolated buildings.
The main feature of the base isolation technology is that it
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
11
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. Dampers were
used since 1960s to protect tall buildings against wind
effects. However, it was only since 1990s, that they were
used to protect buildings against earthquake effects.
Commonly used types of seismic dampers include viscous
Fig 3.20 Pall Friction Damper
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), and yielding
dampers (energy is absorbed by metallic components that
yield) (Figure 3.8).
This is a Pall Friction Damper installed in the Webster
Library of Concordia University in Montreal, Canada. The
damper is connected to the center of some bracing. The
damper is made up from a set of steel plates, with slotted
holes in them, and they are bolted together. At high enough
forces, the plates can slide over each other creating friction.
The plates are specially treated to increase the friction
between them.
2. VISCOUS FLUID DAMPERS
Viscous fluid dampers are similar to shock absorbers in a
car. They consist of a closed cylinder containing a viscous
fluid like oil. A piston rod is connected to a piston head with
small holes in it. The piston can move in and out of the
cylinder. As it does this, the oil is forced to flow through
holes in the piston head causing friction. When the damper
is installed in a building, the friction converts some of the
earthquake energy going into the moving building into heat
energy.
Fig 3.8 Seismic Energy Dissipation Devices – each device
is suitable for a certain building.
The damper is usually installed as part of a building’s
bracing system using single diagonals. As the building
1. FRICTION DAMPERS
sways to and fro, the piston is forced in and out of the
Friction dampers are designed to have moving parts that will
cylinder.
slide over each other during a strong earthquake. When the
Why Use Viscous Dampers?
parts slide over each other, they create friction which uses
some of the energy from the earthquake that goes into the
Viscous Dampers dramatically decrease earthquake induced
motion . .
building.
(i) Less displacement . . . over 50% reduction in drift in
many cases
12
(ii) Decreased base shear and inter-story shear, up to 40%
post-elastic deformation. Redundancy in the structural
(iii) Much lower “g” forces in the structure. Equipment
system permits redistribution of internal forces in the event
of the failure of key elements, when the element or system
keeps working and people are not injured
forces yields to fails, the lateral forces can be redistributed
(iv) Reduced displacements and forces can mean less steel
and concrete. This offsets the damper cost and can
to a secondary system to prevent progressive primary
failure.
sometimes even reduce overall cost.
Earthquake motion causes vibration of the structure leading
IV.CONCLUSION
to inertia forces. Thus a structure must be able to safely
When a structure vibrating. An earthquake can be resolved
in any vibrating. An earthquake can be resolved in any three
mutually
perpendicular
directions-the
two
horizontal
directions (longitudinal and transverse displacement) and the
vertical direction (rotation).This motion causes the structure
to vibrate or shake in all three directions; the predominant
direction of shaking is horizontal. All the structures are
transmit the horizontal and the vertical inertia forces
generated in the super structure through the foundation to
the ground. Hence, for most of the ordinary structures,
earthquake-resistant design requires ensuring that the
structure has adequate lateral load carrying capacity.
Seismic codes will guide a designer to safely design the
structure for its intended purpose.
designed for the combined effects of gravity loads and
seismic loads to verify that adequate vertical and lateral
V. REFRENCES
strength and stiffness are achieved to satisfy the structural
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performance and acceptable deformation levels prescribed
application
in the governing building code. Because of the inherent
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to
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engineering,second
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factor of safety used in the design specifications, most
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[2] Indian society of earthquake technology –proceedings of
shaking. Vertical acceleration should also be considered in
the
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[3] A.r.chandrasekharan and d.s.prakash rao –a seismic
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held iit-roorkee in dec 2002)
1. Minor earthquakes without any damage.
2. Moderate earthquakes with negligible structural damage
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To avoid collapse during a major earthquake, members
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[6] Koh, C.G & Kelly, J.M. 1990 Application of Fractional
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