Earthquake Resistance structures

EARTHQUAKE
RESISTANCE
STRUCTURES
By
D.UDAY KUMAR &
J.PRASADD
NBKRIST,Vidynagar
4/12/2014

EARTHQUAKE RESISTANCE STRUCTURES
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ABTRACT:
Due to mining ,drilling of bore holes and many
other activities, earthquakes are most common in some
places of india and many more countries. And they cause
more damage for life and property. Most of our civil
engineering constructions are failed by forces caused
due to earthquake. Even now also we don’t have
thorough knowledge about the forces caused by
earthquakes, due to which most of our civil engineering
structures are failed. Most of our civil engineering
structures are constructed by concrete it has more self
weight, so it is not possible to reduce the damage caused
by the structures. Due to restless work of scientists we
have a solution to reduce the damage i.e by ‘’Earthquake
Resistance Structure’’. The design of earthquake
resistance structures is called earthquake resistance
design. By providing Base Isolation Devices we can
separate building from ground by some rubber devices
and also by introducing Seismic dampers and special
devices for absorbing the energy caused by earthquakes .
By this additional installations structures can attain
stability . so safety can be possible by this design
methods .
In this article, we are going to discuss about some
design methods which are relating to earthquake
resistance of structures.
INTRODUCTION
Earthquake-resistant structures are structures
designed to withstand earthquakes. While no structure
can be entirely immune to damage from earthquakes, the
goal of earthquake-resistant construction is to erect
structures that fare better during seismic activity than
their conventional counterparts.
According to building codes, earthquake-resistant
structures are intended to withstand the largest
earthquake of a certain probability that is likely to occur
at their location. This means the loss of life should be
minimized by preventing collapse of the buildings for
rare earthquakes while the loss of functionality should be
limited for more frequent ones.
Before designing the buildings to resist
earthquakes we have thorough knowledge about the
behaviour of the earthquakes and how they effect the
stability of buildings.
Earthquakes are induced to movement of
tectonic plates slides over or push one another. In this
process lot of energy was released and the energy is
distributed in the form of waves around the epicenter
and finally reach the ground surface. The magnitude of
earthquake depends upon the movement of plates, type
of soil along which the waves are moved i.e soft soil or
hard rock. In hard rock movement is less but energy is
transferred more quickly than soft soil.
An earthquake (also known as a quake, tremor or
temblor) is the result of a sudden release of energy in the
Earth's crust that creates seismic waves. The seismicity,
seismism or seismic activity of an area refers to the
frequency, type and size of earthquakes experienced
over a period of time.
Earthquakes are measured using observations
from seismometers. The moment magnitude is the most
common scale on which earthquakes larger than
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.
Magnitude 3 or lower earthquakes are mostly almost
imperceptible or weak and magnitude 7 and over
potentially cause serious damage over larger areas,
depending on their depth. The largest earthquakes in
historic times have been of magnitude slightly over 9,
although there is no limit to the possible magnitude. The
most recent large earthquake of magnitude 9.0 or larger
was a 9.0 magnitude earthquake in Japan in 2011 (as of
March 2014), and it was the largest Japanese earthquake
since records began. Intensity of shaking is measured on
the modified Mercalli scale. The shallower an
earthquake, the more damage to structures it causes, all
else being equal.
WHY DO EARTHQUAKES HAPPEN ?
Earthquakes are usually caused when rock
underground suddenly breaks along a fault. This sudden
release of energy causes the seismic waves that make the
ground shake. When two blocks of rock or two plates are
rubbing against each other, they stick a little. They don't
just slide smoothly; the rocks catch on each other. The

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rocks are still pushing against each other, but not
moving. After a while, the rocks break because of all the
pressure that's built up. When the rocks break, the
earthquake occurs. During the earthquake and afterward,
the plates or blocks of rock start moving, and they
continue to move until they get stuck again. The spot
underground where the rock breaks is called the focus of
the earthquake. The place right above the focus (on top
of the ground) is called the epicenter of the earthquake.
TRY THIS LITTLE EXPERIMENT:
1. Break a block of foam rubber in half.
2. Put the pieces on a smooth table.
3. Put the rough edges of the foam rubber pieces
together.
4. While pushing the two pieces together lightly,
push one piece away from you along the table
top while pulling the other piece toward you.
See how they stick?
5. Keep pushing and pulling smoothly.
Soon a little bit of foam rubber along the crack
(the fault) will break and the two pieces will
suddenly slip past each other. That sudden
breaking of the foam rubber is the earthquake.
That's just what happens along a strike-slip
fault
Fig.1
HUMAN ACTIVITIES :
DAMS AND RESERVOIRS:
It's just water, but, man, water is heavy. Large
reservoirs of water created by dams have a long history
of inducing earthquakes, from Zambia to Greece to
India. The 2008 earthquake in Sichuan, China, that
killed nearly 70,000 people was one of the most
devastating in recent memory, and some scientists think
it was triggered by the construction of the Zipingpu Dam
nearby.
The Zipingpu Dam sits just a third of a mile
away from the fault, and the added weight of millions of
tons of water could have hastened the fault's rupture.
"No geological process can come up with such a
concentration of mass in such as small area other than a
volcano," said geologist Christian Klose about the
buildup of water.
GROUND WATER EXTRACTION:
Taking water out of ground, which causes the
water table to drop, can also destabilize an existing fault.
A 2011 earthquake in Lorca, Spain caused a
great amount of destruction for its 5.1 magnitude
because its epicenter was located so close to the surface.
Its shallow epicenter may be related to groundwater
extraction near Lorca, according to research published in
Nature Geoscience. Since 1960, water extraction has
caused the region's water table to drop by an incredible
250 meters.
GEOTHERMAL POWER PLANTS:
At the end of the infamous San Andreas Fault in
California lies the Salton Sea—and, along its southern
shore, is the Salton Sea Geothermal Field. The power
plant extracts hot, high-pressured water out of the
ground and turns it into steam to run turbines generating
power. If it seems like a bad idea to be extracting water
so close to the San Andreas Fault, well, you'd be right.
In a 2011 study published in Science,
researchers at the University of California, Santa Cruz,
found that seismic activity has increased around the
Salton Sea as geothermal field operations have ramped
up. Earthquake swarms—bursts of dozens of small
quakes below magnitude 6 or so—happen regularly
along the Salton Sea. While these earthquake swarms by
themselves may not cause much damage, they could
interact with other bigger faults, like the San Andreas
located so conveniently nearby, to induce far more
damaging quakes.
Several hundred miles north in California is
also the Geysers Geothermal Field, the largest
geothermal field in the world. Because the Geysers don't
sit near a large fault, induced seismicity there is less
likely to be majorly destructive. However, researchers
have found that seismicity in the region has increased

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from basically zero in the 1960s to 20 or 30 small
seismic events per year.
Fig.2
FRACKING AND INJECTION WELLS:
When it comes to hydraulic fracturing, or
fracking, it's actually not the extraction of oil or gas
that's the problem. . It's what happens to those afterward,
when waste fracking fluid is injected back underground
into deep wells. The fluid can seep out and lubricate
faults, causing them to slip more easily. A study in
Geology links a 2011 Oklahoma earthquake to
wastewater injection wells.
Seismic activity in Oklahoma has shot up along
with the rise of fracking: The number of earthquakes
went from about a dozen in 2008 to over 1,000 in 2010.
Earthquake swarms are now regular occurrences in the
region. With fracking in the United States steadily
increasing, the dangers of wastewater injection wells
become more imminent.
SKYSCRAPERS:
The tallest building in the world when it was
built, the Taipei 101 tower in Taiwan was supposed to
be the city's crown jewel, capable of withstanding
typhoon winds and earthquakes. Ironically, the very
things supposed to make it earthquake-resilient may
be… causing earthquakes.
According to a Taiwanese geologist Cheng-
Horn Lin, Taipei 101's especially huge mass of 770,000
tons is putting too much pressure on the soft sedimentary
rock below. This stress is due to all the extra steel and
concrete used to make the skyscraper solid enough to
withstand earthquakes. Since construction began on
Taipei 101, according to Lin, the region has seen several
micro-earthquakes and two larger earthquakes directly
underneath the building.
During its construction in March 2002, a 6.8
earthquake did knock two cranes to the ground. Taipei
101 itself, though, was undamaged. So, if the skyscraper
does cause earthquakes in the future, at least you know
where to go?
Fig.3
NATURALLY OCCURING EARTHQUAKES:
Tectonic earthquakes occur anywhere in the
earth where there is sufficient stored elastic strain energy
to drive fracture propagation along a fault plane. The
sides of a fault move past each other smoothly and a
seismically only if there are no irregularities or asperities
along the fault surface that increase the frictional
resistance. Most fault surfaces do have such asperities
and this leads to a form of stick-slip behavior. Once the
fault has locked, continued relative motion between the
plates leads to increasing stress and therefore, stored
strain energy in the volume around the fault surface.
This continues until the stress has risen sufficiently to
break through the asperity, suddenly allowing sliding
over the locked portion of the fault, releasing the stored
energy. This energy is released as a combination of
radiated elastic strain seismic waves, frictional heating
of the fault surface, and cracking of the rock, thus
causing an earthquake. This process of gradual build-up
of strain and stress punctuated by occasional sudden
earthquake failure is referred to as the elastic-rebound
theory. It is estimated that only 10 percent or less of an
earthquake's total energy is radiated as seismic energy.
Most of the earthquake's energy is used to power the
earthquake fracture growth or is converted into heat
generated by friction. Therefore, earthquakes lower the
Earth's available elastic potential energy and raise its
temperature, though these changes are negligible
compared to the conductive and convective flow of heat
out from the Earth's deep interior.

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EARTHQUAKE FAULT TYPES
There are three main types of fault, all of which
may cause an earthquake:
NORMAL FAULTS AND REVERSE FAULTS:
Normal and reverse faulting are examples of dip-
slip, where the displacement along the fault is in the
direction of dip and movement on them involves a
vertical component. Normal faults occur mainly in areas
where the crust is being extended such as a divergent
boundary. Reverse faults occur in areas where the crust
is being shortened such as at a convergent boundary.
Reverse faults, particularly those along
convergent plate boundaries are associated with the most
powerful earthquakes, including almost all of those of
magnitude 8 or more. Strike-slip faults, particularly
continental transforms can produce major earthquakes
up to about magnitude 8. Earthquakes associated with
normal faults are generally less than magnitude 7.
STRIKE SLIP:
Strike-slip faults are steep structures where the
two sides of the fault slip horizontally past each other;
transform boundaries are a particular type of strike-slip
fault. Many earthquakes are caused by movement on
faults that have components of both dip-slip and strike-
slip; this is known as oblique slip.
Fig.4
Strike-slip faults tend to be oriented near vertically,
resulting in an approximate width of 10 km within the
brittle crust thus earthquakes with magnitudes much
larger than 8 are not possible. Maximum magnitudes
along many normal faults are even more limited because
many of them are located along spreading centers, as in
Iceland, where the thickness of the brittle layer is only
about 6 km
HOW EARTHQUAKES EFFECT
BUILDINGS?
Earthquakes cause damage as a result of the
different waves that they produce as the earthquake
energy moves through and on the Earth. The way that
the ground responds to the energy of earthquake waves
as they pass through depends on the geology of the area.
A hard rock, like granite or limestone, may
vibrate very quickly with short movements, but not
break apart significantly. A wet sand or silt, on the other
hand, could be shaken enough that the pressure of the
water in the soil builds up enough to make the soil
behave like a liquid. This is called liquefaction, and is
responsible for much earthquake damage in low-lying
wet areas.
Damage to the ground during an earthquake
usually takes place in one of the following ways:
SHAKING:
Moves the ground in place. This does not
usually cause significant damage to the ground itself, but
often results in major damage to structures in or on the
ground. This can include, not only buildings, but water,
gas and sewer lines, train tracks, androads.
LANDSLIDES:
Ground is moved (displaced) to somewhere
else.
LIQUEFACTION:
Strength of the ground is removed, causing the
ground and objects on it to sink. Any heavy objects
sitting on liquefied ground will rapidly sink. This
includes all types of natural features as well as
structures. Liquefaction can result in depressions, a type
of landslide called a lateral spread, and the formation of
sand blows. Sand blows are geysers or volcanoes of sand
expelled from cracks or holes in the ground due to high
water pressure in the saturated sand during earthquake
shaking. Sand blows have been known to open large
fissures, create large depressions, and cover large areas
of land with several inches of sand. This can impact
roads and infrastructure, as well as bury large areas of
farmland, making it unable to sustain crops.
The damage to structures can depend on the
material that the structure is made out of, the type of
earthquake wave (motion) that is affecting the structure,

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and the ground on which the structure is built. Wood
structures respond to earthquakes differently than brick
or masonry structures, because wood can bend, and
masonry tends to shatter. Likewise, buildings with
reinforced steel in their walls tend to stand better than
unsupported buildings during shaking. The taller a
building is the more the top of the building moves
relative to the bottom of the building; however all
buildings sway during an earthquake.
Fig.5
Structures tend to respond to earthquakes in one
of the following ways: bending, breaking, sinking and
shaking. Buildings are complex structures though. They
are made of multiple elements and components that are
stressed and interact with one another when shaken by
an earthquake. Buildings vary widely in size, geometry,
structural system, construction material, and foundation
characteristics. These attributes influence how a building
performs when the ground shakes.
The 1989 Loma Prieta earthquake set San
Francisco’s Transamerica Pyramid swaying and rocking.
An array of 22 sensors (small arrows) installed by the
U.S. Geological Survey in the steel-frame structure
documented that the horizontal displacement on the 49th
floor of the building was five times the inches measured
in the basement, as indicated by the recordings (red
lines). No significant twisting of the building was
measured due to the symmetry of the building about its
vertical axis.
Permanent ground deformations can tear a
structure apart. Some foundation types are better able to
resist these permanent ground deformations than others.
For example, the use of pile foundations, with the piles
extending beneath the anticipated zone of soil
liquefaction, can be effective in mitigating the hazard’s
effects. The use of heavily reinforced mats can also be
effective in resisting moderate ground deformation due
to fault rupture or lateral spreading. Most earthquake-
induced building damage, however, is a result of ground
shaking. When the ground shakes at a building site, the
building’s foundations vibrate in a manner that’s similar
to the surrounding ground.
Brittle elements tend to break and lose strength.
(Examples of brittle elements include unreinforced
masonry walls that crack when overstressed in shear,
and unconfined concrete elements that crush under
compressive overloads.) Ductile elements are able to
deform beyond their elastic strength limit and continue
to carry load. (Examples of ductile elements include
tension braces and adequately braced beams in moment
frames .
For economic reasons, building codes permit
buildings to be damaged by the infrequent severe
earthquakes that may affect them, but prevent collapse
and endangerment of life safety. For buildings that house
important functions essential to post-earthquake
recovery, including hospitals, fire stations, emergency
communications centers, etc., codes adopt more
conservative criteria that’s intended to minimize the risk
that the buildings would be so severely damaged they
could not be used for their intended function.
Fig.6
.
HOW BUILDINGS RESPONED TO
EARTHQUAKES:
GROUND ACCELERATION AND BUILDING
DAMAGE:
Comparatively speaking, the absolute
movement of the ground and buildings during an
earthquake is not actually all that large, even during a
major earthquake. That is, they do not usually undergo
displacements that are large relative to the building's
own dimensions. So, it is not the distance that a building
moves which alone causes damage.
Rather, it is because a building is suddenly
forced to move very quickly that it suffers damage
during an earthquake. Think of someone pulling a rug
from beneath you. If they pull it quickly (i.e., accelerate
it a great deal), then they needn't pull it very far to throw

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you off balance. On the other hand, if they pull the rug
slowly and only gradually increase the speed of the rug,
they can move (displace) it a great distance without that
same unfortunate result.
Fig.7
In other words, the damage that a building
suffers primarily depends not upon its displacement, but
upon acceleration. Whereas displacement is the actual
distance the ground and the building may move during
an earthquake, acceleration is a measure of how quickly
they change speed as they move. During an earthquake,
the speed at which both the ground and building are
moving will reach some maximum. The more quickly
they reach this maximum, the greater their acceleration.
It's worthwhile mentioning here that in order to
study the earthquake responses of buildings, many
buildings in earthquake-prone regions of the world have
been equipped with strong motion accelerometers. These
are special instruments which are capable of recording
the accelerations of either the ground or building,
depending upon their placement.
The recording of the motion itself is known as an
accelerogram. Shows an accelerogram recorded in a
hospital building parking lot during the Northridge,
California earthquake of January 17, 1994.
Fig.8
In addition to providing valuable information about the
characteristics of the particular earthquake recorded or
the building where the accelerogram was recorded,
accelerograms recorded in the past are also often used in
the earthquake response analysis and earthquake design
of buildings yet to be constructed.
NEWTON’S LAW:
Acceleration has this important influence on
damage, because, as an object in movement, the building
obeys Newton' famous Second Law of Dynamics. The
simplest form of the equation which expresses the
Second Law of Motion is
F = MA 1.1.
This states the Force acting on the building is
equal to the Mass of the building times the Acceleration.
So, as the acceleration of the ground, and in turn, of the
building, increase, so does the force which affects the
building, since the mass of the building doesn't change.
Of course, the greater the force affecting a building, the
more damage it will suffer; decreasing F is an important
goal of earthquake resistant design. When designing a
new building, for example, it is desirable to make it as
light as possible, which means, of course, that M, and in
turn, F will be lessened. As we've seen in the discussion
of Advanced Earthquake Resistant Techniques, various
techniques are now also available for reducing A
It is important to note that F is actually what's
known as an inertial force, that is, the force is created
by the building's tendency to remain at rest, and in its
original position, even though the ground beneath it is
moving. This is in accordance with another important
physical law known as D'Alembert's Principle, which
states that a mass acted upon by an acceleration tends to
oppose that acceleration in an opposite direction and
proportionally to the magnitude of the. This inertial
force F imposes strains upon the building's structural
elements. These structural elements primarily include
the building's beams, columns, load-bearing walls,
floors, as well as the connecting elements that tie these
various structural elements together. If these strains are

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large enough, the building's structural elements suffer
damage of various kinds.
Fig.9
To illustrate the process of inertia generated
strains within a structure, we can consider the simplest
kind of structure imaginable--a simple, perfectly rigid
block of stone. During an earthquake, if this block is
simply sitting on the ground without any attachment to
it, the block will move freely in a direction opposite to
that of the ground motion, and with a force proportional
to the mass and acceleration of the block.
If the same block, however, is solidly founded in
the ground and no longer able to move freely, it must in
some way absorb the inertial force internally. In Figure
3, this internal uptake of force is shown to result in
cracking near the base of the block.
Fig.10
Of course, real buildings do not respond as
simply as described above. There are a number of
important characteristics common to all buildings which
further affect and complicate a building's response in
terms of the accelerations it undergoes, and the
deformations and damages that it suffers.
BUILDING FREQUENCY PERIOD:
To begin with, as we discussed in the How
Earthquakes Affect Buildings, the magnitude of the
building response – that is, the accelerations which it
undergoes – depends primarily upon the frequencies of
the input ground motion and the building's natural
frequency. When these are near or equal to one another,
the building's response reaches a peak level.
In some circumstances, this dynamic
amplification effect can increase the building
acceleration to a value two times or more that of the
ground acceleration at the base of the building.
Generally, buildings with higher natural frequencies, and
a short natural period, tend to suffer higher accelerations
but smaller displacement. In the case of buildings with
lower natural frequencies, and a long natural period, this
is reversed as the buildings will experience lower
accelerations but larger displacements.
BUIDING STIFFNESS:
The taller a building, the longer its natural
period tends to be. But the height of a building is also
related to another important structural characteristic: the
building flexibility. Taller buildings tend to be more
flexible than short buildings. (Only consider a thin metal
rod. If it is very short, it is difficulty to bend it in your
hand.
If the rod is somewhat longer, and of the same diameter,
it becomes much easier to bend. Buildings behave
similarly.) We say that a short building is stiff, while a
taller building is flexible. (Obviously, flexibility and
stiffness are really just the two sides of the same coin. If
something is stiff, it isn't flexible and vice-versa.)
Stiffness greatly affects the building's uptake of
earthquake generated force. Reconsider our first
example above, of the rigid stone block deeply founded
in the soil. The rigid block of stone is very stiff; as a
result it responds in a simple, dramatic manner. Real
buildings, of course, are more inherently flexible, being
composed of many different parts.
Furthermore, not only is the block stiff, it is brittle; and
because of this, it cracks during the earthquake. This
leads us to the next important structural characteristic
affecting a building's earthquake response and
performance ductility.
DUCTILITY:
Ductility is the ability to undergo distortion or
deformation – bending, for example – without resulting
in complete breakage or failure. To take once again the

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example of the rigid block, the block is an example of a
structure with extremely low ductility. To see how
ductility can improve a building's performance during an
earthquake.
For the block, we have substituted a
combination of a metal rod and a weight. In response to
the ground motion, the rod bends but does not break. (Of
course, metals in general are more ductile than materials
such as stone, brick and concrete.) Obviously, it is far
more desirable for a building to sustain a limited amount
of deformation than for it to suffer a complete
breakagefailure.
The ductility of a structure is in fact one of the
most important factors affecting its earthquake
performance. One of the primary tasks of an engineer
designing a building to be earthquake resistant is to
ensure that the building will possess enough ductility to
withstand the size and types of earthquakes it is likely to
experience during its lifetime.
Fig.11
DAMPING:
The last of the important structural
characteristics, or parameters, which we'll discuss here is
damping. As we noted earlier, ground and building
motion during an earthquake has a complex, vibratory
nature. Rather than undergoing a single "yank" in one
direction, the building actually moves back and forth in
many different horizontal directions.
All vibrating objects, including buildings,
tend to eventually stop vibrating as time goes on. More
precisely, the amplitude of vibration decays with time.
Without damping, a vibrating object would never stop
vibrating, once it had been set in motion. Obviously,
different objects possess differing degrees of damping. A
bean bag, for example, has high damping; a trampoline
has low damping.
In a building undergoing an earthquake, damping – the
decay of the amplitude of a building's vibrations – is due
to internal friction and the absorption of energy by the
building's structural and nonstructural elements. All
buildings possess some intrinsic damping.
The more damping a building possesses, the
sooner it will stop vibrating--which of course is highly
desirable from the standpoint of earthquake
performance. Today, some of the more advanced
techniques of earthquake resistant design and
construction employ added damping devices like shock
absorbers to increase artificially the intrinsic damping of
a building and so improve its earthquake performance.
HOW DO YOU MADE AN EARTHQUAKE
PROOF BUILDING?
The conventional approach to earthquake
resistant design of buildings depends upon providing the
building with strength, stiffness and inelastic
deformation capacity which are great enough to
withstand a given level of earthquake–generated force.
This is generally accomplished through the selection of
an appropriate structural configuration and the careful
detailing of structural members, such as beams and
columns, and the connections between them.
It can be achieved by two ways:
1. Base isolation devices
2. Viscous dampers
BASE ISOLATION DEVICES:
It is easiest to see this principle at work by
referring directly to the most widely used of these
advanced techniques, which is known as base isolation.
A base isolated structure is supported by a series of
bearing pads which are placed between the building and
the building's foundation. A variety of different types of
base isolation bearing pads have now been developed.
For our example, we'll discuss lead–rubber bearings.
These are among the frequently–used types of base
isolation bearings. A lead–rubber bearing is made from
layers of rubber sandwiched together with layers of
steel. In the middle of the bearing is a solid lead "plug."
On top and bottom, the bearing is fitted with steel plates
which are used to attach the bearing to the building and

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foundation. The bearing is very stiff and strong in the
vertical direction, but flexible in the horizontal direction
Fig.12
EARTHQUAKE GENERATED FORCES:
To get a basic idea of how base isolation works.
This shows an earthquake acting on both a base isolated
building and a conventional, fixed–base, building. As a
result of an earthquake, the ground beneath each
building begins to move. In Figure 13, it is shown
moving to the left.
Fig.13
Each building responds with movement which
tends toward the right. We say that the building
undergoes displacement towards the right. The building's
displacement in the direction opposite the ground motion
is actually due to inertia. The inertial forces acting on a
building are the most important of all those generated
during an earthquake.
It is important to know that the inertial forces
which the building undergoes are proportional to the
building's acceleration during ground motion. It is also
important to realize that buildings don't actually shift in
only one direction.
Fig.14
Because of the complex nature of earthquake
ground motion, the building actually tends to vibrate
back and forth in varying directions. So, Figure 3 is
really a kind of "snapshot" of the building at only one
particular point of its earthquake response
In addition to displacing toward the right, the
un–isolated building is also shown to be changing its
shape– from a rectangle to a parallelogram. We say that
the building is deforming. The primary cause of
earthquake damage to buildings is the deformation
which the building undergoes as a result of the inertial
forces acting upon it.
The different types of damage which buildings
can suffer are quite varied and depend upon a large
number of complicated factors. But to take one simple
example, one can easily imagine what happens to two
pieces of wood joined at a right angle by a few nails,
when the very heavy building containing them suddenly
starts to move very quickly — the nails pull out and the
connection fails.
RESPONSE OF BASE ISOLATED BUILDING:
By contrast, even though it too is displacing,
the base–isolated building retains its original,
rectangular shape. It is the lead–rubber bearings
supporting the building that are deformed. The base–
isolated building itself escapes the deformation and
damage—which implies that the inertial forces acting
on the base–isolated building have been reduced.
Experiments and observations of base–isolated
buildings in earthquakes have been shown to reduce
building accelerations to as little as 1/4 of the
acceleration of comparable fixed–base buildings, which
each building undergoes as a percentage of gravity. As

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we noted above, inertial forces increase, and decrease,
proportionally as acceleration increases or decreases.
Acceleration is decreased because the base
isolation system lengthens a building's period of
vibration, 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.
Finally, since they are highly elastic, the
rubber isolation bearings don't suffer any damage. But
what about that lead plug in the middle of our example
bearing? It experiences the same deformation as the
rubber. However, it also generates heat as it does so.
In other words, the lead plug reduces, or
dissipates, the energy of motion—i.e., kinetic energy—
by converting that energy into heat. And by reducing the
energy entering the building, it helps to slow and
eventually stop the building's vibrations sooner than
would otherwise be the case —in other words, it damps
the building's vibrations. (Damping is the fundamental
property of all vibrating bodies which tends to absorb
the body's energy of motion, and thus reduce the
amplitude of vibrations until the body's motion
eventually ceases.)
SPHERICAL SLIDING ISOLATION SYSTES:
As we said earlier, lead–rubber bearings are just
one of a number of different types of base isolation
bearings which have now been developed. Spherical
Sliding Isolation Systems are another type of base
isolation. 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 force needed to move the building
upwards limits the horizontal or lateral forces which
would otherwise cause building deformations. Also, by
adjusting the radius of the bearing's curved surface, this
property can be used to design bearings that also
lengthen the building's period of vibration.
For more information read this article titled
Protective Systems for Buildings: Application of
Spherical Sliding Isolation Systems as it describes one
particular type of spherical sliding isolation system, and
its successful use in making some structures more
earthquake resistant.
Fig.15
DAMPERS:
The second of the major new techniques for
improving the earthquake resistance of buildings also
relies upon damping and energy dissipation, but it
greatly extends the damping and energy dissipation
provided by lead–rubber bearings.
As we've said, a certain amount of vibration
energy is transferred to the building by earthquake
ground motion. Buildings themselves do possess an
inherent ability to dissipate, or damp, this energy.
However, the capacity of buildings to dissipate energy
before they begin to suffer deformation and damage is
quite limited.
The building will dissipate energy either by
undergoing large scale movement or sustaining
increased internal strains in elements such as the
building's columns and beams. Both of these eventually
result in varying degrees of damage. So, by equipping a
building with additional devices which have high
damping capacity, we can greatly decrease the seismic
energy entering the building, and thus decrease building
damage.
Accordingly, a wide range of energy
dissipation devices have been developed and are now
being installed in real buildings. Energy dissipation
devices are also often called damping devices. The large
number of damping devices that have been developed
can be grouped into three broad categories:
1. Friction Dampers– these utilize frictional forces
to dissipate energy
2. Metallic Dampers– utilize the deformation of
metal elements within the damper
3. Viscoelastic Dampers– utilize the controlled
shearing of solids
4. Viscous Dampers– utilized the forced
movement (orificing) of fluids within the
damper

12 | P a g e
FLUID VISCOUS DAMPERS:
Once again, to try to illustrate some of the
general principles of damping devices, we'll look more
closely at one particular type of damping device, the
Fluid Viscous Damper, which is one variety of viscous
damper that has been widely utilized and has proven to
be very effective in a wide range of applications.
The article, titled Application of Fluid Viscous
Dampers to Earthquake Resistant Design, describes the
basic characteristics of fluid viscous dampers, the
process of developing and testing them, and the
installation of fluid viscous dampers in an actual
building to make it more earthquake resistant.
Damping devices are usually installed as part of
bracing systems. Figure 16 shows one type of damper–
brace arrangement, with one end attached to a column
and one end attached to a floor beam. Primarily, this
arrangement provides the column with additional
support.
Most earthquake ground motion is in a horizontal
direction; so, it is a building's columns which normally
undergo the most displacement relative to the motion of
the ground. Figure 16 also shows the damping device
installed as part of the bracing system and gives some
idea of its action.
Fig.16
FLUID DAMPER DESIGN:
The design elements of a fluid damper are relatively
few. However, the detailing of these elements varies
greatly and can, in some cases, become both difficult
and complex. Figure 17 depicts a typical fluid damper
and its parts. It can be seen that by simply moving the
piston rod back and forth, fluid is orificed through the
piston head orifices, generating damping force.
Major part descriptions are as follows, using
Figure 17 as reference:
Piston Rod:
Highly polished on its outside diameter, the piston
rod slides through the seal and seal retainer. The external
end of the piston rod is affixed to one of the two
mounting clevises. The internal end of the piston rod
attaches to the piston head. In general, the piston rod
must react all damping forces, plus provide a sealing
interface with the seal. Since the piston rod is relatively
slender and must support column loading conditions, it
is normally manufactured from high-strength steel
material. Stainless steel is preferred as a piston rod
material, since any type of rust or corrosion on the rod
surface can cause catastrophic seal failure. In addition,
the design of the piston rod should be strain based, rather
than stress based, since elastic flexing of the piston rod
during damper compression can cause binding or seal
leakage.
Fig.17
Cylinder :
The damper cylinder contains the fluid medium
and must accept pressure vessel loading when the
damper is operating. Cylinders are usually manufactured
from seamless steel tubing. Welded or cast construction
is not permissible for damper cylinders, due to concerns
about fatigue life and stress cracking. Cylinders
normally are designed for a minimum proof pressure
loading equal to 1.25 times the internal pressure
expected under a maximum credible seismic event. By
definition, the proof pressure loading must be
accommodated by the cylinder without yielding,
damage, or leakage of any type.
Fluid :
Dampers used in structural engineering
applications require a fluid that is fire-resistant,
nontoxic, thermally stable, and will not degrade with
age. This fluid must be classified as both nonflammable
and non-combustible, with a fluid flashpoint above 90°
C. At present, the only fluids possessing all of these
attributes are from the silicone family. Typical silicone
fluids have a flashpoint in excess of 340° C, are
cosmetically inert, completely non-toxic, and are
thermally stable. The typical silicone fluid used in a

13 | P a g e
damper is virtually identical to the silicone used
incommon hand and facial cream cosmetics.
Seal :
The seals used in a fluid damper must be capable
of a long service life; at least 25 years without requiring
periodic replacement. The seal materials must be
carefully chosen for this service life requirement and for
compatibility with the damper=s fluid. Since dampers in
structures are often subject to long periods of infrequent
use, seals must not exhibit long-term sticking nor allow
slow leakage of fluid. Most dampers use dynamic seals
at the piston rod interface, and static seals where
the end caps or seal retainers are attached to the cylinder.
For static seals, conventional elastomer oring seals have
proven to be acceptable. Dynamic seals for the piston
rod should be manufactured from high-strength
structural polymers, to eliminate sticking or compression
set during long periods of inactivity. Typical dynamic
seal materials include Teflon®, stabilized nylon, and
members of the acetyl resin family. Dynamic seals
manufactured from structural polymers do not age,
degrade, or distort over time. In comparison,
conventional elastomers will require periodic
replacement if used as dynamic seals in a damper.
Fig.18
Piston Head :
The piston head attaches to the piston rod, and
effectively divides the cylinder into two pressure
chambers. As such, the piston head serves to sweep fluid
through orifices located inside it, thus generating
damping pressure. The piston head is usually a very
close fit to the cylinder bore; in some cases the piston
head may even incorporate a seal to the cylinder bore.
Piston heads are relatively simple in appearance.
However, the orifice passages machined or built into the
piston head usually have very complex shapes,
depending on the damping output equation selected.
Seal Retainer :
Used to close open ends of the cylinder, these are
often referred to as end caps, end plates, or stuffing
boxes. It is preferable to use large diameter threads
turned on either the exterior or interior surface of the
cylinder to engage the seal retainer. Alternate attachment
means, such as multiple bolts, studs, or cylinder tie rods
should be avoided as these can be excited to resonance
by high frequency portions of either the earthquake
transient or the building response spectra.
Accumulator :
The simple damper depicted in Figure 4 utilizes
an internal, in-line rod make-up accumulator. The
accumulator consists of either a block of closed cell
plastic foam, a moveable (and gas pressurized)
accumulator piston, or a rubber bladder. The purpose of
the accumulator is to allow for the volumetric
displacement of the piston rod as it enters or exits the
damper during excitation. A second purpose is to
compensate for thermal expansion and contraction of the
fluid. The damper in Figure 4 uses a control valve to
meter the amount of fluid displaced into the accumulator
when the damper is being compressed. When the damper
extends, the control valve opens to allow fluid from the
accumulator to freely enter the damper pressure
chambers. Some types of dampers use a so-called
“through rod,” where the piston rod goes entirely
through the damper cylinder. These dampers do not
require accumulators at all, but do require two sets of
seals.
Orifices :
The pressurized flow of the fluid through the
piston head is controlled by orifices. These can consist
of complex modular machined passageways, or
alternately, can use drilled holes, springloaded balls,
poppets, or spools. Relatively complex orifices are
needed if the damper is to produce output with a
damping exponent of less than two. Indeed, a simple
drilled hole orifice will follow Bernoulli’s equation, and
damper output will be limited to varying force with the
square of the damper velocity. Since “velocity squared”
damping is of limited use in seismic energy dissipation,
more robust and sophisticated orifice methods are
usually required. Depending on the damping output
equation desired, orifice passages may utilize

14 | P a g e
converging or diverging flows, vortexes may be induced
to form at specific areas, or flow passages may bend or
twist radically.
DESIGN AND IMPLEMENTATION OF FLUID
DAMPERS:
A combination caisson/mat system was selected
for the foundation of the tower. The reinforced concrete
mat system connects a series of caissons of up to 1.2m
diameter, reaching down only 40m into a rubble layer
below the soft surface soil.
The concrete mat thickness varies from 1m-2m in
thickness and ties together the caissons and the 0.8m
thick foundation walls. The seismic code requirements
for Mexico City involve the use of shock response
spectra, with the associated site transients. This is
combined with a limitation on allowable soil-bearing
stress. The design team evaluated more than 25 different
structural systems, but was unable to find a structural
configuration allowing a 55-floor building to be
constructed at the site. The best configurations yielded a
design with 35-38 floors maximum. The engineers noted
that it was probably no coincidence that the tallest
existing structures in Mexico City are roughly this
height.
Fig.19
The potential of adding viscous damping to the
structure was evaluated as a means to reduce structural
stress during seismic loadings. The underlying design
concept was to use the dampers to reduce stress, then
lighten the building frame by removing steel until the
stress crept up to the code allowables. Conceptually, the
steel that had been “removed” by this process could then
be used to add additional floors.
Fig.20
For the Torre Mayor, inherent structural
damping in the frame was assumed to be 1% of critical.
Multiple computer runs were made with added fluid
damping in 2% increments. The approach used was to
add damping until a lightweight 55-plus story building
would result or until damping reached a value of 30%
critical, at which point Constantinou and Symans’
research indicated that peak stresses would begin to
increase.
When the added damping in the structure reached 10%
critical the resulting maximum height structure was
calculated to be 57 floors. The structural detailing of the
.
Fig.21
new tower could begin, having achieved the goals of the
building’s owner for a 55-plus story structure. Figure 21
is the architectural drawing of the building
TUNED MASS DAMPERS:
A tuned mass damper, also known as a harmonic
absorber, is a device mounted in structures to reduce the

15 | P a g e
amplitude of mechanical vibrations. Their application
can prevent discomfort, damage, or outright structural
failure. They are frequently used in power transmission,
automobiles, and buildings.
Fig.22
. A schematic of a simple spring–mass–damper
system used to demonstrate the tuned mass damper
system.
Tuned mass dampers stabilize against violent
motion caused by harmonic vibration. A tuned damper
reduces the vibration of a system with a comparatively
lightweight component so that the worst-case vibrations
are less intense. Roughly speaking, practical systems are
tuned to either move the main mode away from a
troubling excitation frequency, or to add damping to a
resonance that is difficult or expensive to damp directly.
Fig.23
Wide span structures (bridges, spectator
stands, large stairs, stadium roofs) as well as slender tall
structures (chimneys, high rises) tend to be easily
excited to high vibration amplitudes in one of their basic
mode shapes, for example by wind or marching and
jumping people. Low natural frequencies are typical for
this type of structures, due to their dimensions, as is their
low damping. With GERB Tuned Mass Dampers
(TMD), these vibrations can be reduced very effectively.
The TMD may consist of:
 Spring
 Oscillating Mass
 Viscodamper
Fig. Tuned Mass Damper
as main components, or may be designed as a pendulum,
also in combination with a Viscodamper.
Each TMD is tuned exactly to the structure and
a certain natural frequency of it. Such TMD have been
designed and built with an oscillating mass of 40 to
10.000 kg (90 to 22.000 lbs) and natural frequencies
from 0.3 to 30 Hz. Vertical TMD are typically a
combination of coil springs and Viscodampers®, while
in case of horizontal and torsional excitation in the
corresponding horizontal TMD the coil springs are
replaced by leaf springs or pendulum suspensions.
CONCLUSION:
In the modern world man has to face challenging
problems due to natural calamities. There is a need to
overcome those problems to survive his life. It is
difficult asses these problems, earthquakes are comes in
that order. If an earthquake occurs it can cause more
damage than other calamities due collapse of structures.
As a civil engineer we have the responsibility to give
healthy full environment to the people. We stated above
some of the techniques to reduce the damage of the
structures due to earthquakes.
‘’We are here only to provide safety to public to lead
their life’’,
15 | P a g e
Fig.22
system.
Fig.23
 Spring
 Viscodamper
CONCLUSION:
their life’’,
15 | P a g e
Fig.22
system.
Fig.23
 Spring
 Viscodamper
CONCLUSION:
their life’’,

16 | P a g e
REFERENCES:
www.multyscience.co.uk
www.institute of structuralengineer.com
www.faddoengineers.com
Technological advance in Japanese building design
and construction
http://www.taipei-
101.com.tw/en/Tower/buildind_13-1.html
http://www.esm-
gmbh.de/EN/Products/Tuned_mass_dampers

Earthquake Resistance structures

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