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Recent years, base isolation designs for isolation and
protection of buildings from damages due to earthquake has become
an increasingly applied structural design technique in highly
seismic prone areas. Many types of structures have been designed
and built with base isolation, incorporating different concept of
building base isolation, and many others are in design phase or
under construction. Most of these completed buildings and those
under construction use rubber base isolation bearings, which are
found to be most efficient in base isolation designs. We at
www.pretread.com, your reliable source for neoprene bridge
bearing, bearing pads, laminated elastomeric bearing, elastomeric
bearing have been involved in many of these projects for base
isolation and our home page and connected links provide
information on a wide range of rubber products for construction
It is seen that conventionally constructed buildings with
seismic protection in mind have been crumbled under the
tremendous destructive strength of earthquake in many parts of
the world. Conventional structure design approach to earthquake
resistant of buildings have found to be followed all over world,
by mostly depends upon providing 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 selection of an
appropriate structural configuration and careful detailing of
structural members, such as beams and columns, and connections
between them. Practically they all proved to be failing under
seismic activates, damaging human lives and properties all over
We are specialized in Neoprene Bearing Products for
base isolation bearing, lead rubber bearing, building base
isolation, base isolation specialist,earthquake base isolation
for buildings, building base isolation by lead rubber bearing
earthquake base isolation for earthquake
Fixed base and base isolated building.
First let us explain a fixed base building and base isolated
building and then explain concept of base isolation. Buildings
with foundation base fixed to the super structure are known as
fixed base, and buildings with rubber or similar isolation
between to base foundation and structure are known as base
There are two basic types of base isolation systems. The
system that has been adopted most widely in recent years is
typified by use of elastomeric bearings, of different sizes and
shapes. In this approach, building or structure is decoupled from
horizontal components of earthquake .. ground motion.. by
interposing a layer with low horizontal stiffness between
structure and foundation.
In base isolation with rubber bearings, large rubber bearings
are used to connect structure and base of building isolating
structure and its movements from foundation. A variety of
different types of base isolation bearing pads have now been
developed, and a base isolated structure will be supported by a
series of bearing pads, which are placed between building and
building's foundation, providing isolation to building base.
These base isolation bearings are manufactured by
vulcanization, elastomer used will be either natural rubber or
neoprene, bonding of sheets of thick rubber to thin steel
reinforcing plates. These bearings are very stiff in vertical
direction and very flexible in horizontal direction, and under
seismic loading, bearing layers isolates building from the
horizontal components of ground movements, while vertical
components are transmitted to structure, relatively remains
unchanged. Although vertical accelerations do not affect most
buildings, the bearings also isolate building from unwanted
high-frequency vertical vibrations produced by underground
railways and local traffic. Rubber bearings are suitable for
stiff buildings up to seven stories in height. For this type of
building, uplift on the bearings will not occur and wind load
will be unimportant.
Rubber base isolation gives structure a fundamental frequency
that is much lower than its fixed-base frequency and also much
lower than predominant frequencies of ground motion. The first
dynamic mode of isolated structure involves deformation only in
isolation system, structure above being to all intents and
purposes rigid. The higher modes that will produce deformation in
structure are orthogonal to first mode and consequently also to
ground motion. These higher modes do not participate in motion,
so that if there is high energy due to ground motion at these
higher frequencies, this energy will not be transmitted into
structure. The isolation system does not absorb the earthquake
energy, but rather deflects it through the dynamics of the
system. This type of isolation works when the system is linear
and even when un-damped however some damping is beneficial to
suppress any possible resonance at the isolation frequency.
Deformation and Damages to fixed base building.
Let us see what happens to fixed base building during an
earthquake. Conventionally constructed buildings with seismic
protection in mind with fixed base will displace to right when
ground moves to left and to left when ground moves to right. This
displacing changes shape of the building from a rectangle to a
parallelogram. We say that building is deforming. The primary
cause of earthquake damage to buildings is this deformation which
building undergoes as a result of the inertial forces acting upon
it. Acceleration is increased, shortening building's period of
vibration, causes damages to structure and probably the magnitude
of earthquake brings the structure down, with permanent damages
including human life losses.
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 suddenly starts to move very quickly--the nails pull
out and connection fails.
Catalogue- Laminated Bearings.
Please download our colored catalogue on Laminated Bearings
in pdf format
Testing - Laminated Bearing.
Laminated Elastomeric Bearing Tesing.Please click to
Response of Base Isolated Building to earthquake.
To get a basic idea of how base isolation works, examine how
earthquake acting on a base isolated building. As a result of an
earthquake, ground beneath each building begins to move, imagine
first to left, building responds with movement, which tends
toward the right. We say that the building undergoes displacement
towards right. The building's displacement in direction opposite
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.
By contrast, even though base isolated buildings too
displaces, base isolated building retains its original,
rectangular shape where as a conventional fixed base building
changes to parallelogram. During displacement, it will be the
base isolated rubber bearings, supporting the building will be
deformed. The base-isolated building itself escapes deformation
and damage--which implies that inertial forces acting on base
isolated building have been reduced. Experiments and observations
of base-isolated buildings in earthquakes have been shown to
reduce accelerations to as little as 1/4 of acceleration,
comparable to fixed-base buildings, which each building undergoes
as a percentage of gravity. As noted above, inertial forces
increase, and decrease, proportionally as acceleration increases
Acceleration is decreased because base isolation system
lengthens a building's period of vibration, the time it takes for
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. It is important to know that,
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. Because of the complex nature of earthquake ground
motion, the building actually tends to vibrate back and forth in
The basic approach underlying more advanced techniques for
earthquake resistance is not to strengthen building, but to
reduce the earthquake-generated forces acting upon it by choosing
the right and appropriate base isolation bearing system.
There has been many experiments and designs followed with
concept of base isolation for the past 30 odd years and at many
places they seem to be out-performing conventional fixed base
with conventional structure strengthen approaches.
Here we notice that the building with base isolation is safer
than the conventional base structure.
These base isolation bearings are very stiff and strong in
vertical direction, but flexible in the horizontal direction.
Finally, since they are highly elastic, the rubber isolation
bearings don't suffer much damages, but the lead plug in the
middle bearing experiences 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. By reducing
the energy entering structure building, it helps to slow and
eventually stop 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
There is a second basic type of base isolation system
typified by the a sliding system. This works by limiting the
transfer of shear across the isolation interface. Many sliding
systems have been proposed and some have been used. Another type
of isolation containing a lead-bronze plate sliding on stainless
steel with an elastomeric bearing has been used. The
friction-pendulum system is a sliding system using a special
interfacial material sliding on stainless steel and has been used
for several projects in the United States, both new and retrofit
Types of Bearings manufactured by us for base isolation.
High Damping Rubber Bearing (HDRB)
High damping rubber bearing (HDRB) are large laminated
elastomeric bearings which is ideal for seismic isolation with
one device - supporting the structure, for base isolation,
providing elastic restoring force and required amount of damping
up to a maximum of 10-15% of critical. Moderate damping is
achieved with this type of the bearing.
HDRB isolation bearings are vertically stiff, capable of
supporting vertical gravity loads, while being laterally
flexible, capable of allowing large horizontal displacements. In
effect, the ground is allowed to move back and forth under a base
isolated during an earthquake, while leaving the building to
remain "stationary." By means of its flexibility and energy
absorption capability, with HDRB rubber bearings base isolation
system partially reflects and partially absorbs some of the
earthquake input energy before this energy can be transmitted to
the structure. The net effect is a reduction of energy
dissipation demand on the structural system, resulting in an
increase in its survivability.
Significantly reductions of structural and non-structural
damage may be achieved through use of HDRB rubber bearings
seismic isolation. Reduction in elastic-force reductions by
factors of 5- to 10- are possible. Expressed in simple terms with
regard to building performance, this is roughly equivalent to a
reduction of a Richter-magnitude-8 event to an event in the
5-to-6 magnitude range. Clearly, this is a very significant
reduction. These potential benefits are greatest for stiff
structures fixed rigidly to the ground, such as low- and
medium-rise buildings, nuclear power plants, bridges and many
types of equipment. Some of the heady duty bearings supplied by
us and installed in structures in Pakistan has helped to minimize
damages to the structure as will as human life.
Recent disasters caused in many parts of the world have due
to earthquake has made many structural designer to start using
with HDRB rubber bearings base isolation systems to building and
structures. We have few Projects in hand are very keen to work on
such Projects and you are requested to contact us.
Lead Rubber Bearings LRB.
A lead rubber bearing is a bigger laminated bearing
manufactured from layers of rubber, sandwiches together with
layers of steel, except for that in middle of bearing there will
be a solid lead "plug." Top and bottom of the bearing is fitted
with steel plates, which are used to attach bearing to building
through its foundation for base isolation.
These lead rubber bearings are designed in such a way that
bearing is very stiff and strong in vertical direction, but
flexible in horizontal direction. Lead, inserted as center core
of bearing dissipates the energy of earthquake while the rubber,
reinforced with steel plates, provides stability, supports
structure and isolates vibrations. Lead plug in the middle
bearing experiences same deformation as 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 reduces energy
entering the structure. Such produced heat energy, melts and
weakens structure in the case of fixed base building and
increases the damages occurred.
Our quality assurance.
Under one roof with stringent quality control, with technical
and marketing support from our Technical Partner we manufacture
neoprene bridge bearings, laminate elastomeric bearings, bearing
pads, pot bearings, PTFE sliding bearing, etc to AASHTO / BS /
This web site has a wealth of information on our product
lines and general information which we try to updated quite
often. We hope you will find our site very informative and will
contact us for further details and inquires.Click on below link,
to obtain regular archive on our site.
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we are seeking enterprising individuals with strong regional
experiences to represent us in your country or area for our
products. Please contact us with your product of interests.
For our up coming new expansion Project we are seeking
partnership with any renowned Elastomeric Bearing or other rubber
products manufacturer. Interested manufacturers please contact
Bearing Load Testing.
We are the first and only laminated bearing manufacturing
facility in Middle East to have an in-house bearing testing
facility to carry out tests confirming to AASHTO
specification in accordance with Acceptance Testing on either
Level I or Level II as well as Short/Long-Duration Compression
Test. Our bearing testing machine can test bearings to Vertical load of 4200
kN with horizontal shear load up to 400kN and movement to 100
Bearing Load Calculations
Let us verify ..load
calculations.. for your bearings. On receipt of corbel
size, and load details of your requirements, and we can provide
calculations and bearings sizes based on results on design
parameters compared to AASHTO LRFD - FREE.
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Installed Bridge Bearing