welcome to home page for www.pretread.com manufacturer for
neoprene bridge bearings, laminated elastomeric bearing, ptfe
sliding bearings, high damping rubber bearings,lead rubber
bearings, plain bearing pads, steel bearings, pot bearings, lead
rubber bearing, for building base isolation, earthquake, base
isolation www.pretpretread.com, from UAE.
Laminated Elastomeric Bearings with one or more lead cylinder
/ plug in the center are named as lead core rubber bearings where
these lead plug facilitates very effective damping during extreme
movements of these bearings.
Lead core rubber bearings and how they can help reduces
damages of a major earthquake is explained here
Recent devastation of many earthquakes and tidal wave
activities around the world has awakened many designers in
construction industry and subject that is much looked up is to
design structures such a way that even after seismic activates
much less damages can be incurred, resulting less human
Few of points raised by structural designers are conventional
approachs - earthquake resistant design of buildings; providing
building with strength, stiffness and inelastic deformation
capacity which are great enough to withstand a given level of
earthquake generated force.
Above can be generally accomplished through selection of an
appropriate structural configuration and with careful detailing
of structural members, such as beams and columns, and connections
between them etc
Few designers have recommended additional to above basic
approach for earthquake resistance, not only to strengthen
building structure, but to look at options to reduce
earthquake-generated forces acting upon it.
Among most important advanced techniques of earthquake
resistant design and construction are base isolation system.
What are base isolated structure. ?
A base isolated structure is one, which is supported on a
series of isolation supports, which are placed between building
and its foundation. Many structural designers have developed
different types of base isolation systems around the world and
one of them, which is practical and cost effictive is usage of
A lead rubber bearing is nothing else but a bigger laminated
bearing manufactured from layers of rubber, sandwiched 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. 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.
How does base isolation work?
To get a basic idea of how base isolation works with lead
rubber bearings, let us examine how will an earthquake act up on
both base isolated building where super structure is attached to
foundations through a sets of lead rubber bearings and a standard
conventional fixed base building where super structure is
attached direct to its foundation.
As a result of an earthquake, ground beneath building begins
to move. Each building responds with movement: which tends toward
opposite side of movement of ground. In reality buildings
undergoes displacement towards opposite side of ground movement.
This 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.
The inertial forces by which a building undergoes at time of
a major earthquake are proportional to building's acceleration
during ground motion so buildings don't actually shift in not
only in one direction but because of complex nature of earthquake
ground motion, building tends to vibrate back and forth in
In addition to displacing toward one side, the un-isolated
building (with out lead rubber bearing) will be changing its
shape-from a rectangle to a parallelogram, basically deforming
the building. The primary cause of earthquake damage to buildings
is deformation by which building undergoes as a result of
inertial forces acting upon it.
By contrast, even though building with base isolation too is
being displaced, under different directional movement of ground
due to earthquake, building with lead rubber bearing
base-isolation retains its original, rectangular shape and it
will be the lead-rubber bearings supporting the building that
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 by the usage of
proper lead rubber bearings.
Experiments and observations of base-isolated buildings in
earthquakes have been shown to reduce building accelerations to
as little as one fouth of acceleration of comparable to
fixed-base buildings, which each building undergoes as a
percentage of gravity as inertial forces increase, and decrease,
proportionally as acceleration increases or decreases.
Acceleration is decreased because lead rubber 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. Advantages of
Lead Center core in Bearings.
Finally, during and after a seismic activities on a building
with lead rubber bearing base isolation, what happens to lead
rubber bearings?. Main body of the bearing, rubber being highly
elastic, does not suffer any damages, where as lead plug in
middle of bearing will experience the same deformation as rubber
but generates heat and reduces in size, or dissipates, energy of
motion--i.e., kinetic energy--by converting that energy into
heat, also thus by reducing the energy entering building. This
helps to slow and eventually stop the building's vibrations
sooner than would otherwise be the case: helping to dampen
(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).
Thus, 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. LRB bearings also provide excellent base isolation
provided there is enough space for bearing and thermal movements
are not too extreme.
Lead rubber bearings can, not only be used with new building
but also can be incorporated into foundations of existing
buildings. We at pretread.com are currently involved with many
designers in designing and manufacture of these lead rubber
bearings from our plant in UAE. We not only consider this as a
challenge but also looks up as our responsibility to mankind and
help save as mush lives as possible. Hence you are requested to
contact us with your requirements and we will be glad to
Design Parameter followed for Lead Rubber Bearings
Design parameters followed for Lead Rubber Bearings are
AASHTO/DIN and BS
High Damping Rubber Bearing (HDRB)
High Damping Rubber Bearing (HDRB) - as an alternative to the
lead rubber bearing. We offer high damping rubber bearing
which is ideal for seismic isolation with one device - supporting
the structure, providing the elastic restoring force and also the
required amount of damping up to a maximum of 10-15% of critical.
High Damping rubber bearing are most advantageous when the
movements encountered are not large and there is room for the
increased height of the bearing. Moderate damping is achieved
with this type of the bearing.
Bearing Load Calculations
Let us verify load calculations for your bearings. Send us
sizes, construction and load details of your bearings and we will
send results on design parameters compared to AASHTO LRFD.
Let us help you to design your requirements of elastomeric
bearings. Please click on the links to
visit our form fill up page and we can design bearings to
The data and commentary contained within this website is for
general information purposes only. It is provided without
warranty of any kind. www.pretread.com shall not be held
responsible for any errors, omissions, or misuse of any of the
enclosed information and hereby disclaims any and all liability
resulting from the ability or inability to use the information
contained herein. Anyone making use of this material does so at
his or her risk. In no event will www.pretread.com. be held
liable for any damages including lost profits, lost savings, or
other incidental or consequential damages arriving from the use
or inability to use the information contained within.
www.pretread.com suggests contacting to contact us for
suitability for a particular application in rubber products.
Thank you very much for visiting us.
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
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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for neoprene bridge bearings, base isolation bearing, lead rubber
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rubber bearing, building base isolation, earthquake base
isolation for buildings,base isolation by lead rubber bearing,
building base isolation, in UAE and we suggests to contact us for
your particular application.