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Friction Pendulum Seismic Isolation TM
Seismic Isolation Bearings for the protection of buildings, bridges and industrial facilities Friction Friction PendulumTM bearings are seismic isolators that are installed between a structure and its foundation to protect the supported structure from earthquake ground shaking. Using Friction PendulumTM technology, it is cost-effective to build structures to elastically resist earthquake ground motions without structural damage. Friction PendulumTM bearings use the characteristics of a pendulum to lengthen the natural period of the isolated Triple Pendulum Bearing TM
structure so as to avoid the strongest earthquake forces. During an earthquake, the supported structure moves with small
pendulum
motions.
Since
earthquake
induced
displacements occur primarily in the bearings, lateral loads transmitted to the structure are greatly reduced. The Single Pendulum Bearing is the original Friction PendulumTM bearing. The single slider maintains the vertical load support at the center of the structural member. This offers construction cost advantages if one structural system is weaker, either above or below the bearing. The bearing also has a low height, which can be advantageous in some Single Pendulum Bearing
installations. The
Triple
PendulumTM
bearing
incorporates
three
pendulums in one bearing, each with properties selected to optimize the structure’s response for different earthquake strengths and frequencies. The Tension Capable Bearing can accommodate structure vertical loads that vary from compression to tension during seismic movements. This bearing can substantially reduce structural framing costs by preventing uplift of a primary structural member, and can eliminate concerns regarding potential structure overturning or large vertical earthquake Tension Capable Bearing
motions.
Triple Pendulum Bearing TM
The Triple Pendulum
TM
bearing offers better
seismic performance, lower bearing costs, and lower
construction
costs
as
compared
to
conventional seismic isolation technology. The properties
of
each
of
the
bearing’s
three
pendulums are chosen to become sequentially active at different earthquake strengths. As the ground motions become stronger, the bearing displacements increase. At greater displacements, Cross Section of Triple Pendulum Bearing TM
the effective pendulum length and the effective damping increase, resulting in lower seismic forces and bearing displacements. The Triple Pendulum
TM
bearing’s inner isolator
consists of an inner slider that slides along two inner concave spherical surfaces. Properties of the inner pendulum are typically chosen to reduce the peak accelerations acting on the isolated structure
and
its
contents,
minimize
the
participation of higher structure modes, and reduce structure shear forces that occur during Concaves and Slider Assembly
service level earthquakes. The two slider concaves, sliding along the two main concave surfaces, comprise two more independent pendulum isolators. Properties of the second pendulum are typically chosen to minimize the structure shear forces that occur during the design
basis
earthquake.
This
reduces
construction costs of the structure. Properties of the third pendulum are typically chosen to minimize bearing displacements that occur during the maximum credible earthquake. This reduces the size and cost of the bearings, and reduces the Concaves and Slider Components
displacements required for the structure’s seismic gaps.
Single Pendulum Bearing Cross Section
Triple Pendulum Bearing Center Position
Single Pendulum Bearing Maximum Credible Earthquake
Inner Pendulum Motion Service Level Earthquake
Lower Pendulum Motion Design Basis Earthquake
Upper Pendulum Motion Maximum Credible Earthquake
Comparison of Triple Pendulum and Single Pendulum Bearing Sizes and Responses to Earthquake Motion
0.35
Shear (W)
Shear (W) 0.36
0.28
0.24
38
23 33
49
Displacement (in.)
Single Pendulum Force-Displacement Hysteretic Loop
Displacement (in.)
Triple Pendulum Force-Displacement Hysteretic Loop
The Single Pendulum bearing maintains constant friction, lateral stiffness, and dynamic period for all levels of earthquake motion and displacements. In the Triple Pendulum bearing, the three pendulum TM
mechanisms are sequentially activated as the earthquake motions become stronger. The small displacement, high frequency ground motions are absorbed by the low friction and short period inner pendulum. For the stronger Design Level Earthquakes, both the bearing friction and period increase, resulting in lower bearing displacements and lower structure base shears. For the strongest Maximum Credible Earthquakes, both the bearing friction and lateral stiffness increase, reducing the bearing displacement. When designed for a severe Maximum Credible Earthquake, the plan dimensions of the Triple Pendulum bearing are approximately 60% that of the equivalent Single Pendulumbearing. TM
Principles of Friction Pendulum Seismic Isolation TM
The period of the Friction PendulumTM bearing is selected simply by choosing the radius of curvature of the concave surface. It is independent of the mass of the supported structure. The damping is selected by choosing the friction coefficient. Torsion motions of the structure are minimized because the center of stiffness of the bearings automatically coincides with the center of mass of the supported structure. The bearing’s period, vertical load capacity, damping, displacement capacity, and tension capacity, can all be selected independently. For the Triple PendulumTM bearing, three effective radii and three friction coefficients are selected to optimize performance for different strengths and frequencies of earthquake shaking. This allows for maximum design flexibility to accommodate both moderate and extreme motions, including near-fault pulses.
Pendulum Motion
Concave, Slider & Housing for Single Pendulum Bearing Sliding Pendulum Motion
Single Pendulum Operation
20 million lbs. Vertical Load Capacity Concave & Slider Triple Pendulum Operation TM
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Earthquake Protection Systems, Inc. 451 Azuar Drive, Bldg. 759 Mare Island, Vallejo, California 94592
Tel: (707) 644-5993 Fax: (707) 644-5995 Email:
[email protected] Website: www.earthquakeprotection.com
