Prepared by:Qadir Raza
M. Tech (Structural Engineering)
CONTENT
 What is Base Isolation?
 Objective of Base Isolation system
 Literature Review
 Methodology
 Isolation Components
Elastomeric Isolators
 Sliding Isolators
Is it feasible?
Results/Discussions
Conclusion
References
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EARTHQUAKE PROTECTIVE SYSTEMS
Earthquake protective systems
Passive
Tuned
Energy
Active
Hybrid
Base
isolation
active
Semi
active
Semi
active
mass
Active
mass
Active
bracing
Adaptive
control
Here we can see that major part of India is prone to
Earthquake, that’s why need of Base Isolation is in high
demand to meet the crisis.
It is a system that may be defined as a flexible
or sliding interface positioned between a
structure and its foundation, for the purpose of
decoupling the horizontal motions of the
ground from the horizontal motions of the
structure, thereby reducing earthquake
damage to the structure and its contents.
Base isolation system absorbs and deflects the
energy released from the earthquake before it is
transferred to the structure.
•The possible risk of loss of life adds a very serious
dimension to seismic design, putting a moral
responsibility on structural engineers.
•In recent times, many new systems have been developed,
either to reduce the earthquake forces acting on the
structure or to absorb a part of seismic energy.
•One of the most widely implemented and accepted
seismic protection systems is Base Isolation.
• Minimizing interruption of use of facility (Immediate Occupancy
Performance Level)
• Reducing damaging deformations in structural and non-structural
component
• Reducing acceleration response to minimize content related
damage
• Preventing plastic deformation of structural elements
• Protection of Building Frame
• Protection of Non-structural Components & Contents
• Provide for an Operational facility after the Earthquake
• Protection of Life - Safety of occupants
• Improvement for Safety of Building
PRINCIPLE OF BASE ISOLATION
 The fundamental principle of base isolation is to modify the
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response of the building so that the ground can move below the
building without transmitting these motions into the building.
A building that is perfectly rigid will have a zero period.
When the ground moves the acceleration induced in the
structure will be equal to the ground acceleration and there will
be zero relative displacement between the structure and the
ground.
The structure and ground move by same amount.
A building that is perfectly flexible will have an infinite period.
So in flexible structures the structure will not move, the ground
will.
RESPONSE OF BASE ISOLATED BUILDINGS
VERSUS FIXED BASE RESPONSE
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Source:-Civildigital.com
LITERATURE REVIEW
Weixing SHI.et.al(2004) In this paper, a new alternative of base isolation
system composed of common rubber bearing and sliding rubber bearing is
invented for structural seismic mitigation Experimental research on dynamic
behaviours of the combined isolation system and seismic response analysis
of a practical structure with the isolation system are carried out. Story drifts,
acceleration and shear force responses of structure with the aforementioned
base isolation and with fixed base are compared. Findings of the present
study are:
1. The combined isolation system possesses suitable initial and post yielding
horizontal stiffness.
2. CIS has excellent capacity of energy dissipation due to frictional sliding.
Dynamic friction coefficient and damping ratio of the isolation system is
approximately 0.08 and 0.15
Fabio MAZZA and Alfonso VULCANO(2004) stated that The
nonlinear response of a typical five-storey r.c. framed building
with different base-isolation systems has been studied under
strong near-fault ground motions. In particular, a first solution
with HDLRB-type isolators has been compared with different
solutions obtained by means of the addition of viscous dampers
(acting in parallel) or steel-PTFE sliding bearings (acting either
in parallel or in series), assuming different values of the
parameters characterizing the behaviour of the supplemental
seismic devices.
METHODOLOGY
ISOLATION COMPONENTS
 Elastomeric Isolators
Natural Rubber Bearings
2. Low-Damping Rubber Bearings
3. Lead-Rubber Bearings
4. High-Damping Rubber Bearings
 Sliding Isolators
1. Resilient Friction System
2. Friction Pendulum System
1.
Elastomeric Isolators
 These are formed of
horizontal layers of natural
or synthetic rubber in thin
layers bonded between steel
plates.
Source:-CivilDigital.com
Natural Rubber Bearing
SLIDING ISOLATORS
In this type of Isolation system , the sliding displacements are
controlled by high-tension springs or laminated rubber bearings,
or by making the sliding surface curved. These mechanisms
provide a restoring force to return the structure to its equilibrium
position.
Source :- CivilDigital.com
Resilient Friction System
Friction Pendulum System
The main objective of this work is to compare different baseisolation techniques, in order to evaluate their effects on the
structural response and applicability limits under near-fault
earthquakes. In particular, high-damping-laminated-rubber
bearings are considered, in case acting in parallel with
supplemental viscous dampers, or acting either in parallel or in
series with steel-PTFE sliding bearings. A numerical
investigation is carried out assuming as reference test structure
a base-isolated five-storey reinforced concrete (r.c.) framed
building designed. A bilinear model idealizes the behaviour of
the r.c. frame members, while the response of the elastomeric
bearings is simulated by using a visco elastic linear model; a
viscous-linear law and a rigid-plastic one are assumed to
simulate the seismic behaviour of a supplemental damper and a
sliding bearing, respectively.
BASIC ELEMENTS OF SEISMIC ISOLATION
The three basic elements in seismic isolation systems are,
 A vertical-load carrying device that provides lateral flexibility
so that the period of vibration of the total system is lengthened
sufficiently to reduce the force response
 A damper or energy dissipater so that the relative deflections
across the flexible mounting can be limited to a practical
design level
 A means of providing rigidity under low (service) load
 Steel plates, vulcanized rubber, and a lead plug in the centre of
the design create these functional contrasting directional
components.
CONSIDERATION FOR SEISMIC ISOLATION
The benefits of using seismic isolation for earthquake resistant design
are:
 Isolation leads to a simpler structure with much less complicated
seismic analysis as compared with conventional structures
 Isolated designs are less sensitive to uncertainties in ground motion
 Minor damage at the design level event means immediate
reoccupation
 The performance of the isolators is highly predictable, so they are
much more reliable than conventional structural components
 Base Isolation minimizes the need for strengthening measures like
adding shear walls, frames, and bracing by reducing the earthquake
forces imparted to the building.
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Base Isolated building are capable of resisting blasts loads and
their ability to move reduces the overall impact of the blast force
on the building
Factor of Safety = Column Strength/Earthquake force > 1
Factor of Safety = Capacity/Demand > 1
Capacity > Demand
The earthquake causes inertia forces proportional to the product of
the building mass and the earthquake ground accelerations. As
the ground accelerations increases, the strength of the building,
the capacity, must be increased to avoid structural damage.
ISOLATOR LOCATIONS
 The requirement for installation of a base isolation system is that
the building be able to move horizontally relative to the ground,
usually at least 100 mm.
 The most common configuration is to install a diaphragm
immediately above the isolators.
 If the building has a basement then the options are to
install the isolators at the top, bottom or mid-height of the building.
basements columns and walls.
Source :- CivilDigital.com
IS IT AN ECONOMIC SOLUTION?
 Base isolation allows for a reduction in structural elements of the
building with less ductile detailing needed in the building.
 Widely held misconception is that seismic isolation is expensive
As a general rule the inclusion of all aspects of seismic isolation in a
new structure will add no more than 3% -5% to total construction
cost and considerably less when assessed against the benefits of
isolation
 Seismic isolation devices require no maintenance during the life of
the building
 Following any significant event they should be inspected to ensure
bolts and load plates are still in place.
 Devices do not need replacing after an earthquake unless the event
was in excess of their design specification in which case removal of
some devices for testing is recommended.
 Because the building is protected from major damage, repair costs
following an earthquake will be lower to non-existent
BASE ISOLATION SYSTEM IN NEW BHUJ
HOSPITAL- A CASE STUDY
The 300 bed Bhuj Hospital that claimed 176 lives when it
collapsed during the major January 2001 Gujarat Earthquake
was studied
This was the first new building in India to be fitted with
earthquake – resistant NZ developed base isolation technology
Structural engineer, Dunning Thornton Consultant from
Wellington was part of the New Zealand design team and
supervised installation of the first bearings on site in late 2001.
280 lead rubber bearings were installed in the structure
NEWLY BUILT BASE ISOLATED BHUJ HOSPITAL ,2003
Source :- Civildigital.com
Base isolation provides an alternative to the conventional fixed
base design of structures.
Base Isolation minimizes the need for strengthening measures
of adding shear walls, frames, and bracing by reducing the
earthquake forces imparted to the building.
Base isolation had the effect of reducing the earthquake force
demands on the superstructure to 30% of the demands for a
fixed-base structure.
Result and Discussion……
1.The first mode vibrations’ period in longitudinal
direction is equal to 1.90 sec and in transverse
direction - 1.91 sec, while the corresponding
periods for the non-isolated structure would be
0.83 sec and 0.86 sec
2.This means that seismic isolation has reduced the
maximum spectral acceleration by a factor larger
than 2
3.These figures prove the high effectiveness of
seismic isolation and reliability of the buildings
during strong seismic action.
Source:- Fabio MAZZA and Alfonso VULCANO[2004] reserch paper
The in-parallel combination of isolators and viscous dampers (BIPD), as well as the
analogous one with isolators and sliding bearings (BIPS), proved to be favourable for
controlling the relative displacement of the isolators: the choice of increasing the
equivalent damping ratio (ξD), for the BIPD system, or the sliding ratio (αS), for the
BIPS system, corresponds to a reduction of the isolator displacement, even though,
for a same increase of ξD or αS, this effect has been ever-smaller. However, the use of
the BIPS system can need re-centring after an earthquake, in case the elastic restoring
force produced by the elastomeric isolators does not exceed the friction threshold
imposed by the sliding bearings. The in-series combination of isolators and sliding
bearings (BISS) is not always favourable, for increasing values of αS, in reducing the
residual displacement of the isolation system. Moreover, the re-centring of this system
may present some difficulty when the residual displacement is a combination of outof-phase movements between the isolators and the sliding bearings placed on them.
The BIPS one does not guarantee in all the cases a better performance
for increasing values of ξD or αS, respectively. However, the BIS system proves to
be generally effective for controlling the structural and non-structural damages
of the framed building, producing an amplification of the fundamental
vibration period and limiting the maximum acceleration transmitted to the
superstructure.
1.Structural Dynamics and Earthquake Engineering by Mudhjeet
mukh Upadhaya.
2.Aseismic design and analysis of Earthquake structures by
Damodar swamy.
3.Mazza F, Vulcano A. “Seismic response of buildings with
isolation & supplemental dissipation at the base.” Proceedings of
the 5th World Congress on Joints, Bearings and Seismic Systems for
Concrete Structures, Rome, Italy, 2001
4. Alfonso Vulcano. “Comparative study of the earthquake and wind
dynamic response of base isolated buildings.” Journal of Wind
Engineering and Industrial Aerodynamics, 1998; 74-76: 751-764
5.Jangid RS, Kelly JM. “Base isolation for near-fault motions.”
Earthquake Engineering and Structural Dynamics 2001; 30: 691707.
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