VIBRATION (seismic response)
CONTROL
2
Seismic Response Control
system
Passive Control Active control
system system
Base Isolation Energy
Dissipation
Rubber Pads Hydraulic Dampers
Devices using Dry Electro-rheological Fluid Dampers Active-tuned Mass Damper
Friction Metallic Dampers Active Braces System
Steel Dampers
Active Tendon System
Lead-extrusion Damper
Tuned Liquid Damper
Shape-memory Alloy
Friction Damper Active Vibration Control
Viscoelastic system
Passive seismic control Active seismic control
system system
Counter balance the motion
Energy transformation principle
(By automated counter weight )
Does not require any additional Additional forces are require to
energy source to operate counter balance the earthquake
( Activated by earthquake motion) motion
Examples – Isolators, Dampers, Examples – TMD’s, Tuned liquid
Oscillators damper, Active braces system
3
Passive seismic control system
1.Base Isolation
• It is a technique that mitigates the effects of an earthquake.
• The aim of Base Isolation is to reduce the energy that is
transferred from foundation to the superstructure due to
earthquake.
• The basic concept is to uncouple the sub structure and super
structure by providing flexible element or bearings.
• Flexibility can be introduced by elastomeric pads, rollers,
sliding plates, cable suspension sleeved piles, rocking
foundation, etc.,
4
Needs
• Building at high seismic intensity zone.
• Important buildings.
• Existing structure is unsafe.
• Minimize the damage to primary and
secondary structural members
5
(i).Rubber pads
• Traditional concept, whereby laminated rubber pads
prevent vibration from foundation into the superstructure.
• More widely used base isolation is made of laminated pads,
similar to bearing pad in bridge deck support.
• They consists of thin layers of natural rubber that are
vulcanized and bonded to steel plates.
• Due to shear stress such pads are very flexible in horizontal
direction.
• They are rather stiff vertically due to presence of the steel
plates, which results in high bearing capacity.
• These sheets made of natural rubber or artificial
elastomers.
6
• The pad damping provided by the viscous behaviour is quite low,
upto approximately 5%.
• For certain rubber composition – upto 20%
• Core lead in the center of the pad – about 30%
(energy absorption is obtained by yielding of the lead, which
remains hooped by the rubber)
7
8
(ii).Device using Dry Friction
• Simplest system consists of friction plates installed above a
rubber pad.
• The upper plate made of stainless steel & is fixed with super
structure.
• Lower plate made of bronze and lead & is fixed above a
classical rubber pad.
• Advantage- avoids self sizing of the two plates and provides
for a suitable friction factor.
• Friction plates may be placed above or under the rubber pad;
in certain cases the second solution is favoured to avoid
eccentricity of the weight on the rubber pad after siliding.
• Friction pendulum have been developed using the pendulum
effect
9
10
2.Energy dissipating devices
11
1.Hydraulic Dampers
• The objective is to allow slowly
developing displacements but
limiting the response under
dynamic action.
• These system dissipate energy by
forcing fluid through an orifice
similar to shock absorbers.
• The fluid may be oil or very high
molecular weight polymer.
12
2.Electro-rheological fluid dampers
• Operate under shear flow.
• Fluid viscous damping
reduces stress and
deflection because the
force from the damping is
completely out of phase
with stresses due to
seismic loading.
13
3. Metallic dampers
• Metallic dampers are based on
the same concept as the lead
cores in rubber pads.
• These can be fabricated from
steel, lead or alloys.
• These system referred to as
amplitude dependent systems
(energy dissipated is usually
proportional to force and
displacement)
• These devices are most often
located within braced frame.
14
4.Steel dampers
• Made of simple bar, plate or
a specially studied shapes.
• Such dampers are inserted
in the bracings, at wall-to-
wall joint or at the border of
a wall and a surrounding
frames
15
5. Lead extrusion damper
• Energy
dissipation
is given by
the
processes
that take
place in the
metal when
it is forced
through the
orifice.
16
6. Shape memory alloys
• Also knows as smart alloys, are
metals that, after being strained,
revert back to their original
shape.
• It can recover from large strains.
• It have potential capability to
dissipating energy without
damage.
• Mostly used alloys are NiTi,
CuZnAl and CuAlNi.
17
7.Friction dampers
• Friction surfaces are clamped
with prestressing bolts. Slide
base
• The amount of energy dissipated
is proportional to displacement.
18
8. Visco-elastic system
• Energy is absorbed by utilizing
the controlled shearing of solids.
• The visco-elastic materials are
bonded to steel and dissipate
energy when sheared.
• Stiffness of visco-elastic materials
depends on temp. and frequency.
While design to consider it.
19
Active Seismic control system
1.TMT’s
• During excitation, a TMD simply
moves in and out of phase to that
main structural system, thereby
imparting opposing inertia force
to earthquake force.
20
2.Active Bracing System
• It consists of a set of prestressed
braces connected to a structure
whose tensions are controlled by
electro-hydraulic servo-
mechanisms.
21
3.Active Tendon system
• Based on active diagonals
consisting in tendons.
• Tendons to provide the limitation
of relative floor displacement.
• Where low excitation, the tendon
will act as passive mode.
• If higher, actuator applies the
required tension in tendons.
22
4.Tuned Liquid Damper
• It is effective when it placed
at top story of structure.
• Only TLD, which can be
properly tuned to natural
frequency of the structure
is supposed to be effective
in controlling the vibration.
• The damping effect of TLD
decreases sharply with its
mistuning
23
24
5.Active Vibration Control
• It consists of Sensors, Hardware
and Software, Actuators.
• Passive damping system only
active above 200Hz
• This starts from 1Hz and is active
until 200Hz.
• It also deduct vibration caused by
machinery, traffic, etc.,
25
26
