8/11/2019 Earthquake Protection System
1/34
EARTHQUAKE PROTECTIONSYSTEM
8/11/2019 Earthquake Protection System
2/34
What is Structural Control?
Mechanical system employed to reduce structural vibrations
Enhance the safety and habitability of structures
Vibration control of civil structures is more in recent ascompared to machines & aerospace vehicles.
Earthquakes and wind loads - main sources of structuralvibrations.
Control vibrations by: changing rigidity, mass, damping,shape, or applying passive or active control forces.
Retrofitting reqd. if new seismic activity detected High strength may result in high acceleration levels, so
increasing strength alone wont always work.
8/11/2019 Earthquake Protection System
3/34
Earthquake protective
system
Tuned massdamping
Active massdamping
Active isolation
Energydissipation
Activebranching
Semi-activeisolation
Seismic isolation Active controlSemi-active
mass isolation
Passive protective
system
Active protective
system
Hybrid protective
system
8/11/2019 Earthquake Protection System
4/34
Passive Structural ControlTend to be very simple systems Requires no external power to operate
Simply impart forces which are developed in response to
structures motion
Passive control system include:
Tuned mass dampers
Energy dissipaters
Seismic isolation
These systems have significant application to buildings,
bridges and industrial plants
8/11/2019 Earthquake Protection System
5/34
Tuned mass dampers
A tuned mass damper, or harmonic absorber, is adevice mounted in structures to preventdiscomfort, damage or outright structural failure
by vibration. Typically, the dampers are hugeconcrete blocks mounted in skyscrapers or otherstructures, and moved in opposition to theresonance frequency oscillations of the structure
by means of springs, fluid or pendulums.
8/11/2019 Earthquake Protection System
6/34
Contd
The TMD consist of
SpringOscillating mass
Viscodamper
As main components, or may be
designed as pendulum, also with
A combination of viscodamper.
8/11/2019 Earthquake Protection System
7/34
Tuned mass dampers are mainly used in the following applications:
Tall and slender free-standing structures (bridges, pylons of bridges,
chimneys, TV towers) which tend to be excited dangerously in one
of their mode shapes by wind,
Taipeh 101
8/11/2019 Earthquake Protection System
8/34
stairs, spectator stands, pedestrian bridges excited by marching or
jumping people. These vibrations are usually not dangerous for the
structure itself, but may become very unpleasant for the people,
8/11/2019 Earthquake Protection System
9/34
steel structures like factory floors excited in one of their natural
frequencies by machines , such as screens, centrifuges, fans etc.,
8/11/2019 Earthquake Protection System
10/34
ships exited in one of their natural frequencies by the main engines
or even by ship motion.
8/11/2019 Earthquake Protection System
11/34
WORKING OF TUNED MASS
DAMPERS
8/11/2019 Earthquake Protection System
12/34
400 kg - 14 Hz
8/11/2019 Earthquake Protection System
13/34
8/11/2019 Earthquake Protection System
14/34
Millennium Bridge
First pedestrian bridge crossing over the river
thames
It is a 325m steel bridge
The maximum sway of the deck was
approximately 70mm.
Research indicated that the movement was caused
by the sideways loads we generate when walking.
When we walk, in addition to our weight, we
create a repeating pattern of forces as our mass rises
and falls. Also a small sideways force caused by the
sway of our mass as our legs are slightly apart.
8/11/2019 Earthquake Protection System
15/34
ContdThere are two fundamental ways to limit dynamic excitation:
Stiffen the structure: The additional structure required to do this woulddramatically change the appearance of the bridge.
Add damping to absorb the energy: It was decided to adopt a dampingsolution, either active damping or passive damping.
Active damping: It was too complex, expensive and production
times were too long for this
Passive damping: The bridge deploys two forms, Viscous dampers
and Tuned Mass Dampers.
Viscous dampers are located under the deck, around the piers tocontrol the lateral motions.
The tuned mass dampers are also located beneath the deck and
reduce vertical movements.
8/11/2019 Earthquake Protection System
16/34
Dampers or Energy Dissipaters
Seismic dampers can be used in place of structural elements, such as
diagonal braces.
Dampers act like the hydraulic shock absorbers in cars.
Dampers were used since 1960s to protect tall buildings against windeffects. It was only since 1990s, that they were used to protect
buildings against earthquake effects.
Four basic types of dampers:Traditional Viscoelastic dampers
Friction dampers
Metallic dampers
Fluid viscous dampers
8/11/2019 Earthquake Protection System
17/34
Traditional Viscoelastic dampers
These are stacked plates separated by inert polymer materials.
Pose problem over varying temperature.
Not achieved much success in practical applications due to
undesirable added spring effect of these devices.
There are no manufacturers that manufacture purely
viscoelastic damper.
8/11/2019 Earthquake Protection System
18/34
Friction dampers
Consist of sliding steel plates
work on the principal that when
two metal surfaces slide, friction
heat is produced and energy gets
dissipated.
susceptible to corrosion and cold
welding which has a direct effect
on the yielding threshold
There are some maintenance
problems.
8/11/2019 Earthquake Protection System
19/34
Metallic dampers
Consist of multiple steel plates
which yield when a threshold force
is reached.
As the metal yields energy is
dissipated.
These dampers are required to be
replaced after every seismic event.
Over a period of time they have also
not been able to catch the
momentum as the technology in the
other damper field has fast
progressed.
8/11/2019 Earthquake Protection System
20/34
Fluid viscous dampers
They have existed for a long time and were
developed and used in the aerospace
industry
Fluid viscous dampers are fluid filled metal
cylinders with pistons and work like shock
absorbers.
superior for both seismic and windapplications
They absorb energy at all frequency ranges
of the earthquake and also do not need to be
replaced after an earthquake.
Have a great flexibility in design and can be
configured to protect against an earthquake
of any magnitude.
8/11/2019 Earthquake Protection System
21/34
Contd
Less displacement . . . over 50% reduction in drift in any
casesDecreased base shear and inter-story shear, up to 40%
Reduced displacements and forces can mean less steel
and concrete. This offsets the damper cost and cansometimes even reduce overall cost
Only fluid dampers reduce both stress and deflection
Easily installed in a structure as diagonal braces or as
part
Stable, predictable performance at any temperature
Long life, no maintenance
8/11/2019 Earthquake Protection System
22/34
8/11/2019 Earthquake Protection System
23/34
Base isolationIs a collection of structural elements of a building that should substantially
decouple the building's structure from the shaking ground thus protecting the
building's integrity.
Structure-foundation interface is occupied by isolators
Deformation of system is in the isolators
Typical for high frequency structures, Short and stocky structures
Objectives:
Reducing the stiffness
Increasing the natural period of system
Provision of increased damping to increase the energy dissipation in the
system.
Concept
8/11/2019 Earthquake Protection System
24/34
Concept
8/11/2019 Earthquake Protection System
25/34
Base isolators
High-damping rubber: Pure rubber isolators are
softer and allow greater movement
Lead-core rubber: lead core isolators absorb some
of the seismic energy by yielding and also force the
isolator back into place quicker.
Friction pendulum: Friction pendulums isolators
permit a lower displacement profile than the
rubber counterparts. They function like a ball on a
curved plate
8/11/2019 Earthquake Protection System
26/34
Base Isolation Systems
A lead-rubber bearing is made from layers of rubbersandwiched together with layers of steel.
In the middle of the bearing is a solid lead "plug." On top
and bottom, the bearing is fitted with steel plates which areused to attach the bearing to the building and foundation.
The bearing is very stiff and strong in the vertical
direction, but flexible in the horizontal direction.
f b l
8/11/2019 Earthquake Protection System
27/34
Types of base isolation
Use of elastomeric bearings
Elastomer made of either natural rubber or neopreneStructure is decoupled from the horizontal components of the
earthquake ground motion
This gives the structure a fundamental frequency that is muchlower than its fixed-base frequency
sliding system
Transfer of shear across the isolation interface is limitedThe friction-pendulum system is a sliding system using a
special interfacial material sliding on stainless steel
l i i l ildi
8/11/2019 Earthquake Protection System
28/34
Base Isolation in Real Buildings
It has been in increased use since 1980s
Base isolation has now been used in numerous
buildings in various countries
Base isolation is also useful for retrofitting
important buildings like hospitals and historic
buildings
In India
Two single storey buildings in Killari town were
built with rubber base isolators resting on hard
ground.
Contd
8/11/2019 Earthquake Protection System
29/34
Contd.Four-storey Hospital building was built with base isolation
technique in bhuj after the 2001 Bhuj earthquake
8/11/2019 Earthquake Protection System
30/34
San Francisco International Airport Terminal
8/11/2019 Earthquake Protection System
31/34
I-40 Mississippi River Bridge
Liquefied Natural Gas Tanks
8/11/2019 Earthquake Protection System
32/34
Liquefied Natural Gas Tanks
8/11/2019 Earthquake Protection System
33/34
THANK YOU
8/11/2019 Earthquake Protection System
34/34
Conclusion
Due to earthquake protection system the dynamic
interaction between the structure and earthquake
ground motion can be modified.
Tuned mass damper prevent discomfort, damage
or outright structural failure by vibration.
seismic damage in buildings and their seismic
performance can be improved by installing seismic
dampers
The buildings integrity can be protected by
providing suitable type of base isolation system.