earthquake protection system

8/11/2019 Earthquake Protection System

1/34

EARTHQUAKE PROTECTIONSYSTEM


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.


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


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


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.


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.


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


8/34

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,


9/34

steel structures like factory floors excited in one of their natural

frequencies by machines , such as screens, centrifuges, fans etc.,


10/34

ships exited in one of their natural frequencies by the main engines

or even by ship motion.


11/34

WORKING OF TUNED MASS

DAMPERS


12/34

400 kg - 14 Hz


13/34


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.


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.


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


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.


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.


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.


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.


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


22/34


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


24/34

Concept


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


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


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


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


29/34

Contd.Four-storey Hospital building was built with base isolation

technique in bhuj after the 2001 Bhuj earthquake


30/34

San Francisco International Airport Terminal


31/34

I-40 Mississippi River Bridge

Liquefied Natural Gas Tanks


32/34

Liquefied Natural Gas Tanks


33/34

THANK YOU


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.

earthquake protection system

Documents