journal of civil engineering and technology issn 2347 ... · during an earthquake the building is...

Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203 (Print),

ISSN 2347 –4211 (Online) Volume 1, Issue 1, July-December (2013), © IAEME

57

INNOVATIVE ISOLATION TECHNIQUES FOR SEISMIC FORCES

Ar.Anurakti Yadav

LNCT College, Bhopal

ABSTRACT

Natural disaster, earthquakes, storms, floods, etc regularly hit the world. Among

these, the most destructive is earthquake since its occurrence is still unpredictable.

Ordinarily the houses are built to withstand only vertical loads and therefore when

they are subjected to horizontal stresses produced by earthquake waves they collapse

resulting in large-scale destruction. Since earthquake are capable of causing severe damage to

environment; physically, ecologically; so it is necessary for an architect or engineers to know

regarding earthquake, their occurrence, its harmful effects and precautionary measures that

can taken to minimize harms and related factors.

Historical evidence tells us that great earthquakes have shaped man’s thinking over

the millennia. While there is no evidence that the numbers of earthquakes are increasing, the

impact in terms of human tragedy and property destroyed is clearly on rise. All this is making

mankind more vulnerable than ever to disasters. In other words earthquakes are not killing

people, but the buildings created by society are it is not fate but plan and design which are

turning destiny’s dark hand.

Earthquakes the hammer of god, as they have been called is beyond human being’s

ability and forecast. It is also true that the intensity of an earthquake makes the condition

worse. But the scale of reduction can be reduced to a large extent by proper planning and

designing of houses and by suitable use of isolation base and seismic dampers.

Conventional seismic design attempts to make buildings that do not collapse under

strong earthquake shaking but may sustain damage to non-structural elements and some

structural members in the building. This may render the building non-functional after the

earthquake, which may be problematic in some structures like hospitals, which need to

remain functional in the aftermath of the earthquake. Special techniques are required to

design buildings such that they remain practically undamaged even in a severe earthquake.

Buildings with such improved seismic performance usually cost more than normal buildings

do. However, this cost is justified through improved earthquake performance.

JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY

(JCIET)

ISSN 2347 –4203 (Print)

ISSN 2347 –4211 (Online)

Volume 1, Issue 1, July-December (2013), pp. 57-63

© IAEME: www.iaeme.com/jciet.asp

JCIET

© IAEME



58

Two basic technologies are used to protect buildings from damaging earthquake effects.

These are Base Isolation Devices and Seismic Dampers.

BASE ISOLATION

If the flexible pads are properly chosen, the forces induced by ground shaking can be

few smaller than that experienced by the building built directly on ground, namely a fixed

base isolation.

The idea behind base isolation is to detach (isolate) the building from the ground in

such a way that earthquake motions are not transmitted up through the building or at least

greatly reduced.



59

The concept of base isolation is explained through an example building resting on

frictionless rollers. When the ground shakes, the rollers freely roll, but the building above

does not move. Thus, no force is transferred to the building due to the shaking of the ground;

simply, the building does not experience the earthquake.

A base isolated structure is supported by a series of bearing pads, which are placed between

the buildings and building foundation.

The isolators are often designed, to absorb energy and thus add damping to the

system. This helps in further reducing the seismic response of the building. Many of the base

isolators look like large rubber pads, although there are other types that are based on sliding

of one part of the building relative to other. Also, base isolation is not suitable for all

buildings. Mostly low to medium rise buildings rested on hard soil underneath; high-rise

buildings or buildings rested on soft soil are not suitable for base isolation.

Lead-rubber bearings are the frequently-used types of base isolation bearings. A lead

rubber bearing is made from layers of rubber sandwiched together with layers of steel. In the

middle of the solid lead “plug”. On top and bottom, the bearing is fitted with steel plates

which are used 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.

Response of Base Isolated Buildings The base-isolated building retains its original, rectangular shape. The base isolated

building itself escapes the deformation and damage-which implies that the inertial forces

acting on the base isolated building have been reduced. Experiments and observations of

base-isolated buildings in earthquakes to as little as. Acceleration is decreased by ¼ of the

acceleration of comparable fixed-base buildings because the base isolation system lengthens

a buildings period of vibration, the time it takes for a building to rock back and forth and then

back again.



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Spherical Sliding Base Isolation

Spherical sliding isolation systems are another type of base isolation. The building is

supported by bearing pads that have a curved surface and low friction. During an earthquake

the building is free to slide on the bearings. Since the bearings have a curved surface, the

building slides both horizontally and vertically. The forces needed to move the building

upwards limits the horizontal or lateral forces which would otherwise cause building

deformations. Also by adjusting the radius of the bearings curved surface, this property can

be used to design bearings that also lengthen the buildings period of vibration.

Base Isolation in India By now, over 1000 buildings across the world have been equipped with seismic base

isolation. In India, base isolation technique was first demonstrated after the 1993 Killari

(Maharashtra) Earthquake [EERI, 1999]. Two single storey buildings (one school building

and another shopping complex building) in newly relocated Killari town were built with

rubber base isolators resting on hard ground. Both were brick masonry buildings with

concrete roof. After the 2001 Bhuj (Gujarat) earthquake, the four-storey Bhuj Hospital

building was built with base isolation technique.

Fig. 1 – view of basement in Bhuj hospital building

SEISMIC DAMPERS



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Another approach for controlling seismic damage in buildings and improving their

seismic performance is by installing seismic dampers in place of structural elements, such as

diagonal braces. These damper acts like the hydraulic shock absorbers.

When seismic energy is transmitted through them, dampers absorb part of it, and thus

damp the motion of the building. Dampers were used since 1960s to protect tall buildings

against wind effects. However, it was only since 1990s, that they were used to protect

buildings against earthquake effects.

Seismic dampers are special devices introduced in the buildings to absorb the energy

provided by the ground motion to the building (much like the way shock absorbers in motor

vehicles absorb due to undulations of the road).

Types of seismic dampers

1) Viscous Dampers (energy is absorbed by silicone-based fluid passing between piston

cylinder arrangement),

2) Friction Dampers (energy is absorbed by surfaces with friction between them rubbing

against each other),

3) Yielding Dampers (energy is absorbed by metallic components that yield).

4) Viscoelastic Dampers (energy is absorbed by utilizing the controlled shearing of

solids).



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Fig. 2 Viscous Damper

Viscous damper It consists of a stainless steel piston with bronze orifice head. It is filled with silicone

oil. The piston head utilizes specially shaped passages which alter the flow of the damper

fluid and thus alter the resistance characteristics of the damper. Fluid dampers may be

designed to behave as a pure energy dissipater or a spring or as a combination of the two.

A fluid viscous damper resembles the common shock absorber such as those found in

automobiles. The piston transmits energy entering the system to the fluid in the damper,

causing it to move within the damper. The movement of the fluid within the damper fluid

absorbs this kinetic energy by converting it into heat. In automobiles, this means that a shock

received at the wheel is damped before it reaches the passengers compartment. In buildings

this can mean that the building columns protected by dampers will undergo considerably less

horizontal movement and damage during an earthquake.

Fig. 3 Friction Damper

Friction damper The novel friction damper device consists of three steel plates rotating against each

other in opposite directions. The steel plates are separated by two shims of friction pad

material producing friction with steel plates.

When an external force excites a frame structure the girder starts to displace

horizontally due to this force. The damper will follow the motion and the central plate

Journal of Civil Engineering and Technology (JCIET), ISSN

ISSN 2347 –4211 (Online) Volume 1, Issue 1, July

because of the tensile forces in the bracing elements. When the applied forces are reversed,

the plates will rotate in opposite way. The damper dissipates energy by means of friction

between the sliding surfaces.

Viscoelastic dampers

The latest Friction-Viscoelastic

of pure frictional and viscoelastic mechanisms of energy dissipation.

consists of friction pads and viscoelastic polymer pads

prestressed bolt in combination with disk spring

maintaining the required clamping force on the interfaces as in original FDD concept

Seismic dampers in India

Friction-dampers for seismic control of la gardenia towers

South city, Gurgaon was

towers of eighteen storeys with two levels of basements. In the chosen structural system, Pall

friction-dampers are provided in steel bracing in concrete frames. The use of steel bracing

eliminated the need of expensive concrete shear walls and the uses of friction

eliminate the need of dependence on member ductility. Friction

in partitions, around staircases or elevator shaft. Their use provided greater flexibility in

space planning because unlike shear walls they do not need to be located conti

over the other. Since friction-damped bracing do not carry any gravity load, these do not

need to go down through the basements to the foundation. This allows more open space for

car parking in the basement. At the ground floor level, the la

transferred through the rigid floor diaphragm to the perimeter retaining walls of the basement.

The architects have exposed some friction

appearance. A total of 66 friction

safeguard the structure and its contents from damage.

REFERENCE

1) M.S. Shetty, concrete technology.

2) Concrete engineer’s handbook.

3) Architectural journals.

4) Internet.

5) Earthquakes and buildings

6) Standard book of engineering

Journal of Civil Engineering and Technology (JCIET), ISSN 2347 –4203

(Online) Volume 1, Issue 1, July-December (2013), © IAEME

63

rces in the bracing elements. When the applied forces are reversed,


Viscoelastic Damper Device (F-VEDD) combines the advantages

of pure frictional and viscoelastic mechanisms of energy dissipation. This new product

viscoelastic polymer pads separated by steel plates.

prestressed bolt in combination with disk springs and hardened washers is used for

maintaining the required clamping force on the interfaces as in original FDD concept

dampers for seismic control of la gardenia towers

city, Gurgaon was used in India. La Gardenia housing complex consists of 7

with two levels of basements. In the chosen structural system, Pall

dampers are provided in steel bracing in concrete frames. The use of steel bracing

eliminated the need of expensive concrete shear walls and the uses of friction

te the need of dependence on member ductility. Friction-damped bracing are located


space planning because unlike shear walls they do not need to be located conti

damped bracing do not carry any gravity load, these do not


car parking in the basement. At the ground floor level, the lateral shear from the bracing is


The architects have exposed some friction-dampers to view as they add to the aesthetic

appearance. A total of 66 friction-dampers were required to extract sufficient energy to

safeguard the structure and its contents from damage.

M.S. Shetty, concrete technology.

Concrete engineer’s handbook.

Earthquakes and buildings

engineering

4203 (Print),

rces in the bracing elements. When the applied forces are reversed,


combines the advantages

This new product

separated by steel plates. A

s and hardened washers is used for

maintaining the required clamping force on the interfaces as in original FDD concept.

La Gardenia housing complex consists of 7

with two levels of basements. In the chosen structural system, Pall

dampers are provided in steel bracing in concrete frames. The use of steel bracing

eliminated the need of expensive concrete shear walls and the uses of friction-dampers

damped bracing are located


space planning because unlike shear walls they do not need to be located continuously one

damped bracing do not carry any gravity load, these do not


teral shear from the bracing is


dampers to view as they add to the aesthetic

rs were required to extract sufficient energy to

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