base isolation and dampers

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Base isolation and

dampers

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This is Haiti presidential Palace before the Earthquake


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And this is the same palace after disaster.


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Classification of Seismic Protection Systems

SEISMIC RESISTANT DESIGN OF

STRUCTURES

DUCTILITY / STRENGTH

BASED DESIGN METHODS

ACTIVE CONTROL

METHODS

PASSIVE CONTROL

METHODS

RESPONSE CONTROL BASED

DESIGN METHODS

HYBRID / SEMI ACTIVE

CONTROL METHODS

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Classification of Seismic Protection Systems

PASSIVE CONTROL METHODS

ISOLATION ENERGY DISSIPATION

BASE ISOLATION FLOOR ISOLATION ROOF ISOLATION

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Base Isolation

Introduction of Flexible Isolator Elements at the foundation level of

the structure so that the sub-structure (below ground level) and

super structure (above ground level) are isolated from each other

The flexible isolation system partially absorbs (through Damping

action) and partially reflects (through Filtering action) a major

portion of the earthquake energy and reduces the energy

dissipation demand of the super structure to a major extent

resulting in increased survivability

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Mechanism of Base Isolation

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Residential Building in Indonesia

Seismically Isolated Structures - Examples


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Residential Complex in China



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Hospital Building, Bhuj, India

The first base isolated structure is the new 300 bed Bhuj Hospital, reconstructed

after the devastating earthquake of 26 Jan 2001



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Types of Base Isolation Devices

Lead – Plug Rubber

Bearing

Friction – Pendulum SystemGERB-Spring System

1. Laminated Rubber Bearings (LRB) : Natural or Synthetic Rubber

2. Laminated Lead – Rubber Bearings

3. Sliding / Friction based isolation systems: Friction Pendulum

4. Spring type (GERB) isolation systems

Laminated Rubber

Bearing

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Suitability of Seismic Base Isolation

• High Seismic Region and if the Existing Structure is Unsafe

• Life-line Structures

• Structural foundations are Weak and have Low Ductility

•Earthquake motions likely to occur are Short Period Accelerograms

• Primary or important secondary structures are more vulnerable to seismic attack and

to minimise the damage

• Irregular structural form, L-shaped building

• Cost economics of the structure with and without isolators

• Reliable and durable isolator components are available at affordable cost


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Application in bridges

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Supplemental damping devices that Dissipates / Absorbs a portion of theenergy input to the structure thus reducing the energy dissipation demandof the primary structure

Damage to the load resisting system is substantially reduced leading to

major reduction in post EQ repair costs

Passive Energy Dissipation (PED) systems (DAMPERS):

Advantages of PED systems:

EQ damaged PED devices can be easily replaced

Ideal for lifeline structures (Structures which are required to functional evenafter EQ)

Effective for wind induced motions also (Unlike Seismic Isolation) 19


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Yielding type ELASTO-PLASTIC energy dissipaters:

The tapered shape of the plate produce uniform

yielding throughout the length

Triangular Device

X - shaped Device

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Lead Extrusion Damping (LED) Device

- Applications (Buildings,Bridges)

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Friction dampersLinear friction dampers

Rotational friction dampers

X-braced damper

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Visco-elastic solid dampers

F

F/2

F/2

Visco Elastic Material

Center Plate

Top & Bottom Cover Plates

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Visco-elastic Fluid Dampers

•Dissipation occurs via conversion of mechanical energy to heat as a piston

deforms a highly viscous substance like silicon gel

•Extremely high energy dissipation is possible by forcing the fluid to pass

through small orifices rather simply deforming the fluid locally

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Spring Friction Damper

•Energy dissipation occurs due to frictional sliding, and consequently the

response is frequency dependent

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Roof Isolation Systems

A roof isolation system is a combination of rubber

isolators and a damping mechanism between the top

story and the roof or between the top story and rest of

the building.

The top story or the roof acts as a tuned mass damper.

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Roof Isolation System

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Efficiency of various methods of

DampingThe hysteresis (force-deflection curve) shows the

efficiency of a damper during an earthquake. The (blue)

area inside the curve is the total dissipated energy. The

curve shows that the rotational friction damper

dissipates more energy than any other damper today.

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