11

Base IsolationBase Isolation

Base isolation is a technique of controlling structural Base isolation is a technique of controlling structural response in which the building or structure is decoupled response in which the building or structure is decoupled from the horizontal components of the earthquake ground from the horizontal components of the earthquake ground motion by interposing a layer with low horizontal stiffness motion by interposing a layer with low horizontal stiffness between the structure and the foundation.between the structure and the foundation.

This layer gives the structure a fundamental frequency that This layer gives the structure a fundamental frequency that is much lower than its fixedis much lower than its fixed--base frequency and also much base frequency and also much lower than the predominant frequencies of the ground lower than the predominant frequencies of the ground motionmotion. .

The isolation system does not absorb the earthquake The isolation system does not absorb the earthquake energy, but rather deflects it through the dynamics of the energy, but rather deflects it through the dynamics of the systemsystem. .

22

Displacement and Acceleration Spectra

33

44

Concept of Seismic Isolation

55

Without base isolation With base isolation

66

Seismic Isolators

Rubber

Steel plates

1. Laminated Rubber Bearings

The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction

xb

yb

kbcb

cb

kb

gx

gy

Mathematical model

77

2. Lead Rubber Bearings

yb

cb

xb

kb

cb

kb

gx

gy

The lead plug reduces, or dissipates, the energy of motion - i.e., kinetic energy, by converting that energy into heat.

88

Lead Rubber Bearing at Building Site

99

1010

3. Friction Pendulum Bearings

1111

Slider

1. The building is supported by bearing pads that have a curved surface and low friction.

2. During an earthquake, the building is free to slide on the bearings.

Friction Pendulum Bearings

1212

BHUJ HOSPITAL PROJECT

1313

Bhuj District Hospital, IndiaBhuj District Hospital, India - completed January 2003 - completed January 2003

1414

Lead Rubber Bearing beingLead Rubber Bearing beingLowered into Position Lowered into Position

1515

Lead Rubber Bearing on Site,Lead Rubber Bearing on Site,Bhuj District Hospital, India 2002Bhuj District Hospital, India 2002

1616

Lead Rubber Bearings,Lead Rubber Bearings, Bhuj District Hospital, India 2002 Bhuj District Hospital, India 2002

1717

PARLIAMENT NEW ZEALAND