What is the Earthquake-Resistant Buildings

Earthquake-Resistant Buildings

* The horizontal movement of earth surface during earthquake is most dangerous to building.

* The point on the fault where the slipping of earth material starts is known as focus or hypocentre.

The point vertically above the focus on the surface of the earth is epicentre. The depth of focus

from the epicentre is focal depth. Distance of the point of interest from the epicentre is called

epicentral distance.

* Magnitude of an earthquake is a quantitative measure of the earthquake, which indicates the amount

of energy released at the source. It is represented by letter M followed by a number. An increase

of one number means it is 10 times higher wave amplitude and 31 times higher energy release.

Thus M6 earthquake has amplitude 10 times more than that is M5 earthquake and energy release is

31 times more.

* Intensity of earthquake is a qualitative measure of shaking at a location. Hence, intensity of a

earthquake varies from place to place. The Modified Mercalli Intensity (MMI) scale is commonly

used to express the intensity of earthquake. It is from I to XII. Very slight, felt only by instruments

is MMI-I whereas MMI-XII is utter catastrophe.

* The first Indian Seismic Code identified seven seismic zones based on the intensity experienced till

1967. In 1970 revised it to five zones. Zone I is the zone of least intensity and zone V is the zone of

highest intensity.

* Earthquake resistance of small buildings can be improved by taking care in proper selection of site,

shape and also in constructing foundations and masonry. Position of doors and widows also

contribute to earthquake resistance. Roof shape, sunshade dimension, height of parapets and

concrete and mortar selection also decide earthquake resistance of a building. It is suggested to

provide plinth band, lintel band roof band and gable bands. Retrofitting of all elements of building

so as to integrate them is desirable. For tall structures apart from providing shear walls, base

isolation and use of seismic dampers are necessary.