Natural calamities are the phenomenon which can’t be prevented, but we can take precautions to minimize their effects. Calamities such as Floods, Cyclones, Volcanic eruptions, Tsunamis and Earthquakes can cause a lot of damage to life and property, and cause disturbance to our day-to-day life.
What is an Earthquake?
An earthquake is a sudden, rapid shaking of the Earth caused by the breaking and shifting of rock beneath the Earth’s surface. For hundreds of millions of years, the forces of plate tectonics have shaped the Earth as the huge plates that form the Earth’s surface move slowly over, under, and past each other. Sometimes the movement is gradual. At other times, the plates are locked together, unable to release the accumulating energy. When the accumulated energy grows strong enough, the plates break free causing the ground to shake. Most earthquakes occur at the boundaries where the plates meet; however, some earthquakes occur in the middle of plates.
Ground shaking from earthquakes can collapse buildings and bridges; disrupt gas, electric, and phone services; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive ocean waves (tsunamis). Buildings with foundations resting on unconsolidated landfill and other unstable soil, and trailers and homes not tied to their foundations are at risk because they can be shaken off their mountings during an earthquake. When an earthquake occurs in a populated area, it may cause deaths and injuries and extensive property damage.
Hence the saying,
“Earthquake don’t kill people, buildings do.”
The dynamic response of building to earthquake ground motion is the most important cause of earthquake-induced damage to buildings. The damage that a building suffers primarily depends not upon its displacement, but upon acceleration. Whereas displacement is the actual distance the ground and building may move during an earthquake, acceleration is a measure of how quickly they change speed as they move. The conventional approach to earthquake resistant design of buildings depends upon providing the building with strength, stiffness and inelastic deformation capacity which are great to withstand a given level of earthquake-generated force. This is generally accomplished through the selection of an appropriate structural configuration and the carefully detailing of structural members, such as beams and columns, and the connections between them.
In contrast, we can say that the basic approach underlying more advanced techniques for earthquake resistance is not to strength the building, but to reduce the earthquake-generated forces acting upon it. By de-coupling the structure from seismic ground motion it is possible to reduce the earthquake-induced forces in it. This can be done in a number of ways. Some popular techniques are
- Increase natural period of structure by “Base Isolation Techniques”.
- Increase damping of the system by “Energy Dissipation Devices”.