Due to mining ,drilling of bore holes and many other activities, earthquakes are most common in some places of india and many more countries. And they cause more damage for life and property. Most of our civil engineering constructions are failed by forces caused due to earthquake. Even now also we don’t have thorough knowledge about the forces caused by earthquakes, due to which most of our civil engineering structures are failed. Most of our civil engineering structures are constructed by concrete it has more self weight, so it is not possible to reduce the damage caused by the structures.
Due to restless work of scientists we have a solution to reduce the damage i.e by ‘’Earthquake Resistance Structure’’. The design of earthquake resistance structures is called earthquake resistance design. By providing Base Isolation Devices we can separate building from ground by some rubber devices and also by introducing Seismic dampers and special devices for absorbing the energy caused by earthquakes . By this additional installations structures can attain stability . so safety can be possible by this design methods.
Earthquake-resistant structures are structures designed to withstand earthquakes. While no structure can be entirely immune to damage from earthquakes, the goal of earthquake-resistant construction is to erect structures that fare better during seismic activity than their conventional counterparts.
According to building codes, earthquake-resistant structures are intended to withstand the largest earthquake of a certain probability that is likely to occur at their location. This means the loss of life should be minimized by preventing collapse of the buildings for rare earthquakes while the loss of functionality should be limited for more frequent ones.
Before designing the buildings to resist earthquakes we have thorough knowledge about the behaviour of the earthquakes and how they effect the stability of buildings.
Earthquakes are induced to movement of tectonic plates slides over or push one another. In this process lot of energy was released and the energy is distributed in the form of waves around the epicenter and finally reach the ground surface. The magnitude of earthquake depends upon the movement of plates, type of soil along which the waves are moved i.e soft soil or hard rock. In hard rock movement is less but energy is transferred more quickly than soft soil.
An earthquake (also known as a quake, tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.
WHY DO EARTHQUAKES HAPPEN ?
Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don't just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up. When the rocks break, the earthquake occurs. During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again. The spot underground where the rock breaks is called the focus of the earthquake. The place right above the focus (on top of the ground) is called the epicenter of the earthquake.
HOW EARTHQUAKES EFFECT BUILDINGS?
Earthquakes cause damage as a result of the different waves that they produce as the earthquake energy moves through and on the Earth. The way that the ground responds to the energy of earthquake waves as they pass through depends on the geology of the area.
A hard rock, like granite or limestone, may vibrate very quickly with short movements, but not break apart significantly. A wet sand or silt, on the other hand, could be shaken enough that the pressure of the water in the soil builds up enough to make the soil behave like a liquid. This is called liquefaction, and is responsible for much earthquake damage in low-lying wet areas.
Damage to the ground during an earthquake usually takes place in one of the following ways:
Moves the ground in place. This does not usually cause significant damage to the ground itself, but often results in major damage to structures in or on the ground. This can include, not only buildings, but water, gas and sewer lines, train tracks, androads.
LANDSLIDES: Ground is moved (displaced) to somewhere else.
LIQUEFACTION: Strength of the ground is removed, causing the ground and objects on it to sink. Any heavy objects sitting on liquefied ground will rapidly sink. This includes all types of natural features as well as structures. Liquefaction can result in depressions, a type of landslide called a lateral spread, and the formation of sand blows. Sand blows are geysers or volcanoes of sand expelled from cracks or holes in the ground due to high water pressure in the saturated sand during earthquake shaking. Sand blows have been known to open large fissures, create large depressions, and cover large areas of land with several inches of sand. This can impact roads and infrastructure, as well as bury large areas of farmland, making it unable to sustain crops.
The damage to structures can depend on the material that the structure is made out of, the type of earthquake wave (motion) that is affecting the structure, and the ground on which the structure is built. Wood structures respond to earthquakes differently than brick or masonry structures, because wood can bend, and masonry tends to shatter. Likewise, buildings with reinforced steel in their walls tend to stand better than unsupported buildings during shaking. The taller a building is the more the top of the building moves relative to the bottom of the building; however all buildings sway during an earthquake.