EARTHQUAKE-RESISTANT BUILDING DESIGN

 

EARTHQUAKE-RESISTANT BUILDING DESIGN

Earthquake is a sudden and great misfortune. It is a very serious problem since they affect human life in various ways. It Causes vibration of the earth's surface in a certain region for a certain time.due to tectonic Movement, Volcanic Eruptions, landslides, blasts in  Mines, Nuclear Explosions etc. Earthquakes do not kill people, but actually, people are killed by the collapse of badly designed and constructed buildings. But, with the different types of new materials available in our inventory, it is feasible to construct an earthquake-resistant building.

The most destructive of all earthquake hazards is caused by seismic waves reaching the ground surface at places where human-built structures, such as buildings and bridges, are located. When seismic waves reach the surface of the earth at such places, they give rise to what is known as strong ground motion. Strong ground motions cause buildings and other structures to move and shake in a variety of complex ways. Many buildings cannot withstand this movement and suffer damages of various kinds and degrees. The seismic waves travel for great distances before finally losing most of their energy. At some time after their generation, these seismic waves will reach the earth’s surface, and set it in motion, which we surprisingly refer to as earthquake ground motion. When this earthquake ground motion occurs beneath a building and when it is strong enough, it sets the building in motion, starting with the building's foundation, and transfers the motion throughout the rest of the building in a very complex way. These motions in turn induce forces that can produce damage

What makes a building or structure fail in earthquakes?

An Earthquake moves the ground. It can be one sudden movement, but more often it is a series of shock waves at short intervals, like our ripples from the pebble in the pond analogy above. It can move the land up and down, and it can move it from side to side.

All buildings can carry their own weight (or they would fall down anyway by themselves). They can usually carry a bit of snow and a few other floor loads and suspended loads as well, vertically; so even badly built buildings and structures can resist some up-and-down loads. But buildings and structures are not necessarily resistant to side-to-side loads, unless this has been taken into account during the structural engineering design and construction phase with some earthquake proof measures taken into consideration. This weakness would only be found out when the Earthquake strikes, and this is a bad time to find out.

 

How can we make buildings resistant to earthquakes with earthquake engineering?

To be earthquake proof, buildings, structures and their foundations need to be built to be resistant to sideways loads. The lighter the building is, the less the loads. This is particularly so when the weight is higher up. Where possible the roof should be of light-weight material. If there are floors and walls and partitions, the lighter these are the better, too. If the sideways resistance is to be obtained from walls, these walls must go equally in both directions. They must be strong enough to take the loads. They must be tied in to any framing, and reinforced to take load in their weakest direction. They must not fall apart and must remain in place after the worst shock waves so as to retain strength for the aftershocks.

The behaviour of a building during earthquakes depends critically on its overall shape, size and geometry. Hence, at the planning stage itself, architects and structural engineers must work together to ensure that unfavourable features are avoided and a good building configuration is chosen. If both shapes and structural system work together to make the structure a marvel. There are a wide variety of earthquake effects - these might include a chasm opening up or a drop of many metres across a fault line. Therefore, it is not possible to design an earthquake-proof building which is guaranteed to resist all possible earthquakes. However, it is possible during your design and construction process to build in a number of earthquake-resistant features by applying earthquake engineering techniques, which would increase enormously the chances of survival of both buildings and their occupants.

Some care should be taken while constructing a building in earthquake-prone areas. Special attention should be given to Structural Design of the structure. Here are some tips for designing safer structures.

Ø  During design period live load , dead load ,wind load & seismic load should be consider,M20 grade concrete (1:1.5:3) should be used.

Ø  Simple geometric shapes should be used i.e. square, circle, rectangle, Avoid curves and angles

Ø  There should no odd shapes in elevation and the whole building should be in balance. The centre of gravity of building should not move, CG of the buildings, as low as possible & light materials used in roof.

Ø  For strengthening the brickwork, a sill or a lintel band should be provided

Ø  Cantilever projections should be minimum and their length should not be more than 3 to 4 feet.& Cast in-situ is better than the pre-cast system

Ø  Avoid hanging or floating columns, roof garden, and swimming pool on top floor.

Ø  The span between the columns should be as small as possible. Column must be stronger than the beam.

Ø  The ratio of Building Length: Breadth<4:1,

Ø  Spacing of ties in column & beam as follows.

Ø  Column & beam steel reinforcement tie as follows.

Ø  Avoid the short column (short column effect)

Ø  The opening should be minimized in ground floor.

 Conclusion: Earthquake can neither predicted nor be prevented. But the damage can be minimized by adopting earthquake-resistant measures during building design and construction.