Adoption of the following safety measures can make the building earthquake resistant.
Building materials:
Building materials are crucial too. The safest modern building material is steel, as it is an extremely good shock absorber.
Cellular lightweight concrete and wood substitute are frequently used for earthquake resistant buildings.
A wooden frame house absorbs shock evenly and is unlikely to collapse. The Japanese traditional bamboo and wood used in Kashmir are sturdy and cause minimal damage.
Glass is not earthquake-friendly as a rule. However glass can be safe. The latest technology suggests lightweight plastic or silicon frames to hold the glass, ensuring safety without subtracting from the aesthetics.
A stone or a mud house comes apart even with slight tremors.
Concrete lintel beams can hold up the structure.
The above safety measures may set the tone but public awareness is essential for their enforcement. Every time an earthquake strikes, the need to enact proper laws and to make earthquake safety norms on buildings is highlighted. Earthquake resistant design of structures has grown into a true multi-disciplinary field of engineering. Creating public awareness about all aspects of earthquake and post- earthquake scenario is essential.
Codes and guidelines for earthquake resistant building have been developed by the Bureau of Indian standards Code of Practice. Earthquake-resisting designs have been known to structural engineers since the 1960’s. But who cares?
When seismic hotbed Japan can construct as high as 35-40 storey tall earthquake resistant buildings capable to withstand severe most seismic forces, why can’t we?
It is not that our present day technology doesn’t permit us but it is our attitude that forms a hurdle.
Fifty four percent of India is earthquake-prone, only a major retroffing movement and laws can prevent another disaster. The greatest fear now is that none of the other densely populated and earthquake prone metros like Delhi or Mumbai has earthquake-resistant buildings. Quake resistant buildings does not cost extra. Then why shouldn’t we go for it?
Preventing another catastrophe depends on how well we understand the issue and take measures in this direction. Other wise many more mothers will become childless and many more children motherless.
Foundations:
Foundations should be at a uniform depth.
Foundations on sloping grounds should be avoided.
A concrete slab raft foundation is more difficult to sink in an earthquake, as the pressure gets spread over a much greater surface area.
Shallow foundations should have a metal strip within the columns rising up from the foundation for strength.
Shock absorbents should be laid deeper than the footings in order to prevent vibrations.
Shock absorber bearings with layers of steel and rubber absorb the side ways motion making the structure more resistant.
Seismic bearings under the foundation allow the building to shift several inches with the ground movement providing safety.
Loads:
Effect of the horizontal force is directly proportionate to the weight of the building, it is therefore safer to have lighter buildings.
The traditional practice in Japan to construct houses as light as possible is due to severe earthquakes occurring very frequently.
In view of the rare occurrence of the earthquake the permissible stresses are increased when the earthquake forces are considered along lower load factors.
Walls:
Corners of walls are generally subjected to enormous stress. A steel bar bound to the edges with concrete allows the structure to withstand it. A concrete core such as a lift-shaft along with concrete walls holds up the adjoining structure during a quake. Concrete lintel beams above doors and windows bind the walls and prevent them from flying out.
Beams and Columns:
A framed construction with some horizontal bracing is the best suited to resist earthquake stresses as compared to load bearing constructions. If beams and columns of the buildings are properly joined, fifty percent of earthquake design is taken care of. As a thumb rule in any building adding a steel frame and concrete in the columns and beams and joining them well, adds to safety. Plinth beams of concrete tie the columns into a composite that is more stable.
Building Shape:
Unsymmetrical buildings in plan should be avoided. Irregular shape results in uneven distribution of forces, causing buildings to collapse. Uneven structures can be safe, but they have to be appropriately reinforced to resist such forces.
Pure geometric shapes like squares, rectangles and triangles disperse the seismic forces equally in all directions and so are safer. Simple cubes are more resistant than any other form. L or U shaped building connected together should be avoided. They should be divided into separate buildings whenever possible, Or else joints should be provided in between them. They should be preferably linked with R.C.C. strips.
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