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Combating Tremors |
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It is not possible to declare a building as an earthquake proof one. Unpredictable things can always happen and you never know when an earthquake of such high intensity that is beyond your imagination strikes the earth. If we really try to build an earthquake proof building that may withstand the maximum intensity of all the earthquakes that have rocked the earth in the past, it will be too uneconomical. Yes, earthquake resistant buildings can definitely be constructed and we should really strive for them.
An earthquake resistant building is in fact 99% safe and 1% has to be left for the uncertainty factor. Buildings are designed to withstand the impact of natural vagaries like floods, earthquakes, cyclones and wind storms by considering the magnitude of these forces in the past and their recurring interval. As and when we experience a force higher in magnitude and direction than that assumed in our design, we face devastation.
Don’t compromise: What has been happening in actual is that many builders compromised on the issue of earthquake resistant design and made ignorant people suffer losses of life and property. Bhuj Earthquake of 2001 is a classic example of Gujarat Builder’s greed when buildings came tumbling down like houses of cards and thousands of people lost their lives. This harrowing incident left the builders and their designers stunned. Their conscience was pricked by the colossal loss that the country suffered. Today, every builder is aware of importance of adopting an earthquake resistant design for his buildings. What is important to realize is that with time, this awareness shouldn’t get eroded and no compromise should be made on adopting earthquake resistant design of buildings.
Adopt latest design criteria: Large scale loss of human life and property in Bhuj has made the designers put their heads together and review the seismic division of the country. As a result, the laid criteria for earthquake resistant design of buildings has been revised by the Bureau of Indian Standards and a revised code has been enforced now. There are significant changes in the revised code. All architects, builders and structural designers should therefore, follow the new version of IS 1893 issued in 2002 and design their buildings as per its provisions.
Check your seismic zone: To make a building Earthquake resistant, first thing to check is the seismic zone in which it falls. Zone V is most earthquake prone and Zone II is least seismic. Now Zone I has been merged with Zone II. When a building has to be constructed in area that lies on the border of any two zones, then the building should be designed as if situated in the higher seismic zone.
Build stronger but lighter buildings: For earthquake resistance, a building must be stronger and lighter. A structural engineer can make it so. Get your building designed from a competent structural Engineer. All buildings must be designed keeping in view the provisions of Bureau of Indian Standards IS:1893 and IS:13920. Avoid terrace gardens and swimming pools on the roof. Avoid heavy water tanks as these make the top of building heavier causing more effect of earthquake on it.
Design for soft storey: Buildings with soft storey (Parking space at ground floor) are more vulnerable to earthquake. Therefore, extra precautions need to be taken to counter the effect of soft storey in multi-storeyed flats. Due to increased use of soft storeys in buildings such as provision of open parking space below multi-storeyed flats, definitions of soft storey and extreme soft storey have been elaborated in the new IS code and design criteria to be used for soft storeys has been provided.
Adopt RCC framed structure: RCC framed structure should be used for the buildings. Provide beams network at plinth level, door level and roof level. Try to restrict the number of storeys of the building in earthquake prone area. Keep the minimum width of beams and columns in RCC framed structures as 300 mm. Make the beams doubly reinforced to avoid effect of reversal of stresses. Prefer a strong column-weak beam combination to a strong beam-weak column combination. These measures will help a lot in making the building earthquake resistant.
Restrict the size of openings: Restrict the number and size of openings in the building. So don’t keep the size of doors and windows as too large. Always provide steel reinforcement around the openings to counter torsional effects of earthquake forces on the building.
Don’t build on filled ground: The vibrations due to earthquake compact the filled soil to smaller volume, thereby causing excessive settlement of the building. This would cause cracks in the buildings. If the building is constructed over saturated, submerged & sandy soil, such soils lose strength due to liquefaction, even if the intensity of the earthquake is not very high. In such cases, the buildings may collapse. So try not to raise a building on filled ground. If the area is low lying and a lot of filling is involved, try to utilize it by providing basement in houses and parking in multi-storeyed flats. Prefer to take foundations deeper, to the natural ground. Otherwise ask the structural engineer to account for this factor and choose a safer type of foundation.
Some More guidelines: Let the projections be small, not too large. Avoid or minimize false ceiling and plaster on ceiling. These come down easily during an earthquake. If a wall length is more than 20 feet, provide a pillar in it. Keep the doors and windows away from corners by at least 2 feet. Stagger the laps provided in the reinforcement steel.
Recheck the existing structures: If you have already got your building constructed, get its design rechecked for earthquake resistance as per new provisions. Get your building strengthened if required. Today, many retrofitting specialists are providing this service.
Give priority to safety over beauty! Happy building!!
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