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February, 2001 Heart-rending scenes of death and devastation in Bhuj and Ahmedabad have left everybody gasping for breath. Cries of a child sitting under a slab and calling her mother, her hopes diminishing with every call returning unanswered, have pierced the hearts, the bones and reached the bone-marrow. While watching the impeccable coverage of the grievous disaster by the news channels and grasping the magnitude of tragedy, one question repeatedly raises its head in our minds: Why didn’t we have a plan ready to cope with such a disastrous situation? There is no answer! The question leaves us cursing ourselves, bringing forth the stark truth: We act only when it hits our heads hard! We don’t learn from the past! Let’s learn this time. Let’s now allow the shock and the memory to fade with time. Let’s gear ourselves to cope with such disasters — whenever, wherever they occur in future, howsoever long the recurrence interval may be. If we can maintain a huge army, spend billions of rupees on its maintenance and upgradation every year without having a battle for decades together, why can’t we spend something equivalent to a small percentage of defence budget on disaster-management even after knowing very well that disasters and calamities can leave trails of destruction no lesser than those left by the wars? The question arises: Is it possible to evolve a plan to cope with disastrous earthquakes? The answer is in affirmative. Examples are there before us. When a country like Japan, virtually sitting over an earthquake zone, can cope with it, why can’t we when India too is having most of its area prone to earthquakes? Let’s look into the steps to be taken to meet with such an eventuality in future: Revision of seismic zoning map of India: The first step to be taken by us is the revision of seismic zoning map of India. At present, the Meteorological Department of India has divided the country into five zones from seismic activity point of view. Zone I is declared least prone to earthquakes and Zone V is most prone. This map has not proved realistic at all. Even the cities shown in Zone I have experienced severe earthquakes. This map carries high importance as the design of all structures in a city is to be done by keeping in view the seismic zone in which that city falls. We can very well imagine the fate of structures built in Zone I when an area shown under this zone faces a severe earthquake! Instead of five, the country needs to be divided into six zones with respect to the intensity of the earthquakes that different areas may experience. The areas that may experience Class X, XI and XII of earthquake on Modified Mercalli Intensity Scale should be kept under Zone IV. Kutch in Gujarat, the whole of Assam, Andaman islands and some parts of Himachal Pradesh and J&K should be kept in Zone VI and the structures built there should be designed accordingly. Jabalpur, considered to be in least earthquake prone Zone I has experienced major earthquakes in the past. It needs to be placed in Zone III. Similarly Latur needs to be shifted to Zone V, Khandwa region in MP to Zone IV and Mumbai to Zone IV. Bangalore, now kept in Zone I is a classic example of incorrect seismic zoning of India. This city should be assigned Zone IV in view of the intensity of earthquake it has experienced recently. Avoiding collapse of buildings: It is not the earthquake but the collapse of buildings that causes destruction and loss of human lives. Earthquakes will do least harm to us if the collapse of buildings is avoided. It must be borne in mind by us that the main criteria in design of buildings should be to prevent loss of human lives. The buildings may deform, sway, crack or distort but must not collapse! This requires taking into account the seismic zone in which the area where the building is to be erected falls while designing the building. A few factors as suggested below should prove quite helpful in design of earthquake resistant buildings to be built in earthquake prone areas: 1. For buildings taller than 30 metres, model analysis should be carried out to study the behaviour of the building under random motion of ground. 2. For buildings taller than 75 metres dynamic behaviour of the structures should be studied to evolve their design. 3. For all buildings taller than 30 metres, effect of positive torsion should be taken into account. 4. Natural frequency of buildings should be mistuned with that of earthquakes. There are a number of empirical formulae available to find the natural frequency of buildings. The vibration period of earthquakes is normally 1.5 to 2.5 seconds. 5. Higher factor of safety should be used in design of tall structures such as chimneys, towers and tanks. 6. Intensity of shocks due to earthquakes may vary with variation in soil conditions. Soil conditions should, therefore, be studied to work out seismic coefficients for hard, medium or soft soils. 7. Stiff buildings are more prone to earthquakes. In earthquake prone areas, buildings should be ductile and flexible. 8. Circular buildings are least affected by earthquakes as compared to other buildings. Buildings should be symmetrical and having minimum corners. 9. Slenderness ratio of buildings should be limited. 10. A large damage occurs due to breakout of fires on occurrence of an earthquake. No time may be available to operate fire fighting equipment when an earthquake occurs. The structures should, therefore, be built by designing them to be safe against fire. 11. The vibrations due to earthquake rise in buildings from foundation upwards. The buildings should therefore be provided with bearings that are able to absorb shock waves. Many kinds of effective and useful bearings have been developed by engineers for use in other structures bearing dynamic loads such as bridges. So there is no dearth on this account. 12. A multi-storeyed building having a tube structure proves highly effective in resisting seismic loads. Such a structure was first suggested by Owings and Merril, Chicago. In such a structure, the core of the building is kept stiff while columns are provided along its periphery and are connected by spandrel beams. 13. Wherever possible, a flat slab design should be preferred for ceilings as it does away with the beams. 14. Mass of the buildings should be kept as low as possible. Light weight materials should be brought under use. Lesser is the self weight of buildings, lesser will be the earthquake force affecting it. 15. Joints of a building should be so designed that cumulative effect of deflection does not occur in any member. Deflection diagram of the buildings should be well studied. 16. The structural framework should be kept highly redundant or indeterminate during design. Such a structure will provide better resistance to earthquake.
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