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Surviving earthquake
FE Report
10/26/2005
Following the severe earthquake in Pakistan and parts of India and Afghanistan on October 8 experts started making predictions about earthquake in Bangladesh and possible affects on life and property.
In fact earthquakes do not kill by themselves. Casualties during earthquakes arises mainly from the collapse of buildings and structures. In cities and villages alike, it is the same story. Tremors leave behind heaps and heaps of man-made rubble, in which human beings lie buried, dead or alive. Homes, that people take a whole lifetime to build, and that people hold to be the safest havens on earth, turn into graveyards.
Earthquakes can never be predicted, not in the near future at least, say the experts. So the question is how do we reduce the blow of the catastrophe? The answer is simple --- making buildings safer by using sound construction techniques.
The last few decades of the 20th century, especially from the 1970s, had seen a proliferation of unsafe and unscientific construction in the cities and towns. The so-called modern architecture, making use of reinforced concrete cement (RCC) for flat roofs, was gaining fast popularity, replacing the older and smaller tile-thatched houses. Then, the buildings also started to grow taller.
Yet, nobody had heard of making a structure earthquake-resistant. The need was not felt then. But the onset of 21st century changed all that. Structures needed reinforcement, people began to say.
So, are people becoming more aware now? Are the engineers ready to make structures that can withstand the tension created by tremors in the ground? "Yes," says the engineers and builders. "The awareness level has increased considerably these days," says a front ranking real estate developer. Clients are much more aware of the need for added reinforcements, even though the cost factor becomes a little higher.
After every earthquake around the globe the planners in Bangladesh start talk about constructing buildings in line with Bangladesh National building Code (BNBC). They talk about earthquake resistant design of buildings.
The public works authorities say that the BNBC cannot be enforced as it was not made mandatory by promulgating a law. Experts feel that authorities should draw up a new set of building codes and regions should be re-divided into new zones of earthquake possibility. The October 8 quake that rocked the Himalayan slopes of India and Pakistan has triggered demands to make the codes more effective.
The experts are of the opinion that many of the buildings in Dhaka will crumble the way they did in Gujarat or Muzaffarabad. It will happen as the buildings do not have enough steel; the builders tried to save money.
Incidentally, the period of a building is simply the time taken by the building to make one complete vibration. It is the inverse of the frequency of the building, which is the number of times per second that the building will vibrate back and forth.
Builders say all buildings above six floors are now being given extra protection. Steel content in the foundation has also been increased. On the basis of soil conditions of locations measures are taken to make buildings tough.
The vulnerable components of a building including the lift ducts and balconies need more attention. The walls of lift ducts should be strengthened with concrete.
The another criteria is strengthening the ordinary two or three-storied buildings also. For such smaller buildings, small columns should be given in corners, with tie up at base levels for strengthening the walls. Giving a continuous concrete belt at beam level is also common now. As the corners of the walls are the first to suffer the impact of an earthquake, strengthening the walls and corners has the utmost importance.
Likewise, connecting the porches and balconies with the main structure is also stressed now. Porches, particularly vulnerable to earthquake damage, needed to be tied up with the main structure using plinth beams.
Cantilevered balconies are not considered suitable these days, as the free-standing length of the balcony considerably reduces the earthquake resistance of the building. Often, the balcony is the first to fall. And projections are generally affected during quakes. Balconies, in general, become more stable with less width, whether they are free-standing or not.
Accurate calculations are needed before increasing the quantity of steel. Earthquakes are natural calamities you can't avoid. You can't run away from them. At best, you can find means to survive their onslaught.
However, with all the avowals by the engineering community, it remains true that no official system has been evolved to verify if all the buildings do prescribe to the norms for earthquake prevention. It has been suggested that the local self-governing bodies should be made to demand full compliance with the criteria for earthquake resistant construction for getting the building permission.
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