12 mn houses under fear of quakes: YP Gupta

ALLAHABAD: Nearly 12 per cent of the country’s landmass, comprising Bhuj, Jammu and Kashmir, Uttaranchal, the north-east, north Bihar and Andaman and Nicobar Islands, lie in the most sensitive seismic zone, exposing an estimated 12 million households to maximum risk from earthquakes.
The entire country has been redrawn into four seismic sectors by a “Draft Revised Code 2000,� from the five existing since 1893.Based on the risk factor, these sectors have been further graded into five zones.
The most damage prone area has been designated as zone V, next in descending order is zone IV, III and on and forth, progressively lower down the Indian peninsula, Dr YP Gupta, a structural engineer and former professor, MLN Institute of Technology, told the Times News Network here on Monday.
The intense tremors of an earthquake practically turn the soil into jelly. The force shakes buildings violently from side to side, making it well nigh impossible for the super-structures to balance themselves constantly. Consequently, the swaying motion snaps the buildings like matchsticks and pulls them down, Prof Gupta said.
Quakes generate motion in any random direction, which causes any structure to vibrate.
The ‘amplitude’ of motion normally builds up over the duration of the earthquake, Dr Gupta pointed out. The longer the duration, more is the amplitude of vibration, resulting in a greater damage.
Buildings can be made quake-proof with a nominal investment of only six to eight per cent of the total cost, he said, allying fears that expenses would be prohibitive. Prof Gupta is currently on a quality control assignment for the bridge across Yamuna. In contrast, retro-fitting is very cumbersome and expensive. It may cost well over 20 per cent of the building value.
He also suggested a host of simple and inexpensive remedial measures. For instance, light roofs, flexibility in structure itself, so that it oscillates a little and deflects the force, minimising damage.
Besides, materials used in construction should be ductile, which does not break like glass. Strengthen load bearing walls at the edges with reinforcing bars. The building should rest on firm ground or on compacted soil and floor levels should preferably be the same. He also suggested filling sides of foundation walls with sand to partially absorb quake vibrations from both sides.