How strong an earthquake will Noida twin towers cause when they come down?

Noida: Supertech’s twin towers, when they come cascading down in just 13 seconds from the instance that blasts, separated by milliseconds, turn loose its foundations, will cause shockwaves comparable to one-third of a typical earthquake that measures one on the Richter scale.

This is how Edifice Engineering’s Uttkarsh Mehta described the impact on the ground. Edifice Engineering has partnered with South African Jet Demolitions to being down the twin towers.

“Delhi NCR is categorised in the seismic zones 4-5. This means that most buildings are already constructed to be able to withhold high frequency earthquakes. The vibrations emanating from the blast will be way mild than any minor earthquake,” Mehta said.

Mehta also explained that the blast has been designed in such a way the debris will touch ground in a stepwise manner, and not all at once. The demolition men have also put in place additional safety measures such as creating debris pile, trenches, bunkers in the basement, that will cushion the fall and reduce vibrations.

While the company has assured residents of neighbouring buildings, especially some towers of Supertech Emerald Court and ATS, that no harm would come to their structures and flats, it has also got a vibration analysis done by British firm Vibrock Limited to put their minds to rest.

According to the report, explosives cause both ground as well as air vibrations. “In general, the use of explosives for the demolition of structures is liable to give rise to both ground and airborne vibration. Detonation of the explosive itself may generate ground vibration, although it is usual for the majority of explosive to be located within the structure and above ground level and hence this source of vibration is generally minimal.”

“It is usually the airborne vibration or air overpressure generated by the explosive that is of most significance owing to the fact that the individual charges, albeit relatively small, are often not able to be totally confined. Once detonation occurs, as the structure impacts with the ground, will be a further source of vibration. In this case the vibration will be predominantly generated within the ground with any air vibration of a minimal magnitude,” the report said.

The operative part of the report that is reassuring is as follows: “There are significant differences between the characteristics of demolition induced vibrations and those produced by earthquakes. Specifically, the vibration generated by this demolition event will be of relatively high frequency content (10 to 40 Hz) and short duration (2 to 5 seconds) in comparison to earthquake vibration that can last for many minutes and will generally comprise of energy at less than 1 Hz. As such the relatively high frequency content of demolition vibration ensures that the actual ground displacement is so low as to generally not be problematic.”

Therefore, only minor damages, if any, is expected after the blast. However, cracking of some windows has been predicted for which Edifice Engineering has kept experts on stand-by who will repair the damages at the earliest.

When the twin towers come hurtling down, an estimated 41,720 tonnes will hit the ground under the Apex tower, while Ceyane approximately weighs 18,150 tonnes.

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