By Sandeep Donald Shah, IANS
It is time the people of India understand the serious dangers high-rise buildings in many leading cities face from possible earthquakes because of flaws in construction.
The last two years have seen an increased number of conferences and workshops on earthquake risk mitigation. There is interaction among members of the scientific and engineering community specializing in earthquake-related issues.
The engineering fraternity is unanimous in identifying the building category considered the most vulnerable among all the buildings in our country: buildings on stilts. A simpler explanation would be buildings that have an open ground floor area and which on most occasions are used as car parks.
Constructing multi-storey buildings with an open ground floor is a common practice in all cities because the ground floor car park area is not counted in the building FAR/FSI by the municipality while sanctioning the plans.
If not all, then a majority of the buildings on stilts will collapse in the event of a major earthquake, whether in Seismic Zones 3, 4 or 5. Nearly 60 percent of the Indian landmass comes under these three zones, with Zone 5 denoting the highest danger. (There are a total of four zones, with Zone 2 denoting the least danger.) Most of our main cities, including Mumbai, Delhi, Hyderabad, Pune, Chandigarh and Kolkata, come under Zone 3, 4 or 5.
To make matters worse, all the buildings on stilts are multi-storeyed. Hence the casualty rate would be much higher compared to low-rise buildings.
Is the government aware of this grave problem? If yes, what’s it doing about it?
The answer is not as simple. Although the government is fully conversant with the problem, it has become so massive that most feel it is an issue easier brushed under the carpet. With each passing day, the problem keeps getting bigger and bigger as more unsafe building stock gets added to our cities.
The problem isn’t insurmountable, however, if one has the resolve and approaches it in a systematic and time-bound manner.
To start with, the government will have to generate awareness among the masses that all buildings on stilts be prima facie considered unsafe until a structural consultant issues a safety certificate. In most Indian cities, multi-storey buildings are constructed and continue to be constructed on 9-inch to 12-inch (22.5-cm to 30-cm) thick columns, which are highly inadequate, even by Zone 3 standards. These buildings will come crashing down in the event of a major quake.
The government should ensure that the owners/occupants are guided to having a structural audit done for their building so as to positively identify those at risk that will need structural retrofit to upgrade. India has many thousands of structural engineers who can help in this gigantic task; a public-private partnership model may also prove to be highly successful with tiny cells of individual consultants working on a building each.
Most buildings in our cities and especially the ones on stilts are stiffness deficient. In case a building is found to be stiffness deficient, one can easily compensate it by going in for concrete jacketing or additional columns or shear walls. Care has to be taken that jacketing is done all the way down to the foundation. Although a minimum stiffness criterion is to be met, care must also be taken not to make the building over stiff because it will then attract higher earthquake forces that may prove detrimental.
Based on computer analysis, the engineer can recommend a retrofit methodology that can then be communicated to the owners of the building for implementation. Once this process is completed, the responsibility of making the building safe should rest with the owners. As an incentive, the government can evaluate the possibility of a tax incentive on the money spent on retrofit of residential buildings.
(Sandeep Donald Shah is an M.Sc in Earthquake and Civil Engineering Dynamics, University of Sheffield. He can be reached on [email protected])