Last two years has seen an increased number of conferences and workshops on earthquake risk mitigation and this has resulted in valued interaction amongst members of the scientific/engineering community specializing in earthquake related issues. Most of these formal gatherings have aimed at better understanding of earthquake effects on the built environment and the mitigation techniques that need to be adopted.
The engineering fraternity has been unanimous in identifying the building category which is considered the most vulnerable amongst all of the engineered buildings in our country today - ‘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 park.
Constructing multi storey buildings with open ground floor is a common practice in all cities as the ground floor car park area is not counted in the building FAR/FSI by the municipality while sanctioning the plans.
If not all majority of the buildings on stilts will collapse in the event of a major quake whether it is zone 3, 4 or 5. To make matters worse all of these buildings are multi storey and hence the casualty rate would be much higher when compared to a low rise building.
The fatal casualties due to collapse of this single building type would be in thousands. What happened to buildings in Ahmedabad when an earthquake struck Bhuj is a live testimony.
One may ask is the Government aware of this grave problem and if so what’s it doing about it? However the answer is not as simple as even though the Government is fully conversant with the problem it is so massive that most feel it is an issue easier brushed under the carpet rather than have to deal with it.
The irony of the matter is that even though we are not ready to deal with this issue which has the potential of becoming a nightmare just yet, with each passing day it keeps getting bigger as more of the similar unsafe building stock is getting added to our cities.
A few months back a formal study was initiated to look into the gravity of the matter and a core team of seismic experts from IIT-Rourkee conducted the survey in the National Capital Region to study this aspect. The findings are truly astounding and would be an eye opener even to the Government. The survey studied the recently constructed multi-story buildings, most having been constructed in the last 4-5 years. All buildings were found to be constructed on stilts and none of them had additional shear walls in the open ground story to compensate for the stiffness deficiency. Amongst these 78% were found to contain additional design deficiencies and thus can be said to be potentially dangerous. 75% of the buildings had more than one configurational deficiency in addition to the stilt problem.
All of these can be said to be potential time bombs waiting to explode.
The problem isn’t insurmountable 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 amongst the masses through print and electronic media that all buildings on stilts be prima-fascia considered unsafe until a safety certificate is issued by a structural consultant. In most Indian cities multistory buildings are constructed and continue to be constructed on 9 to 12 inch 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 then 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.
Based on the computer analysis the engineer can recommend a retrofit methodology which can then be handed over 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 tax incentives on the amount spent on retrofit.
One of the administrative issues that requires attention at the highest level is the perfect understanding and co-ordination between the Ministry of Home Affairs which is responsible for Disaster Management and Ministry of Urban Development which influences the shape of policies and programmes with respect to construction of buildings and development of cities. The need of the hour may well be to have a joint task force handling the issue.
By Sandeep Donald Shah, has done his Masters in Earthquake and Civil Engineering Dynamics from University of Sheffield (UK). He is Director with Taylor Devices India Pvt. Ltd.
Source: http://www.indiaprwire.com/pressrelease/real-estate/200802187430.htm?aid=2324
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