Six months after the mega earthquake in Nepal, north India experienced yet another jolt on Monday. This time the epicentre was in north-eastern Afghanistan. While it was strong enough to revive memories of the destruction in Nepal, it was feeble compared to the ‘design basis earthquake’ (the earthquake which the structure is required to safely withstand with repairable damage) for Delhi. Here’s the reason why buildings collapse like a pack of cards when earthquakes strike: A large number of those buildings fall in the ‘non-engineered’ structures category, while many others are unauthorised constructions that have not been designed and scrutinised by structural engineers. Then sometimes people make modifications in their structures without consulting competent engineers and those changes make the building structurally weak.
Earthquake engineering is a young discipline. The codification of the design for earthquake-resistant constructions was tried in India in 1962 first. Since then there have been five revisions of the design criteria. The National Building Code of India (2005), published by the Bureau of Indian Standards, incorporates this criterion. But the poor quality of construction, poor implementation of codes and undue attention to looks and aesthetics of buildings rather than robustness become the primary cause of buildings performing badly when the ground shakes, impacting the building’s skeleton. So our buildings need to be resilient, not bulky. Unlike what many people think, architects don’t have the expertise, experience or education to design earthquake-resistance construction. That job is done by structural engineers.
So how can Delhiites determine if their building is likely to survive the next big one? You need to answer these questions first: Was the structure designed before 2002? Is the building on stilts where the ground floor is used for car parking, thereby creating a ‘soft’ storey inadvertently? Does your building have a non-rectangular plan or an irregular elevation? Are the columns not provided for the full height of the building? Is your building located in the vicinity of the Yamuna or located on the eastern bank? Have you made any structural changes such as cutting beams or columns? If your building is a concrete framed structure, then is the minimum dimension of the column less than 300 mm or has a width that is merely equal to that of the brick wall? If the building is a masonry structure, have you made openings for doors or windows or made other structural changes including the addition of extra floors? Are there any signs of distress in the building structure such as wide cracks or settlements or tilt of the building?
{{/usCountry}}So how can Delhiites determine if their building is likely to survive the next big one? You need to answer these questions first: Was the structure designed before 2002? Is the building on stilts where the ground floor is used for car parking, thereby creating a ‘soft’ storey inadvertently? Does your building have a non-rectangular plan or an irregular elevation? Are the columns not provided for the full height of the building? Is your building located in the vicinity of the Yamuna or located on the eastern bank? Have you made any structural changes such as cutting beams or columns? If your building is a concrete framed structure, then is the minimum dimension of the column less than 300 mm or has a width that is merely equal to that of the brick wall? If the building is a masonry structure, have you made openings for doors or windows or made other structural changes including the addition of extra floors? Are there any signs of distress in the building structure such as wide cracks or settlements or tilt of the building?
{{/usCountry}}If your answer is yes to any one or more questions, get it examined by a structural engineer who is an expert in the design of earthquake-resistant structures.
Mahesh Tandon is president, Indian Association of Structural Engineers
The views expressed are personal