Monday, 4 May 2015

Are soft storey buildings earthquake safe?

Open ground storey buildings are the prevalent building designs adopted by developers. In metropolitan cities especially, where land space is a major hassle, most of the developers construct underground parking area to accommodate safe parking of its residents. However, it might come as a surprise to you that mostly ground floors in such buildings are relatively flexible and weak.  Rather than keeping your cars safe, in natural calamities such as earthquakes it poses a threat to not just your cars but also your lives. Therefore, it becomes extremely necessary to know the forces behind the vulnerability on the structures during earthquakes.

Housing options abound, but is your home earthquake safe?

It’s the unsafe building that kills people and not the earthquake. So, a well-designed structure will not collapse until and unless wrong planning and execution is introduced. These days Reinforced concrete (RC) frame buildings are becoming increasingly common in urban India including the cities and towns situated in moderate to severe seismic zones (namely III, IV and V).

More about open ground storey buildings:
Open ground storey buildings are also called the RCC-framed structure and building on stilts. Many such type of buildings has open ground storey open which is used for parking. The columns in the ground storey do not have any partition walls between them.

The problem with soft storey building:
As per the earthquake preparedness guide by National Disaster Management Division, Ministry of Home Affairs, “The presence of walls in the upper storeys makes them stiffer than the open ground storey. Therefore, during movement they move together as a single block. As the columns in the open storey are not strong enough in resisting sideways shaking from the earthquake, they get severely damaged subsequently further leading to collapse of the upper structure.”

The guide also quotes, “Studies have shown that buildings on stilts do not perform well in earthquakes unless the columns and beam connections on the ground have been specially designed to withstand the shaking load.”    

Before buying a house in an open ground storey one should ensure that that the building is designed as per the norms laid down for earthquake safety in the Bureau of Indian Standards code.

If you are already living in a multistoried building and not sure it has been designed to resist earthquake or buying a new one, your next step should be to get the building reviewed for earthquake safety by a experienced structural engineer.

Make sure the structural engineer checks the below mentioned 5 elements:
  • Corner columns and beams
  • Peripheral columns and beams
  • Stair walls and column and lift walls
  • Columns at upper levels
  • Infill and partition walls
  • Beams, columns as well as their junctions at levels must be checked

Seismic retrofitting is a necessity for ensuring safety of both structural elements and of non-structural elements.

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