Real Risk

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OST OF THE

lives lost in past earthquakes have been

due to the collapse of buildings. In developing coun-

tries, these are generally non-engineered buildings

constructed informally in the traditional manner with little or

no intervention by engineers. Across the world, in zones of

moderate to severe seismic risk, more than 90 per cent of the

population still lives and works in such buildings.

In view of

this, the safety of such structures from the fury of earthquakes

is a subject of the highest priority.

In developing countries, the risk to lives is further increasing

also due to rising populations, poverty, lack of awareness and a

lack of the necessary skills and technology for safe construction.

The scenario is the same for buildings in all parts of Nepal.

Nepal lies in a ‘high’ seismic zone along which the Indian plate

is subducting under the Eurasian plate. Many large earthquakes have

occurred consistently in the past, with Kathmandu having suffered

devastation due to large earthquakes several times since 1833.

Due to the concentration of economic, political, administra-

tive and cultural activities in Kathmandu Valley, the demand for

buildings has increased tremendously, leading to unplanned

development which has in turn resulted in an ever-increasing

vulnerability to earthquakes. According to a study by the

National Society for Earthquake Technology in Nepal under the

Kathmandu Valley Earthquake Risk Management Project

(KVERMP) in 1998, an earthquake measuring 9 on the

Medvedev-Sponheuer-Karnik (MSK) seismic intensity scale in

Kathmandu Valley today would cause over 40,000 deaths, over

95,000 injuries, leave more than 700,000 homeless, damaging

60 per cent of the existing building stock beyond repair. The

main risk factors are low awareness, lack of proper knowledge

and technology dissemination mechanisms, and a high popu-

lation density accumulated in haphazardly constructed

buildings without any consideration of earthquake risk. Despite

the knowledge of historical seismicity, and continued geologi-

cal researches in the Nepal Himalayas, implementation of

earthquake risk management efforts is poor.

As a result of rapid urbanization and continuously rising land

prices, building height has increased tremendously in recent

times. Reinforced concrete framed building with masonry infill

has become the most the common construction system, account-

ing for about 25 per cent of the buildings in urban areas of

Nepal.

However, most of these buildings are not designed and

constructed to meet the seismic requirements specified by the

National Building Code. Many of them do not even meet the

requirements for vertical load design. Disproportionate height

and large occupancy means that most of these buildings pose

significant risk in urban areas. The situation is worse in inner city

areas, which have narrow streets with tall buildings on both sides.

Rescue and relief operations may encounter problems during

large earthquakes. The tendency to neglect seismic design recom-

mendations in building reconstruction, repair and refurbishment

has dramatically increased the percentage of highly vulnerable

structures within the existing stock. The National Building Code

addresses the earthquake resistance of new constructions only –

it does not advise on the seismic strengthening of existing build-

ings. The most recent earthquake events (Bhuj, 2001; Turkey,

1999; Iran, 2003 and Pakistan, 2005) showed that this class of

building suffered catastrophic damage, causing larger-scale losses

of life and property. Therefore, the seismic retrofit of these build-

ings is a pressing need, especially given the fact that a large

earthquake is considered overdue in Nepal.

Vulnerability and risk reduction:

existing non-engineered buildings

in urban areas of Nepal

Hima Shrestha, Structural Engineer, National Society for Earthquake Technology, Nepal

Rapid urbanization has increased the height of buildings,

but not their safety