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Nepal Decoded - Earthquake Resistant ArchitectureBy Sanjana John, Nilofer Afza
Architecture Tweet 0 Comment(s)
A comprehensive look at eiective strategies that could be applied to building a more resilient future.
On April 25th 2015, an earthquake rocked central Nepal. Measuring 7.8M on the Richter scale, it was the deadliest earthquake in the history of Nepal. A second one occurred on the 12th of May with a magnitude of 7.3M.
The kind of earthquake that hit Nepal is a periodic event in the country. The earthquake itself was inevitable Nepal lies on a tectonic fault line. Despite having foreseen such an event, haphazard urbanization and lack of suicient precautionary measures around the Kathmandu Valley, ampliied the fatal force of nature.
Here's how a 2013 World Bank report summed up the problem in an article titled 'How Urban Planning Failed Nepal (by Tanvi Misra):
Unplanned urban development in the Kathmandu Valley has led to rapid and uncontrolled sprawl; irregular, substandard, and inaccessible housing development; loss of open space, and decreased livability. It has also increased vulnerability to disasters, making Kathmandu one of the most earthquake-vulnerable cities in the world.
An earthquake is a completely natural phenomenon. It releases a tremendous amount of energywhich in turn generates diierent kinds of waves at the surface. These seismic waves shake the ground surface which then impacts the building by inducing movement at the base of the building. This movement will force the lower part of the building to move along with the lateral movement while the upper part of the building will be in a position of rest. This is due to the eiect of inertia which is what makes the building vulnerable. Usually the eiect on the built structure is more when the upper part is heavily loaded. Thus lightness of the building, especially the upper part is essential in terms of earthquake engineering.
Earthquake-resistant design aims at ensuring acceptable damage to the structure and zero fatalities. The legally built buildings are either load bearing or Reinforced Cement Concrete (RCC) structures. In case of load bearing structures, the walls (9’’ to 1’ thick) carry the load to the foundation. The RCC structures, also referred to as framed structures, have a column, beam and slab system. The columns carry the load to the foundation generally resting on a concrete pile. Load bearing structures, typically built prior to the 1970s have low earth resistance. They have brittle failure and instantly fail like a pack of cards. In framed structures, the bricks are stii and have the ability to pull the structures opposite to the direction of the swaying forces and are ductile enough to allow small movement in the structure and hence perform better in terms of earthquake resistance. Most building that fell within seconds of the quake were load bearing structures like the Dharahara Tower in Kathmandu.
Kathmandu's Pashupatinath Temple is one the few structures that was left unscathed during the earthquake and it oiers a lesson in earthquake-resilient building. Unlike the Durbar Square or Dharahara Tower, the Pashupatinath Temple isn't very tall. It is also made of solid material; its brick (as opposed to mortar) walls are held together by the strong metal sheets in its roof.
"The square pan of the temple, its light weight, the roofs and ioors uniting with the walls and a strong jointing system helped. The quality of construction ... is also very high." - R.S. Jamwal of the Archeological Survey of India.
Brittleness of the masonry wall lies on the thickness of the wall as they ought to carry the inertia force along the direction of the thickness. If a masonry wall stands vertically high, untied, unsupported and with less thickness, there is high possibility of brittle failure. So, vulnerability of the building lies on the brittle property of materials. By providing good anchorage, the brittle failure of the building can be restricted. This anchorage is done by ensuring the masonry courses are interlocked at the junctions. Ensuring horizontal bands or lateral ties at regular intervals in order to strengthen the structure is also an important strategy to be applied in earthquake resistant design. Further measures include restricting the size of the opening, maintaining a good proportion of the thickness of the wall and by monitoring the height of the masonry.
Kathmandu's Pashupatinath Temple is one the few structures that was left unscathed during the earthquake and it oiers a lesson in earthquakeresilient building.
Most buildings that have collapsed in the past have failed due to their poor plan, form and the height as well. The behaviour of a building during earthquakes depends critically on its overall shape, size and geometry. A structure with simple geometry and minimal corners tends to hold good rather than one with multiple edges. Earthquake engineering suggests that the building should be not too high, not too long, neither wide in relation to the ground. Also symmetry is essential to make the buildings less vulnerable to torsion which is the twist caused by lateral forces during an earthquake. Flexibility of the building could also help reduce the vulnerability. Flexible buildings undergo larger relative displacements which may result in damage to the non-structural components and content of the building. Although it may cause economic loss or panic, the building remains safe for its residents.
In a well-designed earthquake resistant building, the soil must be stronger than the foundations, the foundations must be stronger than the columns and the columns must be stronger than the beams. One of the main reasons for the large scale devastation during the earthquake was unplanned and unregulated development. ‘’Disasters are “when” not “if” events.’’ The greatest lesson we can take is the need to incorporate sensitivity and resilience to everything we do. Physical resilience must be embedded throughout all development, permanently, not just months or years after an earthquake.
This Article is part of Agam Sei Volume: 01 Issue: 10.
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