The rise of high-rises
Nine years after the 2015 earthquake, Kathmandu has to ask: how safe are the new tall structuresFor a year or two after the 25 April 2015 earthquake, the residents of Kathmandu were too terrified to return to their high-rise apartments. None of them collapsed in the 7.8 disaster, but many sustained serious structural damage.
Fast forward nine years, and they have all but forgotten that frightful day. Kathmandu is back to building substandard structures, even as land prices drive developers to build taller.
With no more space to spread horizontally, Kathmandu is going vertical. But structural engineers say most of the high rises do not take into account seismicity, soil condition, construction methods, quality of raw materials, fire hazard, and search and rescue in collapsed concrete structures.
“Much of our focus since the 2015 earthquake has been on building and construction, but not as much on where we are building,” warns Sangeeta Singh, Professor of Urban Planning and Deputy Director of Centre for Disaster Studies at the Institute of Engineering.
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She adds: “Kathmandu is not really suited for high-rises. We have to first test the condition of the soil, but building permits are being issued without this fundamental step.”
Kathmandu Valley is a former lakebed with soft topsoil prone to liquefaction and excessive shaking, as seen during the 1934 megaquake. Many ruptures tore up the surface in 2015.
During an earthquake, the rock layers below Kathmandu ring like a bell and the vibrations on the surface take between 0.5 to 2 seconds for one oscillation. Buildings also vibrate, but at different frequencies depending on their height, construction material, and arrangement of their structural components.
At five floors, the vibration period of a building is 0.5 seconds, which is the same as that for Kathmandu Valley, and this could cause more damage, says structural engineer Surya Narayan Shrestha at the National Society for Earthquake Technology - Nepal (NSET).
“Building anything that is five storeys or higher in Kathmandu needs special design and structural considerations,” says Shrestha.
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Technologies exist to reduce seismic risk in high-rises, and these are used in earthquake-prone cities like Tokyo, Los Angeles, Jakarta or Mexico City.
Base isolation, for example, separates the vibration of the land and the building, reducing damage from soil-building resonance. Base isolators move and stretch under pressure, absorbing much of an earthquake's impact by reducing swaying and shaking.
Seismic dampers change the pattern of vibration altogether, dissipating energy as vibrations move across a structure. But these are all expensive technologies, and none of the high-rises in Kathmandu use them.
However, Nepali engineers who can help with technology transfer are working in the field in Nepal and overseas. Kathmandu’s high-rises are already very expensive, and making them seismic-resistant would be an incremental cost.
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The shape of high-rises also matters. Reinforced concrete buildings with asymmetric designs of the kind that are seen in newer structures in Kathmandu experience more torsion and shear during quakes. High-rises with regular geometry are stronger.
An even bigger concern is that of emergency evacuation and rescue in case of fire or earthquake. Kathmandu fire services do not have ladders that reach the higher floors of most new structures.
“High-rises mean more people and potentially higher casualties,” explains Shrestha. “We need immediate evacuation routes, fire escapes, emergency ladders, and fire trucks that can reach higher. Right now, safety features are voluntary and not mandatory.”
The street access, shelters, open spaces, and evacuation routes are integral to disaster preparedness and the safety of neighbourhoods and not just buildings. Most new high-rises in Kathmandu have narrow access roads.
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Since most of the buildings that survived the 2015 disaster were reinforced concrete structures, it fed the misconception that they are safer. But Himalayan seismologists say that if the intensity and duration of the shaking had been just a little higher, many substandard concrete structures would have collapsed.
And that is the final gap: Nepal’s limited expertise and equipment for search and rescue inside collapsed concrete structures. Kathmandu’s high-rises need to be better prepared for the next Big One.
“Structural safety and design were at the front and the centre after the 2015 earthquake, we also revised some building codes but we are back to square one with contractor-driven construction, especially in peri-urban areas,” says Sangeeta Singh, who is also with the National Planning Commission. “We need to monitor construction as much as design.”
Shrestha at NSET agrees there have been improvements in building practices in the past nine years, but adds, “We have both learnt and unlearnt lessons from 2015. The awareness hasn’t yet translated into action on safety.”
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writer
Sonia Awale is Executive Editor of Nepali Times where she also serves as the health, science and environment correspondent. She has extensively covered the climate crisis, disaster preparedness, development and public health -- looking at their political and economic interlinkages. Sonia is a graduate of public health, and has a master’s degree in journalism from the University of Hong Kong.