Nepal’s traditional seismic resistant designs
After the April 2015 earthquake, the National Reconstruction Authority (NRA) released two manuals to address the repair and retrofit of masonry and reinforced concrete structures. Later, it added an updated guideline for masonry structures.
The NRA advisory is consistent with international approaches for earthquake-resistant houses, with a focus on using new, commercial products available in the construction market. But we can also learn a lot from Kathmandu Valley’s historical building traditions about alternative designs.
There are many ways of building resilience into structures, but the most historically prevalent and still important today is flexibility. Strong but flexible jointing of ductile and appropriately-sized structural members that hold a building together allow it to sway with movement loads during an earthquake, making it less likely to collapse.
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Such design is seen in old timber-framed and intricately jointed buildings in Japan and China, and also in structures across Nepal. For example, roof rafters are jointed to ridge poles and wall plates to allow a pivoting motion that helps isolate the roof structure from the rest of the building in case of ground movement.
Traditionally, buildings in Nepal were constructed with timber and brick walls. Timber is now a scarce resource, and masonry has fallen out of favour in the face of the militant march of concrete. From the plains to the mountains, buildings were made of stone, timber, mud, bricks, thatch and tiles.
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Just as the frames and jointing were made to be flexible, the walls were thick, rigid and robust, which is another stabilisation technique. These days, because building with concrete and bricks means walls are thinner and weaker, corner ties and banding can help keep flimsier walls intact.
Other earthquake-resilient building techniques include lightweight roofing, which in the past was done with wood and bamboo sub-structures to thatched roofs — especially in the Tarai — and triangulation, seen today in trusses and pitched forms, traditional Newari scroll capitals and decorated tundaal (struts).
At a seminar this month on seismic risk organised by the National Society for Earthquake Technology and the United States Geological Survey, experts said Nepal had a strong tradition of resilient construction.
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Modern skyscrapers in earthquake-prone places like Tokyo use base isolation to counter seismic movement. The Nyatapola Temple in Bhaktapur, Nepal’s tallest, has similarly stood the test of time and two massive earthquakes by combining base isolation with triangulation. The ziggurat form that supports the five-storey timber and brick tower is essentially a robust plinth, separating the sacred relic and its towering housing from the shaking, while providing ample seating for the beautiful carved guardians of the venerated god.
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But just as important as building resilience into a structure is caring for it. In the past, buildings lived and breathed within settlements, cared for on a daily basis, and would fall apart if neglected. Ritual care, for example yearly renovations for Dasain, ensure that homes and community buildings are regularly maintained and kept intact, and thus less prone to falling apart in the event of a natural disaster.
In the old towns of the Kathmandu Valley, Newari dwellings and temples were built with both tensile and rigid elements — timber, bricks and clay clustered together in courtyard configuration, each courtyard effectively creating braced squares that are more capable of withstanding shakes.
Similarly, communities in the high Himalaya build settlements one atop another into a hillside, or side by side on contours in maze-like configuration. These buildings, rising from the ground as an agglomerated system of dwellings, are a breathtaking symbol of communities leaning on one another, in a telling, enduring tradition of deep-rooted resilience.
Building Resilience
Flexibility/shock absorbency (timber, steel, pinned joints, hydraulicised mud mortars)
Rigidity/integrity/banding/corner reinforcements/buttresses (thick masonry walls, rammed earth, interlocking blocks, corner reinforcements, symmetry, opening sizes + locations)
Base isolation (dampers, deep foundations, robust plinths)
Bracing/triangulation/shear walls/lateral loading/banding (struts, capitals, corbels, lintels, top plates, reinforced concrete or timber banding, metal ties, plywood bracing wall panels)
Lightweight Roofs (metal sheet, thatch, shingles, bituminous tiles)