Building earthquake-resilient structures

Experts suggest adopting strict building codes, using hybrid materials, and conducting regular seismic evaluations during construction

March 31, 2023 04:09 pm | Updated 05:01 pm IST

Hours after the Turkey-Syria earthquake, a video on Japanese techniques to deal with such calamities began doing the rounds on social media. It showed how Japanese engineers and architects had developed different methods to tackle earthquakes as their country was geographically prone to it. They used two main techniques — seismic isolation and base isolation. Seismic isolation is the technique of installing a system of bearings and sliders under the building that reduces its responses to ground motion during an earthquake. Base isolation is an anti-seismic design strategy that can reduce the effect of earthquake ground motion by uncoupling the superstructure from the foundation.

“Japan uses various techniques to make earthquake-resilient structures. At the core of Japan’s infrastructure is Taishin — an earthquake-resilient code every building must follow. Beams, pillars, and walls can absorb intense ground shaking since construction is of minimum thickness,” says Delhi-based Sneha Gurjar, Director, CEM Engineers.

Japan had witnessed two major earthquakes in the past century — the great Kanto earthquake in 1923 and the Hanshin earthquake in 1995. In 1923, over one lakh people were killed, while in 1995, the earthquake claimed over 6,000 lives. That’s when Japan decided to bring changes in the construction scenario. Now, it is one of the best modern techniques in the field of construction across the globe, minimising damage to property and saving thousands of lives.

Possible methods

Can these be implemented in India? Architects and engineers reply in affirmation, validating it with research and groundwork.

“The frequency and intensity of earthquakes in each country differ depending on the tectonic action below the surface. So, only research can say how the Japanese method can be made possible in India. That will provide avenues of technological adaptation and can lead to the invention of hybrid forms of resilience more suited to our climatic and geological conditions,” says Chennai-based Creative Architects & Interiors founder Pramod Jain.

Though India has made rapid progress in technology and infrastructure sectors, the cost of construction is the big hurdle. Gurjar says, “Adapting some of these international strategies and integrating them with meticulous analysis and simulations based on the climate, geography and ecosystems here will be a leap ahead. However, the cost of constructing such buildings is definitely one of the main factors pulling us back.”

Om Prakash Mishra, Director, National Center for Seismology (NCS), and Scientist G, Union Ministry of Earth Sciences, says that the government is studying several ways to implement Japanese technology in India.” A team of scientists from IIT Delhi, Madras, Roorkee, among others, is conducting the study.

Hybrid systems

What kind of technology is adopted to build these structures? Gurjar says, “As seen in the video, the results were achieved using strategies that isolate the building from the ground to resist the lateral forces and provide flexibility to the structure during an earthquake. To achieve the performance of a base isolation system, passive devices, including dampers and isolators, can be incorporated into the buildings. Options include elastomeric systems, sliding systems and hybrid systems. However, these alone are not enough. A careful selection of hybrid materials, strict building codes, regular seismic evaluations, and retrofitting older buildings are important to bring about the change.”

Jain confirms the view. He says that Japan has strict laws in the construction sector. “Along with base and seismic isolator techniques, they use seismometers and seismic intensity meters; their building codes mandate a building should withstand and not collapse with an earthquake magnitude of even 5-7. In India, unfortunately, for a long time, earthquake-resilient buildings have been an option, not the norm. So building these structures in a country that still needs to follow basic building codes may mean more work,” he says.

Traditional architecture

That said, it is also true that old structures in India have a proven track record of being quake-resistant. There are several old buildings constructed almost half-a-century or a century ago which are still standing strong.

Uroosi, a Mughal-era home architectural element, is one such. Uroosi are wooden shutters used as partition walls within homes, instead of concrete walls.

A five-storey house with uroosi in Srinagar’s Safa Kadal area.

A five-storey house with uroosi in Srinagar’s Safa Kadal area. | Photo Credit: Peerzada Ashiq

Gurjar says, “Very similar to Japanese vernacular architecture, uroosi provides a wooden framework that strengthens the smaller structures, as seen in Kashmir. Much of earthquake-resistant modern Japanese architecture seen today is inspired by their vernacular structures and building techniques, which have translated successfully with the use of technology and innovations in building materials.”

Jain adds that traditional styles may not be suitable for high-density regions, but they can however be modernised with technology.

He says, “The vernacular practice called Taq or Bartar prevalent in the Himalayan regions of Kashmir uses dry stone rubble masonry along with horizontal timber frames. The stones absorb shock and efficiently dissipate energy through vibration/ friction, and the timber frame’s elasticity prevents the structure’s disintegration. In some extreme cases, we have seen that the stones dislodged due to the earthquake could be easily put back into place using simple hammering. However, these vernacular, time-tested methods may not be suited for high-density regions or multi-storey buildings. Still, many mechanism aspects are derived from vernacular architecture in India.”

Soil conditions

The nature and quality of soil are important in preventing major losses due to earthquake. Usually, the bedrock layer is stiff and can take the vibratory impact without disintegrating. It absorbs the shock and dampens the earthquake’s effect, reducing its intensity. As the soil gets loose, smaller particles amplify the seismic waves and are hence more disastrous, says Jain.

The shock intensity can vary depending on variations in the soil condition. The National Building Code (NBC) provides design guidelines with response spectra for three founding strata types: rock and hard, medium, and soft soil. Some soil types are useful for all kinds of construction; however, the wrong foundation can cause disastrous effects in weak soils, fissures and tears, sinking, or worse, collapse, says Gurjar.

Clay soil is often sticky when wet and does not drain well. It is not an ideal soil to use when building a foundation because it is not stable. Sand and gravel in sandy soil are more suitable because they have large particles that aid quick water drainage. This means that there is less risk of putting a building under stress. Loam soil is ideal for building a foundation due to its sand, silt, and clay constituents, which are the right combination for construction. Rock is the right choice to construct larger buildings like skyscrapers, duplexes, and multi-storey buildings because of its high bearing capacity.

G.P. Ganapathy, Professor at Centre for Disaster Mitigation and Management, Vellore Institute of Technology (VIT), says that it cannot altogether be confirmed which soil is good for construction. It depends on soil amplification, which happens only when shear and surface waves pass through water-saturated soil.

Almost 59% of India’s land area is vulnerable to earthquake. Deben Moza, Senior Executive Director - Head of Project Management, Knight Frank India, says, “Lack of strict enforcement of codes in India allows developers to build structures in an unplanned manner, sometimes even violating the regulations of construction. Other major challenges are lack of technical expertise, land-use regulation and dearth of incentives to build earthquake-resistant structures.”

The NCS has installed 152 permanent seismic stations across India to detect seismic waves and the most susceptible regions, the Ministry of Earth Sciences told the Lok Sabha in February 2022. “This will help us identify vulnerable regions and act fast to prevent damages,” says Mishra.

Stating that the rules framed under the NBC and Bureau of Indian Standards are strict enough to prevent the collapse of buildings during an earthquake, Mishra says that fresh policy changes will be applicable for the construction of new buildings, but that “we have to safeguard the buildings that are already there”.

How safe is Chennai?
The geology of Chennai comprises mainly clay, shale and sandstone. Hence the city has a mixture of sandy, clayey and hard-rock formations. Chennai falls in the Moderate Damage Risk Zone-classified as Zone 3 by the National Center for Seismology, Ministry of Earth Sciences. “However, to be generic, we can say that we have to enhance resilience by introducing policy changes that make adopting earthquake mitigation measures mandatory in every building, especially in high-rise buildings; quality monitoring must be diligently done at different stages and policies that curb encroachments and violations must be made stringent,” says VIT professor Ganapathy. “Chennai is in Zone III (expected maximum earthquake magnitude of 6.9). The safety of a building depends on the foundation and structural design of a building. The city has a mixture of sandy and clayey soil with shallow bedrock. Even though the soil gets amplified due to earthquake, if the foundation is proper, we don’t need to worry about soil conditions.”
Referring to safety measures, Suresh, Designer Architect at ICONS BDC, Chennai, and professor at Hindustan University, says Chennai is just above mean sea level. The city is warm and humid. Buildings with glass facades are not meant for Chennai as they increase atmospheric heat generated by air conditioning systems.”

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