‘59% of buildings in India vulnerable to quakes, make ideal case for retrofitting to reduce seismic risks’

Among various retrofitting techniques, base isolation has proven to be one of the most effective methods for minimising earthquake damage. It works by reducing the seismic forces transmitted to the structure, rather than just strengthening the building to resist shaking. Retrofitting with base isolators involves temporarily lifting or supporting the building using a jacking system, followed by installing isolators at the foundation level. While this process requires careful engineering and precise execution, it has been successfully implemented in several countries to protect heritage buildings, hospitals, and other critical infrastructure. Despite technical challenges, base isolation remains a practical and highly effective solution for making older buildings earthquake-resistant. If implemented correctly, this technology can be adapted for a wide range of structures, ensuring safer buildings and better protection against future earthquakes.

Air cushion base isolation is an experimental earthquake protection technique where a building is temporarily lifted on a cushion of compressed air during an earthquake, acting like an air-based shock absorber. This concept has been tested in Japan for light-weight houses, where sensors detect tremors and instantly pump air under the house, allowing it to float about 3 cm off the ground to reduce shaking. As of 2011, around 88 homes in Japan were equipped with this system, demonstrating its ability to absorb seismic shocks and minimise structural damage. However, for large, multi-story buildings in urban areas, this technology is not yet practical. Lifting a heavy apartment or office tower weighing thousands of tons on a cushion of air within seconds poses significant engineering challenges. Additionally, this system requires a constant power supply to function, and any air leakage issues during an earthquake could lead to system failure, potentially causing more damage than the earthquake itself. Moreover, non-uniform air distribution could create instability, making the structure unsafe. While air cushion isolation is an innovative idea, it is still in the experimental stages for heavy buildings due to the challenges involved.

Friction Pendulum Bearings allow buildings to slide gently during an earthquake, reducing the force transmitted to the structure. The system works by placing the building on curved sliding surfaces, so when the ground shakes, the building moves like a pendulum, slowing down the impact and minimising damage. This technology has been successfully implemented in New Zealand, the US, Japan, and Chile, where it has proven highly effective in protecting critical infrastructure, bridges, and high-rise buildings. In India, these are technically feasible and could offer strong seismic protection, particularly for structures in high-risk zones such as the Himalayas, North-East India, and major urban centres like Delhi. However, their widespread use is still limited due to high costs, complex installation requirements, and a lack of awareness. While they are used in some special projects, such as hospitals and important government buildings, they remain too expensive for most residential and small commercial constructions. Another challenge is lack of well-defined building codes for base-isolated structures in India. Until the recent release of IS 1893: Part 6 (2022), there were no standardised guidelines for design and implementation of base isolation techniques.

Energy-absorbing devices act like shock absorbers, reducing force transferred to the structure. Many earthquake-prone countries have implemented these systems in high-rise buildings, bridges, and older structures through retrofitting. Among the most widely used devices are tuned mass dampers, which involve a large suspended weight that moves in the opposite direction of building sway during an earthquake, effectively counteracting vibrations. A famous example is the 730-ton golden sphere in Taipei 101 (Taiwan), which helps stabilise the tower during seismic events. Another widely used technology is viscous dampers, which contain a thick, high-viscosity fluid inside a cylinder with a piston. When earthquakes cause shaking, the piston moves through the fluid, dissipating seismic energy as heat. These are commonly found in high-rise buildings and bridges, especially in Japan and the US. Friction dampers rely on controlled sliding between solid surfaces, allowing movement while gradually dissipating energy. These dampers are commonly used in steel-frame buildings and bridges and have been widely installed in retrofitted buildings across Japan. Another effective system is tuned liquid dampers, which use a tank of liquid, such as water, to counteract movements. When an earthquake or strong wind sways a structure, the sloshing motion of the liquid stabilises the building. These are cost-effective and low-maintenance, making them an attractive option for high-rise buildings and industrial structures. Shape memory alloy dampers use advanced materials that can return to their original shape after being deformed. These dampers can absorb energy and restore stability, offering high durability and reusability. They are currently being tested and used in Japan and the US.

Above technologies significantly reduce damage: they can prevent beams and columns from bending too much and also keep the building’s contents from shaking violently. In short, countries globally have embraced these vibration-control devices, from high-tech dampers to base isolators, as a key part of earthquake-resistant design. While energy-dissipation devices are effective in reducing earthquake damage, they still allow some seismic forces to transfer to the structure before absorbing the energy. In contrast, base isolation offers a more proactive approach by reducing seismic forces at the foundation level, preventing them from reaching the building in the first place. This significantly enhances structural safety. However, in India, the biggest challenge remains cost and accessibility, making techniques difficult to implement in residential and low-rise buildings. This is where the low-cost base isolation system being developed at BITS-Pilani, Hyderabad campus plays a crucial role. By making earthquake-resistant technology affordable and practical, this innovative system can be widely adopted, helping to protect ordinary homes and smaller structures, which are often the most vulnerable during earthquakes.