From the lab – Old tyres: Cheap solution for quake-proof high-rises

With the number of vehicles growing in India, we may face problems with the disposal of used tyres in an environment-friendly manner in the future. Though in many countries, people have to pay to dispose of their old tyres, in India, we just throw them away or burn them, causing pollution.

At the Department of Civil Engineering at the Indian Institute of Science in Bangalore, earthquake engineering is one of our priority research areas. Our team is well aware of the intrinsic capability of rubber to absorb vibrations and for some time now we have been working to figure out an effective way of adapting this potential to reduce seismic impact. We wanted to use waste tyres to reduce the vibrations that the high-rises witness at the time of an earthquake.

When a building is constructed, first the earth is dug to lay its foundation. After the foundation has been laid, the vacant spaces in the base are filled up with soil. At this stage we thought of mixing crushed tyre in the soil, so that the building becomes better prepared to absorb the vibrations during an earthquake.

To test this hypothesis, we bought crushed tyres and mixed them with sand in different proportions, to see how the properties of the mixture varies with the quantities. We then zeroed down on a suitable tyre crumb size for effective vibration reduction and carried out numerical model studies. Our computer models showed that the mixture could indeed help in reducing the vibrations of seismic waves and mitigate the seismic impact.

So far our study shows that the vibrations can be reduced considerably when rubber and sand were mixed in a 75:25 ratio. Our initial models showed that such a mixture improved the seismic resistance of the structure by 40 to 50 per cent. However, 75 per cent tyre content might affect the stability of the building, which we are trying to reduce by introducing reinforcements and altering the composite material.

We are also looking for opportunities to carry out large-scale model studies in the laboratory and to construct a typical building with the proposed isolation scheme in the Himalayan region with continuous monitoring. We want to check the effectiveness of the proposed scheme during a real earthquake, before going in for commercial implementation. This could turn out to be a simple and cost-effective way of making earthquake-resistant buildings in the future. It is also a very effective process for disposing of waste tyres.

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