Base Isolation

Base isolation is a seismic-protection strategy that inserts a layer of laterally flexible, energy-dissipating bearings (lead-rubber bearings, high-damping rubber bearings, or friction-pendulum sliders) between the superstructure and its foundation. The isolation layer lengthens the structure's fundamental period well beyond the period range of strong ground shaking, so the superstructure moves almost rigidly while most of the seismic displacement is concentrated — and damped — in the isolators, drastically reducing the accelerations and inter-storey drifts transmitted into the building.

It is used where the contents or function must survive a major earthquake essentially undamaged — hospitals, emergency-response and data centres, museums, and seismic retrofit of important/heritage structures — and is recognised within Indian seismic practice (IS 1893 framework, with detailed isolation design typically following specialist/international provisions). Design must provide for the large isolator displacement (a wide seismic 'moat' and flexible service/utility connections crossing the isolation plane), check the isolators for gravity plus seismic, and verify behaviour by response-history analysis; it is a higher-cost solution justified by performance, not economy.