Isolation for tall buildings, a Japanese case study

Base isolation practice has flourished in Japan, especially after the 1995 Kobe Earthquake. Its widespread acceptance has allowed its use to spread to more nonconventional applications such as in high-rise (taller than 60m) buildings. While only a handful of tall isolated buildings exist in the rest of the world, almost 200 isolated high-rises have been built in Japan, most of which are residential condominium buildings. In this application, the primary function of implementing isolation is to decrease engineering demand parameters to levels below which damage will occur for nonstructural content. Protecting content including water pipes and HVAC is important for maintaining the continued occupancy of buildings post-earthquake, which becomes of upmost importance in a high-rise building which provides shelter for an extremely large number of people. The Japanese design code has clear outlines for the design procedures, ground motions, acceptance criteria and peer review process for tall-isolated buildings. By contrast the US design code provides limited guidelines. This paper utilizes a representative isolated high-rise building design and a counterpart fixed base building to illustrate the performance increases gained through isolation. The building is run with both Japanese and US level ground motions to evaluate the feasibility under the different design codes.