Future Direction for Base Isolation Design Provisions

摘要

Guidelines for design of base isolated structures were first developed in the mid 1980's in response to the need for a consistent approach for implementing the newly developing technology. The first inclusion of these guidelines in a building Code was in an appendix in the 1991 Uniform Building Code (UBC). These provisions have somewhat evolved over the years and have been incorporated in later versions of UBC, IBC, NEHRP provisions, and most recently in the ASCE 7-02 Standard. However, the provisions have not benefited from a comprehensive review and modification to reflect the maturing nature of the base isolation technology and the knowledge that has been gained over the past 20 years about its reliability. The early provisions were naturally conservative as they were developed at the infancy of the base isolation technology. Such conservatism is no longer justified, as much research has been done over the years confirming the reliability of isolators, raising the confidence level about their seismic performance. An overly conservative approach in designing isolated buildings unfairly hinders the use of what can be the most effective seismic protection system for most buildings and other structures. This paper highlights the Code provisions deserving possible improvements where appropriate, with the intent of making seismic isolation technology accessible and affordable when its use is technically appropriate.