Empirical Selection Equation for Friction Pendulum Seismic Isolation Bearings Applied to Multistory Woodframe Buildings

Base-isolation systems have been increasingly used in concrete and steel structures for seismic design, but their application to woodframe structures remains largely unexplored with only several hundred buildings isolated, primarily post-and-beam buildings in Japan. This paper examines the incorporation of friction pendulum (FP) bearings into the performance-based seismic design (PBSD) for woodframe structures using nonlinear time-history analysis. Specifically, a regressive equation for the selection of the bearing radius (R) based on the fundamental period and the seismic weight present on each FP bearing is developed. Six generalized models representative of 1- to 6-story woodframe buildings were analyzed and used to develop a regressive design equation. Based on rigorous multi-incremental dynamic analysis (M-IDA), a regressive linear relationship between the spectral acceleration and bearing radius of the FP bearing was developed. An illustrative application to a 4-story residential woodframe building is presented to illustrate use of the approximate design expression. Furthermore, the expression allows one to achieve a PBSD using base isolation with no specific need to consider the detailing of the superstructure configuration with the exception of the elastic period. (C) 2014 American Society of Civil Engineers.