Comparison of SEAONC Base Isolation Tentative Code to Shake Table Tests

Abstract

The base isolation subcommittee of the seismology committee of the Structural Engineers Association of Northern California (SEAONC) prepared a tentative code in 1986 for base‐isolated structures. Two main procedures were proposed by the tentative code for the seismic analysis of base‐isolated structures. The first approach uses simplified formulas similar to the equivalent static‐analysis formulas recommended by the uniform building code. The second approach uses dynamic‐analysis procedures (time history and response spectra analyses). In this paper, the values obtained from code‐simplified formulas are compared to experimental results from an earthquake‐simulator testing of a nine‐story steel structure mounted on a combined sliding‐bearing and rubber‐bearing isolation system. Of particular interest is the validity and accuracy of such simplifications when the isolation system is nonlinear. A simplified analysis for base‐isolated structures is possible, and more careful consideration should be given to the ground‐shaking parameters and to the base shear reduction factor.