12. Design Using Seismic Isolation

This chapter presents various methods for the seismic design of steel building structures equipped at their base by seismic isolation devices. The most well-known isolation devices are the lead rubber bearings and the friction pendulum bearings. These isolation devices or isolators succeed to uncouple the seismic response of the structure from the ground motion and thus to reduce the structural seismic forces. There are basically two kinds of design methods for base isolated steel building frames: the force-based and the displacement-based ones. The design methods according to ASCE provisions are either the equivalent lateral force method or methods based in dynamic analysis including the response spectrum analysis and the nonlinear time-history analysis. The design methods according to Eurocode 8 are analogous to the aforementioned ones of the ASCE provisions. A method using an improved linear analysis is also presented. In addition to these force-based methods of design employing acceleration spectra, a displacement-based design method employing displacement spectra for high damping values is also presented. Three numerical examples involving steel building frames are presented to illustrate the design methods of ASCE and Eurocode 8 as well as the method using the improved simplified linear analysis and demonstrate the effectiveness of base isolation in seismic design.