ASCE 7-16 Lateral Force Distribution Equations for Static Design of Seismically Isolated Buildings

Abstract

Chapter 17, “Seismic Design Requirements for Seismically Isolated Structures,” in the 2016 edition of the ASCE 7 Standard, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, includes major revisions to the design requirements for seismically isolated buildings. One important objective of the revisions was to simplify the design process by expanding the applicability of the Equivalent Lateral Force (ELF) procedure. The ELF procedure is now permitted for the design of typical regular isolated structures with effective periods less than 5 s. To support extended application of the ELF, a robust method to estimate lateral design forces in the superstructure was developed. The ASCE 7-16 Seismic Subcommittee Task Committee 12 (TC-12 committee) proceeded with a rigorous review of a previous study, and developed lateral force distribution equations based on a revised data set that more rigorously considered the effects of superstructure flexibility, long period and highly damped isolation systems, and hysteresis loop shape. In this paper, the dynamic analysis parameter study and statistical analysis procedures to develop the lateral force equations are explained and validated, and the new ELF code design equations are summarized. Design case studies demonstrating the application of the equations are presented and compared to response history analysis results.