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This presentation describes changes to the seismic design criteria of Chapter 11 of ASCE 7-16
and specifically the new requirements for site-specific ground motions. New site-specific design requirements were developed to address an identified short-coming with ELF and MRSA seismic design procedures related to the use of only two response periods, T = 0.2 s and T = 1.0 s, to define seismic design forces in the domains of constant acceleration and constant velocity, respectively. Although approximate, the domains of constant acceleration and velocity provide a reasonably accurate and conservative representation of the frequency content of design ground motions when peak response spectral acceleration occurs at or near T = 0.2 s and peak response spectral velocity (i.e., peak response spectral acceleration divided by response period) occurs at or near T = 1.0 s.
Such is the case for response at stiffer sites governed by smaller magnitude earthquakes, but generally inaccurate and un-conservative at softer sites (e.g., Site Classes D and E), in particular sites for which seismic hazard is dominated by large magnitude earthquakes. Exceptions to the new site-specific design requirements permit ELF and MRSA design using values of seismic design parameters increased by as much as 50 percent to avoid potential underestimation of design earthquake ground motions.
Dr. Charles A. Kircher, a Principal at Kircher & Associates Read Bio
Dr. Charles A. Kircher is a registered professional engineer with more than 35 years of experience in earthquake engineering, focusing on vulnerability assessment, risk analysis, innovative design solutions, as well as seismic code development. Dr. Kircher holds B.S., M.S., Engineer and Ph.D. degrees from Stanford University and is a Fellow of the Structural Engineers Association of California (SEAOC) and an Honorary Member of the Northern Section (SEAONC). As Principal of Kircher & Associates, he provides consulting services to a variety of clients that include commercial and industrial businesses, military and government organizations, and other engineering companies.
Dr. Kircher is a member of the Seismic Subcommittee of ASCE 7 (ASCE 7-16), and Project 17 and the Provisions Update Committee of the Building Seismic Safety Council (2015 NEHRP Provisions) and long-standing participant with SEAONC activities including the Board of Directors (1994 – 1996), Seismology Committee Chair (1992 – 1993), Base Isolation Subcommittee Chair (1986 – 1992), Blue Book Co-author, "Tentative General Requirements for the Design and Construction of Seismic-Isolated Structures," Appendix 1L, 1990 (Division III, 1991 UBC), and the Seismology Ground Motion Subcommittee.
Upon completing this course, you will be able to:
- Learn the seismic design criteria and seismic ground motion values;
- Learn the concept of site classes and the effect of site classes on the seismic design;
- Learn the site-specific ground motion procedures; and
- Learn the new changes to the seismic design criteria of Chapter 11 of ASCE 7-16 and specifically the new requirements for site-specific ground motions.