Section 1613.1/Earthquake Loads
IBC 1613 establishes earthquake load requirements by referencing ASCE 7 Chapters 11 through 23, with mapped acceleration parameters and seismic design category determination.
Every structure must be designed for earthquake loads per ASCE 7 Chapters 11 through 23, with exceptions for detached dwellings in SDC A, B, or C and agricultural buildings. The process begins with the mapped spectral acceleration parameters SS and S1 from ASCE 7 Section 11.4, adjusted for site class to produce the design parameters SDS and SD1. The Risk Category and design parameters together determine the Seismic Design Category (A through F), which sets the level of seismic detailing, analysis method, and design requirements. The structural general notes must include the mapped parameters, site class, design parameters, Risk Category, Seismic Design Category, seismic force-resisting system, and the response modification coefficient R.
Why this section exists
Earthquakes produce ground accelerations that subject buildings to lateral forces and deformations. The design process uses the site-specific seismic hazard combined with the building importance (Risk Category) to determine how much seismic detailing is required. The Seismic Design Category is the key classification: it determines whether standard construction detailing is adequate (SDC A and B) or whether special seismic detailing is required (SDC C through F). The equivalent lateral force procedure in ASCE 7 converts the seismic hazard into design forces applied to the structure.
What plan reviewers look for
Plan reviewers check the structural general notes for all required seismic design parameters: SS, S1, site class, SDS, SD1, Risk Category, Seismic Design Category, seismic system, R factor, and the analysis procedure. They verify the site class matches the geotechnical report. They verify the SDC is correctly determined. They check that the seismic system is permitted for the SDC. They verify that special detailing requirements are specified where required by the SDC.