Seismic and Structural Requirements: Design, Retrofit, and Geotechnical Practice in California
The design framework
CBC Chapter 16 adopts ASCE 7 for seismic design with California amendments, and Chapters 17 through 23 carry special inspection, soils, and material detailing rules. Design starts with a site class (A through F, from the geotechnical report) and mapped spectral accelerations, adjusted for site effects to SDS and SD1. The Seismic Design Category is assigned from both SDS and SD1 with the more severe governing; nearly all urban California falls into D, E, or F, triggering stricter analysis, detailing, and inspection.
California-specific statutes
Alquist-Priolo prohibits structures for human occupancy over a mapped active fault trace. The Seismic Hazards Mapping Act requires geotechnical investigation in mapped liquefaction and landslide zones before permits issue. The Field Act puts K-12 school design and inspection under DSA. SB 1953 governs hospital seismic retrofit under HCAI. Unreinforced masonry buildings are addressed through local ordinances and CBC Appendix A1, and existing buildings are evaluated using ASCE 41 tiered procedures.
Traps
Choosing the SDC from SDS alone; ignoring overstrength and redundancy factors; treating a geotechnical report as optional in a liquefaction zone; confusing near-fault site proximity with near-source amplification; assuming a voluntary retrofit triggers full current-code upgrade of the whole building.
Rule of thumb
Before sketching, answer two questions: what is the site class, and what is the SDC? Every lateral system, detailing requirement, and inspection threshold follows from those answers. If the geotechnical report is silent on liquefaction or expansion, request supplementation before submitting.