New Near-Fault Adjustment Factors for Caltrans Seismic Design Criteria (SDC)

This report covers analyses of Caltrans’ near-fault adjustment factors as recommended in the Caltrans Seismic Design Criteria. The report has two large chapters. Chapter 1 builds on prior the University of California Los Angeles studies that performed probabilistic seismic hazard analyses at numerous California sites across a range of return periods and multiple site classes. Using that dataset, the chapter develops simplified, distance- and period-dependent models that quantify directivity amplification of elastic response spectra statewide. Because many bridges are expected to respond inelastically during major earthquakes, the models are further adapted to capture period elongation consistent with typical bridge ductility demands. In Chapter 2, the impacts of the near-fault directivity factors proposed in Chapter 1 were evaluated on the seismic performance of two Caltrans ordinary long-span bridge configurations: a single-column bent and a two-column bent. Using nonlinear time history analysis (NTHA), three-dimensional bridge models were evaluated under 20 bidirectional near-fault ground motions, scaled to three different target spectra. Analyses were performed for return periods of 1000 and 2475 years at two sites, Los Angeles and Oakland, and included an investigation of the influence of ground-motion directionality on bridge responses. Finally, the results obtained from elastic and inelastic analyses of single-degree-of-freedom systems, and NTHA were compared.

• Record URL:
  • https://dot.ca.gov/-/media/dot-media/programs/research-innovation-system-information/documents/final-reports/v3-01-final-report-04417-december-2025-a11y.pdf
• Record URL:
  • https://rosap.ntl.bts.gov/view/dot/89075
• Corporate Authors:

  Natural Hazards Risk and Resiliency Research Center

  Los Angeles, CA  United States  90095

  California Department of Transportation

  1120 N Street
  Sacramento, CA  United States  95814

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Mazzoni, Silvia
  • Zengin, Esra
  • 0000-0002-6543-4526
  • Bahrampouri, Mahdi
  • Bozorgnia, Yousef
• Publication Date: 2025-12

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Appendices; Figures; References; Tables;
• Pagination: 146p

Subject/Index Terms

• TRT Terms: Earthquake resistant design; Faults; Hazard analysis; Long span bridges; Seismicity
• Identifier Terms: California Department of Transportation
• Geographic Terms: Los Angeles (California); Oakland (California)
• Subject Areas: Bridges and other structures; Highways; Maintenance and Preservation;

Filing Info

• Accession Number: 01980812
• Record Type: Publication
• Report/Paper Numbers: CA25-4417, GIRS-2025-04
• Contract Numbers: 65A0774 TO 010
• Files: NTL, TRIS, USDOT, STATEDOT
• Created Date: Feb 23 2026 11:19AM