Efficient Methods for Determining Seismic Site Class for Alabama Bridges

Details

• Creators:
  McLeod, Joshua ; Okafor, Chukwuma ; Saha, Alok Kumar ; Montgomery, Jack ; Barnes, Robert ; Calderon, Maria Emilia Clavijo
• Corporate Creators:
  Auburn University. Highway Research Center
• Corporate Contributors:
  Alabama. Department of Transportation ; United States. Department of Transportation. Federal Highway Administration
• Subject/TRT Terms:
  • S waves
  • Velocity
  • Earthquake resistant design
  • Seismicity
  • Bridge design
  • Geospatial data
  • Measurement
  • Shear wave velocity
  • Seismic design category
  • Site class
  More +
• Publication/ Report Number:
  931-101
• Resource Type:
  Tech Report
• Geographical Coverage:
  United States ; Alabama
• Edition:
  Final Report
• Corporate Publisher:
  Alabama. Department of Transportation
• Abstract:
  Shear wave velocity (VS) profiles are critical inputs for seismic design of bridges because they influence the amplitude and frequency content of predicted ground motions. Site class, determined using the time-averaged shear wave velocity of the upper 30 meters (100 feet) of a site (VS30), is used in the AASHTO Guide Specifications for LRFD Seismic Bridge Design to define seismic demand through the Seismic Design Category (SDC). This study developed a flexible and efficient approach for determining seismic site class at bridge sites in Alabama. Updated SDC maps were created for the state using the 2023 AASHTO Guide Specifications and gridded seismic hazard values from the USGS. Direct measurements of VS were collected at 15 sites across Alabama using Multichannel Analysis of Surface Waves (MASW) and seismic refraction surveys. Passive Horizontal-to-Vertical Spectral Ratio (HVSR) measurements were also collected. The direct measurements were then used to evaluate a range of VS and VS30 estimation methods, including SPT-based correlations, RQD-based correlations for rock, HVSR-based correlations, and geospatial correlations. Of the correlations evaluated, geospatial methods performed best overall. The model presented in Geyin and Maurer (2023) is recommended for general use across the state, while the model presented in Gann-Phillips et al. (2024) provided the most accurate estimates for sites within the Atlantic and Gulf Coastal Plains. SPT-based correlations tended to underpredict VS for stiffer materials, which can lead to conservative SDC estimates and unnecessary design effort. Recommendations are provided to determine SDC, including guidance on when direct VS measurements are likely to be beneficial.
• Format:
  PDF
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/93188/dot_93188_DS1.pdf
• File Type:
  [PDF - 6.39 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:52cf068d52b7b211b1a847b94552499475f83385f9bc16a4b867dd082a18aee4b22826c31970789d72a933697945a1753752e0a141ffe376ae2c0714056e73b9