Impact of LRFD Seismic Bridge Design for Georgia

The objectives of this study were to evaluate the impact of American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) seismic detailing on Georgia bridges under various seismic hazards. Significant findings from this study are the following: (1) The analytical results show significant influences of lap-splice length, rebar size, and transverse reinforcement (TR) spacing on the ductility behavior of lap-spliced columns. (2) For multi-span simply supported concrete girder bridges, results for Site Classes A, B, and C show a lower than 25% probability of exceeding Limit State 1 with non-seismic TR spacing. For Site Class D, 3-in. TR spacing is recommended in Regions 1 and 2 to reduce the risk of exceeding Limit State 1 (initial longitudinal rebar yield) from 40.15% to 13.16% and 29.38% to 8.07%, respectively. For Site Class E, 3-in. TR spacing is recommended in Regions 1, 2, and 3 to reduce the risk of exceeding Limit State 1 from 68.53% to 33.87%, 51.39% to 19.88%, and 42.37% to 14.36%, respectively. (3) For multi-span continuous steel girder bridges, the 9-ft lap splice can be provided at the base of the column. 3-in. TR spacing is recommended to reduce the risk of exceeding Limit State 1 by 20-30% for Seismic Zone 2. Lap splice is not recommended for Zone 2. (4) For multi-span simply supported steel girder bridges, having one stirrup in each direction (two total legs in each plane) compared to two stirrups in each direction (four total legs in each plane) show less than a 2% difference in probability of exceeding defined limit states. Regions 1 and 2 for Site Classes B and C; Regions 1-3 for Site Class D; Regions 1-5 for Site Class E show relatively high risk values (>25%) of exceeding Limit State 1, and based on parametric studies of seismic risk from other bridge classes, reducing TR spacing is recommended. (5) For pile bents, for Seismic Zone 1, at least 12-in. embedment of piles into bents is the only requirement. The pile embedment length does not significantly affect the pile lateral strength. (6) The results of the seismic risk assessment on columns with varying TR spacing showed similar responses. The risk probabilities for the #3 @ 3 in., #6 @ 4 in., and #6 @ 6 in. cases for Georgia bridges are similar, with a difference of approximately 5% under the maximum factored peak ground acceleration of 0.35 g in Georgia.

• Record URL:
  http://g92018.eos-intl.net/eLibSQL14_G92018_Documents/14-20.pdf
• 
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/40888
• Corporate Authors:

  Georgia Institute of Technology, Atlanta

  School of Civil and Environmental Engineering
  Atlanta, GA  United States  30332

  Georgia Department of Transportation

  600 West Peachtree St
  Atlanta, GA  United States  30308

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • DesRoches, Reginald
  • Tien, Iris
  • Yang, C S Walter
  • Sood, Piyush
  • Zhang, Yijian
  • Zarco, Borja
• Publication Date: 2018-11

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Figures; Photos; References; Tables;
• Pagination: 142p

Subject/Index Terms

• TRT Terms: Bents; Bridge design; Columns; Earthquake resistant design; Girder bridges; Load and resistance factor design; Risk assessment; Transverse reinforcement
• Identifier Terms: AASHTO LRFD Bridge Design Specifications
• Geographic Terms: Georgia
• Subject Areas: Bridges and other structures; Design; Highways;

Filing Info

• Accession Number: 01689037
• Record Type: Publication
• Report/Paper Numbers: FHWA-GA-19-1420, RP 14-20
• Contract Numbers: 0013421
• Files: NTL, TRIS, ATRI, USDOT, STATEDOT
• Created Date: Dec 18 2018 3:05PM