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Bridges & Structures

MoDOT's Concerns with Proposed Seismic Specifications

Bryan A. Hartnagel for Shyam Gupta
State Bridge Engineer
Missouri Department of Transportation (MoDOT)

Presented to the Midwest Seismic Workshop
Collinsville, Illinois, February 10-11, 2003

PowerPoint version (200 kb)



Current Seismic Hazard (slide 2)


  • Current AASHTO map (10% PE in 50 years, return period of ~500 years)
  • Includes approximately 1,900 state owned bridges


Proposed Seismic Hazard (slide 3)


  • USGS 1996 map (2% PE in 50 years, return period of ~2,500 years)
  • Includes approximately 4,000 state owned bridges


Peak Ground Acceleration (PGA) (slide 4)

______ New (1996) U.S. Geological Survey Map (2%)
- - - - - Current AASHTO Map (1988 USGS) (10%)
Missouri state map with districts and counties identified. Contours of peak ground acceleration are based on the current AASHTO map (1988 USGS - 10 percent probability of exceedance in 50 years) and the map in the Guidelines (1996 USGS - 2 percent probability of exceedance in 50 years). Locations A, B, C, and D are shown.


Implications (slide 5)


  • Number of bridges in seismic zone increases by 110% (2100 state owned bridges)
  • Cost increase due to proposed seismic specifications changes around $ 300 million (state owned bridges only)
  • County bridges outnumber state bridges by 13 to 10


Questions for Ourselves (slide 6)


  • As guardians of national infrastructure, what level of seismic protection is justifiable and affordable?
  • As design provisions and seismic hazard definitions change, what retrofits are necessary for existing bridges?


Recommendations (slide 7)


  • Provide additional funding for site specific ground motion studies in the NMSZ
  • Provide information on return interval to use based on a justifiable criteria (ADT, cost, route type, importance, etc.)
  • Leave the current research findings as a stand alone document


Thank You! (slide 8)

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Updated: 06/13/2013
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000