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Scour Plans of Action and Unknown Foundations. Timothy Rogers FHWA Oregon Division Bridge Engineer Local Agency Bridge Design and Inspection January 8, 2010 Oregon State University, Corvallis, Oregon. What is a bridge? Federal definition is 20 feet and longer What is scour?

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scour plans of action and unknown foundations

Scour Plans of Actionand Unknown Foundations

Timothy Rogers

FHWA Oregon Division Bridge Engineer

Local Agency Bridge Design and Inspection

January 8, 2010

Oregon State University, Corvallis, Oregon

definitions
What is a bridge?
    • Federal definition is 20 feet and longer
  • What is scour?
    • Removal of streambed material from around bridge foundations
  • What is a Scour Critical Bridge
    • Bridges that are unstable if the estimated scour occurred (by analysis or observation)
  • What is an Unknown Foundation
    • No as-built foundation plans available
  • What is a Scour Plan of Action?
    • Plan for monitoring and repairing scour critical bridges
Definitions
snapshot of oregon s national bridge inventory
Snapshot of Oregon’s National Bridge Inventory
  • Total Number of Bridges = 7299
    • Local and others =4069
    • State = 2690
  • Bridges Over Waterways = 5627 or 77%
    • Locals and others = 3907
    • State = 1742
  • Scour Critical Bridges = 1175 or 16%
    • Locals and others =635
    • State =540
  • Bridges with Unknown Foundations = 1859 or 25%
    • Locals and others =1684
    • State = 175
scour plans of action
Scour Plans of Action
  • Required for all Scour Critical Bridge
  • Required on all Unknown Foundation Bridges
slide5
FHWA POA Template
  • 10 Parts
  • FHWA POA Template
    • http://www.fhwa.dot.gov/engineering/hydraulics/bridgehyd/poaform.cfm
unknown foundations program 1 9 2008 memorandum key points
Unknown Foundations Program 1/9/2008 Memorandum Key Points
  • Establishes November 2010 target date for elimination of bridges with unknown foundations
  • Suggested a process for eliminating or reducing population
  • State examples of implementing an evaluation process
unknown foundations program 6 3 2009 memorandum key points
Unknown Foundations Program 6/3/2009 Memorandum Key Points
  • Presented answers to some frequently asked questions by bridge owner and division offices regarding bridges with unknown foundations
  • Clarified the intent of Item 113 in the coding guide with respect to the code U
  • Clarified the requirements for bridge owners to meet the November 2010 target date for addressing bridges coded U
unknown foundations program
Unknown Foundations Program
  • Goal of the program and the procedures presented by the FHWA is to reduce the inventory of bridges coded U in item 113
  • There will be an inventory of bridges that remain coded U in Item 113 if sufficient information can not be obtained to advise recoding
unknown foundations program21
Unknown Foundations Program

For bridges that will remain coded U, FHWA recommends that a POA be developed and implemented until:

a) properly designed countermeasures can be installed to protect the bridge foundations

b) the bridge can be replaced

unknown foundations program22
Unknown Foundations Program

FHWA guidance is intended to offer a rational approach for:

a) determining enough about bridge foundations to conduct a scour evaluation, or

b) appropriately address bridges that will remain coded U

unknown foundations program risk based approach
Unknown Foundations ProgramRisk Based Approach
  • Identify Risk

Lowest Risk

      • Performed Well
      • No Scour
      • Consequences of failure minimal

Highest Risk

      • Evidence of scour
      • Consequences of failure significant
unknown foundations program risk based approach24
Unknown Foundations Program Risk Based Approach
  • Take Action Commensurate with Risk
    • Lowest Risk
      • Monitor Biennially and After Flood Event
    • Highest Risk
      • Monitor more frequently than low risk
      • Timely schedule of replacement or countermeasures
      • If significant scour observed, in-depth foundation investigation and scour analysis
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