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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

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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


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  • 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


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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


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Scour Plans of Action

  • Required for all Scour Critical Bridge

  • Required on all Unknown Foundation Bridges


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FHWA POA Template

  • 10 Parts

  • FHWA POA Template

    • http://www.fhwa.dot.gov/engineering/hydraulics/bridgehyd/poaform.cfm


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Part 1


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Part 2


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Part 3


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Part 4


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Part 5


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Part 6


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Part 6 (continued)


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Part 7


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Part 7 (continued)


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Part 8


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Part 9


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Part 10


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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


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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


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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


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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


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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


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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


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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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Questions?


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