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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 Actionand 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? • 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 • 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 • Required for all Scour Critical Bridge • Required on all Unknown Foundation Bridges
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 • 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 • 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 • 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 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 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 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 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