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Transportation Research Board 2002 Annual Meeting Presentations from Workshop on Plan of Action for Scour Critical Bridges


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Slide 1

Approach to Developing a Plan of Action for Scour Critical Bridges

Presented at TRB annual meeting January 16, 2002

by:
J. Sterling Jones
Jorge E. Pagán Ortiz

Slide 2

A Plan of Action (POA) should be Developed
for Each Existing Bridge Found to be Scour Critical

Per FHWA guidance contained in Technical Advisory T 5140.23, "Evaluating Scour at Bridges" dated October 28, 1991

Slide 3

Scour Critical bridge

A Scour Critical bridge is one with foundation elements that are determined to be unstable for the calculated and/or observed stream stability/scour conditions.

Includes the following categories from the NBI Coding Guide item 113:

Code Description
3 Assessed or calculated condition
2 Comparison of calculated and observed condition
1 Comparison of calculated and observed; failure is imminent
0 Bridge failed and is closed

Slide 4

Goal of POA

Provide guidance for Inspectors and Engineers that can be implemented before, during, and after flood events to protect the traveling public.

Slide 5

Elements of the POA

  • Management Strategies
  • Inspection Strategies
  • Closure Instructions
  • Countermeasure Alternatives and Schedule
  • Other Information

Slide 6

Management Strategies

  • Location of Bridge
  • Bridge Identification
  • Type of Foundation and Foundation Material
  • Source of Scour Critical Rating
  • Importance of Roadway to the Transportation Network
    • ADT, Access Route to Emergency Facilities, Evacuation Route, Detour

  • Programmed for Replacement (may suggest a risk- based analysis)

Slide 7

Inspection Strategies

  • Type and Frequency of Inspection
    • Normal frequency is 2 years for superstructure and visual or probing underwater where applicable.
    • 5 years for general underwater inspection.

  • Need for continuous Monitoring
    • When to start?
    • When to stop?

  • What Constitutes a Scour Critical condition?
  • Instructions for Action when the Scour Critical Condition is Reached

Slide 8

Closure Instructions

  • Can be Load Restrictions, Lane Closure or Complete Bridge Closure
  • Criteria for Closure should be Established by Scour Team based on one or more of:
    • Observed scour, movement of riprap, monitoring bed movement, water level, discharge, rainfall, flood forecasting, debris build-ups

  • Identify Authority for Closing and Reopening a Bridge
    • Communication and coordination


Slide 9

Countermeasure Alternatives

  • Alternatives Considered
    • More intense monitoring can be one of the alternatives

  • Preferred Alternative
  • Engineering Feasibility
  • Schedule for Timely Design and Construction

Slide 10

Other Information

  • Author and sign-off on POA
  • Media Alert Instructions
  • Sources of Emergency Repair Materials
  • Detour Instructions

Slide 11

Generic POA

  • Bridge Identification: _____; Location of Bridge: ____; Year Built: ____; Replacement Plans (if scheduled):____________  Foundation Type: ____________________________ Foundation Soils Types: _______________________________________
  • ADT: ________________; Service to Emergency Facilities or Evacuation (Y/N): ______________________________________
  • Sources of scour critical rating (Assessment, Analysis, and/or Observation): ______________________________________
  • Comments about rating (e.g., analysis did not account for erosion resistant material; emergency riprap placed after last flood, etc.): ______________________________________________________________________________________
  • Inspection and Monitoring:      -Increase inspection frequency: ___________________________________________________________________________      -Types (Probing, diving, inspection of banklines): __________________________________________________________      -Special Inspection Criteria (after bankfull events, during major events): ______________________________________
  • Monitoring Type (Fixed instrumentation, Portable instrumentation): ______________________________________________
  • Criteria for monitoring: _____________________________________________________________________________________
  • Closure Plans (Limit loads; Lane closure; Full closure): ________________________________________________________
  • Criteria for Closure (Discharge; Floodwater Elevation; Flood Forecast; Scour Soundings): _________________________ ___________________________________________________________________________________________________________
  • Authorization for Closure (Bridge Maintenance engineer; Inspector; Police; Statewide Bridge Closure Procedure): ___________________________________________________________________________________________________________
  • Detour Route: ______________________________________________________________________________________________
  • Criteria for reopening bridge: _______________________________________________________________________________
  • Countermeasures considered : (1) ____________________________________; Cost: $ ________________________
    (2)____________________________________ ; Cost: $ ________________________
    (3)____________________________________ ; Cost: $ ________________________
  • Countermeasure Recommended: ____________________________________; Status: _________________________________
  • Author(s) of POA:___________________________________________________; Date: ___________________________________
  • Concurrences on POA: _______________________, __________________________, __________________________________

Slide 12

POA Examples from DOT's

  • Oregon
    • Dave Bryson

  • Florida
    • Rick Renna
    • Seta Koroitamudu

  • Maryland
    • Andy Kosicki
    • Stan Davis


Slide 13

Oregon DOT underwater monitoring guideline showing inspection frequency for a bridge over waterways

Slide 14

Closer look at Oregon DOT underwater monitoring guidelines which highlights steps in a plan of action for a scour critical bridge

Slide 15

I-84 Bridges over the Snake River near Ontario, Oregon

Photo of I-84 bridges of the Snake River near Ontario, Oregon

Slide 16

Oregon Snake River

  • Determined to be Scour Critical, Code 3. Scour has been observed to shale layer.
  • Foundation material is Shale that is continuously wet.
  • Annual Underwater Inspection; Murky Water; All Inspection by Feel.
  • Re-Evaluation by Annandale procedure might elevate Item 113 to Code 5.

Slide 17

SR 44 Bridge over St. John's River
District 5, Florida

Photo: SR 44 Bridge over St. John's River District 5, Florida

Slide 18

SR 44 Bridge over St. John's River
District 5, Florida

Photo: SR 44 Bridge over St. John's River District 5, Florida

Slide 19 - 23

SR 44 Bridge over St. John's River
POA Example

  • Bridge Number: 110063
  • Location:          SR 44 over St. John's River
  • Foundation:      Pile
  • Scour Mode:    Riverine
  • Status:
       -Phase I: Data Collection and Qualitative Analysis          --> Final
       -Phase II: Hydrologic Assessment for Scour Analysis     --> Final
       -Phase III: Geotechnical & Structural Scour Assessment --> Final
       -Phase IV: Recommended Plan of Action                       --> Final
  • Scour Rating: 3 --> Critical
  • POA Summary
    • To mitigate active scour, riprap was recently installed from Bent 5 to the West Side of bascule Pier 1.
    • Although a temporary scour countermeasure, the riprap in conjunction with a monitoring program may be an effective permanent scour countermeasure.
    • Should the monitoring program find significant degradation below the elevation of the riprap lined channel, a structural based countermeasure may be warranted.

  • Countermeasure Alternatives
    Alternatives Cost
    1. Permanent Monitoring Program/Portable Instrument $313 per monitoring event
    2. Permanent Monitoring Program/Fixed Instrument $18,500
    3. Install Crutch Bents Not feasible, riprap in vicinity
  • Closure Plan
    • If a scour condition develops, it may be necessary to close the bridge.
    • If bridge closures, immediate implement District 5 bridge closure plan for state bridges.

  • Plan Developer
    • Ayres Associates, Brian A. Acken, P.E., 01/30/98

  • Consultant Recommendation
    • Alternative #1

  • Action taken by FDOT
    • Routine monitoring/riprap already in place

  • Work Program
    • 238328 (2-98); Project file 8


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Updated: 04/07/2011

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