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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

Changes to FHWA's NBI Coding Guide (Items 60 and 113)

Plan of Action Workshop
January 16, 2002
Jorge E. Pagán-Ortiz
Senior Hydraulics Engineer
(e-mail:jorge.pagan@fhwa.dot.gov)

Federal Highway Administration
Office of Bridge Technology
Washington, D.C.

Slide 2

Implementation

  • Revisions implemented by April 27, 2001, memorandum (Mr. James D. Cooper)
  • Coordinated with National Bridge Inventory Steering Committee

Slide 3

Goal

  • Provide new guidance for coding bridges over waterways for:
    • Observed and assessed scour condition
    • Scour and stream instability countermeasures


Slide 4 - 5

Objectives

  • Make coding of Items 60 (Substructure) and 113 (Scour Critical) consistent when a rating of 2 or below is determined for Item 113
  • Expand description of Item 113 codes 1, 2, 3, 4, 5, 7, 8, T and U
  • Encourage bridge owners to develop a plan of action for:
    • Scour critical bridges (codes 1-3)
    • Bridges coded "7" and "U"
    • Improve communication between the engineer and inspector


Slide 6

Highlights of Changes to Item 60

  • Description changed to emphasize that rating factor given to Item 60 should be consistent with the one given to Item 113 when:
    • Rating factor of 2 or below is determined for Item 113.


Slide 7 - 8

Highlights of Changes to Item 113

  • Description changed to emphasize that:
    • Rating factor of 2 or below requires revising Item 60 and other affected items (load ratings and superstructure rating)
    • Plan of action should be developed for each scour critical bridge
    • Coding is based on an engineering evaluation, which includes consultation of NBIS field inspection findings

  • Refers to FHWA's Hydraulic Engineering Circulars 18 and 23 for guidance on scour and countermeasures.

Slide 9

Specific Changes to Rating Factors (Codes U and T)

  • Code "U" - plan of action should be developed to reduce the risk of failure during and immediately after a flood event.
  • Code "T" - tidal bridges should be monitored until an evaluation is performed

Slide 10

Code 8

  • Expanded guidance for a bridge foundation determined to be stable:
    • Assessment --bridge foundations on rock formations determined to resist scour within the service life of the bridge
    • Calculations
    • Installation of properly designed countermeasures


Slide 11

Code 7

  • Countermeasures installed to mitigate an existing scour problem and to reduce the risk of bridge failure during a flood event
  • Instructions in a Plan of Action have been implemented to reduce risk to users from a bridge failure during or immediately after a flood event

Slide 12

Code 5

  • Foundation determined to be stable for the assessed or calculated scour condition
  • Scour within the limits of footings or piles based on an assessment, calculation or installation of properly designed countermeasures

Slide 13

Code 4

  • Bridge foundation stable for the assessed or calculated scour condition

Slide 14

Code 3 (Scour Critical)

  • Bridge foundation unstable for the assessed or calculated scour condition

Slide 15

Code 2 (Scour Critical)

  • Field review indicates that extensive scour has occurred at bridge foundations, which are determined to be unstableby:
    • Comparison of calculated and observed scour during bridge inspection
    • Engineering evaluation of the observed scour condition reported by the bridge inspector in Item 60


Slide 16

Code 1 (Scour Critical)

  • Field review indicates that failure of bridge foundations is imminent based on:
    • Comparison of calculated and observed scour during bridge inspection
    • Engineering evaluation of the observed scour condition reported by the bridge inspector in Item 60


Slide 17

Current Status (04/15/01)

Bridges over waterways: 481,530  
Screened by Categories: 481,319 (100%)
     Low risk (9, 8, 7, 5 or 4): 336,401 (69.9%)
     Unknown foundations (U): 89,611 (18.6%)
     Tidal (T): 987 (0.2%)
     Scour susceptible (6): 29,461 (6.1%)
     Scour critical (3, 2, 1, or 0): 24,859 (5.2%)
Not Screened: 211 ---

Slide 18

Scour Evaluation Status

Pie Chart: Low Risk = 70%, Unknown and Tidal = 19%, Susceptible = 6% Critical = 5%

Slide 19

Scour Evaluation Summary

  • Evaluations Completed:  361,260 (92.4%)
  • Evaluations Needed:        29,672 ( 7.6%)
  • Evaluations Total:          390,932 (100.0%)

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Updated: 04/07/2011
 

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