AASHTO SubCommittee on Highway Transport

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AASHTO Sub-Committee on Highway Transport

• Cleveland, Ohio
• June 10-11, 2004

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Uniformity in Bridge RatingsSome Review - Some
New Stuff

• James R. Braden
• Asst State Maintenance Engineer Permits
  Operations
• Alabama Department of Transportation

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Important Note

• Increased uniformity in permitting is a good
  thing.
• Purpose is to explain and clarify those issues
  that impact the move towards uniformity.
• Dont take any of these comments as saying that
  increased uniformity is impossible or
  undesirable.

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Why So Many Standards?

• Configurations vary
• Span lengths
• Widths
• Skews
• Materials vary
• Steel
• Concrete

• New standards replace older ones
• Changes in code provisions
• Correct problems that were discovered in the
  field
• Correct construction problems

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Specifications

• Specification Choices
• Allowable Stress, Load Factor, Load and
  Resistance Factor
• Specification Customization
• States can fine tune
• Example allowable tension in prestressed
  concrete beams

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Rating Practices

• Rating required by FHWA.
• Uniform reporting of results is required, but
  analysis method not specified
• Much variation between states
• End up with some variation within states
• Variety of rating tools - BARS, Virtis, BAR7,
  BRASS, BRUFEM, LARS, etc.

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Can We Try to Quantify?

• Try to create a scenario that isolates rating
  practices
• Give each state an identical truck and bridge
• Ask them to rate it according to their practices
  and policies
• Provide results to ALDOT for summary and
  presentation
• Discussed at N.O. SASHTO meeting

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Chose an ALDOT H15 Bridge(C-2411 Standard)
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Cross Section View
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Chose an Overweight Truck
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Solicited Participation

• SASHTO Multi-State Permit Group Members
• Attendees at the BRASS/Virtis/Opis Users Group
  Meeting in Albuquerque, NM

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Assumptions Specified

• Date of Construction is 1964
• Bridge was constructed with 34 ft long simple
  spans
• The condition of the bridge is good.
• Axle widths on the overweight vehicle are
  standard.

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Assumptions Made by States

• Bridge was built according to their standard
  construction practices in 1964.
• Material strengths used in the bridge matched
  those in common use in their state in 1964.
• Allowances for rail and curb deadloads
• Allowances for overlays

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Responders On First Survey

• Kentucky Transportation Cabinet
• Kansas DOT
• Mississippi DOT
• Nebraska DOR
• Ohio DOT
• South Dakota DOT

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Responders On First Survey

• Tennessee DOT
• Virginia DOT
• West Virginia DOT
• Wyoming DOT

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Permitting Results Summary
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Permitting Results Summary
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Permitting Results Summary
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Summary

• All participating states would permit that truck
  on that bridge
• Some states would require restrictions
• Variation of results was reasonable
• Least rating was 218,000 lbs (no margin for
  error)
• Maximum rating was for 298,000 lbs

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Summary Statistics

• No participating state would have denied a permit
  for that truck on that bridge
• Average rating was 253,000 lbs
• Standard Deviation 0.104
• 95 of the published ratings were within 22,000
  lbs of the average
• Low range 231,000 lbs
• High range 275,000 lbs

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Summary

• Even though there was variation, a permit would
  have been received for that truck on that bridge
• Reports of rampant non-uniformity depend on
  where you are in those ranges

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Summary

• Dont take this one study and extrapolate it to
  areas where it does not apply
• Only way an extrapolation would be valid would be
  if
• This is the only truck that haulers used
• This bridge is the only one that states have.

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Brief Conclusion to the Exercise

• Non-scientific statement
• Existing inventory of bridges is a tremendous
  hurdle to address in the quest for uniformity
• Differences between states are not arbitrary.
  They are the product of hard lessons learned or
  successful practices repeated.
• Variations are perhaps not as great as anecdotal
  evidence indicates

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Bridge Raters Meeting in N.O.

• Purpose
• In-depth discussion among those who actually
  perform the bridge analysis on permit requests
• Share tips and tricks of the trade
• Discussion of rating practices between states
• Foster relationships within this silent
  community portion of the overload permitting
  process.

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Bridge Raters Meeting in N.O.

• Discussions
• Bridge Rating exercise results
• Identification of special routes for permitting.
• Bottom-up approach from industry to promote
  more work on uniformity issues.
• Top-down approach by specification and research
  organizations to conduct work and publish
  research results on uniformity issues.

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Review of First Survey

• Decisions
• Recruit additional states to participate in
  bridge rating exercises
• Define certain parameters more closely.
• Ask for more detailed background calculations
  on other parameters (dead load distribution,
  distribution factor calculations, effective
  flange widths, etc.)

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Second Survey Sent 10-16-2002
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Responders To-Date

• Iowa DOT
• Kansas DOT
• Minnesota DOT
• Mississippi DOT
• Missouri DOT
• Ohio DOT
• Oklahoma DOT
• South Dakota DOT

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Software Used
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Permitting Status by State
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Restrictions by State
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Rating Factor by State (Permitted)
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Rating Factor by State (Maximum)
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How Can You Help?

• Industry
• Disseminate information and processes versus
  anecdotal reports
• Support top down studies on these issues by
  transportation organizations (AASHTO, etc.)

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How Can You Help?

• States
• Promote this effort among your bridge rating
  coworkers and senior staff.
• Encourage attendance of bridge rating personnel
  at regional and national meetings.
• Support and promote top-down efforts to study
  and understand issues regarding uniformity in
  bridge rating.

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How Can You Help?

• States and Industry
• Support and promote top-down efforts to study
  and understand issues regarding uniformity in
  bridge rating.

• Update
• Decision Pursue a synthesis study by NCHRP.
• Last one completed is many years old and only
  covers one national region
• Not started yet.

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How Can You Help?

• States
• Encourage attendance of bridge rating personnel
  at regional and national meetings.

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How Can You Help?

• Industry
• Disseminate information and processes versus
  anecdotal reports

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T H E E N D

• SASHTO Multi-State Permit Group