RiskBased Bridge Evaluation

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Risk-Based Bridge Evaluation A Texas
Perspective 2009 ASCE Structures Congress
Alan Kowalik, P.E. Texas Department of
Transportation Bridge Division
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Bridge Inventory

• 50,572 Total Number of Bridges
• 33,118 On-System
• 17,454 Off-system
• 18,743 Culverts
• 787 Underwater Inspections
• 566 Fracture Critical

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Past Risk Base Practices

• Routine Inspections some culverts inspected at
  48 month frequency
• Fracture Critical up to 60 months

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Past Risk Base Criteria

• Routine Inspections Culverts
• Must be owned by TxDOT
• Must be older than 2 and less than 50 years old
• Must have ADT less than 100,001(lt25,001 trucks)
• Must be concrete
• Max span length must be less than 12 feet
• Must load rate better than HS 20
• Must have an inspection rating greater than 5

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Past Risk Base Criteria

• Fracture Critical Inspections (1994-2005)
• 60 month
• Must have remaining fatigue life
• No signs of fatigue related distress
• 24 month
• Expired fatigue life and/or
• Cracks either fatigue related or Out of Plane
  Bending
• 12 month or less
• Crack growth

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Current Risk Base Practices

• Routine Inspections some culverts inspected at
  48 month frequency
• Fracture Critical up to 60 months
• What happened??????????

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Changes in Code of Federal Regulations (CFR)
January 2005

• Title 23 CFR, Part 650.311 Inspection
  frequency
• (c) (1) Inspect FCMs at intervals not to
• exceed twenty-four months

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5 Year Inspection Cost
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2 Year Inspection Cost
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New Inspection Requirements

• More than double of FC Inspections
  performed each year
• Increase statewide inspection costs by _at_
  least 10,000,000 per year
• Equivalent to the amount of funds required to
  replace 6 on-system bridges or 29 off-system
  bridges

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Road User Cost

• 16.95 per vehicle based on 1.25 passengers
  per vehicle
• Example
• ADT 245,000 vehicles/day (Austin IH 35)
• 16 Lanes includes Mainlanes, frontage roads.
• RUC 16.95(245,000/16)/24
• RUC 10,814.45/lane/hour

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Recommendations

• Ongoing AASHTO FC Committee is working on a
  proposal to persuade FHWA to consider allowing
  the following factors to set inspection
  frequencies
• Age
• Traffic volume
• Stress cycles
• Fatigue resistant details
• Improved material properties
• Better fabrication practices

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Just a Proposal Fracture Critical Inspection
Interval Decision Process
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• 08-115-0005-06-043 IH 20 over Missouri-Pacific
  Railroad
• Description Built in 1956. The fracture
  critical elements consist of several rolled
  I-beam bent caps supported on three columns. AADT
  12,150 with 49 truck traffic carried by four
  lanes. The worst fatigue detail is Category E
  longitudinal beam seat to bottom flange welds.
  The calculated fatigue life has expired. There
  are no active fatigue cracks. The superstructure
  received a condition rating of 6.
• TxDOT Inspection Interval Y24 due to expired
  fatigue life.
• Recommended Inspection Interval Assessment
  Spreadsheet 48 mos.

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• 14-227-0113-13-114 US 290 Eastbound over
  Manchaca Rd/Westgate Blvd
• Description Built in 1997. The fracture critical
  members are two welded plate caps on single
  columns that help support a 4-span continuous
  plate girder unit, which frames into the caps. A
  note in the plans states the following The web
  and top flange are fracture critical and shall
  conform to Fracture Control Plan. AADT 24,500,
  with 4 truck traffic carried by three lanes.
  The fracture critical members have an infinite
  calculated fatigue life. There are no active
  fatigue cracks.The worst fatigue detail is
  Category C - transverse stiffener to web and
  flange welds. The substructure received a
  condition rating of 7.
• TxDOT Inspection Interval 60 month (24 due to
  CFR)
• Recommended Inspection Interval - Assessment
  Spreadsheet 72 mos.

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• 15-015-0017-02-047 IH 35 NB over Medina River
• Description Built in 1937 and widened in 1974.
  The fracture critical portion of the bridge is
  composed of two riveted, built-up, three-span
  continuous plate girder units. There is a
  suspended span in the center span that uses a pin
  and hanger system. AADT 19340 with 23 truck
  traffic carried by three lanes. The calculated
  fatigue life has expired. Several fatigue cracks
  are present at the location where welds were made
  at the floorbeam flange to girder flange
  connection. Several welds are cracked at the
  connection of intermediate stiffeners with the
  bottom flange of the floorbeam. Tack welds are
  present at several locations. The worst fatigue
  detail is Category E several different types.
  The superstructure received a condition rating of
  6.
• TxDOT Current Inspection Interval 12 months due
  to cracking.
• Recommended Inspection Interval Assessment
  Spreadsheet 12 mos.

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Recommendations

• Amend the CFR to allow for frequencies based on
  risk
• Determine is there is a better definition of
  fracture critical
• Allow engineers to use engineering judgement

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Questions??? Contact Info Alan Kowalik (512)
416-2208
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