Structural Condition Assessment of the Herbert C' Bonner Bridge

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Structural Condition Assessmentof the Herbert
C. Bonner Bridge

• Prepared by
• Mark Moore, P.E.
• Travis Green, P.E.
• Wiss, Janney, Elstner Associates, Inc.
• Ted Bartelt, P.E.
• Alpha Omega Group, Raleigh, NC

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Overview of Presentation

• Introduction
• Description of Bridge
• Scope of Condition Assessment
• Assessment Tools
• Summary of Conditions

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Description of Bridge

• Located at Oregon Inlet
• Bodie Island on north
• Pea Island on the south
• Opened April 7, 1964
• Length of 12,865 feet
• 2 lanes of traffic
• Vital link between Kitty Hawk and Hatteras Island
• 2 million vehicles/year

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Proposed Bridge Replacement

• Bonner Bridge schedule for replacement in next 10
  years
• 3 new alignments being studied
• Environmental impact studies underway
• Detailed condition assessment needed to extend
  service life approximately 15 years

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Basic Components of Bridge
Bodie Island
Pea Island
Low Level
Navigation Spans
High Level Approach
Low Level
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Overview of Bridge
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Typical Cross Section
7 ¼ inch cast-in-place deck 45 inch deep
prestressed concrete girders w/ 7/16 inch
diameter strand
33 feet 3 inches
28 feet
8 feet
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Typical Low Level Bents
Pile Cap 3 x 2 6 x 28 6
22 prestressed concrete piles
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Typical High Bent 2 Frame
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Typical High Bent 3 Frame
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Non Typical Bents
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In-Depth Condition Assessment

• Routine NBIS Inspection
• Detailed visual inspections
• Materials sampling and testing
• Petrographic examinations
• Chloride content testing
• Nondestructive testing
• Ultrasonic pulse velocity
• Half-cell potential measurements
• Structural analysis
• In-place load testing
• Repair recommendations

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Routine NBIS Inspection

• Each structural element was rated
• Standard scale of 0-9
• Good (7-9) Fair (5-6) Poor (3-4) Critical (0-2)
• Overall condition rating was Poor
• Elements rated Poor included
• Deck, girders, bent caps, bent columns, pile
  caps, plate girder bearings
• Prompt action items limited to replacement of
  missing plate girder bearings and one pile

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Detailed Visual Inspection

• Up close visual inspection and sounding
• Wide spread occurrences of spalling,
  delaminations and corrosion
• Common conditions
• Delaminations in both original and repaired
  concrete
• Spalls at ends of girders
• Varying degrees of cracking in concrete elements

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Typical Conditions
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Materials Testing

• 178 cores removed from selected areas
• Compressive strength
• Girder and pile concrete 6,200 8,320 psi
• Bent and pile cap concrete 3,830 8,430 psi
• Bridge deck concrete 5,310 7,470 psi
• Design strength
• 3,000 psi for cast-in-place
• 5,000 psi for prestressed concrete

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Petrographic Examinations

• Concrete generally of very good quality
• No significant deleterious reactions were
  observed
• Cast-in-place concrete found to have consistent
  constituent course and fine aggregates
• Precast concrete contained different course and
  fine aggregates
• Depth of carbonation generally less than 0.25 inch

Coral fragments in limestone aggregate
Carbonate crystals in cavity
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Chloride Content Testing

• 3 general areas of focus
• Bridge deck
• Pier caps and bent frames
• Prestressed concrete girders
• ASTM C1152 acid soluble chlorides in concrete
• FHWA recommended threshold of 0.2 acid soluble
  chlorides by weight of cement
• Corresponds to a threshold of 0.02-0.03 by mass
  of concrete
• Assess chloride levels at the level of primary
  reinforcing

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Chloride Contents
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Ultrasonic Pulse Velocity

• UPV measurements provided two indicators of
  overall concrete condition
• Comparative by location
• Underlying discontinuities
• Sound, good quality concrete 11,500 14,000 fps
• Delaminated areas
• 6,500 to 9,000 fps
• UPV measurements were conducted on selected core
  samples

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Compressive Strength v. UPV
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Half Cell Potential Measurements

• Conducted in accordance with ASTM C876
• Areas of focus
• 9 high level bents
• 21 approach bents
• 13 spans of deck
• HCP measurements
• More positive than -200mV ? 90 probability of no
  corrosion activity
• More negative than -350mV? 90 probability that
  corrosion is occurring
• Between -200mV and -350mV ? uncertain

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HCP Measurements - Deck
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HCP Measurements - Girder
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Summary of Conditions

• Common condition evaluation techniques were used
  assess existing conditions
• Detailed visual inspection and sounding
• Compressive strength testing
• Petrographic examinations
• Chloride content evaluations
• Ultrasonic pulse velocity testing
• Half cell potential measurements
• Delaminations, spalling, and cracking are
  widespread and the bridge received an overall
  NBIS rating of Poor.
• Testing indicates that the concrete is generally
  of good quality and strength
• Chloride ions above the corrosion threshold exist
  to a depth of 4-1/2 inches in the columns and
  pile caps
• Active corrosion is occurring and will continue
  to accelerate

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Conclusions

• The Bonner Bridge is in advanced stages of
  deterioration and is nearing the end of its
  useful life
• In its current state, the bridge is safe for use
  by the traveling public and does not require any
  weight limit posting
• Due to the advanced stages of deterioration,
  replacement within the next ten years remains a
  necessity
• Repairs of deteriorated concrete are necessary to
  minimize the advancement of deterioration,
  maintain the structural capacity of the bridge,
  and allow continued use over the next ten years

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Thank you !

• A special thanks to the
• Structural Engineering Institute
• for the opportunity to be here today

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