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Inspection and Maintenance of Weathering Steel Bridges Michael J. Todsen, P.E.

Inspection and Maintenance of Weathering Steel Bridges Michael J. Todsen, P.E. Iowa Department of Transportation. Investigators. Douglas D. Crampton, P.E., S.E. Wiss, Janney, Elstner Associates. History of Weathering Steel Bridges in Iowa. 1930’s: Weathering steel first evolved

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Inspection and Maintenance of Weathering Steel Bridges Michael J. Todsen, P.E.

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  1. Inspection and Maintenance of Weathering Steel Bridges Michael J. Todsen, P.E. Iowa Department of Transportation

  2. Investigators Douglas D. Crampton, P.E., S.E. Wiss, Janney, Elstner Associates

  3. History of Weathering Steel Bridges in Iowa • 1930’s: Weathering steel first evolved • 1964: First used for a bridge application • 1980: Michigan moratorium, Iowa followed • Research studies • Mid-1990’s: Weathering steel bridges reintroduced in Iowa • Recent years: Certain Iowa bridges are not performing properly • Currently Iowa has approximately 139 weathering steel bridges • 97% were constructed after 1994

  4. Age of Weathering Steel Bridges Number of Bridges Year of Construction

  5. Questions for study • A few of bridges with flaking patina, heavy chloride contamination • What is a good patina? • Objective evaluation method? • Inspection procedures? • Effectiveness of washing? • Washing methods?

  6. Typical Patina Behavior Excessive chlorides, poor exposure, increased time of wetness Protective Rust

  7. Project Objectives • Identify problematic bridges • Identify problematic locations or details • Evaluate inspection techniques • Prioritize bridges: • Condition • Location • Exposure • Recommend maintenance program

  8. Field Investigation

  9. Inspection and Testing Methods • Visual Inspection • Chloride Testing • Tape Adhesion • Color Testing • Core Samples • SEM/FTIR/XRD

  10. Inspection and Testing Methods • Goals of Inspection Method: • Consistent • Reliable • Repeatable • Objective Results • Visual Inspection: easy and practical, but not always objective • Tape Adhesion Tests: simple, practical, and objective • Color Testing: not always consistent • Chloride Testing: not always reliable • Core Samples, SEM, XRD: not practical or cost effective

  11. Inspection and Testing Methods Non-Protective Thick Rust Increasing Flake Size Protective Rust

  12. Proposed Rating Scale (NBIS Format) • Overall Appearance • Flake Size and Density • Color and Consistency

  13. Example 1: No Chloride Exposure

  14. Example 1: No Chloride Exposure

  15. Example 1: No Chloride Exposure

  16. Example 2: Chloride Exposure

  17. Example 2: Chloride Exposure

  18. Example 2: Chloride Exposure

  19. Example 2b: Chloride Exposure

  20. Example 2b: Chloride Exposure

  21. Example 2b: Chloride Exposure

  22. Example 2b: Chloride Exposure

  23. Iowa Weathering Steel BridgesConditions Affecting Patina Performance • Chloride Use: • Salted from above • Salt spray from below • Both • Time of wetness • Location: • Urban • Suburban • Rural • Exposure: • Bold • Sheltered • Tunnel Effect • Service Below: • Interstate or waterway • Low clearance? • High % trucks? • Detailing

  24. Iowa Weathering Steel Bridges

  25. Iowa Weathering Steel Bridges

  26. Iowa Weathering Steel Bridges

  27. Iowa Weathering Steel Bridges

  28. Iowa Weathering Steel Bridges

  29. Prioritization and Maintenance

  30. Washing methods • Existing washing specifications (flushing): • Designed to not damage paint • Minimum 5 gallons/minute • Maximum 1000 psi • Proposed specifications (power wash): • Remove contaminations from surface • 3.5 gallons/minute • 3500-5000 psi, 15deg nozzel • Tip 12” from surface, 3-6 sf/gallon

  31. Prioritization and Maintenance

  32. Prioritization and Maintenance Proposed Washing Intervals

  33. Prioritization and Maintenance Proposed Patina Maintenance

  34. Questions? http://www.iowadot.gov/research/bridges_structures.html Michael J Todsen, P.E. Iowa Department of Transportation (515) 233-7726 michael.todsen@dot.iowa.gov

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