Michael R. Christensen, P.E. Deputy Executive Director October 23, 2009
Inspection and Maintenance of Weathering Steel Bridges Michael J. Todsen, P.E. Michael J. Todsen,...
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Transcript of Inspection and Maintenance of Weathering Steel Bridges Michael J. Todsen, P.E. Michael J. Todsen,...
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Inspection and Maintenance of Weathering Steel Bridges
Michael J. Todsen, P.E. Iowa Department of Transportation
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Investigators
Douglas D. Crampton, P.E., S.E.
Wiss, Janney, Elstner Associates
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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
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Age of Weathering Steel Bridges
0
2
4
6
8
10
12
14
16
18
20
Year of Construction
Num
ber
of B
ridge
s
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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?
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Typical Patina Behavior
Protective Rust
Excessive chlorides, poor exposure, increased time of wetness
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Project Objectives
Identify problematic bridges
Identify problematic locations or details
Evaluate inspection techniques
Prioritize bridges: Condition Location Exposure
Recommend maintenance program
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Field Investigation
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Inspection and Testing Methods
Visual Inspection Chloride Testing Tape Adhesion Color Testing Core Samples SEM/FTIR/XRD
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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
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Inspection and Testing Methods
Protective Rust
Non-ProtectiveThick Rust
Increasing Flake Size
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Overall Appearance Flake Size and Density Color and Consistency
Proposed Rating Scale (NBIS Format)
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Example 1: No Chloride Exposure
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Example 1: No Chloride Exposure
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Example 1: No Chloride Exposure
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Example 2: Chloride Exposure
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Example 2: Chloride Exposure
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Example 2: Chloride Exposure
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Example 2b: Chloride Exposure
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Example 2b: Chloride Exposure
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Example 2b: Chloride Exposure
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Example 2b: Chloride Exposure
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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
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Iowa Weathering Steel Bridges
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Iowa Weathering Steel Bridges
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Iowa Weathering Steel Bridges
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Iowa Weathering Steel Bridges
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Iowa Weathering Steel Bridges
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Prioritization and Maintenance
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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
Washing methods
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Prioritization and Maintenance
Structure Type and Exposure
Bridge Prioritizati
on and Washing Interval
Environment
Patina Condition
Rating
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Prioritization and Maintenance
Proposed Washing Intervals
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Prioritization and Maintenance
Proposed Patina Maintenance
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Questions?
http://www.iowadot.gov/research/bridges_structures.html
Michael J Todsen, P.E. Iowa Department of
Transportation (515) 233-7726