How inspectors rate railroad bridges
When inspectors assess the condition of a rail bridge, they analyze the bridge's substructure — its columns and foundations — and its superstructure — the beams and supports carrying the bridge deck. Each is rated separately, on a scale of 0 to 9. A score of 9 is the best rating and a 5 is considered 'fair.'
State and local inspectors only assess the condition of rail bridges that cross highways or streets.
The substructures or superstructures of seventy-one rail bridges in Minnesota were given a rating of 4 last year. Twelve bridges that year had superstructures, substructures or both rated at 3.
Most bridges that raise concerns with inspectors fall within the ratings of 3 to 5 for either superstructure or substructure. The Federal Highway Administration, which determines the rating system, lays out the parameters for each of those most common red-flag ratings:
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Superstructure
A bridge's superstructure includes the beams and supports that hold up the bridge deck.
Condition 5: Fair
Superstructure has moderate deterioration. Members may be bent, bowed, or misaligned. Bolts, rivets, or connectors may be loose or missing, but connections remain intact.
• Steel: Extensive corrosion (initial section loss in critical stress areas). Fatigue cracks (if present) have been arrested or are not likely to propagate into critical stress areas.
• Concrete: Extensive scaling or cracking (structural cracks may be present), moderate spalling or delamination (reinforcement may have some section loss).
• Timber: Extensive weathering or splitting (moderate decay or crushing).
• Masonry: Extensive weathering or cracking (joints may have slight separation or offset).
Condition 4: Poor
Superstructure has advanced deterioration. Members may be significantly bent or misaligned. Connection failure may be imminent. Bearings may be severely restricted.
• Steel: Significant section loss in critical stress areas. Un-arrested fatigue cracks exist that may likely propagate into critical stress areas.
• Concrete: Advanced scaling, cracking, or spalling (significant structural cracks may be present - exposed reinforcement may have significant section loss).
• Timber: Advanced splitting (extensive decay or significant crushing).
• Masonry: Advanced weathering or cracking (joints may have separation or offset).
Condition 3: Serious
Superstructure has severe deterioration — immediate repairs or structural evaluation may be required. Members may be severely bent or misaligned — connections or bearings may have failed.
• Steel: Severe section loss or fatigue cracks in critical stress areas.
• Concrete: Severe structural cracking or spalling.
• Timber: Severe splitting, decay, or crushing.
• Masonry: Severe cracking, offset or misalignment.
Substructure
A bridge's substructure includes its columns and foundations.
Condition 5: Fair
Substructure has moderate deterioration — repairs may be necessary. There may be moderate scour, erosion, or undermining. There may be minor settlement, movement, misalignment, or loss of bearing area.
• Concrete: Extensive scaling, cracking or leaching (isolated structural cracks may be present) — there may be moderate delamination or spalling.
• Steel: Extensive paint failure and/or surface corrosion (moderate section loss).
• Timber: Extensive weathering or splitting (moderate decay or crushing).
• Masonry: Extensive weathering or cracking (joints may have slight separation or offset).
Condition 4: Poor
Substructure has advanced deterioration — repairs may be necessary to maintain stability. There may be extensive scour, erosion, or undermining. There may be significant settlement, movement, misalignment, or loss of bearing area.
• Concrete: Advanced scaling, cracking, or leaching (significant structural cracks may be present) — there may be extensive delamination or spalling.
• Steel: Advanced corrosion (significant section loss).
• Timber: Advanced splitting (significant decay or crushing).
• Masonry: Advanced weathering or cracking (joints may have separation or offset).
Condition 3: Serious
Substructure has severe deterioration. Immediate corrective action may be required. Scour, erosion, or undermining may have resulted in severe settlement, movement, misalignment, or loss of bearing area.
• Concrete: Severe spalling or structural cracking.
• Steel: Severe section loss.
• Timber: Severe decay or crushing.
• Masonry: Severe cracking, offset or misalignment.