How inspectors rate railroad bridges

Large crack in the concrete abutment
Large cracks in concrete abutments prompted an Otter Tail County bridge inspector to list the substructure of this Canadian Pacific Railroad bridge in poor condition.
Ann Arbor Miller | MPR News

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.