Aashto Fatigue Categories: A to C_PRIME
AASHTO LRFD fatigue detail categories A through E-prime with Constant-Amplitude Fatigue Thresholds (CAFT) in ksi and detail constant A (x10^8 ksi^3) for S-N curve fatigue design of steel bridges
| detail category | CAFT ksi (ksi) | constant A e8 ksi3 (ksi3) | detail description | notes |
|---|---|---|---|---|
| A | 24 | 250 | Base metal; rolled or cleaned surfaces; plain plate with no attachments; flame-cut edges with surface roughness less than 1000 micro-in | Highest fatigue resistance; infinite life above 24 ksi stress range |
| B | 16 | 120 | Base metal at gross cross-section of high-strength bolted slip-critical connections; base metal at net section of fully tensioned high-strength bolted connections; welded joints with full-penetration groove weld ground flush | Common category for bolted connections and smooth groove welds |
| B_PRIME | 12 | 61 | Welded joints with full-penetration groove weld not ground flush; base metal at longitudinal stiffener terminations; shear connectors (studs or channels) on bridge girders | Between B and C; applies to shear stud connectors |
| C | 10 | 44 | Base metal at detail with shorter attachments on plate or bar; transverse stiffeners welded to flange or web; fillet-welded connection plates; cover plates shorter than 2 in parallel to stress | Most common fatigue category for welded details on girder web and flanges |
| C_PRIME | 12 | 44 | Shear on the throat of fillet welds transmitting shear; shear connector welds on bridge girder with 100% inspection | Same constant A as C but higher CAFT; applies to fillet weld shear |
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