Fatigue evaluation of highway bridges

The present work provides a comparison of current AASHTO bridge fatigue guidelines with fracture mechanics procedures. Specifically, the remaining fatigue life of several actual bridges with welded cover plate ends is estimated using the AASHTO specifications. The estimates are compared with predictions made using linear elastic fracture mechanics principles where the time required for an initial flaw to propagate to a critical depth is calculated. It is found that fatigue lives of actual steel highway bridges as determined using fracture mechanics far exceed the remaining safe fatigue life predictions made with current AASHTO guide specifications. For the case of redundant bridges, an adjustment factor is introduced which, at various probability levels, can produce closer estimates of bridge fatigue lives between the AASHTO specifications and fracture mechanics.