Evaluation of AASHTO LRFD Fatigue Design with Weigh-in-Motion Data

The current AASHTO LRFD Bridge Design Specifications lists a fatigue load factor of 0.75, and for finite life design, assumes that the maximum stress range experienced by a bridge is equal to two times the effective stress range on the bridge from the truck traffic. Using weigh-in-motion data from three sites in the state of Texas, the load factor was compared to the ratio of the effective truck moment to the moment caused by the AASHTO fatigue truck, and to the ratio of the effective gross vehicle weight to the AASHTO fatigue truck gross vehicle weight. Also using the weigh in motion data, the maximum moments and gross vehicle weights were compared to twice the effective moments and gross vehicle weights. Variables that were considered included the year of the data, the span length on which the moments were calculated, and local site characteristics.