Calibrating the steel-members fatigue limit states of the AASHTO LRFD bridge design specifications

Berwick, Benjamin
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University of Delaware
It is important to develop and incorporate the knowledge needed to design, construct, and maintain bridges to have the longest service life as possible. Consequently, the fatigue effects on bridges need to be considered and more accurately reflected within the proper bridge design specifications. This thesis describes the calibration process used to select the load and resistance factors for the fatigue limit states of steel bridge members within the AASHTO LRFD Bridge Design Specifications. The process presented within this thesis builds upon work completed as part of the Strategic Highway Research Program No. 2 including the determination of the fatigue load model. The resistance model was developed using available fatigue test data and statistically analyzed using specially developed techniques. Target reliability indices of 1.0 were chosen for all steel detail types based upon a procedure using Monte Carlo simulations and engineering judgment. Load and resistance factors were finally chosen for both Fatigue I and Fatigue II service limit states. The load and resistance factors for the Fatigue I limit state are 2.0 and 1.0 respectively. Similarly, the load and resistance factors are 0.80 and 1.0 for the Fatigue II limit state. We expect the new load and resistance factors for the fatigue service limit states to more accurately capture the fatigue effects of steel bridges and thus increase their service life.