This report presents a fatigue evaluation procedure for existing steel highway bridges and a compatible fatigue design procedure for new steel highway bridges. Both procedures realistically characterize the actual fatigue stress and cyclic conditions in bridges. Both procedures use the same detail categories and corresponding fatigue strength data as the present AASHTO specifications; they also use methods of calculating stress ranges that are similar to present AASHTO methods. The evaluation procedure, which is recommended for inclusion in the AASHTO Manual for Maintenance-Inspection of Bridges, gives accurate estimates of the remaining mean and safe fatigue lives and permits these estimates to be updated in the future to reflect changes in traffic conditions. An alternative procedure is also given for monitoring the accumulated fatigue damage during the life of the bridge; it is intended for use in conjunction with the routine inspections that are normally conducted at two-year intervals. An assessment of remaining fatigue life is needed in bridge management systems to assist in scheduling inspection, maintenance, rehabilitation and replacement. It is also useful in evaluating administrative and legislative policies such as truck-weight and overload policies. The design procedure, which is recommended for inclusion in the AASHTO Standard Specifications for Highway Bridges, is consistent with the evaluation procedure and utilizes many of the same concepts. However, it is presented in a format convenient for design; a calculated design stress range is compared with a permissible stress range corresponding to a desired safe design life. The procedure is much more flexible than present AASHTO fatigue procedures; it permits rigorous analysis methods and designs for any desired design life, initial truck volume, and truck-volume growth rate.
Abstract