Fatigue life assessment for a composite box girder bridge

Two conventional methods, the nominal stress method and the hot spot stress method, are examined for the fatigue assessment of a steel box girder bridge while considering the effect of the modeling options on the estimated fatigue life. Two analytical models, a simplified global analytical model and a refined local finite element analytical model, are developed for the evaluation of the stress ranges induced by a fatigue truck. The field tests are conducted for validating the analytical models as well as for direct fatigue assessment via an ambient vibration test. The local modeling options that are examined are the inclusion of the fillet weld itself in the refined analytical model and the mitigation of the concentrated stress at the web plate, considering stress dispersion over the width of the attachment. The fatigue life is estimated for three different nonexceedance probabilities, considering different partial factors according to the accuracy of the analysis method as well as the reliability of the estimated fatigue loading for a specific bridge site. Through a comparative analysis, the potential differences in estimated fatigue lives according to the assessment methods and the modeling options are quantitatively discussed.