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In recent years, a large number of fatigue damages in steel bridges has been successively reported in Japan and the numbers still show tendencies to increase with the progressive aging of the Japanese bridge stock. To assure the bridge safety and its adequate structural performance, appropriate fatigue counter‐measures are required, not only to retrofit the weakened structural members, but also to avoid the further growth of the existing cracks and prevent the occurrence of new ones. The present study focused on two different fatigue damage types, one occurring at the connection details of transverse beam flanges inserted through a slot in the intersecting girder web, and the other, occurring at the welding line between the upper end of vertical stiffeners and the girder upper flange. Preventive retrofitting measures were proposed for these details and applied to a bridge in service that had been constructed more than 40 years ago. Stress measurements under service load were carried out in situ, before and after the execution of fatigue preventive retrofitting works so as to verify the effectiveness of the proposed retrofit methods. The results showed that, for the details of transverse beam lower flange inserted through an intersecting girder web, the stresses around the slot end area were considerably reduced after the execution of the proposed retrofits. As for the details of vertical stiffeners upper end, the stresses around the plate edge after the execution of the retrofitting works decreased significantly. Based on the stress range obtained from field measurements, fatigue life for each location was evaluated. The results for the details of the transverse beam flange intersecting the girder web, lead to fatigue life values that were at least 4 to 6 times of their values before retrofitting and, with one exception, the results for vertical stiffener upper end detail retrofits presented fatigue life values that were more than 2 times the fatigue life of that of their original detail, confirming thus the effectiveness of the proposed retrofitting methods.

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