RESISTANCE OF WELDED DETAILS UNDER VARIABLE AMPLITUDE LONG-LIFE FATIGUE LOADING

This study was carried out with the objective of providing additional experimental data on the effects of infrequently exceeding the fatigue limit of welded steel highway bridge details. To accomplish this objective, eight full-size welded girders with Category E' web attachments and cover-plated flanges and Category C transverse stiffeners and diaphragm connection plates were subjected to long-life variable amplitude loading. It was found that fatigue cracking developed at the Category E' details when the constant amplitude fatigue limit was exceeded by more than 0.05% of the stress cycles. For the Category C details, fatigue cracks did not develop unless the peak stress range exceeded the constant amplitude fatigue limit by more than 33%. The results continued to support the extension of the exponential S-N relationship even when the effective stress range is below the constant amplitude fatigue limit.