Abstract
Fracture mechanics approach has been used to analyze the behavior of fatigue resistance of welded details existing in highway steel bridges under variable amplitude long life loading which means most of the stress ranges will be below constant amplitude fatigue limit. First of all, fracture mechanics models are established based on linear elastic fracture mechanics. Two methods are employed to compute the crack growth and fatigue life under variable amplitude fatigue long life loading. They are direct cycle-by-cycle integration method and simplified summation method. The general behavior of long life fatigue of welded details such as cover plate, web attachment, and transverse stiffener are studied and discussed. The effect of the initial flaw size, the stress concentration, and the small stress ranges on the long life fatigue is discussed based on the results of fracture mechanics analysis. The Q parameter is defined for the long life loading in order to characterize the fatigue limit effect and provide reasonable estimates of fatigue life, The relationship found between the Q parameter and fatigue lives based on the S-N curves can be easily applied to accumulated fatigue damage estimates for welded details in highway steel bridges. The application of this method for highway steel bridges shows that the fatigue limit effect can be very significant that the current design approach might be affected if the beneficial effect of fatigue limit would be taken into account.
Zhou, Minjian (1993). Fracture mechanics analysis on the resistance of welded details under variable amplitude long life loading. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1993 -THESIS -Z647.