A structural member subjected to cyclic loadings may eventually fail through initiation and
propagation of cracks. This phenomenon is called fatigue and can occur at stress levels considerably below the yield stress.
Extensive research programs conducted to determine the fatigue strength of structural members and connections have provided information on the factors affecting this property.
These programs included studies of large-scale girder specimens with flange-to-web fillet welds, flange cover plates, stiffeners, and other attachments. The studies showed that the stress range (algebraic difference between maximum and minimum stress) and notch severity of details are the most important factors. Yield point of the steel had little effect. The knowledge developed from these programs has been incorporated into specifications of the American Institute of Steel Construction, American Association of State Highway and Transportation Officials, and the American Railway Engineering and Maintenance-of-Way Association, which offer detailed provisions for fatigue design.
