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The objective of this study was to determine the crack propagation life of a weldment and to assess the significance of the results with regard to the design and inspection of bridge girders. The experimental part consisted of marking initial crack sizes in 68 fillet-welded transverse stiffeners subjected to constant-amplitude loading or spectrum loading typical of highway bridges. The crack propagation lives were then calculated with fracture mechanics methods using average crack growth rates and a reasonably simple method of determining the stress intensity factor. In general, more cycles were needed to grow the crack than were calculated in this study. The predictions were conservative in the sense that they underestimated the observed lives. The results correlated better for the larger than for the smaller marked crack sizes. The propagation life of the specimens tested in this study corresponded to the stage of part-through crack growth in transverse stiffeners welded to the web and the flange of girders, or to the web alone. The generally low crack detection probabilities with ultrasonic and radiographic inspection and the results of this study suggest that it would be prudent to design structures with long service lives, such as highway bridges, to the fatigue limit so that in most cases cracks would not initiate.
fatigue, cracks, welding, steel, crack detection, bridges
Engineer, Blunt and Evans Consulting Engineers,
Professor, University of Maryland, College Park, Md.