Analysis of Cold-Worked Crack-Arrest Holes Subjected to Distortion-Induced Fatigue

Abstract

A major source of damage to bridges in the United States is fatigue cracking, particularly in the small web gap region located at the top of a steel girder web, between the transverse stiffener-to-web weld and the top girder flange. The web gap region experiences combined in-plane and out-of-plane loading caused by the differential displacement of lateral bridge members. This mixed mode loading, combined with the geometry of the web gap, makes the girder web susceptible to distortion-induced fatigue.A relatively inexpensive and simple method for mitigating the propagation of fatigue cracks in steel bridges has been to drill a crack arrest hole at the tip of the fatigue crack. This strategy has been shown to be effective when the hole is subjected to in-plane loading and when the hole is sized appropriately. However, research has shown the benefits of crack arrest holes are limited when the holes experience out-of-plane loading. Furthermore, the tight space in the web gap area can limit the size of the crack arrest holes to diameters less than that recommended in the literature. A relatively new technique in the field of bridge repair and rehabilitation is to apply a mechanical expansion to the inside of the crack arrest hole. The process creates compressive residual stresses in the area surrounding the hole, enhancing its effectiveness at resisting crack reinitiation. The purpose of this paper is to investigate the effectiveness of the mechanical expansion technique when applied to a range of hole sizes and under various mixed mode loading scenarios.