Effectiveness of Crack-Arrest Holes under Distortion-Induced Fatigue Loading

Drilling crack-arrest holes is a simple technique, commonly used by bridge owners to control and/or repair fatigue cracks in steel bridges. Although well-established relationships exist for sizing the diameter of crack-arrest holes for in-plane fatigue loading, the effectiveness of such holes in preventing reinitiation of out-of-plane (distortion-induced) fatigue cracks is not well understood and has received little attention in the literature. This paper presents the findings of experimental and numerical studies on the effectiveness of crack-arrest holes for repairing cracks in bridge girders damaged by distortion-induced fatigue. The experimental study was performed on segments of plate girder loaded out-of-plane with cyclic forces applied through a crossframe. Crack-arrest holes of various diameters were drilled at the tips of fatigue cracks having different lengths, and their effectiveness in preventing crack reinitiation was evaluated. The experimental results were complemented with a suite of three-dimensional, solid-element, finite-element analyses. Parametric study was used to investigate the effect of crack-arrest hole diameter, placement, and crack length on stress demands in the web gap region of a girder similar to a physical model tested in the laboratory. The experimental and numerical findings of the study were evaluated in the context of common industry practices. The results showed that in bridge girders susceptible to distortion-induced fatigue damage, crack-arrest hole placement (inherently tied to cracking location and geometry) was the most important parameter and had much greater influence on the effectiveness of crack-arrest holes than hole diameter.