Numerical investigation of the cope hole shape impact on fatigue life of welded joints in steel bridges

Abstract

Holes in the bridge girders are usually made at the joint of strips. In most cases, they are made when there is a need to make double-sided butt welds and in order to avoid welds crossing. Size of the hole is selected in order to allow full penetration of the strips across their whole width and also to ensure free access to the welds during NDT. Welded joints with holes, due to low fatigue life, are critical elements affecting durability of large-span steel bridge structures. Low fatigue life of joints with holes results mostly from high concentration of stresses near the weld toe caused by local reduction of cross-section. The paper covers parametric studies based on finite elements method in order to determine the impact of geometrical changes of the hole shape on distribution of stresses within probable areas of cracks initiation and durability of such joint. With reference to experimental studies results, four different holes geometries were analysed: semi-circle (conventional), triangle, parabola of second degree and oval. Assessment of the fatigue was performed using the so-called hot spot method, i.e. geometrical stresses. Results of the studies show that geometrical change of the hole shape affects the stresses concentration change, but it does not translate to the increase of fatigue life of such joint.