INFLUENCE OF ROOT IRREGULARITY ON FATIGUE STRENGTH OF PARTIALLY-PENETRATED LONGITUDINAL WELDS

Partially-penetrated longitudinal weldings are often used for assembling box-section members. In the previous studies1)-3), it was shown that weld defects such as blowholes existed at the root of this joint and these defects decreased fatigue strength of the joint. In the case that root gap of this j oint becomes wide, some melted weld metal spills down into the root gap of the joint. After the welding is completed, the weld metal stays in the root gap as if it is hanging-down from the root. In the pilot members for Ohnaruto Bridge, hanging-downs remained when root gap was wider than 0.6mm4(Fig. 1). This root irregularity causes stress concentration and may reduce the fatigue strength. The main objective of this study is to examine the influence of this root-irregularity on the fatigue strength of this joint and to clarify the properties of initiation and propagation of fatigue crack experimentally. Fracture mechanics analysis of fatigue crack propagation is also carried out to predict the fatigue life of this joint.