Fatigue behaviour of load-carrying, fillet-welded, cruciform joints with plates of different thickness

Large numbers of fillet-welded cruciform joints are extensively employed at the connection zones of steel structural members because of their superiority from consideration of ease of construction and economy. Where this welded cruciform joint becomes a load-carrying type, the fatigue fracture starting point will be either at the weld toe zone, the root zone or both, so the fatigue behaviour becomes complex. In particular, when root fracture takes place, the fatigue strength is low compared with other welded joints and also it is difficult to detect by means of non-destructive inspection at the initial stage of crack occurrence; consequently there are some cases where fatigue becomes a problem.