Analysis of Fatigue of Welded Crane Runway Girders

In recent years, mill building owners and constructors world-wide have observed structural distress in welded crane runway girders. The distress is in the form of fatigue cracks in the vicinity of the juncture of the web and top flange. Structural analyses were made using finite element and classical methods in order to rationally explain the observed cracks and to develop new fatigue-resistant details. The results of the analyses confirmed that the local stresses produced by the passage of concentrated wheel loads were sufficient to cause fatigue cracks in the presently used structural details. It was concluded that the fatigue cracks were caused by the local effects of the crane wheel loads and the high stress range that occurs due to lack of proper bearing between the stiffeners and flange when a fitted stiffener is used. Therefore, an improved fatigue resistant detail was developed which consists of stiffeners with a deep cope (10-in., 254-mm) welded to the underside of the top flange with full penetration welds.