Cracks were occurring in the running surface of the Newark International Airport monorail guideway. Some of these cracks have occurred in butt welded sections of the guideway; others have occurred in the plate surface well away from any welds. Due to the cyclic nature of the loading from the continuous passage of the monorail tires, fatigue cracking was the suspected mode of failure. We were asked to analyze the guideway and determine the stresses in the typical areas of cracking.
The typical areas fall into the following three configurations: Continuous plate, Gapped plates (free edge), Butt welded plates. Three different finite element models were constructed to represent each of the typical configurations. For each, critical loading conditions were identified. All stresses were found to be significantly over the design allowable. Design recommendations were then made.