At ATECH we have been performing FEA (Finite Element Analysis) for 30 years plus on cargo tank trailers and the components installed on cargo tank trailers.  Our approach is to utilize both classical method analysis along with FEA, when and where applicable.  The Department of Transportation (DOT) allows several components to exceed the yield strength of the material and use the ultimate strength of the material as a design basis, therefore the FEA method of analysis can be a very useful in ensuring compliance.