Abstract: A reinforcing structure for a railway car having a fishbelly type underframe including a center sill having tapered transition sections connected between the center section of the sill and each end section. At each transition section a pair of longitudinally extending horizontal plates are provided which are contiguous and affixed to the respective vertical webs of the sill and extend from the center section through the transition section and into the end section, thereby directing structurally deleterious fatiguing loads away from the bent portions of the sill at the junctures of the transition section and the center and end sections.