bearing stress, allowable, between roller and flat surface

huangyhg

bearing stress, allowable, between roller and flat surface
for a steel roller or wheel riding on a beam flange or rail head, with material spec's. known for both surfaces, how can i determine the allowable contact stress. for example, a roller of known ultimate stress, hardness, diameter, contact length on rail, and rail or beam of known ultimate stress, hardness, etc.
i found an example regarding this topic.