Remember CAESAR II is a beam element analysis program. Imagine everything modeled as a piece of spaghetti. Now, what is the difference between a concentric reducer and an eccentric reducer? None as far as beam elements are concerned.
If one reducer model passes and the other fails, you're splitting hairs, which the beam element really can't do. Determine why the one model fails and solve that issue.
While Michael's solution may solve your problem in this instance, I'll argue that you're close to the (pass/fail) edge to start with. More accurate modeling is always a good thing, but you need to remember the limitations of the beam element.
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Regards,
Richard Ay - Consultant