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BRIDGE DESIGN: Questions re Live Load Distribution Factors in AASHTO-LRFD

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In studying some of the background material from development of this portion of the LRFD Spec (notably regarding the NCHRP Project 12-26 which provided much of the basis), I have come to realize that the methods used in the older versions of AASHTO had oversimplified this procedure, sometimes detrimentally.

The new procedures, while they are much more involved, also seem to have a larger confidence factor attached.

However, I notice that among the "limitations" of the simplified equations shown in Article 4.6.2.2 of the Spec, it is mentioned that you have "beams which are parallel and approximately of the same stiffness," and "have in-plan curvatures less than" a certain limiting amount."

I would like to know what any of you, experienced with this Spec, think about the implications for a very common geometry: a bridge with skewed supports and a roadway that is curved in plan.

We have a lot of these, and so of course the beams will in most instances not be parallel.  And the curvatures can be pronounced (although not necessarily always as much as the Spec limit).

Does this mean I need to use a grillage model, or "worse," just to come up with the moments in these girders?

Your comments are very welcome.