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bridge crane runway beams

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I'm designing a bridge crane runway.  The owner's
specifications require adherence to CMAA 74, which in
turn requires that lateral deflection be held to less
than L/400 based on 10 percent of maximum wheel load
without impact.  Does anyone know the intent of this? 
What section properties are expected to be used?

I assume that I should check the runway beam for
bending based on this same lateral load in conjunction
with the full vertical load.  Does anyone have a
comment on this?

In my particular case,  I have a 40 foot runway beam
span (only a 2 ton crane). I find that a W21x83
wideflange is adequate by itself, with vertical
deflection of about L/1100 and lateral deflection of
L/640. The lateral deflection is based on the 10
percent of vertical moment acting laterally on the
full beam Iy; i.e., I pretend that the lateral load is
at the centroid of the beam instead of maybe 6 inches
above the top flange.  Alternatively, I can weld a
channel on top of a lighter wideflange, saving not
very many pounds of steel but increasing lateral
stiffness a good deal.  This is what I'm used to
seeing, but I can't see a reason to do it here.  Am I
missing something?

Any help or comments would be appreciated.

Mike Hemstad, P.E.
St. Paul, Minnesota

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