The Michigan Building Code gives a Live Load for cat walks. I imagine the IBC would give it also. As for the deflection I'd think that l/240 would work for the Total Load and l/360 for the Live Load.
IBC gives a catwalk LL of 60 psf. But this is for catwalks of stages and other assembly type areas. Its' not clear if it applies to industrial catwalks as well.
ASCE 7-02 gives 40 psf and 300 lb concentrated load as minimum values for "Catwalks for Maintenance Access".
If this is for an industrial project, suggest that you consider at least 60 psf since it may be necessary to take heavy "equipment parts" on the catwalk during maintenance operations.
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