If you are looking for an HS-20 truck, the concentrated wheel load is 16 kips.

I have some catalogue information relating the truck loading vs. the bearing bar size and spacing.  I couldn't find it on line.  I could fax it to you.  It's only a few pages.
One strange thing about grating loading.  An H-15 wheel loading sometimes controls over an H-20 due to its smaller footprint.

Concur with broekie & JedClampett. H-20 loading is also 16 kips per tire (like HS-20). An H-20 truck has 2 axles - 8 kips on the front (4 kips/tire) and 32 kips on the back (16 kips/tire). HS-20 is essentially an H-20 truck pulling a one axle trailier, 32 kips on the trailer axle (16 kips/tire).

Here is a fairly good summary: http://www.ce.memphis.edu/3121/pdf_notes/notes_06c.pdf

Also you may want to get the free .pdf downloads from the metal grading bar trade association:
http://www.naamm.org/mbg/literature.php
They do not answer your question but have good background information (probably similar to the catalogs you have).

A final thought - be sure to consider banding the grating for your heavy duty application.

Thanks everyone for the links and info.  It confirms what I found myself.  I found that Most heavy duty grating companies will design a grate just from specifying H-20 loading.  Good stuff to know though.  Thanks again.

Derek Medved