[Beowulf] removing tiles around heavy racks?

[Mark Hahn]

around a heavy rack, how many floor tiles can you safely remove?

I'm about to embark on a large installation: compute racks will contain
38 1U servers and so weigh ~1500 lbs each.  the network (Quadrics) will
be installed first, before rolling in the compute racks.  partly for 
space reasons, but also because it doesn't seem safe to have a bunch 
of 1500 lbs racks surrounded by a sea of missing tiles...

but it would be good to know what the threshold is - how many tiles 
you can remove around a heavy rack before becoming crazily risky...
any horror stories?  ;)

thanks, mark hahn.
PS: 16" over slab, feet glued, stringers screwed-on, composite tiles.