hollow core slab for warehouse mezzanine

I'd call your local prestressed concrete supplier that deals with hollow core and ask them if they have any records of the project. There's a limited number of manufacturers for hollow core and they tend not to ship it very far.
If that doesn't work, I'd measure the depth and go to the PCI design handbook and pick a conservative capacity for the span/depth from their tables.
Even if you could find all the reinforcing, you'd just have to make a lot of additional assumptions to calculate anything meaningful.

When was it constructed?
I would check out the PCI Design Handbook and make some conservative assumptions. You really need to get a good idea of the cross-section, since this will play a large role in the serviceability considerations. You will also need to assume an initial jacking stress (typically 0.7fpu for cast plank and 0.65fpu for extruded plank). There are a lot of variables involved and unless you have a good deal of information and are comfortable doing the calculations you should really contact a local supplier and see if they can help you out.
You should also get on the owners of the warehouse to try to dig up some existing shop drawings for you.

The warehouse was built in 1976-77. I talked with the owner and he didn't have any shop drawings. I'll get in touch with the contractor and architect to see if they have any information. I sure appreciate both of your responses.

No records on microfische with the local building jurisdiction? (I go back a ways)...

If you have an 8" slab, you're probably looking at either an office loading (50 + 20), or 125 psf light storage.

If you have a 12" slab, then mostlikely 250 psf heavy storage, or even heavier.

Hopefully you do not have a 6" slab...

Mike McCann
MMC Engineering

Add a concentrated load at midspan and measure the deflection. Thus EI can be calculated.