We are working on some equipment that is going to be attached to existing, 3,000 psi reinforced concrete floor slabs. In some locations, the best way to do this is to through-bolt and 'sandwich' the slab with a piece of threaded rod (5/8" rod in our case.) On the top side of the slab, our equipment has a large steel bearing surface. On the bottom side, we expect we'll need steel plate washers. We were thinking of using square washers cut from 1/2" A36 steel. What I don't know is how big of a square would be 'standard.'
Is there a chart or standard practice for what size plate washer to use on what size fastener? I couldn't find one in AISC, but may have missed it, or maybe it's in an ACI standard? If there's no prescriptive chart, what checks would typically be done to size it by calculation?