On Fri, 18 Apr 2008 09:27:37 -0500, "Jeff D."
wrote:

I'm building a wall of storage shelving for my 45 record collection (appx.
20,000). The records are stored 200/box and each box is 16x8x9, weighing
15lbs. Will 3/4" plywood shelving 4 feet long support this load without
deflecting, each shelve will be loaded to 75lbs with supports on the ends
only.


There are many different types of 3/4" ply, so there is no one
'correct' answer to your question.

Personally, I'd not expect a 4' span to support that much weight, over
a longer term. Eventually it *will* sag.