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Re: concrete topping on plywood floor sheathing

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The concept is not workable unless you can guarantee buckling stability of topping, and sufficient cover to the rebar to get a real reinforced shear diaphragm action.  Unreinforced topping will, of course, crack and you will lose diaphragm action pretty quickly.  Most toppings here are only 2", and we consider it as a dead load only.  Use of fibre allows serviceability of the slab and leaving it un-covered.
If you are having trouble with shear, try a thicker plywood for the sheathing, blocking all edges, using steel strap X-bracing across the floor, etc. 
You are better off using the timber framing for your diaphragm.

Thor Tandy P.Eng MIStructE
Victoria, BC
----- Original Message -----
Sent: Thursday, January 04, 2007 1:58 PM
Subject: concrete topping on plywood floor sheathing

I?m looking for design information for concrete topping over plywood floor sheathing, but haven?t found anything.  Typically, I haven?t needed to consider any shear capacity from the topping, but I have a project that I am not getting enough capacity from the plywood and thought I?d explore the shear capacity of the topping.  Can this be done?  Anybody know what computer program to use?  (Just kidding? I mean do you know of any references?)  And how do I get the shear load into / out of the concrete topping?  Thanks!




Bruce D. Holcomb, PE, SE

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