Concrete topping on CLT

[bobby83]

Hello all,
We are working on the design of a new high school and the client's intent is to go with CLT floor panels covered by a non structural concrete topping. They want the topping to be maximum 2 inches thick. I found papers and case studies where they had 2 in toppings, but my concern is the behavior of the concrete itself. My understanding from ACI and PCA is that unbonded toppings should not be thinner than 3 in (for light traffic). Is there something different with timber structure? Am I nervous for nothing? I would appreciate if someone had real standards regarding this issue; it seems like a big project to test something new.
Cheers

 

[ChorasDen]

Lightweight topping is typical on light frame construction for sound performance. Typically it's dictated as <= 1.5" in thickness as that is how ASCE 7 defines the cutoff point for flexible diaphragm analysis. Not sure I understand how it would differ for your situation. Might try talking with a gypcrete provider regarding what they expect for typical thickness in this application?

 

[structSU10]

AISC has a design guide for composite steel with concrete over CLT - I haven't used it myself and am unsure if it covers non-composite toppings but it may be a place to look.

 

[bobby83]

Thanks guys, when comparing to lightweight topping in light frame construction, my main concern is the heavy traffic in a high school (I would not be certain with the lightweight gypsum topping...)