Saw-Cuts In Precast Concrete Topping

[BSVBD]

In twenty years I've never been asked nor have i considered this:

The General Contractor wants to know where to put their typical 1/4" wide x 1" control joint cuts in the precast concrete topping.

The typical standard with this G.C. is 156 SF max concrete area for saw-cut boundaries.

The current project is 10" hollowcore precast plank with 4" structural, 4,000 psi concrete topping.

Approximate camber = 1".

Our plan specifies 6"x6" #10/10 W.W.M.

Do any of you ever specify saw-cuts in structural precast concrete topping?

I will also be contacting the precast supplier for advice and guidance.

Thank you!

 

[JAE]

Do any of you ever specify saw-cuts in structural precast concrete topping?

Nope - never

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[BSVBD]

JAE... has the discussion of cracking ever been addressed on any of your projects?

 

[JAE]

OK - for the structures I typically do (buildings with covered topping - it is typically a bonded slab topping to the precast so longitudinal cracking will usually occur between the double tees or planks along their joints (natural upside down control joints).
Cracking across the span is not a huge issue as the topping is most always in compression which will close the joints.

For cases like parking garages, where the topping is also the wearing surface - then yes, the joint between each plank or tee is usually tooled and later filled with a sealant after the joint has been cleaned out and prepped for the sealant.

Again, this is longitudinal only - not transverse to the span.





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[KootK]

If you're structurally bonded to the plank, joints shouldn't really affect the cracking pattern as you won't really accumulate large shrinkage strains between the joints. Rather, you should see distributed topping cracks commensurate with the restraint condition provided by the plank.

If the topping is structural then you're presumably using the topping as your compression block. As such, it's undesirable to be sacrificing 1" of that at the joint locations.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[irishengdave]

I hope you're not using the topping as a diaphragm for lateral loads? Saw cutting it will kill the concrete shear capacity. I've never seen this done before. I'd imagine the plank will restrain shrinkage in the topping. Ask the contractor why they want to do this.

 

[TehMightyEngineer]

Agreed with JAE, I would expect cracking to almost entirely be longitudinal and at the plank joints. I'd definitely avoid saw cutting the topping as I see little benefit to it. As commented before the plank should be done with the majority of it's shrinkage/cambering at erection and will restrain the topping.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

http://www.americanconcrete.com