Tooled Joints in Topping over Hollowcore Joints

[astructurale]

When using hollowcore in a parking deck are tooled joints required in the topping at every plank joint? The PCI recommendations for parking structures indicates that they are recommended, but is it necessary at every joint? Would every 12ft or another spacing corresponding with 4ft plank work to minimize uncontrolled cracking in the topping?

 

[JAE]

Each plank has its own unique parameters that affect long term deflections - primarily due to creep in the concrete and somewhat due to strand relaxation and bond slip. Because of this you will generally have some differential movement between adjacent planks and thus, cracks along those joints.

For a building - interior - with floor coverings such as carpet, the slight differential doesn't create much of a problem but in an exposed garage you definitely want the cracks sealable.

 

[astructurale]

Thanks for reply JAE. This forum is always such a quiet one I was not sure that I would even get a response.

A recommendation I recieved was to use the same as for a cast-in-place system. Example- For a 24ft spacing requirement in CIP use every sixth plank joint. (Note: the topping is 3" and also has a mat of #3 bars, plus the hollowcore has grouted keyways.)

Another way I thought of was to base it on the effective resisting width of slab. Example: for a 32ft bay the slab width would be 16ft, every 4th plank.

Placing these joints at every plank just seems like a lot of additional and possibly unnecessary work.

Andy thoughts on theses ideas?

 

[JAE]

Perhaps if you add rebar between the individual panels (in the "v" shaped key that is formed parallel to each plank, and grout it solid, you will minimize the differential movement between the planks and your larger spacing of joints would work.

I also would look carefully at how much reinforcing you place in the topping - trying to ensure that it can keep any minor cracks closed as tightly as possible.

You might also call PCI or your local precaster to see what they've seen in other similar projects. Most precasters have experienced engineers who can help.

 

[astructurale]

Thank you for the advice. I've found that hollowcore is not used frequently in parking decks these days. The double tees seem to be the product of choice for parking decks.