Hollow Core Slab Camber

[lutein]

This may be an old question that everyone has asked before, would really appreciate the help.
Looking thru the hollow core planks catalog for my project, I noticed that the planks may have 1" camber in it.

1. What does this really mean for the topping slab? Should I increase the topping slab thickness to accommodate the camber? From 2" to 3" thick?
2. What is the negative impact of 1" camber in planks? I would imagine the planks will settle once the topping weight is on, so I cannot think of any negative impact on topping slab thickness, am I missing anything here?

Thank you all for your help.

 

[Agent666]

Usually we set down the supports to accommodate some proportion of the expected camber so we achieve the minimum specified topping thickness at midspan. We allow for the additional topping weight at the ends due to the additional thickness. This assumes a topping that is screeded to a level.

Alternatively you can screed to a topping thickness with the top of the slab following the camber.

Regarding point 1, if the strength/serviceability of the unit works for a lesser topping thickness and you have no concerns with a thinner diaphragm, or issues fitting in reinforcement, then it may be acceptable to reduce the topping thickness. It's really up to you as the designer to assess if this is a possibility.

Regarding point 2, don't always count on the planks coming right down to no camber after the topping self weight is supported. Hollowcore designer should be able to tell you that. It is pretty variable in practice.

 

[dik]

The upward curvature tends to increase with time, in particular with long span hollowcore. If you can 'feather' the keyway so that the joint is somewhat level and use a suitable floor covering. Else, you can put a leveling topping on it and it could be suitable.

One of the features of HC slabs that you have to live with.

About 40 years ago, we tried jacking adjacent hollowcore to level the surface. We applied 14,000 lbs and it didn't budge it.

Dik

 

[JLNJ]

2 inches is pretty skinny for a topped slab. The camber could easily be more than 1" and then you'll be left answering questions about the remaining slab being "too thin".

Give the precaster the option of designing it as composite or non-composite and force him to take the camber and reduced thickness section into account in his design. I expect that they will choose to design them as non-composite to avoid the net topping thickness question. I also put a limit on camber in the spec (since PCI does not) but I'm not sure how much control the precaster really has over it. Using the hollowcore design guides you can see what combination of thickness, span, and load tends to cause camber issues and choose your plank size accordingly.