drop panel length in 2-way flat slab 1

[ajk1]

ACI 318 requires that the length of the drop panel parallel to the span, from support centreline to drop edge, be at least 1/6 of the span length(at least the ACI 2008 edition does - that is the latest edition that we have on our office library).
CSA A23.3 does not have this requirement.

Question: Does anyone know why ACI has this requirement?

 

[JoshPlumSE]

This is really just a guess, but....

I know that in ACI, the presence of drop panels allows you to reduce your minimum slab thickness. The rational being that the extra thickness at the drop panel reduces deflection and such. It would make sense that this would only apply if the drop panel obeyed some dimensional restrictions. If the CSA code does not allow different deflection or thickness criteria for drop panel systems, then maybe they wouldn't need that minimum width requirement.

 

[MisterBill]

A23.3 clause 13.2.4 gives a maximum limit of Xd = Ln/4 ... Xd/Ln < 1/4
When you design start with Xd/Ln = 1/6 and if needed work there way up to 1/4

 

[rapt]

The rule is the drop panel must extend L/6 each side of the column. This is to ensure that the top reinforcement in the column strip, outside the width of the drop panel can use the effective depth of the drop panel. If the drop panel is too small, bars well away from the column would only be able to use the effective depth of the slab. So it is actually the width dimension of the drop panel that is important in each direction.

 

[ajk1]

ok, thanks