Thickened Edge 3

[EIStructural]

I have a very basic question. I have a thickened edge and the typical detail always shows to slope the grade at 1:1 from the bottom of the thickened edge to bottom of slab on grade. My questions is why cant this be a straight vertical edge and why does it have to be at 1:1 slope?

 

[huntley101888]

I think a sketch would be helpful, as I'm not sure I completely understand what you're asking. Are you asking why the subbase/subgrade has to be shown at a 1:1? If so, it's because you can't properly compact fill with a vertical face on one side.

 

[SkiisAndBikes]

My typical detail shows the slope to be 2H:1V. From a practical viewpoint, forming the transition in the subgrade granular material on a slope is easy, creating a vertical transition with the subgrade is often not possible nor easy.

Also, the gradual transition reduces stress concentrations that would otherwise develop at an abrupt transition in slab thickness.

 

[csd72]

It also acts as less of a restraint against shrinkage.

Why do you ask? Surely someones not trying to save that tiny bit of concrete!

 

[EIStructural]

Thank you all for prompt replies.

I am attaching a sketch here.

skiisandbikes - as shown in the section there is a horizontal rebar at 12" o.c. I believe this should take care of any stress.

I hope the sketch answers a lot of questions and also you will know where this question came from.

 

[csd72]

You are never going to be able to drill those dowels into the 4 inch slab without cracking it.

I would also consider putting a lip under the edge of the existing slab to support it.

 

[EIStructural]

Surprisingly for me as well. They have already installed the dowels and poured the first 3 ft. They slab only cracked at one locations out of numerous around the pit.

csd72 - Thanks for the replies. What do you mean by saying "putting a lip"? Can you please elaborate? The slab is already connected to the new pour with epoxied dowels and there is existing grade under it. Adding to it when the contractor pours the secondary pour for the top of the pitwall and the proposed thickened edge the vertical edge of exposed grade has no place to move and will be stable.

Just to add a piece of information that the first 3 ft pour has already been done and now the contractor will be pouring the top 1 ft with the proposed vertical faced (including the blue hatched area in the picture above) thickened edge.

I hope I am making sense and now creating confusion.

Thanks a lot.

 

[csd72]

EIStructural,

And this dowels with less than 2" of concrete to push against will not amount to much. I was suggesting that you continue the pour 1 to 2 inches under the edge of the existing slab edge so you are not just relying on the dowels to prevent differential settlement.

 

[EIStructural]

Thank you csd72.

Thanks to rest of the people as well.