Retaining wall with a varying sections. How far to extend upper rebar? 1

[Quade999]

If I am designing a retaining like shown below, how far should I extend the upper layer of rebar into bottom section to ensure adequate development and load transfer between the tension steel in the two sections? Would 2 times the development length be required?

Thanks

 

[Enable]

Oh you are in for a treat

Take a look at this old thread. I suspect not much more can be added beyond what you'll find there.

 

[rapt]

I would suggest that you add a top U bar in the thicker wall to provide continuity of the reinforcement on the tension face as well!

 

[Quade999]

From the old thread there seems to be a lot of differing opinions. Seems like you could treat it like an anchor rod/bolt connection at the top piece.
I was thinking that in this situation if you had 2x the required development length into the bottom pour, then both tension bars would more or less be able to act independently and wouldn't need to transfer much load to one another through the use of the non-contact struts.
I also suppose that without a U-bar at the top of the bottom piece, you'd get a tension force that would want to crack downwards though the middle of the bottom piece.

 

[Enable]

I'm afraid KootK already addressed both issues (doubling Ld and using a non-contact lap splice) in the above referenced thread. I would spend more time with it as it cannot be digested very quickly.

TLR

1. You cannot lap or x*Ld (x>1) your way out of the problem as transfer of forces from reinforcing steel to either another bar or else parent concrete happens mostly in the first part of the length. Leads to potential for an unzipping failure (see KootK 16 Oct 19 20:51)

2. While non-contact lap splices out-of-plane do not appear to be prohibited by code, research seems to indicate it to be a very bad idea. A 60% reduction in predicted capacity in some cases (see KootK 17 Oct 19 19:35)

 

[dik]

Great link... Unlike JAE, I slope the visible side so if it rotates, it becomes more vertical... also, I don't add 'U' bars at the top.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JoelTXCive]

Monday morning and we are already off to a topic that everybody agrees on! (ha! not really!)

Here is how I put together my wall after that old post...... I forget the reason, but either the client or someone high up at my company did not want to do battered walls, which would have been easier.

I have U bars at the top of the lower region; and I tied the whole "transition" region.

In my mind, the tension that exists in the upper vertical bar must make it's way to the lower region vertical bar. The only way for that to happen is through shear in the concrete.