Connection between wall and slab of ground floor

[Kirill]

Hello everyone from Russia!

I'm in the process of building a house. This autumn I did a basement slab (floor) and walls of house and now the time has come for the first (ground) floor. For now, I have situation shown on the pictures. The drawings of basement and walls are also attached. On the drawing you can see basement walls, residual reinforcement and future slab (all reinforcement of walls are not shown). So, I have a question. What should I do with residual reinforcement? According to Russian standarts and designers books I should bend them and connect with the main bars of slab reinforcement or cut them out. But how should I bend them? I mean, what length should be? How they should be connected to main bars? The problem is that I can't find single solution for this problem, moreover I can't understand which one is better and why it's good solution. Unfortunately Russian designers in this case just say: "It doesn't matter which one you will use. They are the same" or "I would use this one because...because...I like it"😁

I am really intrested what will you do with this reinforccement. I attached some ideas, I hope my problem will be clear for you😀
P.S If It's possible, send me maybe some typical projects or drawings and proofes why your or my solution the best.
P.P.S If you have any other qustions according to my project I am ready to discuss them with you.

Best regards,
Kirill

[Ayesha]

3 hours ago, Kirill said:

But how should I bend them? I mean, what length should be?

You should bend them and the length should be equal to development length of a hook. Below is the concept:

 

Normally, the width of wall should be kept enough wide that you are able to achieve the ldh length and from the face of the wall you need to extend the rebar a distance of ld. You can find the values of Ldh also called development length of hooked bar and ld - development length of straight bar in your Russian code. For US Code, you can use this link:

https://structuralcalc.com/rebar-development-length-calculator-to-aci-318/

 

3 hours ago, Kirill said:

How they should be connected to main bars?

If you extend your wall bars a distance of Ld from the face of the wall, you need to just place the slab/ beam bars to the end as your wall reinforcement which is bent will take of of flexural moment at end of slab. No need to connect or anything.. Just extend your slab bar to the end of wall horizontally using a straight bar.

3 hours ago, Kirill said:

Unfortunately Russian designers in this case just say: "It doesn't matter which one you will use.

This can also be correct because in houses the loads are small and if you aren't in seismic zone, and the design is over-reinforced the development lengths can be reduced. Also, not bending the wall reinforcement into slab means that your slab will have more positive moment. Nothing is wrong with this approach.

 

Edited January 26, 2022 by Ayesha

[Muhammad Hashmi]

I don't know whether I am understanding your question correctly.  

Extend the vertical rebars of retaining wall up to the development length inside the reinforced concrete slab.

In that case retaining wall design is somehow taking the action of fixed connection from the slab and from the foundation as well that will reduce the bending moment and crack width value of retaining wall itself. 

Second don't allow the contractor to place the backfill around the retaining wall unless you cast the slab.

[Badar (BAZ)]

As  I understand, you want to know what to do with residual rebars of basement walls. This is what I have to say about it:

[Kirill]

1 hour ago, Muhammad Hashmi said:

I don't know whether I am understanding your question correctly.  

Extend the vertical rebars of retaining wall up to the development length inside the reinforced concrete slab.

In that case retaining wall design is somehow taking the action of fixed connection from the slab and from the foundation as well that will reduce the bending moment and crack width value of retaining wall itself. 

I suppose you understood me in a correct way. 
I want to create connection between wall and slab, as you wrote in the third sentence.
But I can't understand how to bend existing rebars (you can see them on the picture above), because there are different ways how to do that. 

1 hour ago, Muhammad Hashmi said:

Second don't allow the contractor to place the backfill around the retaining wall unless you cast the slab.

Yeah! Of course, I will not allow to do that!
First of all I should finish with ground slab and necessary communications, then should be installed waterproofing and thermal insulation of basement walls. Only after that I will provide backfill. So...It's not very close event😀

[Kirill]

16 hours ago, Badar (BAZ) said:

As  I understand, you want to know what to do with residual rebars of basement walls. This is what I have to say about it:

Thanks a lot for your type of reinforcement!
Unfortunately, I didn't get your P.S

First P.S.

Could you explain what does negative rebars mean? Where should it be located? Could you add example on your drawing? 

Second P.S.

Did I get your idea correctly? You said that if have length of span more than 4m I should do something else with residual rebars? I have span more than 4m, so could you also draw what do you mean?

Also I have another question, I don't know if I should create another thopic. I attached drawing of house basement. With stars I marked a place with a large span. One side is min 4890mm, another one is 8690mm. Main bars will be located along short span (I suppose you will agree). Bars are 12mm, step 200mm. The planned thickness of the slab is 200mm. Should be installed additional supporting or will the walls indicated in the drawing be enough? If there are similar projects with large spans or calculations, I would be very grateful

[Badar (BAZ)]

• Negative rebars are the ones near the top of slab. With respect to my figure, it is the wall-rebar bent into the slab near its top face.
• It is a widely accepted practice to extend the top (negative) rebars to a distance of about span/4 from the face of support. For a 4m span, this would mean that you require 1m. But, as per your drawings, you do not have 1m; the available length of residual bars from the face of wall is about 1200 -150-300= 750. So you need extra rebars as per the detail shown in the comments of Ayesha for those spans.

PS: In RCC structures there is no one-fits-all solutions. There are multiple loads paths. Even if you do not provide the lengths mentioned above, the slab can still have the required strength if you have provided extra reinforcement in the mid-span (i.e bottom bars).

The difference will be that you might get wider cracks (on top near slab to wall connection) if you do not follow the detail suggested in my comments.

But, you may not get to see them ever as flooring on the slab will make them invisible. This is the reason many engineers and contractors will say to you that do not worry about top rebars.

[Kirill]

On 1/28/2022 at 6:43 AM, Badar (BAZ) said:

Negative rebars are the ones near the top of slab. With respect to my figure, it is the wall-rebar bent into the slab near its top face.

Thanks! I didn't know that they are called negative rebars. 

On 1/28/2022 at 6:43 AM, Badar (BAZ) said:

It is a widely accepted practice to extend the top (negative) rebars to a distance of about span/4 from the face of support. For a 4m span, this would mean that you require 1m. But, as per your drawings, you do not have 1m; the available length of residual bars from the face of wall is about 1200 -150-300= 750. So you need extra rebars as per the detail shown in the comments of Ayesha for those spans.

Ok! I got it! But, Unfortunately, I can't agree with your calculations. We have total length equals to 1200mm. Required length of rebar according to math in place with radius: L=2*pi*r (length of circule) / 4 = 2*3.14*r (5*diameter of bar (12)) / 4 = 94.2. Plus 115 taking into account the protective layer. Total is 210 mm, 1200 - 210 = 990 mm. So we have 990 mm of bar! However, this is also not enough🙃. So, I need extra bars according to your recommendations. But It's only about "stars" area, am I right? 

Also I add drawing from my designer. Orange line - residual bar. So, Now, I can see that it's very short. 

What should I do with residual bars in places where spans<4. Should I cut them? Is it possible to leave them everywhere not cut off?

On 1/28/2022 at 6:43 AM, Badar (BAZ) said:

PS: In RCC structures there is no one-fits-all solutions.

Unfortunately, I already understood it😒. I just want to get good solution, to be sure in my project. I just want to build house and forget about this forever. Not thinking will my slab crack or not.
The most awful thing that  my designers just create drawings and when I ask them: "Why did you do that" They are answering: "I always do this". I hope you are understanding my idea.

On 1/28/2022 at 6:43 AM, Badar (BAZ) said:

The difference will be that you might get wider cracks (on top near slab to wall connection) if you do not follow the detail suggested in my comments.

I don't need them at all!😀

On 1/28/2022 at 6:43 AM, Badar (BAZ) said:

But, you may not get to see them ever as flooring on the slab will make them invisible. This is the reason many engineers and contractors will say to you that do not worry about top rebars.

You are saying terrible things! But you are right...In my case engineers and contractors are not responsible for anything

On 1/28/2022 at 6:43 AM, Badar (BAZ) said:

Even if you do not provide the lengths mentioned above, the slab can still have the required strength if you have provided extra reinforcement in the mid-span (i.e bottom bars).

Yeah, of course! There will be bottom bars (main and non main) and upper bars (main and non main).

Edited January 29, 2022 by Kirill

[Badar (BAZ)]

11 hours ago, Kirill said:

Plus 115 taking into account the protective layer. Total is 210 mm, 1200 - 210 = 990 mm. So we have 990 mm

It appears that you have misunderstood the point about available length of residual bar  that can serve the demand of negative moment. You do not have 990mm.

 

 

11 hours ago, Kirill said:

What should I do with residual bars in places where spans<4. Should I cut them? Is it possible to leave them everywhere not cut off?

I have already addressed that: You can provide extra rebars as per details shown by Ayesha.

 

11 hours ago, Kirill said:

You are saying terrible things!

It is what it is!

 

11 hours ago, Kirill said:

I don't need them at all!😀

You cannot avoid them. What you can do is to limit their width so that the structure can have an longer service  life, and the rebars remain corrosion free.

11 hours ago, Kirill said:

There will be bottom bars (main and non main) and upper bars (main and non main).

I hope you understand that main/non-main depends on whether there is one-way or two-way action.

[Kirill]

Hello everyone! The working season almost ends. Time to sum up!

For new readers:
The task was to create a concrete slab for basement floor of 12x15m house in Russia. At the beginning of season we just had basement walls and bar releases (see attached photoes at the beginning). 

During summer the floor slab was filled in, waterprofing and thermal insulation of basement walls were finished

Now, It is the good opportunity to show obtained results. Maybe someone will find something them interesting. I would not say that we completely followed by advices from this forum, but still, all suggestions were considered. Thanks everyone who answered, espesially big thanks for Badar!

There is video how we bend bars. We did a "special" machine for this operation

Grid pitch (step) is 200 mm in some places it is only 100 mm

Slab height is 210 mm

I wrote everything briefly, but if there are questions, I can add!

[UmarMakhzumi]

Thank you for sharing and getting back to the post. Its great. Congrats on getting it done