Control crack width for flat slab

[Anonymous]

I am working on a flat slab design.
 
For the bending moment, the provided reinforcement matches my hand calcs. However when i activate the option to control the crack width with additional reinforcement then the provided reinforcement is higher than what i expect from the hand calculations.
 
For crack width 0.2mm and BM (Quasi Permanent combination) (412 KNM/M) I expect 6400 mm2/m reinforcement
 
The results i get from the model is 9400 mm2/m reinforcement
 
Attached the model and the detailed calcs

[Artur.Kosakowski]

Hi @Anonymous

Assuming that you display M(W&A)X(+) in the automatic direction you should look at Ax(+) rather than Ay(+) as you set automatic direction of reinforcement.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Hi Artur,

Thanks for your response.  The issue is that for the y direction the BM (QP) moment is 417.59kNm/m and the reinforcement I get from Robot is 9500 mm2/m ( I expect approx. 6400mm2/m).

The RC discrepancy appears only when I choose to control the crack width with additional reinforcement.

See the attached pdf

Tks

[Artur.Kosakowski]

Hi Andreas,

What would be the value you get for 73 mm cover?

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Hi @Artur.Kosakowski

The 73mm is :

the cover to compression reinforcement + bar diam +bar diam/2  (35+25+25/2=72.5)

I would expect robot to calculate this value automatically.

Tks

[Artur.Kosakowski]

Hi @Anonymous

What I meant was the value of 35 mm in your calculations which I assume was used. Shouldn't it be 73 mm instead?

I should have wrote what would be the value of reinforcement area you get when you use 73 mm instead of 35 mm. 

[Anonymous]

Well the cover 35 mm is applied to d therefore the 35mm is correct.

The d2 value is 75 as : cover +25+25/2

[Rafal.Gaweda]

Dear @Anonymous

We are unable to find QPR moments you used in hand calcs in the model you posted on forum.

Take a look below:

[Anonymous]

Hi @Rafal.Gaweda

Thanks for your reply. Did you reduce the load above the columns ?

[Rafal.Gaweda]

Hi @Anonymous

I am sorry, my mistake, you are right.

Could you be so kind and enter reinforcement areas calculated by Robot to your spreadsheet + all required data, make a screen shot and post on the forum?

(BTW Robot does not consider reinforcement for cracking moment caclulations)

[Artur.Kosakowski]

Hi @Anonymous

I'm sorry for not being able to contact you earlier but I was out of the office and wasn't able to continue working on this topic.

I'd like to ask you if could help us with the investigation by (as Rafal already wrote in his message) entering the values of area of reinforcement as calculated by Robot (red frame) in your spreadsheet and attach the obtained results (green frame). Thank you for your help.