How robot calculates the slab reinforcement and why at is so different from ar.

[Anonymous]

Hallo,
I am having trouble calculating slabs. I am using Eurocode and my calculation doesn´t exactly match with Robot Reinforcement.
First, I don’t understand how the Robot calculates the reinforcement. I don’t understand which moment Robot uses to calculate the bending reinforcement (complex, only xx direction, xx direction + xy) and also, I don’t understand if Robot uses envelope or just a combination in the calculation.
I tried to read the notes, but they are less understandable that the beam and column notes.
The second problem is that sometimes the required reinforcement its different from the provided reinforcement, like the picture attach.

[Artur.Kosakowski]

Hi @Anonymous

Robot Structural Analysis 2019 Help: Method of calculating plate and shell reinforcement - Wood&Armer

Reinforcement is calculated in such way that it provides sufficient slab capacity fro each of the combinations.

As Robot tries to distribute reinforcement in 'regular' way with spacing being half of the previous one e.g.:

160mm/80mm/40mm

in some areas provided one can be larger than what would be enough for irregular spacing.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Ok.Thanks
I have another question. The moments from geometry seems different from the reinforcement slabs note moments. I tried to compare the complex and the details moments and the result of both are not like the notes moments.
I am doing something wrong or exist a difference between these moments?

[Artur.Kosakowski]

Hi @Anonymous

Could you attach the Robot model and screen capture showing what did you compare?

[Anonymous]

I reinforced a slab. If you check the moments of the reinforced slab in the notes, they are different from the geometry moments from the same slab.

[Artur.Kosakowski]

Hi @Anonymous

As far as I can see you compare the results from the analytical method (which you cannot easily see in the model as you can't tell which direction was the governing one) with the Wood and Armer ones.  By the principles of the both methods they have to be different.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

I have manually calculated an armor with the complex moments from the analytical method (figure 1). This manually calculated armor does not equal the reinforcement armor of the Robot, due to the moments.

I know the Robot moments in Figure 2 are moments of detail (xx, yy, and xy). So, I used the link you sent me to calculate the complex moments (xx + xy) of the moments in figure 2.

Also, when i use results>>maps>>detailed>>moments yy, the result is the figure 3. The moments from the detailed yy are also different from figure 2.

I don’t understand why they should be different. I am using only bending to equal both values.

If they are different, how can I compare a manually calculated armor with the Robot's armor?

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

If you want to make the comparison you should compare the same kind of output meaning you should compare WandA maps with the calculation note for WandA method. 

For the analytical method it is hard to even think about values of bending moments as there is a set of them for each of the point projected on the directions shifting each 12 degrees and the calculated reinforcement is such that it  is sufficient to transfer each of these moments. and has the smallest possible area calculated as combined AX and AY value. In the situation when you have unidirectional bending what you should compare with the note is pure bending M rather than M WandA)

As you can see the note shows the same value of bending in the same location for both Axx(+) and Ayy(-) as per the results projection and the minimal 'combined' area of reinforcement principle.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Oh ok, thanks very much, now i understand!
Last question, how Robot pick this moments points (the coordinates points)?

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

The value of the maximal moment in the note corresponds to the location of the maximal reinforcement.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

The picture attached show that Robot picked a point different from the maximum moment. It is 6 kN.m less than the maximum moment.
Should it not pick the maximum moment that represent the maximum reinforcement?
Thanks for all the answers