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Hi @Anonymous
The stress is calculated as for a panel with uniform 'equivalent' thickness. If you need the exact stress distribution you may consider modelling its real shape instead.
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Artur Kosakowski
Dealing with a very delicate and thin concrete orthotropic shell , I wanted to know the acting stresses. This below is the orthotropic thickness togeher with the main orthotropy direction section (32cm width) calculated in Section definition module .
Then I created an experiment model with a 5mx1m cantilever slab with a 10Kn.m distributed moment applied on farthest edge. Figure below shows the map stress calculated by Robot and the real stresses due to moment calculated manually.
As all stress calculations are done considering the equivalent thickness for the plate self weight , results are obviously very wrong even for normal forces ,as orthotropic directions have not the same geometry.
I wonder why Robot even shows the stress results for orthotropic panels if "he" knows that the results are wrong???? And (again) without any warning!!!
Of course ,everything has to be checked manually as I did right now ,but how hard can it be for RSA to give the correct results for stresses on orthotropic panels???
Rafael Medeiros
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Hi @Rafacascudo
I wonder why Robot even shows the stress results for orthotropic panels if "he" knows that the results are wrong???? And (again) without any warning!!!
Let me start with the statement that I'm not the person who made the decision if it should be or should not be displayed but again this is not that (as almost always) black and white. Imagine that your panel is not a slab with ribs but it is a flat one with the reduction of the stiffness for one of directions - would you like to see the stresses? Or you have just small openings in its cross section?
Of course there might have been as you wrote a warning (I agree on that till the moment you start complain that you already know when it is displayed each time you show this type of results 
) but I'd say by the principle of the definition of such thickness where you don't have the determined positions of the 'beams' in the panel you IMHO may assume that we are having 'just equivalent' properties rather than exact definition of the ribbed slab with the additional option for seeing bending moments for each of the T beams and design its reinforcement 
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Artur Kosakowski
Hi @Artur.Kosakowski ,
Sorry for the delay , but I still think that a structural software could never provide wrong results knowing they are wrong. Or it shows nothing for certain cases like my example or show the correct values for upper and lower stresses. Nothing is said on manual and if it wasn´t this thread it would remain unknown.
As I said in another thread I am experimenting with other structural software packages and in those few that have specific orthotropy types like those in Robot , I modelled the same cantiliver orthotropic slab.
In 2 of them with plenty orthotropy types like in Robot they address the issue.
The 1st chooses to not show results for orthotropic panels
The 2nd , does it right and provide upper and lower stresses with the same values I calculated manually in a picture on my previous post.
I think Robot should go with one of these 2 options. Or gives nothing , or gives max and min values stresses that the panel can have regardless if there is a rib on that exact point or not. It would be already a very good point to start the design.
But ,again , I insist that it should never provide wrong results being aware of that mistake!!!!!
Rafael Medeiros
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Hi @Rafacascudo
I do understand your point. Is there any technical documentation which describes the way they post -process the results for stresses?
Artur Kosakowski
Sorry Artur , Not that I could find . But in this case of mine , I cannot see the dificulty on calculating the right stresses for a T section.
What exactly are you looking for??
Rafael Medeiros
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Hi @Rafacascudo
Not knowing the locations of 'webs' and not having 'uniform' bending and axial force distribution across the panel how would you determine stress in given location? I assume one could 'extract' such panel 'outside' the program and 'tell' where they are to obtain the correct values of stresses based on maps of bending moments and in-plane forces but that would require additional 'side' application (or result post-processor if you prefer to call it this way) which doesn't exist in Robot.
Perhaps there is some other option that I'm not able to thibnnk of at the moment too.
Artur Kosakowski
Giving correct max and min stresses for each finite element ,don´t bothering with orthotropy layout(ribs), it would already be good enough, .
But if dev team wants to go further , then they can develop a more detailed "arbitrary" layer on "parameters" tab so the user can know the stress value exactly where he wants/needs , according to his ribs layout.
Rafael Medeiros
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Hi @Rafacascudo
Thank you for your suggestion. I have forwarded them to the development team.
Artur Kosakowski
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