Dear Colleagues
As we know that RSA calculates the carked deflection based on the reduced E modulus ( Ec,eff)
So, I am wondered to know when the modulus of elasticity is reduced as in the attached captures. It seems there is no influence on the deflection values which are calculated by two methods (Equivalent Stiffness & Stiffness update) .
May I get any explanations?
Thanks in advance
Refaat
Hi @Refaat
You need to change the creep value to see the difference:
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Dear Artur
Thank you for your response.
You need to change the creep value to see the difference:
Yes, But of course there is another parameter should effect to see the difference (modulus of elasticity)
As we know the final creep deformation depended on final creep coefficient and modulus of elasticity.
Therefore I would like to see the difference due to (different values of elasticity modulus).
As I used to leave concrete creep coefficient (Auto) status in RSA. Robot should calculate this coefficient based on relative environmental humidity and concrete age as described (Annex B).
Regards
Refaat
Hi @Refaat
You can check the difference due to the concrete grade in the provided reinforcement calculation note:
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Hi @Refaat
The change of the material properties in Job preferences doesn't influence the object which already existed in a model. The better option is to define a new material in Job Preferences and crate another panel along the C35/45 one. Then use the reinforcement label like this for both of them:
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Dear Artur ,
Good morning
I believe that the reduction of (E) should have clearly influence of the deflection values which isn’t obvious in the deflection results of RSA.
Could we reach together to a point to clarify this sensitive issue?
Best Regards
Refaat
Hi @Refaat
Looking at the picture you inserted my assumption is that it is intended to include the described effect at the stage of the static analysis of a model. I'm sure you will also see the different for your model when you look at the displacements for selected load case / combination using this dialog:
For 'cracked' deflection (panel reinforcement calculations) Robot doesn't use the E value as defined in the material properties but calculates it based on the defined concrete grade resistance instead. IMHO this approach makes a lot of sense as otherwise e.g. reduction of the panel Ig (or E as you did) intended only to influence the values of internal forces due to cracks for model calculations would also (in addition to the reduction of panels stiffness as required by the selected code for deflection calculations) influence the 'cracked' deflection (being already reduced as per code provisions). In other words instead of changing E change concrete resistance to observe the effect you want to see:
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Dear, @Refaat
Dear, @Artur.Kosakowski
The discussion is so much interesting talking about long term deflection.
I have made an example like Eng. Refaat, my dear friend, and found it is already changes when changing the material an so E. like pics. May have something definition of slab calculation type.
Interesting discussion !
Hi @Refaat
Please, may I know which formula Robot is used to calculate (E) for deflection calculation stage?
Robot follows exactly the formulas from the selected code. The only difference is that the initial E value (for uncracked material) is not taken from materials properties as defined in Job Preferences (this value is used for model calculations) but calculates it based on concrete resistance (again with the code provided formula). The other values are calculated as per your screen captures from (given) code formulas.
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Hi @Refaat
This is based on the table 3.1. If concrete fck is exactly as the value in the the first row then Ecm is assumed as the corresponding value from the Ecm row. If other than Robot uses the formula highlighted in yellow.
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