topic Re: Deflection / Modulus of elasticity (Ec,eff) –EC2 in Robot Structural Analysis Forum

Deflection / Modulus of elasticity (Ec,eff) –EC2

Refaat — Mon, 12 Feb 2018 21:18:18 GMT

Dear Colleagues

As we know that RSA calculates the carked deflection based on the reduced E modulus ( E_c,eff)

https://forums.autodesk.com/t5/robot-structural-analysis-forum/deflection-control-rc-design-creep-and-cracking/m-p/7739246/highlight/true#M63381

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

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Artur.Kosakowski — Tue, 13 Feb 2018 08:44:02 GMT

Hi @Refaat

You need to change the creep value to see the difference:

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.

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Refaat — Tue, 13 Feb 2018 10:37:37 GMT

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

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Artur.Kosakowski — Tue, 13 Feb 2018 10:56:21 GMT

Hi @Refaat

You can check the difference due to the concrete grade in the provided reinforcement calculation note:

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Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Refaat — Tue, 13 Feb 2018 11:14:13 GMT

Dear Artur

Thank you for your response.

My main inquiry about (E) , when I changed E = 34 Gpa to E = 4 Gpa for the same concrete class C35/45 . I didn’t see any difference of deflection values.

I look forward to get explanation for this matter ???

Regards

Refaat

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Artur.Kosakowski — Tue, 13 Feb 2018 11:43:59 GMT

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:

If one or more of these posts answered your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Refaat — Tue, 13 Feb 2018 12:04:45 GMT

Dear Artur,

I did your approach. But still doesn’t work.

Refaat ,

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Refaat — Wed, 14 Feb 2018 08:19:31 GMT

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

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Artur.Kosakowski — Wed, 14 Feb 2018 09:32:21 GMT

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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Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Refaat — Wed, 14 Feb 2018 11:20:24 GMT

Dear Artur

Thank you so much for this information.

Robot doesn't use the E value as defined in the material properties but calculates it based on the defined concrete grade resistance instead.

Please, may I know which formula Robot is used to calculate (E) for deflection calculation stage?

Best Regards

Refaat

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Mohammed_Ata — Wed, 14 Feb 2018 11:21:31 GMT

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 !

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Artur.Kosakowski — Wed, 14 Feb 2018 11:28:24 GMT

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.

If one or more of these posts answered your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Artur.Kosakowski — Wed, 14 Feb 2018 11:29:32 GMT

Hi @Mohammed_Ata

This is as expected as you changed the material resistance.

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Refaat — Wed, 14 Feb 2018 13:38:53 GMT

Dear Artur ,

Thank you for your patience and help

But calculates it based on concrete resistance (again with the code provided formula).

If possible to get this formula . I will be grateful.

Best Regards

Refaat

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Artur.Kosakowski — Wed, 14 Feb 2018 14:01:40 GMT

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.

If one or more of these posts answered your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.

Re: Deflection / Modulus of elasticity (Ec,eff) –EC2

Refaat — Wed, 14 Feb 2018 14:27:11 GMT

Dear Artur,

Thank you so much our hero

Refaat