## Robot Structural Analysis

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# Slabs Deflection

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*Dear Colleagues*

* *

*Could I get responses for the following Inquiries :*

* *

*Why does the max. slab deflection value in the capture (01) is greater than in the capture (02) for the same slab parameters?*

* *

*Which deflection value shall I consider as " Long term deflection "?*

* *

*Is there any possibility to get the elastic slab deflection directly from ROBOT ?*

* *

* *

__Note : If you use any capture for explanation . Kindly , send it as attached .__

*Thanks in advance.*

*Refaat*

Solved! Go to Solution.

# Re: Slabs Deflection

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Why does the max. slab deflection value in the capture (01) is greater than in the capture (02) for the same slab parameters?I assume that in the first scenario you calculated the deflection for all of SLS combinations (case 40 being the compound case with many components) whereas for the second one only for a single selected one (apparently not the one that gives max. value of deflection).

Which deflection value shall I consider as " Long term deflection "?Which design code is concerned?

Is there any possibility to get the elastic slab deflection directly from ROBOT ?If you mean uncracked then check the results of the static analysis instead.

**Artur Kosakowski**

# Re: Slabs Deflection

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*Dear Artur*

*Thanks for response , but may I clarify the followings : *

*- Do you mean that ROBOT in capture (01) doesn't calculate the deflection for the case (40) ? It means that I Can not specify a case to calculate the long term deflection without running the " deflection verification " ?*

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*- " ACI318-80M" is concerned for long term deflection calculation .*

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*- Elastic deflection , I meant " Short term deflection " for slab . if possible to get in ROBOT . Kindly , send me a capture for explanation.*

* *

*Thanks *

*Refaat*

# Re: Slabs Deflection

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- Do you mean that ROBOT in capture (01) doesn't calculate the deflection for the case (40) ? It means that I Can not specify a case to calculate thelong term deflectionwithout running the "deflection verification" ?

If you have a case that include more than one component (e.g. SLS code combinations) and you use it for calculations of deflection than the result is sort of 'envelope' of deflections. On your screen captures you used case 40 for calculations of deflection and 37 for its verification. Mind that for the simplified approach it is important that you divide your slab into panels with 'clearly' defined boundary conditions (line of supports) as it based on the scaling off results from the static analysis. The description of the method is available in Help.

- " ACI318-80M" is concerned for long term deflection calculation .

For ACI displayed values of deflections are the total long-term ones. See the attached picture.

- Elastic deflection , I meant "Short term deflection" for slab . if possible to get in ROBOT .

No, these values are not available for display.

**Artur Kosakowski**

# Re: Slabs Deflection

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*Dear Artur*

*Thanks , well done*

*Refaat*

# Re: Slabs Deflection

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I am trying to get "short term" (initial) deflection of a simple slab, I've made short video that displays what I am doing.

http://screencast.com/t/KCmKZ0JGS

I put those Φ12's first, then I tried to get deflection for characteristic SLS load combination.

I used "With stiffness update" verification type and I get 12,29mm deflection.

Then I done all that again but with Φ18's and I got smaller deflection.

Any way, Robot keeps warning me about quasipermanent combination.

Is this correct way around to get initial deflections for provided reinforcement?

Code: EN 1991-1-1

# Re: Slabs Deflection

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Robot calculates the value of total displacement and there is no option for calculating the initial ones. This is done for QPR SLS combinations and when there are no such combinations defined Robot assumes that all defined SLS combinations are of such type.

**Artur Kosakowski**

# Re: Slabs Deflection

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# Re: Slabs Deflection

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Hi! I also made my own Design Using Robot, Placed Reinforcement to it and Run Deflection Checks. Cracking seems too much and Deflection is out of this world.. I used SLS Envelope for this case

And Also, What is the Meaning of this? how can I fix this issue?

# Re: Slabs Deflection

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Hi! I also made my own Design Using Robot, Placed Reinforcement to it and Run Deflection Checks. Cracking seems too much and Deflection is out of this world.. I used SLS Envelope for this case

Check what values of displacements you obtained for static analysis of the model itself.

And Also, What is the Meaning of this? how can I fix this issue?

Please check: http://forums.autodesk.com/t5/Robot-Structural-Ana

lysis/SLS-combination/m-p/3316923

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.

**Artur Kosakowski**