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Contributor
pta_simon
Posts: 18
Registered: ‎10-23-2013

Load History and Creep

922 Views, 7 Replies
11-18-2013 03:44 AM

Does Robot consider creep when calculating deflections?

 

I am trying to simulate the deflections of a floor slab over a period of time to determine how it will affect the cladding panels. I have calculated the deflections due to cracking in the "slab - required reinforcement" RC design section but not sure if this is the best way to do this. Can you please suggest the best way to model these deflections?

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Product Support
Rafal.Gaweda
Posts: 5,604
Registered: ‎04-26-2010

Re: Load History and Creep

11-18-2013 05:37 AM in reply to: pta_simon

creep.jpg



Rafal Gaweda
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Contributor
pta_simon
Posts: 18
Registered: ‎10-23-2013

Re: Load History and Creep

11-18-2013 06:46 AM in reply to: Rafal.Gaweda

Rafal,

 

Thank you for highlighting this option. I had noticed the option previously, therefore I will reiterate my query.

 

I am looking to obtain deflection plots for multiple stages along the slab's load history (specifically, I require a deflection plot at initial loading, full loading and long term loading) however, I am unsure how to go about this.

 

Please could you provide guidance.

 

 

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Product Support
Rafal.Gaweda
Posts: 5,604
Registered: ‎04-26-2010

Re: Load History and Creep

11-20-2013 03:30 AM in reply to: pta_simon

Rather, you can not easily use the robot calculations.
For EC2 , Robot computes only the deflection for long term combinations with creep.
Creep is considered from time t0 to infinity.
Of course, if youmake QPR combinations manually entered creep factor as 0.0, you will get "momentary deflection", then calculate on the side manualy creep factor, enter to program and redesign then subtract deflections. You can do this multiple times until you are satisfied.

 

In general:
- For EC2 deflection is calculated for QPR combinations only
- 0.0 creep factor means the lack of creep because Ec,eff = Ec / (1 + fi)
- robot automatically calculated creep coeff is from t0 to inf.



Rafal Gaweda
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Distinguished Contributor
Jummybear
Posts: 140
Registered: ‎11-16-2011

Re: Load History and Creep

02-25-2014 07:59 AM in reply to: Rafal.Gaweda

In general:
- For EC2 deflection is calculated for QPR combinations only

Can you explain about that? When I design somekind of plate I make some of ULs combinations and also 3 SLS: CHR, FRE and QP. When i run calculation i can select all of SLS combinations. Does it mean that Robot takes only QP SLS combination into account? For example i limit cracks by 0.3mm and deflection by 30mm, but i thought that robot pick the worst SLS combination to fulfill the criteria... Same question about verification with provided reinforcement. I can pick only 1 combination here nad if i pick not QP SLS then i get a message from Robot that there are no QP combinations and calculations may be incorrect. And true, just made an example with plate and i get sucj results:

Max plate displacements as elastic object (before req. reinforcement calculations): 6,8 mm

Max plate deflection for req reinforcement (there are also 3 SLS combinations, which one is picked for calc here, also QP?): 25,7 mm

Max plate deflection for prov. reinforcement (SLS CHR combination + robot message, that calculations may be incorrect): 6,3mm!!! Even less than in 1 case (elastic object)

Max plate deflection for prov. reinforcement (SLS FRQ combination + robot message, that calculations may be incorrect): 5,0mm!!! Even less than in 1 case (elastic object)

Max plate deflection for prov. reinforcement (SLS QP combination, no additional message from robot): 13,3mm. Seems to be OK.

 

If Robot calculate/verificate displacements for QP SLS combination only, then is there any other way to get real verifed displacements for provided reinforcement in Robot?

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Distinguished Contributor
Jummybear
Posts: 140
Registered: ‎11-16-2011

Re: Load History and Creep

02-26-2014 02:21 AM in reply to: Jummybear
PS Related to this topic http://forums.autodesk.com/t5/Robot-Structural-Analysis/deflection-smaller-in-a-heavier-loadcase/m-p... where last message is without answer. I have similar problem/question.
PPS Is it possible to edit own messages?
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Product Support
Rafal.Gaweda
Posts: 5,604
Registered: ‎04-26-2010

Re: Load History and Creep

02-26-2014 06:46 AM in reply to: Jummybear

According to EC code : 

 

EN 1992-1-1: 2004

7.4 Deflection control

7.4.1 General considerations

(4) The appearance and general utility of the structure could be impaired when the calculated

sag of a beam, slab or cantilever subjected to quasi-permanent loads exceeds span/250. The

sag is assessed relative to the supports. Pre-camber may be used to compensate for some or

all of the deflection but any upward deflection incorporated in the formwork should not generally

exceed span/250.

(5) Deflections that could damage adjacent parts of the structure should be limited. For the

deflection after construction, span/500 is normally an appropriate limit for quasi-permanent

loads. Other limits may be considered, depending on the sensitivity of adjacent parts.



Rafal Gaweda
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Distinguished Contributor
Jummybear
Posts: 140
Registered: ‎11-16-2011

Re: Load History and Creep

02-26-2014 07:43 AM in reply to: Rafal.Gaweda

I know that, but sometimes i want to check not only QP SLS but CHA or FR. Robot dont provide calculations for that cases. Am i right that if i want to simulate any other SLS combination i must manually create SLS FR combination type and manually pick loads with needed coefficients (for example if i used 0.3 coef. for live load for QP then now i can try with 0.5?)

 

One more question about reinforcement maps dialog box (See pic.)

Its a simple example, harder with more complicated models. When i run calculations and get the results i can assign the reinforcement bars manually (i wonder if smb use automatically provided reinforcment by Robot). I try to turn req. reinforcement maps or whatever it is (circled box in my pic) to "helptool" but with no success. Is it possible to show in orange mesh 12-200 (and its area) and in red also mesh 12-200+additional bars for example 16-200? I cant combine that 2 thing in one row...

 

RC maps.JPG

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