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Error: RCC Column design to EC2, miscalculation of eccentricities

4 REPLIES 4
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Message 1 of 5
patkson
635 Views, 4 Replies

Error: RCC Column design to EC2, miscalculation of eccentricities

Hi All,

I have been cracking my head around this situation with robot on the columns design to ec2 on the eccentrities and the Moment Resistance saftey factors and I think I know why.

After running some manual verifcations and comparing the two results I finally figured it out.

The reason is actually an error from robot which took me a lot observation to notice it. If you go through the column calculations note tab under buckling analysis for Z direction there is been some miscalculation of the eccentricities on the columns. 
 
I have well illustrated this in a simple rcc design module for a 600x600 column. And I have also attached the manual calculation report
for your appraisal.
Greetings,
Patrick.

 

4 REPLIES 4
Message 2 of 5
AIIAK
in reply to: patkson

Hey

IĀ“m working on the same issue trying to verify the Robot calculations by hand. So far everything checks out for the method based nominal curvature, but the limit of slenderness is not equal to what I calculate and I can see also that the same is occurring in your situation. You get lambda lim =64 and Robot shows 19.57, any Idea why ? I use EN 1992-1-1:2004 AC:2008 too.

Considering the other problem with the imperfection. Are you suppose to consider it only in one direction may be, the more critical. In your case both direction are equally critical, so one of the them is fine.

Otherwise it is a mistake which you need to take a count for in the design.
Message 3 of 5
patkson
in reply to: AIIAK

Hi,
Thanks for the response, but if i understand you clearly then the
geometric imperfection doesn't necessarily needs to applied on both
directions. Bravo!
But I think it will be conservative to approach them for both directions.

However regarding your issue raised about the slenderness limit I totally
agree with you,
Infact I didn't even notice Robot was giving a small value of 19.57 for the
600x600 column!!

And going by cl 5.8.3.1 of EN 1992 's approach we should end up with a
limit of 64!!

*Slenderness limit for buckling about z axis (cl. 5.8.3.1)*
Factor A;A = *0.7*
Mechanical reinforcement ratio;ļ· = As ļ‚“ fyd / (Ac ļ‚“ fcd) = *0.837*
Factor B;B = ļƒ–(1 + 2 ļ‚“ ļ·) = *1.635*
Moment ratio;rmz = -1.0 ļ‚“ M01z / M02z = ;*-1.000*
Factor C;Cz = 1.7 - rmz = *2.700*
Relative normal force;n = NEd / (Ac ļ‚“ fcd) = *0.931*
Slenderness limit;ļ¬limz = 20 ļ‚“ A ļ‚“ B ļ‚“ Cz / ļƒ–(n) = *64.0*


Regards,

Patrick.
Message 4 of 5
AIIAK
in reply to: patkson

Hi,
Will IĀ“m not sure if youĀ“re suppose to apply it on both direction, some EC2 expert can answer that question. But I would like to hear Autodesks thought about the this issue and the issue of the slenderness. What I noticed is, that when using the danish annex then I get the same value as Robot. Stil donĀ“t know how it is calculated when EN 1992-1-1:2004 AC:2008 is used.

Message 5 of 5
Artur.Kosakowski
in reply to: AIIAK

5.2 Geometric imperfections - in Robot the eccentricity is applied only in the 'worst' direction.

The same is assumed for 5.8.9 Biaxial bending 

(2) Separate design in each principal direction, disregarding biaxial bending, may be made as a

first step. Imperfections need to be taken into account only in the direction where they will have

the most unfavourable effect.

 

I think it is better communicated in the French NAD for EC2

 "L'imperfection lgeomĆ©trique ei (EC2 EN 5.2 (1)) est prise en compte dans le sens le plus dĆ©favorable Ā»

 

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

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