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Valued Contributor
RRufino
Posts: 89
Registered: ‎07-22-2011
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Buckling Analysis

1485 Views, 9 Replies
01-19-2012 09:49 AM

Hello, i´m starting to use Buckling Analysis (Analysis type) to find if is possible to know in a three-dimensional model if my structure is sway or non sway.  I´m asking your help to verify if my thought is correct:

 

I go to analysis case and in every load combinations that I will use to design structure elements, I’m selecting Buckling analysis, using a number of modes = 3xstories. After run calculations I go to tables->critical loads and for each combination i´m founding the lower coeff, this will be my critical coefficient. Now depending country codes, but generally, in elastic analysis, if crit. coef > 10 my structure is non sway.

 

If this is correct i´m wondering how to know if the structure is non sway in both directions or just in one direction, should i have to think in the same way but finding the corresponding excitement mode to each direction?

 

Other question, in this last table, when I ask critical forces it shows me bar forces, the same to buckling length. It’s correct to think that displayed bar buckling length corresponding to lower critical force in each bar is the one to perform local second order effects calculations?

 

Last question, after this, should I transform combinations to linear combinations again before of design any element?

 

Best regards,

 

RRufino

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pp2008
Posts: 528
Registered: ‎06-23-2008

Re: Buckling Analysis

01-20-2012 12:59 AM in reply to: RRufino

It is enough to run buckling analysis for the combination with the highest vertical load.

Then it is necessary to display buckling shapes to find buckling modes corresponding to global buckling in X or Y and not to some local effects.

Buckling shapes can be displayed selecting buckling load case, activating display of deformation and activating display of modes instead of displacements - appropriate icon shown on the attached screen capture.

Depending on structure type and display layout this icon may be not displayed - in such case using from pull-down text menu: Loads>Select Result Type>Modes

 

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Regards,



Pawel Pulak
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Valued Contributor
RRufino
Posts: 89
Registered: ‎07-22-2011

Re: Buckling Analysis

01-20-2012 01:32 AM in reply to: RRufino

Thanks pp2008,

 

Can you answer to my last 2 questions also?

 

Best Regards,


RRufino

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Product Support
pp2008
Posts: 528
Registered: ‎06-23-2008

Re: Buckling Analysis

01-20-2012 02:09 AM in reply to: RRufino

Sorry for omitting it.

 

Other question, in this last table, when I ask critical forces it shows me bar forces, the same to buckling length. It’s correct to think that displayed bar buckling length corresponding to lower critical force in each bar is the one to perform local second order effects calculations?

 

No, in general case these results cannot be used for this porpose.

Critical forces displayed in this table for each mode for any member under compression are calculated multiplying compression force in appropriate member by critical coefficient of appropriate mode.

Buckling lengths are calculated from above mentioned critical forces and Euler's formula.

Detailed description of these calculations is given in this forum topic:

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Buckling-Analysis/m-p/3280269/highlight/true...

 

 

Last question, after this, should I transform combinations to linear combinations again before of design any element?

 

No, it is not necessary. Buckling analysis load cases contain both results of static analysis and buckling analysis.

 

Other topics, where global buckling is discussed:

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Negative-critical-coefficients-in-buckling-a...

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Displaying-buckling-shapes/m-p/3213564/highl...

 

---------------------------------------------
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Regards,



Pawel Pulak
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Valued Contributor
RRufino
Posts: 89
Registered: ‎07-22-2011

Re: Buckling Analysis

01-20-2012 09:20 AM in reply to: pp2008

Thanks again pp2008, now other question refering to local analysis:

 

Using R/C member type definitions and assembling to each one the bucking schemes, is there any table who has the every bars buckling lenght? I'm not seing this possibility on any table at Geometry or RC design tabs...

 

Best Regards,

 

RRufino

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Product Support
pp2008
Posts: 528
Registered: ‎06-23-2008

Re: Buckling Analysis

01-23-2012 01:47 AM in reply to: RRufino

No, the information related to buckling length of RC members is not displayed in any summary table. It is given in calculation notes of specific columns.

 

Regards,



Pawel Pulak
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Valued Contributor
RRufino
Posts: 89
Registered: ‎07-22-2011

Re: Buckling Analysis

01-23-2012 02:11 AM in reply to: pp2008

OK, please set it to Robot 2013 wishlist :smileywink:

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Product Support
pp2008
Posts: 528
Registered: ‎06-23-2008

Re: Buckling Analysis

01-23-2012 03:27 AM in reply to: RRufino

Sure:smileywink:

 

Regards,



Pawel Pulak
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*Expert Elite* | International Moderator
Romanich
Posts: 584
Registered: ‎09-29-2009

Re: Buckling Analysis

03-06-2013 06:45 AM in reply to: pp2008

Hi, can you add to the wish list this feature:

normilized.png

   
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Product Support
pp2008
Posts: 528
Registered: ‎06-23-2008

Re: Buckling Analysis

03-08-2013 03:22 AM in reply to: Romanich

Hi Romanich,

your suggestion added to the wish list :smileyhappy:

 

Regards,



Pawel Pulak
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