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## Robot Structural Analysis

Active Member
Posts: 6
Registered: ‎01-25-2013

# Lateral buckling verification in several sections

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02-01-2013 08:03 AM

Hi

I'm trying to calculate an old steel girder bridge in 3D using RSA and I came across a problem regarding the verifications for lateral buckling.

Because it’s an old bridge, all sections are riveted sections formed with plates and angles. These sections are not available in RSA, so I create them myself and created a user database.

There is one particular beam who is heavily loaded, and it has several sections all along. The areas of the sections in middle span are grater than those close to the supports.

The problem is that the change in the sections does not correspond to the distance between supports (5 supports in total), i.e. in one span I have 2 or 3 different sections.

So I’m forced to create several bars in one span, for example, in a 3.9 m span I have 3 sections, so I create 3 bars of 1.3m each, and create the supports only at the beginning of the first bar and at the ending of the last.

When I do the verification of the beam for lateral buckling, RSA takes 1.3 m as the buckling length for each bar, and I want it to take 3.9 m instead !

Now, I know that there is a way around this, I only have to specify Lcr=3lo in my example. But the problem is that when I go to Detailed Analysis to specify stiffeners and all that, RSA only takes one bar of 1.3 m with supports at the beginning and the end of this bar, which is not true.

Is there a way to take all the 3 bars and make a detailed analysis and lateral buckling verification?

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Product Support
Posts: 4,608
Registered: ‎12-17-2010

# Re: Lateral buckling verification in several sections

02-01-2013 08:09 AM in reply to: omar.ratp

Try the following approach:

1. Create a new superbar (member) typing the numbers of 'several bars' you refer to in the list field

2. Define a positions of LTB bracings for such created member

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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Active Member
Posts: 6
Registered: ‎01-25-2013

# Re: Lateral buckling verification in several sections

02-04-2013 11:57 PM in reply to: Artur.Kosakowski

It worked perfectly !

Thank you

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Valued Contributor
Posts: 80
Registered: ‎05-29-2012

# Re: Lateral buckling verification in several sections

02-06-2013 07:31 AM in reply to: omar.ratp

Hi,

kind of having the same problem.

Can you please show somehow: 1. Create a new superbar (member) typing the numbers of 'several bars' you refer to in the list field.

Thanks

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Product Support
Posts: 4,608
Registered: ‎12-17-2010

# Re: Lateral buckling verification in several sections

02-06-2013 08:01 AM in reply to: CKDDIZ

Out of curiosity - haven't you discussed this in http://forums.autodesk.com/t5/Autodesk-Robot-Structural/member-design-upper-chord/m-p/3765119

Artur Kosakowski
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Valued Contributor
Posts: 80
Registered: ‎05-29-2012

# Re: Lateral buckling verification in several sections

02-06-2013 08:10 AM in reply to: Artur.Kosakowski

Yes, I did discuss buckling,

this was regarding a bar with different sections, so in this case we use group- group the bars with different sections in a new superbar, and analyze it. Is it correct?

Thanks

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Product Support
Posts: 4,608
Registered: ‎12-17-2010

# Re: Lateral buckling verification in several sections

02-06-2013 08:15 AM in reply to: CKDDIZ

You should look at the element you want to design as it was the real one. You determine where it actually starts (is supported) and where it ends (is supported again). If in the model this element is divided into smaller parts (regardless of their sections)you create a super bar.

Artur Kosakowski
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New Member
Posts: 2
Registered: ‎04-10-2014

# Re: Lateral buckling verification in several sections

04-10-2014 01:09 AM in reply to: Artur.Kosakowski

Hello,

i have one question, didn't want to make onother post.

If i have beam let's say HEB360, and when i do verification of this beam, program says to me, that "For bar ... the program has not performed lateral buckling verification. And so on..."

Can you tell me why? See files atatched. Its from a big structure and design ratio is not important.

Thank you.

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Product Support
Posts: 4,608
Registered: ‎12-17-2010

# Re: Lateral buckling verification in several sections

04-10-2014 01:49 AM in reply to: donisk2000

Robot displays the verification result from the point where the ratio is the larges x=1.0L -> 0.84 where there is no My bending (therefore no LTB check is done). If you force the verification in the pint you indicated you can see that the obtained ration is smaller (0.76) with LTB verification (My is not zero).

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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New Member
Posts: 2
Registered: ‎04-10-2014

# Re: Lateral buckling verification in several sections

04-10-2014 02:38 AM in reply to: Artur.Kosakowski
Thank you. If i understand correctly my calculations are correct?
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