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## Autodesk Robot Structural Analysis

Contributor
Posts: 16
Registered: ‎06-05-2012

# STEEL DESIGN - DIVIDED BAR - 2 identical structures one pass and one fails

221 Views, 7 Replies
07-11-2012 02:44 PM

On the example give the 2 structures is exacly the same with same moments

beam 1 is 8m ipe300

beam 2,3,4,5  in total is 8m ipe300

beam 1 fails steel design with ec3

beams 2,3,4,5  ok with steel design with ec3

why this difference?

thank u

Active Member
Posts: 6
Registered: ‎12-16-2009

# Re: 2 identical structures one pass steel design and one fails

07-11-2012 05:04 PM in reply to: tigrouis
Buckling and lateral buckling length.
Each node is beeing considered fixed for instability purposes
Active Contributor
Posts: 29
Registered: ‎01-26-2010

# Re: 2 identical structures one pass steel design and one fails

07-11-2012 10:46 PM in reply to: tigrouis

Hi tigrouis,

Both have been defined with the same LateralBuckling Parameters. They have LateralBuckling Lenght Lcr=lo

Bar 1 has Lcr=8m whereas 2,3,4,5 have Lcr=2m.

Please check code parameters before analysing(attached image).

Product Support
Posts: 2,875
Registered: ‎12-17-2010

# Re: 2 identical structures one pass steel design and one fails

07-11-2012 11:16 PM in reply to: tigrouis

In case your 'real' beam is divided into number of smaller bars you should create a new member for code checking. Assigning the same design parameters as for the beam 1 you will have exactly the same result.

Artur Kosakowski
Support Specialist
Product Support
Autodesk, Inc.

Contributor
Posts: 16
Registered: ‎06-05-2012

# Re: 2 identical structures one pass steel design and one fails

07-12-2012 03:07 PM in reply to: Artur.Kosakowski

For beam 1 I change the lateral buckling length coefficient as shown in photo 1

Still i get different results as you can see on photo 2 which is for beam 1 with lateral bucking length now is 2 and critical moment of lateral bucking 140

On photo 3 is for beam 2 with different results

thank you

Product Support
Posts: 2,875
Registered: ‎12-17-2010

# Re: 2 identical structures one pass steel design and one fails

07-13-2012 12:08 AM in reply to: tigrouis

Why do you want to compare beam 1 with beam 2 when one of them is 4 times longer than the other? In my opinion (as I wrote in my previous answer) the correct approach is to compare the same beams. In such case instead of running verification of beam 2 you should create a new beam for verification that is built from bars 2 to 4.

Anyway if you want to make the comparision in your way you shold  assign the parameters shown on the attached picture to Beam1.

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
Support Specialist
Product Support
Autodesk, Inc.

Contributor
Posts: 16
Registered: ‎06-05-2012

# Re: STEEL DESIGN - DIVIDED BAR - 2 identical structures one pass and one fails

07-13-2012 01:27 AM in reply to: tigrouis

Hello

the reason is that the member from node 3-4 (beam1) and the members frome nodes 5-9 (beams 2,3,4,5) is excalcly the same and have the same length 8 meters.   In design check the first case fails and in the second pass.

I have another post with tittle lateral buckling parameters with different example.  Can you please check that example please and you will understand my point

thank you so much for your support

Product Support
Posts: 2,875
Registered: ‎12-17-2010

# Re: STEEL DESIGN - DIVIDED BAR - 2 identical structures one pass and one fails

07-13-2012 03:30 AM in reply to: tigrouis

In the design module you shoud group bars 2 to 5 into a new (single) element for verification. See the attached file (check bars 1 and 6).

Artur Kosakowski
Support Specialist
Product Support
Autodesk, Inc.