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## Elastic critical moment for member with discrete restraints

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Message 1 of 4
Anonymous
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## Elastic critical moment for member with discrete restraints

Hi! Due to non-negligible differences between the elastic critical moment calculated in RSA (2016) and another software, I am very curious about some basic assumptions that are made in RSA regarding this topic. I have of course gone through the other threads related to the elastic critical moment in RSA, but it seems to me there are still a few things that could use some clarifications. I should also say that I am interested in how RSA calculates various parameters when EN1993-1:2005/A1:2014 is used for steel structures (although I dont know if this matters much for the questions below).

1. For members restrained at discrete points, which 'segment' between restraints is used for the calculation of Mcr? Is it the one where the maximum design moment acts? Is it the one where the distance between restraints is the largest? What happens when the position of the maximum bending moment along the beam is not located between the largest unrestrained segment?

2. For cases in which the user specifies the moment diagram as end moments (+linear variation), I assume equation F.3 in the ENV is used in order to calculate the C1 factor. This means RSA automatically calculates the psi value (ratio of end moments between restraints). Again, how is the segment on which this value is calculated chosen?

Finally, a small suggestion that could be implemented in the future, directly related to the thread below. There do seem to be some differences between some of the C factors specified in the ENV and the ones specified in SN003a (see for instance the second case in table F.1.2); maybe the section referred to for the C factors, when using BS EN should show the (correct) SN003a document and not the section in the ENV?

https://forums.autodesk.com/t5/robot-structural-analysis-forum/lateral-buckling-critical-moment/m-p/...

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Message 2 of 4

For both two first points the calculations are done for the segment between the two neighboring bracing points where the actual verification point is located. The maximum bending is determined from this part of the member (and from the next one when the verification point 'jumps' there) and the same applies to the end moments (being at the ends of the given segment).

I have forwarded your suggestion from the 3rd point to RSA development team.

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
Message 3 of 4
Anonymous

Thanks for the quick reply. If I understand correctly then, assuming I have a beam restrained at 2 points along its length and assuming I have verification points in all 3 segments, RSA checks each segment separately and only the information about the critical (worse) segment 'makes it into' the calculation note. Furthermore, I assume that at the moment there is no way of assigning a different moment diagram for each segment individually and the moment diagram assigned to the full member will be used for the calculation of the C1 and C2 factors for all segments. Are these two points correct?

Message 4 of 4

If I understand correctly then, assuming I have a beam restrained at 2 points along its length and assuming I have verification points in all 3 segments, RSA checks each segment separately and only the information about the critical (worse) segment 'makes it into' the calculation note.
Correct.
Furthermore, I assume that at the moment there is no way of assigning a different moment diagram for each segment individually and the moment diagram assigned to the full member will be used for the calculation of the C1 and C2 factors for all segments.
In such case the diagram will be 'divided' into 3 segments and values from ends of each of them will be used for calculations so you may say you have different bending moment diagrams for each of the segments rather than the end values from the end nodes of the whole member are used for each off the segments.
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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