Lateral buckling verification in several sections

[omar.ratp]

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?

[Artur.Kosakowski]

As far as I can see you changed way you assigned the buckling parameters for these columns. For the intermediate bracings you should indicate (or allow Robot to detect them automatically) 2 positions of restrains along the columns and then you should decide what is the buckling coefficient for the parts among them (the default is set as 1). 

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