Wind crosses and and DSC algorithms

[Anonymous]

Hey

I've been trying to make windcross in a structure I can't really seem to get the hang of it.

I've made the windcross in a fixed frame with rigid corners. The cross is made from two truss/tension bars with Fixed-Pinned releases. When ever I try to calculate I am suggested to use 'DSC algorithm' I've looked through the help file but I can't really figure out what exactly this algorithm does?

Also, is there any way to "seperate" the two bars in the windcross from each other? so they're not joined on the middle, but are able to move seperatly?

- regards Martin

[Anonymous]

Hey

I've been trying to make windcross in a structure I can't really seem to get the hang of it.

I've made the windcross in a fixed frame with rigid corners. The cross is made from two truss/tension bars with Fixed-Pinned releases. When ever I try to calculate I am suggested to use 'DSC algorithm' I've looked through the help file but I can't really figure out what exactly this algorithm does?

Also, is there any way to "seperate" the two bars in the windcross from each other? so they're not joined on the middle, but are able to move seperatly?

- regards Martin

[Francois.Augiere]

In this case, as these bars are already truss bars (transferring only axial forces), you shouldn't apply releases.

These bars are not joined, so they will be able to move separatly

[Artur.Kosakowski]

I've been trying to make windcross in a structure I can't really seem to get the hang of it.

I've made the windcross in a fixed frame with rigid corners. The cross is made from two truss/tension bars with Fixed-Pinned releases.

Truss bars (applies to all tensioned only bars) are by default not capable of transferring bending therefore have 'pinned' ends. No releases should be defined.

When ever I try to calculate I am suggested to use 'DSC algorithm' I've looked through the help file but I can't really figure out what exactly this algorithm does?

Check this part of the help please:

http://docs.autodesk.com/RSA/2012/ENU/filesROBOT/GUID-16BFFEDB-D4E0-496D-B002-C361E21FEF8-254.htm

Also, is there any way to "separate" the two bars in the windcross from each other? so they're not joined on the middle, but are able to move separately?

By default they are not joined. To join them you would need to mark the option I indicated on the attached picture (or create a node at their intersection). You can check if the bars are joined at their intersections displaying numbers of calculation elements after generating the computational model of a structure.

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.

[Anonymous]

thanks alot guys.

I have already read through that help file, and I do understand that it makes a new virtual node, but what I do not understand is why it is necessary to run this algorithm?

[Artur.Kosakowski]

It is only a suggestion rather than a 'must'. The 'standard' approach for modeling releases ('removing of d.o.fs) may in some extreme situations (dynamics, non-linearity) produce inaccurate results (e.g. some bending moment value at releases end of a bar) but not for such types of model. Yet as this is possible (limitation of the method itself) the corresponding information is displayed.

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.

[Anonymous]

I don't really get a choice in the matter. It suggests that I should use the 'DSC Algorithm', but if I say no it won't do the calculations

[Artur.Kosakowski]

Assuming that we are talking about the same warning the question is if to continue and the answer should be yes. If this is not the solution send me the rtd file after compressing it (*.zip) please.

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]

Martin,

Have you managed to calculate your model? If you need any additional help let me know please. If the issue is solved please press the Accept as Solution button so that other users can find the solution faster. Thank you.

[Anonymous]

As it is a 'suggestion' and not a 'must' i would believe that I should be able to turn down the suggestion, as i don't really understand what this algorithm does.

I've attached the file in zip format for you to take a look at.

The wind beams is at the vertical wall at (x,y)=(0,0)

[Artur.Kosakowski · Accepted solution]

As I wrote previously the reason for this algorithm being available to decide on (in addition to the 'classic' approach for modeling releases) is the fact that is some 'extreme' cases (e.g. non-linear analysis that is 'difficult' to converge plus dynamics) it may produce more accurate results (e.g. eigenfrequences) than the other approach.

In the model you set in Job Preferences the use of the DSC algorithm. If you do so then the 'suggestion' is no longer displayed. You can save such Job Preference as the default one to 'avoid' this message to be displayed but mind that the DSC algorithm has got its limitation - it cannot be used together with offsets (to model e.g. a pinned ended beams under a slab or to generate additional bending on columns due to shear plate connection with beams) and this is one of the reasons it is not set as the default (despite the fact that is some 'extreme' situations it can be more accurate). In addition it doubles the number of nodes at released bar ends.

I hope this clarifies the situation.

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.