Movements at releases

[Anonymous]

Hi,

I've got some bars with axial releases, how can I find out the magnitude of axial movement taking place at the joints? Ability to envelope movement for several load combinations would also be very useful. Same with rotation at pins etc.

Thanks,

Rory

[Rafal.Gaweda]

I've got some bars with axial releases,

Do you mean unidirectional?

[Anonymous]

I'm not entirely sure what you mean by unidirectional. It's not a non-linear release or anything like that. Just a standard release in Ux at one end of a bar. Want to know the magnitude of differential movement between both sides of the release.

The context is that this is a simple structural movement joint, so I need to know the movement that needs to be allowed for in design of the joint.

[Artur.Kosakowski]

Check bar displacements. Mind to switch DSC on.

[Anonymous]

This might be a stupid question - where do I find the table from your screenshot titled "Displacements", and how do I get the "Bar value selection" window? I'm using Robot 2010 if that makes any difference.

I can't turn DSC on anyway because I have offsets in the structure.

Thanks

[Artur.Kosakowski]

---

This might be a stupid question - where do I find the table from your screenshot titled "Displacements",

and how do I get the "Bar value selection" window?

RMB > Table columns

I can't turn DSC on anyway because I have offsets in the structure.

Only when you have defined offset on the bar with releases. In such case you need to add an additional node close to the end one with the release and check its displacements instead.

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, couldn't find it because the table changes title when you change from "Maximum deflections" to "Bar displacements". Have tried this now but I'm just getting absolute deflections of each end of the bars in global axes, not a relative displacement in local axes which is what I need. Is this correct behaviour? Screenshot attached.

If this is correct it seems I can only work out the movement in line with the joint by calculating the difference in deflection components (UX, UY, UZ) between the end of one bar and the end of the connecting bar in global axes, and then working out the resolved magnitude of these differential components.

Not the end of the world but seems like a disproportionate amount of effort to post-process that manually for each load case for each joint, then envelope the results, to get what seems like a simple output? I was just hoping the results for this would be available as it must be a common set of results to require for joint design.

Thanks

[Artur.Kosakowski]

Bar results are displayed in their local coordinate systems

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]

So these results are overall absolute deflections of the end of each bar, in the bar's local co-ordinates? Even less useful then as I can't easily post-process in a spreadsheet to work out the difference between deflections of the the bar ends either side of the joint, as they are not in a consistent axis system due to different orientatons of the bars.

Seems like the output I'm after is not easily available, so I'll find a different approximate method estimate the values. Thanks anyway.

Rory

[Artur.Kosakowski]

I'm afraid that I'm lost at this point. Perhaps you could just make some sketch that illustrates the kind of results you need?

[Anonymous]

Hi Artur, try this attached as an idealised representation. I'm after the relative movement between the two sides of the release, in the released bar Ux direction. This is the amount of movement the joint should be designed for, eg. length of the slotted bolt holes, or size of the bearing, etc.

[Artur.Kosakowski]

In such case you can try to use the displacements of nodes (they are in the global coordinate system). To see the displacement in the calculation node (node 4 on the attached picture) you need to use the DSC algorithm.

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. I'll still need to work out the difference between the displacement of node 2 and node 4. That's OK, but I have quite a lot of these joints to check for several load cases each. Think it will still be easiest to estimate the numbers by hand.

Also as I can't turn on the DSC algorithm presumably I won't be able to see the calculation nodes anyway.

Cheers,

Rory

[Artur.Kosakowski]

Or 'allow' e.g Excel or API do this for you using the data imported from Robot

[Rafal.Gaweda · Accepted solution]

Try this:

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/API-macro-for-nodal-displacements-in-local-c...

[Anonymous]

The spreadsheet looks great, could definitely do a little light Excel work on the results and get exactly what I'm after, but there's still one big problem - I'm not picking up the calculation node at the end of the bar with the release, probably because DSC is turned off!

Is there any way around that, given that I have offsets elsewhere on the structure?

[Artur.Kosakowski]

You need to have DSC switched on to access this kind of results. Mind that the only limitation is when you have both offset and release defined on the SAME bar which I don't think is the case in your model. If it is you need to replace the offset with movement of the bar to its 'offseted' location and connect it with the rest of the model with rigid links or dummy (short) bars.

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 can't run the analysis with the DSC algorithm turned on - it gives an error to say it is not possible with offsets defined. I also have thousands of offset bars so changing those is not an option!

[Artur.Kosakowski]

Do you have the situation where you have releases and offsets defined on the same bars or the bars with offsets do not have releases?

What is your Robot version?

[Anonymous]

Yes there are some bars with releases and offsets elsewhere in the model, but the ones I want results for just have releases with no offsets.

Robot 2010. Apparently the scripts we use don't work with later versions so we need to stick with this. If 2012 would let me run the model with DSC enabled I could give it a go just for extracting results for these connections.