topic Re: Loose cable - thermal load in Robot Structural Analysis Forum

Loose cable - thermal load

Anonymous — Wed, 03 Apr 2013 12:40:52 GMT

Hello everyone

Hope you can enlight me on my problem.

I have two colums where there are a loose cable dangling between(se attached picture/sketch).

I wonder if it's possible to make the model, just with a thermal load and deadload?

The temperature goes from +30 oC to -20oC, i want to find the forces in the upper corners of the colums(the horizontal force) so i can figure out the moment in the foundation.

The big quastion is: it is possible to make the model?

Re: Loose cable - thermal load

Pawel.Pulak — Wed, 03 Apr 2013 12:52:44 GMT

Yes, it is possible to model and calculate such structure.

As concerns the sag of 2 meters in starting conditions it will be necessary to iteratively change cable parameters to obtain such value.

Regards,

Re: Loose cable - thermal load

Anonymous — Wed, 03 Apr 2013 13:30:02 GMT

Okay, good to know it's possible.

In the cable parameters i can choose "Elongation dl (or relative elongation)" or choose length (L). the model just seems straight, does it happes behind in the "background" so you cant see it?

I can't really see the difference in reactions, when just looking at two difference thermal loads.

I am a bit lost in how to set it up right.

I have attached my robotfile. the file is a bit of a mesh, but i have temp 1 og temp 2 too see if there where any difference in the reactions, temp 1 = -40 oC temp 2 = 0oC

Cant upload the .rtd file so i have put the extension txt to it, please let me know if you cant open it.

Best regards

Kim C.

Re: Loose cable - thermal load

Pawel.Pulak — Wed, 03 Apr 2013 14:56:34 GMT

Remarks related to your model:

1/ in structures containing cables the first load case is treated in Robot as assembling load case and it is automatically added to other load cases. That is why it is strongly recommended to apply selfweight and other dead loads in this load case for cable structures. In your model your have applied temperature load in load case 1 and dead loads in load case 2. I have inversed it in my modification of your model

2/ When I checked properties of the cable defined by you I have noticed that you have defined "Cable_2" with elongation of 2 meters. The distance of end nodes of this cable is 16 meters so cable elongation of 2 meters corresponds to unloaded length of the cable equal 16+2=18 meters. This cable length corresponds to the sag of this cable under dead loads exceeding 3 meters. I have modified it replacing it by relative elongation and finding (iteratively) such value of it that the cable sag for load case 1 is close to 2000mm. In such case after applying temperature load of -40 deg the sag is reduced only very slightly to 1989mm and the horizontal reaction is also changing very slightly - from 0.4891 kN to 0.4921 kN (see the screen capture below). It is so because the starting sag of the cable is significant, tension force in the cable is low and shortening of the cable caused by negative temperature is relatively small.Attached the model modified this way

The influence of temperature load would be more visible for the cable with smaller elongation and sag

3/ Other remarks related to the model

- I have not touched other properties of the cable - section of 1cm2=100mm2, material S 355. Probably it will be necessary to define something closer to reality:)

- there is no self-weight defined in load case 1 - I assume that UDL of -0.03 kN/m takes into account the self-weight of the cable

- there is no problem to consider in one model also the columns shown in the drawing from the 1st post

Regards,

Re: Loose cable - thermal load

Anonymous — Thu, 04 Apr 2013 07:46:12 GMT

That worked perfect!! thank you were much!!

It did just what i wanted!!

I didn't know that the first load was applied to every case, i normally do choose deadload as first but guess things went a little to fast to test this scenario!

Thank you again

Best regards

Kim Christensen

Re: Loose cable - thermal load

Anonymous — Wed, 01 May 2013 11:35:43 GMT

Hello again

This post is just to wrap it up.

I have made a couple of models afterwards with different scenarios and i will rather use the length parameter so i know how long the cable is, i can't find a feature that calculate the length of the cable if i use elongation length.
The final sag is iterated from the length.

Re: Loose cable - thermal load

Pawel.Pulak — Wed, 08 May 2013 14:59:39 GMT

Adding some info to already provided by ihk090040 :

it was mentioned that the length parameter of cable was used because "i can't find a feature that calculate the length of the cable if i use elongation length".

The picture below shows relation between them

Regards,

Re: Loose cable - thermal load

Anonymous — Thu, 23 May 2013 14:16:01 GMT

Hello Pawel

Thank you for the explaining

How do your show the length i the "bars" window?

I can't choose length when i right click -> Speciel filters -> Cables. All the checkboxes can't be checked.

Best Regards
Kim

Re: Loose cable - thermal load

Pawel.Pulak — Fri, 24 May 2013 08:28:31 GMT

Length of bars (including cables) is not available on the Edit tab of the Bars table:

It is available by default on the Value tab of the Bars table:

As concerns the availability of Length in Special Filter it is available also on the Value tab of the Bars table.

Regards,

Re: Loose cable - thermal load

Anonymous — Wed, 05 Jun 2013 10:54:11 GMT

Hello once angain

At first it worked perfectly i think, but when i look at my new model the length of my cables is the direct horizontal line from one node to the other.
Is it possible to show the exact length of the cable in the values tab??

When i change the Force the length is the same, but when i choose to change the Length L, the length in values is changed.