topic Re: Truss Frame Structure in Robot Structural Analysis Forum

Truss Frame Structure

Anonymous — Thu, 26 Jul 2018 09:06:47 GMT

Hi, I'm designing a truss frame structure with roof and wall bracing, however, I'm getting a stability error 2 when I change my supports to pinned and not sure why. I have made all truss and bracing members compression/tension elements with N/A supports. Does anyone have a solution for this?

I have attached the model.

Thanks

Re: Truss Frame Structure

saclovitzky — Thu, 26 Jul 2018 13:27:16 GMT

I do not have any problems running it.

Re: Truss Frame Structure

Anonymous — Thu, 26 Jul 2018 13:42:56 GMT

Hi, running it is not a problem. I want to change the supports to pin
ended, however, it gives me stability errors when I do that.

Re: Truss Frame Structure

Artur.Kosakowski — Thu, 26 Jul 2018 15:51:11 GMT

Hi @Anonymous

Set the posts and diagonals as truss bars (no bending) but keep the chords continuous.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

Re: Truss Frame Structure

Anonymous — Thu, 26 Jul 2018 16:13:43 GMT

Thanks for the reply Artur,

I tried changing them to truss bars, however, it automatically ticks tension/compression box. I'm also not getting any tension in my bottom chord when I apply an area load, it shows everything acting in compression. I have uploaded the updated model with area load.

Thanks for you help, really appreciate it.

Re: Truss Frame Structure

Artur.Kosakowski — Thu, 26 Jul 2018 18:06:20 GMT

Hi @Anonymous

I unmarked tension/compression box leaving only truss marked on my picture :-).

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

Re: Truss Frame Structure

Anonymous — Thu, 26 Jul 2018 18:28:15 GMT

Hi Artur, sorry I was highlighting them all and then opening the dialogue box expecting them to be on just truss, bit it's a command. However, i'm still getting a instability type 2 when i convert all the base connections to pinned as shown below. There is something which is also affecting my axial force, the bottom chord is showing that it is in compression as well as the top chord which cannot be correct. I can't seem to find what the problem is with this one.

Thanks

Re: Truss Frame Structure

Artur.Kosakowski — Thu, 26 Jul 2018 18:56:14 GMT

Hi @Anonymous

Why RZ at the reactions shouldn't be blocked? Do you allow the columns to rotate about their own axes?

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

Re: Truss Frame Structure

Anonymous — Thu, 26 Jul 2018 19:12:18 GMT

Hi artur, thanks for the reply. I thought by having beams at the other end, this takes care of rotation of columns, I've seen other models with pinned bases and no stability error. Do you know why I'm getting compression in the bottom chord?

Re: Truss Frame Structure

Artur.Kosakowski — Thu, 26 Jul 2018 19:35:05 GMT

Hi @Anonymous

Try to block RZ at supports (otherwise you'd need to carefully explore the releases and truss bar arrangement) so that there is no instability. Calculate the model - hopefully tere should be no compression there. If there is and check the deformation shape which should give you the answer for your question.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

Re: Truss Frame Structure

Anonymous — Thu, 26 Jul 2018 20:12:41 GMT

Hi Artur, I understand the releases, however, the deformation shape shows the correct outcome. I really don't know what's causes compression in the bottom.

Re: Truss Frame Structure

Artur.Kosakowski — Thu, 26 Jul 2018 20:36:28 GMT

Hi @Anonymous

Could you attach the latest version of the model?

Try to display diagrams in this way:

Re: Truss Frame Structure

Anonymous — Thu, 26 Jul 2018 21:02:17 GMT

Hi Artur, i've uploaded it. The numbers also show that the bars are in compression. I've double checked everything. If you could have a quick look over it, it will be much appreciated. I currently don't have anyone in office to look over it.

Thanks

Re: Truss Frame Structure

Artur.Kosakowski — Thu, 26 Jul 2018 22:01:03 GMT

Hi @Anonymous

You either need to allow the bottom chord to move horizontally (so that it is not restrain by columns) or change its shape:

If one or more of these posts answered your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.

Re: Truss Frame Structure

Anonymous — Thu, 26 Jul 2018 22:13:56 GMT

Hi Artur, the bottom chord should go into tension no matter what due to the
truss load.

Re: Truss Frame Structure

Artur.Kosakowski — Thu, 26 Jul 2018 22:41:52 GMT

Hi @Anonymous

I disagree. IMHO this depends on the column deformation.

Re: Truss Frame Structure

Anonymous — Fri, 27 Jul 2018 00:25:57 GMT

Thanks for the reply and sorry for all the questions. I created a separate
model and it shows the results differently. I have attached it.

Re: Truss Frame Structure

Anonymous — Fri, 27 Jul 2018 10:11:12 GMT

Hi Artur, I agree with what you said and I've checked it. I'm not sure why, but i'm getting stability errors after changing the bases to fix in rotation about it's own axis. I have attached the model if you have time to have a quick look.

Thanks

Re: Truss Frame Structure

Artur.Kosakowski — Wed, 01 Aug 2018 13:45:03 GMT

Hi @Anonymous

What about the top roof purlins?

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

Re: Truss Frame Structure

Artur.Kosakowski — Thu, 02 Aug 2018 07:38:23 GMT

Hi @Anonymous

Can we consider this topic as solved?