topic Re: BMD in Robot Structural Analysis Forum

BMD

Martinagrech27 — Tue, 05 Apr 2022 10:53:54 GMT

When using the automatic self-weight function in robot the BMD is coming incorrect and the model isn't even working as though it is symmetrical.

Any ideas

Re: BMD

EduardoMeruvia — Tue, 05 Apr 2022 11:22:48 GMT

Hi @Martinagrech27 ,

Would be easier to help if you can you upload your model.

If you can't upload your model due to privacy reason, some comments I would make is:

-Are your assumed end releases properly represented in your model, i.e. pinned, fix, rotational releases, etc.
-What elements are you using in your model? From the geometry of your model, seems like you might be using "cable" elements in combination with beam elements. Has the Joint between these two been checked as what is intended to be desgined?

-Is it a 2D or 3D model?

Re: BMD

Martinagrech27 — Tue, 05 Apr 2022 11:44:28 GMT

https://drive.google.com/file/d/1LELaoXtd6um2BeF367xBbrwOFk7_e0M9/view?usp=sharing

I have attached the model link.

Re: BMD

Simau — Tue, 05 Apr 2022 14:09:28 GMT

@Martinagrech27

Correct some errors:

- Select all PIPE_1 members and remove releases

- For non linear parameters

Check PDelta and Large displacements,

Check the 2 boxes Martix updadte...

Re: BMD

Martinagrech27 — Tue, 05 Apr 2022 14:34:04 GMT

@Simau thank you for your reply unfortunately after correcting these errors my model still doesn't seem to be behaving as it should. The pipe members which I made tension only members don't seem to be having a similar effect to cables and only large moments in the two pylons seem to be appearing.

Re: BMD

Simau — Tue, 05 Apr 2022 17:13:46 GMT

@Martinagrech27

Share your new model for verification

Re: BMD

Simau — Tue, 05 Apr 2022 18:27:30 GMT

@Martinagrech27

Sorry, the file a i attached previously was wrong.

Please find attached the good one.

I didn't try pipe members as cables

Re: BMD

Martinagrech27 — Tue, 05 Apr 2022 18:50:10 GMT

I am attaching my new model after making the amendments.

https://drive.google.com/file/d/12XiupFMyn5cUiLuT2hKAMJ9wf8keauIn/view?usp=sharing

Re: BMD

Simau — Tue, 05 Apr 2022 21:52:50 GMT

You didn't set non linear parameter for case 2 as i told you in message 4

Re: BMD

Martinagrech27 — Wed, 06 Apr 2022 06:25:14 GMT

@Simau These are set this way am I missing something else please ?

Re: BMD

Simau — Wed, 06 Apr 2022 12:57:38 GMT

@Martinagrech27

You have to set case 3 as auxiliary as you can't use moving loads directly with non linear analisys.

File attached

Re: BMD

Martinagrech27 — Wed, 06 Apr 2022 15:25:44 GMT

@Simau Yes thank you now the model seems to be working well although the influence line function isn't