topic Re: P-Delta not converging in Robot Structural Analysis Forum

P-Delta not converging

tom.krok — Wed, 06 Dec 2017 14:20:47 GMT

Hi,

I am trying to design the top chords of bridge trusses using initial imperfection as a bow (robot feature - geometrical imperfection) and running a P-Delta analysis but it cannot converge. What is wrong?

Also, I would imagine the larg deformation would be needed.

Please advise.

the file is there https://inertiaconsulting-my.sharepoint.com/personal/tom_krok_inertiaconsulting_co_uk/_layouts/15/guestaccess.aspx?docid=1a6ebcf84f0f2481093e8ab6313290f06&authkey=ASlLZl407FaKY1-sDGpzvAo&e=4c983974eee44c10a1309903c2dd86fa

Re: P-Delta not converging

mustafahesenow — Mon, 15 Jan 2018 08:39:45 GMT

Hi @tom.krok

Sorry for late reply . I had checked this model .In order to check the problem I deactivate the nonlinear analysis of case no 1312 then I run simple static analysis to check if there is problems .

1- I found out that there is 2 panels assigned as cladding No 95 and 96 are not attached to the structure and every time I delete them they come back .

I made repair mode not working . Then I open new file and I copy your structure to it without this panels but still the same .

See attached picture :

Re: P-Delta not converging

tom.krok — Mon, 15 Jan 2018 08:52:24 GMT

Thanks Mustafa,

Sometimes I create another model where the deck, a steel plate, is modelled as a cladding (floor can only be in true horizontal plane) to avoid using FEM shell. This is because the deck/shell is much weaker than the main structure and when performing the buckling analysis, deck buckles first for a vast amount of modes. So, having a deck as a cladding gives me the possibility to do the buckling analysis of the main structure and find the buckling mode relevant to top chords.

Best regards.

Tom

Re: P-Delta not converging

mustafahesenow — Mon, 15 Jan 2018 09:29:38 GMT

Hi Tom ,

I already solve this issue related to panels .

I did one thing as you mentioned for the steel plate i had made it as cladding and I run linear static calculation .

There is instability on Uy direction which is almost 304 mm which is very large displacement and for sure if you go to P-delta will give non convergence .

Re: P-Delta not converging

tom.krok — Mon, 15 Jan 2018 09:47:48 GMT

Thanks Mustafa,

It seems you have a higher version of Robot than mine 2017. I tried to find the install for 2018 and could not find it on Autodesk web page, where it is?

Best regards,

Tom

Re: P-Delta not converging

mustafahesenow — Mon, 15 Jan 2018 09:51:03 GMT

Hi @tom.krok

Here it is

https://www.autodesk.com/products/robot-structural-analysis/overview

You can also open it in 2017 with repair mode .