Lattice Tower

[Anonymous]

Hi everyone.

I have a problem with my lattice tower project in Autodesk ROBOT 2015. 

At the beggining i must admit that the function of this tower is to support chimney.

So, I have added loads (permanent, dynamic, wind via claddings and forces from chimney), then added some releases and finally tried to calculate. Unfortunately a lot of errors and warnings appeared -especially "the instability in nodes", "matrix is not positive definity" and "No convergence of nonlinear problem". The last one problem is connected to every case which includes horizontal forces - wind.

I have also tried to chenge analysis type and parameters but nothing really happend.

http://www.filemail.com/d/bsfswjkcoaonlrn Here is my ROBOT file; if anyone can help me to solve this problem and get "real results" (not 1km displacement of nodes) i will appreciate it.

[Rafacascudo · Accepted solution]

on the released bars , use truss bars(geometry/additional atributes/advanced bar properties) instead.

Instabilities will vanish.

If you want P-delta analysis , your combinations also need to be P-delta , not only the simple cases.

Analysis do not converge.

Increasing the section sizes makes the analysis converge to all load cases and combinations

[Anonymous]

Hi Rafacascudo, thank you for your post.

"on the released bars , use truss bars(geometry/additional atributes/advanced bar properties) instead.

Instabilities will vanish."

I have used truss bars to all "X" bars (elements no 43to84) and now i have error "Incorrect use of tension/compression bar attribute for elastic-plastic member"...?

If you want P-delta analysis , your combinations also need to be P-delta , not only the simple cases.

Analysis do not converge.

Increasing the section sizes makes the analysis converge to all load cases and combinations

I have changed the type of analysis to P-delta but I do not understand your last sentence - what do you mean by "section sizes", and how can I increase them?

[Rafacascudo]

have you used truss bars(1st line on advanced bars properties)or tension only bars? No warnings here using truss bars.

Increase the size of your diagonal tubes , RO 63.5x5  and RO 88.9x6. If not enough  , increase also for the main vertical tubes

[Anonymous]

have you used truss bars(1st line on advanced bars properties)or tension only bars? No warnings here using truss bars.

Ok, now everything is right, and no warnings connected to this problem.

Increase the size of your diagonal tubes , RO 63.5x5  and RO 88.9x6. If not enough  , increase also for the main vertical tubes

I have tried to increase all tubes size, but still an error appears.

[Rafacascudo]

You have to test it. Increase more and more until it converges

[Anonymous]

Thank you my friend, everything works fine now!