Space truss anaylsis

Forum for asking and answering questions related to use of the OpenSeesPy module

Moderators: silvia, selimgunay, Moderators

Post Reply
vamsio
Posts: 6
Joined: Sat May 09, 2020 8:34 am

Space truss anaylsis

Post by vamsio » Sun May 10, 2020 8:39 am

Can nay one help me with the analysis commands to be given ofr a space truss analysis?

zhum
Posts: 11
Joined: Fri Apr 01, 2016 3:03 pm

Re: Space truss anaylsis

Post by zhum » Wed May 13, 2020 7:34 am

It's not clear what analysis commands are you talking about?

vamsio
Posts: 6
Joined: Sat May 09, 2020 8:34 am

Re: Space truss anaylsis

Post by vamsio » Thu May 14, 2020 4:59 am

Thanks for your reply.

Im new to opensees so im struggling to understand what are the exact commands to be given for executing analysis of space frame

Can you please suggest whether below commands are correct for a space truss analysis

model('basic', '-ndm', 3,)


# create SOE
system("BandSPD")

# create DOF number
numberer("RCM")

# create constraint handler
constraints("Plain")

# create integrator
integrator("LoadControl", 1.0)

# create algorithm
algorithm("Linear")

# create analysis object
analysis("Static")


Im getting belwo error

WARNING BandSPDLinLapackSolver::solve() - the LAPACK routines returned 3
WARNING Linear::solveCurrentStep() -the LinearSOE failed in solve()
StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at load factor 1
OpenSees > analyze failed, returned: -3 error flag

My code is available at below link

https://colab.research.google.com/drive ... sp=sharing

zhum
Posts: 11
Joined: Fri Apr 01, 2016 3:03 pm

Re: Space truss anaylsis

Post by zhum » Fri May 15, 2020 2:49 pm

It's generally difficult to say if they are correct without the model. The error suggests there are errors in the model not in the analysis.


vamsio wrote:
> Thanks for your reply.
>
> Im new to opensees so im struggling to understand what are the exact commands to be
> given for executing analysis of space frame
>
> Can you please suggest whether below commands are correct for a space truss analysis
>
> model('basic', '-ndm', 3,)
>
>
> # create SOE
> system("BandSPD")
>
> # create DOF number
> numberer("RCM")
>
> # create constraint handler
> constraints("Plain")
>
> # create integrator
> integrator("LoadControl", 1.0)
>
> # create algorithm
> algorithm("Linear")
>
> # create analysis object
> analysis("Static")
>
>
> Im getting belwo error
>
> WARNING BandSPDLinLapackSolver::solve() - the LAPACK routines returned 3
> WARNING Linear::solveCurrentStep() -the LinearSOE failed in solve()
> StaticAnalysis::analyze() - the Algorithm failed at iteration: 0 with domain at load
> factor 1
> OpenSees > analyze failed, returned: -3 error flag
>
> My code is available at below link
>
> https://colab.research.google.com/drive ... sp=sharing

vamsio
Posts: 6
Joined: Sat May 09, 2020 8:34 am

Re: Space truss anaylsis

Post by vamsio » Fri May 15, 2020 10:30 pm

Once again thanks for reply.

The model data and code is available at below google colab notebook link

https://colab.research.google.com/drive ... sp=sharing

Pl. review and suggest the corrections

mhscott
Posts: 444
Joined: Tue Jul 06, 2004 3:38 pm
Location: Corvallis, Oregon USA
Contact:

Re: Space truss anaylsis

Post by mhscott » Mon May 18, 2020 8:10 pm

You need to set 3 degrees of freedom per node (ndf=3) for space truss analysis. The default is ndf=6 for ndm=3 models, so there are three rotational DOFs at each node that assembly zero stiffness, and thus the errors with the equation solver.

model('basic', '-ndm', 3,'-ndf', 3)
Was my answer helpful to you? https://www.buymeacoffee.com/mhscott
Do you need extra help with OpenSees? https://courses.silviasbrainery.com/

Michael H. Scott, Ph.D.
OpenSees blog: www.portwooddigital.com

vamsio
Posts: 6
Joined: Sat May 09, 2020 8:34 am

Re: Space truss anaylsis

Post by vamsio » Tue May 19, 2020 10:54 pm

I missed basic input :) . Thanks for correcting me, Professor.

But my problem is still not solved. Same error is coming after charging the supports and load to match 3 dof.

Can you please again look into my code?

In general we get matrix singularity problem for space trusses quite often in Staad pro analysis and it adds weak spring at that location and direction. Is there any thing similar tweaks we have to do in openness also?

code link:

https://colab.research.google.com/drive ... sp=sharing

mhscott
Posts: 444
Joined: Tue Jul 06, 2004 3:38 pm
Location: Corvallis, Oregon USA
Contact:

Re: Space truss anaylsis

Post by mhscott » Wed May 20, 2020 6:57 am

No, there's no way to add weak springs automatically. You probably have a missing element leading to a local rigid body mechanism. Have you tried plotting your model using the rendering functions in OpenSeesPy?

https://openseespydoc.readthedocs.io/en ... tcmds.html
Was my answer helpful to you? https://www.buymeacoffee.com/mhscott
Do you need extra help with OpenSees? https://courses.silviasbrainery.com/

Michael H. Scott, Ph.D.
OpenSees blog: www.portwooddigital.com

vamsio
Posts: 6
Joined: Sat May 09, 2020 8:34 am

Re: Space truss anaylsis

Post by vamsio » Sun May 24, 2020 2:54 am

Your observation is correct professor. The structure has some element not connected properly I fumbled with Y and Z axis . I thought Y as vertical axis.
Now its working fine Thanks for your support

model pot command has some issues in google colab environment (Im not testing in other environment) I think there is no option to control scale. Without applying scale factor we are unable to view entire structure in the small window.

Post Reply