Learning Forum

[Mazin Mahrouqi]

Hello everyone,

I'm conducting a nonlinear static pushover analysis on a transmission tower model in Ansys to assess its behavior under wind loading, considering the potential for buckling. However, I'm encountering convergence issues after applying approximately 33% of the wind load. I would greatly appreciate any insights or suggestions on resolving this problem.

Model Details:

• The transmission tower is modeled using BEAM188 elements.
• Material properties, including Young's modulus, Poisson's ratio, and density, are defined for different sections of the tower.
• Bilinear kinematic hardening is used to model the nonlinear behavior of the materials.
• The tower geometry is created using keypoints and lines, and the lines are assigned appropriate sections and material properties.
• Fixed boundary conditions are applied to the base of the tower.
• The first buckling mode shape is obtained through an eigenvalue buckling analysis.
• The tower geometry is updated with an imperfection factor based on the first buckling mode shape, and then static nonlinear analysis is applied for gravity load only first, and then wind load afterwards.

Loading and Analysis:

• Dead loads, including the self-weight of the tower and conductor weights, are applied.
• Wind loads are calculated based on the tower height, section properties, and wind speed using appropriate wind load coefficients.
• The wind loads are applied incrementally to the tower in the nonlinear static analysis.
• The pushover analysis is set up with nonlinear geometry (NLGEOM,ON), arc-length method (ARCLEN), and convergence tolerances for force, moment, and displacement.

Here is a snippet of my code for applying the wind pushover analysis:

antype,0    

TIME,2

CNVTOL,f,1e11,0.1,,-1

CNVTOL,m,1e9,0.1,,-1

CNVTOL,u,1e9,0.1,,-1

nlgeom,1    

outres,all,all  

arclen,1,25,0.00001  

arctrm,u,0.4,1886,ux ! this is only for trying to push the model past the nonconvergence point where the drift is around 0.15, using arctrm,l gives the same results

nsubst,10000,,,1  

ALLSEL

solve  

Issue:

• The analysis progresses smoothly up to approximately 33% of the wind load.
• Beyond this point, the analysis fails to converge, and the solution does not proceed further. I believe this is due to local buckling in some elements, but I can't seem to push the structure past this element buckling (since the tower itself did not buckle yet).
• I have tried adjusting the meshsize (currently 4 for all elements, tried 2,3,8, and 16), using the stabilize command, arc-length parameters, convergence tolerances, and substep settings, but the issue persists.

I would be grateful for any suggestions on troubleshooting this convergence problem. Are there any specific settings, modeling techniques, or analysis modifications that could help overcome this issue? Any guidance on improving the model's stability and achieving a successful nonlinear static pushover analysis would be highly appreciated.

Thank you in advance for your assistance. This is my first time posting on the forum, so if there is anything else I can provide to help clarify the issue, please let me know.

[Ashish Khemka]

Hi,

Please see if following forum thread helps: Arclength method does not gives converged solution in buckling analysis (ansys.com)

Regards,

Ashish Khemka