Learning Forum

[ravi123rkj]

Hi,

     I am working on a project on buckling analysis of stepped column. I got results for two modes. First mode seems correct to me but the second mode give a shape which I don't think is correct. Because it is showing local buckling. Please have look and tell me if it is correct or  there is something wrong with model itself.

[ravi123rkj]

And also when I decrease the load first mode shape is showing the similar pattern but in upper column

 

[jj77]

You have duplicate posts - delete one.

 

As for your model it seems that the web is buckling locally - it could be ok. 

 

To verify you can try doing a mesh refinement study or if possible some hand calcs - or compare with another software - to validate you would need to do tests.

 

If you also upload your model then some one might have a look

 https://forum.ansys.com/forums/topic/saving-sharing-of-working-project-files-in-wbpz-format/

 

[ravi123rkj]

Hi, 

   Thanks for such a quick reply.

   I have attached the project file please have look and tell me if something wrong in model. As I have already mentioned that when I decrease the load local buckling appears and this does not seem right to me.

[jj77]

OK - to verify the model :

 

Make a beam model also and compare the first global mode (first image in your post - Load Multiplier =18.689) to the shell model - then you will know that the model is OK (does not mean reality is like this - only validation can tell)

 

Realised you have 3D parts - at most use shells or beams (for global modes only - no web buckling). 

 

Also have in mind that the load multiplier multiplies the total load (so gravity too - which is not completely correct - you can take it of)

[ravi123rkj]

I think it will give me inaccurate results if I use beam elements instead of 3D elements that I have used. Since I am pretty new to the ansys could you please tell me how to take self-weight  off from being multiplied by load multiplier.

 

[jj77]

You model wit 3d elements that is not used for frame structure and way to coarse mesh. First thing. The beam model would be to verify the solid model. The gravity was just to delete it, otherwise it is part of the total load. Finally think why you are doing this analysis. Often the codes will tell you have to assess a frame type of structure. So figure out why you are doing this analysis. Are you designing this look on relevant codes then.

[ravi123rkj]

Hi,

      Actually we are working on a project in which we want to determine the critical buckling load of stepped column and will compare the values with relevant codes to see if there is a significant difference between these two.

[ravi123rkj]

Hi Are you suggesting that I should use the line body in the place beams instead of 3d body.
Please if you could clarify with in elaborate way what you are trying to say it would be a great help for us.

[jj77]

It depends what you want to do.

 

If you are looking on global buckling (Euler type), then beam elements are fine.

 

If you think that you might have some local buckling effects (e.g., web or flange buckling), then a shell model is needed.

 

Finally the results depend on the amount of imperfections and other factors that are there - so you need to apply those (imperfections) as it is on the built structure in order to match the two and in order to represent the real structure as much as possible.