bush or bar element, which is more conservative or accurated and why?

[marulanda]

As the title I'would like to know which is more conservative or accurated and why?
Considering bush or bar elemnt to simulate a fastener.

Regards

 

[SWComposites]

Depends on how you set up the model. They can be made to give the same result, with appropriate input properties.

And "accurated" is not a correct term.

 

[rb1957]

Please explain further, since CBUSH and CBAR are very different elements.

Maybe you're referring to modelling fasteners ?

another day in paradise, or is paradise one day closer ?

 

[marulanda]

I'm referring to the fasteners, as I wrote in the first post,
Thanks for your interest,
Regards.

 

[rb1957]

oops, mea culpa.

either works, both have "issues". Beam elements look more natural but you need to ensure the correct end conditions, particularly if you are joining solid elements (which don't have rotational freedoms.



another day in paradise, or is paradise one day closer ?

 

[AMA_Colin]

Hello Marulanda
You probably don't realize that you just waded into a topic of much discussion in FEA. The short answer to your question is: Neither is necessarily more accurate/conservative than the other since you can tailor the properties (stiffness) of either to be whatever you want.

I typically will use a CBUSH element where the connecting joint is coincident. Beam elements won’t work here because they need to have a finite length. CBUSH elements are also great because you can easily pull the forces that go through the joint just by looking at the element forces. They can also be easily tailored (ie. You can easily change the stiffness right in the bulk data deck for quick parametric studies of joint stiffness).

That being said, beam elements are easy to get forces just from the element force output and you don’t have to worry about putting in the orientation system. And as rb1957 mentioned, with beams you need to make sure to get your end conditions correct based on the element you are connecting to. Also, with beam elements you have to be concerned about the length of the beam. If it gets “long” (this is relative) enough it can potentially make your joint more flexible than you might want.

All in all, you can use either, and I have found that it’s mostly a preference of the engineer. Hope this helps!