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Pin - Semi rigid - Fixed 1D beam analysis

Dirk76

Hello to everyone,

since, on a daily basis, I use Optistruct in order to perform analysis on steel structures I was wondering if there's the possibility to have semi-rigid constraints (see the image attached). Indeed in specific softwares used for steel strcutures it's possible, during the modeling phase, to choose a flexible hinge member by adding a torsional/translational spring coefficient in order to recreate a real situation of the joint (let's say I calculated the proper connection rigidity of my joint and I want to add it in my analysis to evaluate realistic deformations/internal forces of the steel members). In Optistruct you can choose between a pin member or a rigid member, but is it possible to choose a semi-rigid member? When I have to add a translational spring it's pretty easy and celas elements work fine, but when it comes to torsional springs things get complicated. I was trying a correlation with FTOOL, but I cannot find a way to make things work in Optistruct. Can someone give me an insight on a possible solution? Maybe you can help me correlate a simple model like the one in the image. Thanks in advance for any answers.

scheme.PNG

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OptiStruct

v2020.0

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Adriano Koga_20259

I believe you need to use the spring approach, but you can use the CBUSH element.

Inside the PBUSH property you can define the stiffness in all directions, including torsional stiffness. This would fit your needs.

The process is the same as creating a CELAS, the only change is the element type (CBUSH) and the property (PBUSH).

image.jpg

Dirk76

I believe you need to use the spring approach, but you can use the CBUSH element.

Inside the PBUSH property you can define the stiffness in all directions, including torsional stiffness. This would fit your needs.

The process is the same as creating a CELAS, the only change is the element type (CBUSH) and the property (PBUSH).

Hi Adriano,

thanks for the reply. In the image attached I usually use this approach for translational springs (celas instead of cbush), constraining at one end of the celas all DOF. If I use the same approach with cbush, the results obtained differ a lot from the one in FTOOL (displacement and internal moments). What am I missing? Can you explain me the passages I have to do, in the modeling phase, in order to define the correct behaviour of the rotational spring?

image.jpg