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Instability and Large Deformation

AX.GRAVITY
Explorer

Instability and Large Deformation

AX.GRAVITY
Explorer
Explorer

I have a 3D steel frame model (version 2020)with gravity load applied ( no lateral load applied). There is no bracing member in the model because I assume the lateral load will be taken by reinforced masonry walls around the perimeter. Here is my the problem/questions regarding the attached models:
- Initially, I released all the beams as pinned-pinned to sizing the members, you can see there are lots of instability warnings in Model "Steel Frame_v20(All Released)" and huge deformations

- Then I tried to change back some released beams back to N/A, around the nodes which were warned had instability; and end up with the model "Steel Frame_v20(Not All Released)"  WITHOUT ANY WARNING.

 

My questions(please see the attached models):

1. Was it a correct way I tried to eliminate the warnings?

2. I changed some beams as non-released, so there will be some negative moment at end of the beam and the positive moment in the mid-span would be smaller than that when the beam is pinned-pinned. Will this influence the beam size?

3. In the model "Steel Frame_v20(Not All Released)", the frame has side-sway under only gravity load. Is there something wrong or is it normal because of the unbalanced gravity loads? 

4. If the side-sway is normal and due to unbalanced gravity load, why there is no side-sway in the model "2D FREAM" which I applied unbalanced load for testing purpose? 

 

Appreciate your response

 

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Stephane.kapetanovic
Mentor
Mentor

Too much released: degrees of freedom must be reviewed

- Columns nodes turn free around Z global Axis 

Capture.JPG

 

- in that case, beams nodes turn free around XZ global Axis (check also Y along all beams - instability 1)

Capture1.JPG

best regards

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AX.GRAVITY
Explorer
Explorer

Thank you so much for your response.

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Stephane.kapetanovic
Mentor
Mentor
Accepted solution

If my answers enabled you to solve your problem, you can close the subject by accepting the solution.

Best regards

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