RFEM6 - Problems with form-finding of cable structures

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1

Hello everyone,
I am currently working on the form finding for a suspension bridge. However, I am having trouble handling it. I want to shape the main cable into a parabola with a large sag, but I only get a parabolic sag of about a quarter of the height. How can I achieve this? I would also be open to a video call.
Here is the link to my program file: https://we.tl/t-XiZKhwtk5W
Thank you very much!

3

Hi fdoetsch,

Welcome to the community! :waving_hand::blush:

In form finding, the resulting shape always directly depends on your boundary conditions and loads. You can find a good overview in the online manual here:
:backhand_index_pointing_right: https://www.dlubal.com/de/downloads-und-infos/dokumente/online-handbuecher/rfem-6-formfindung/003571

If you don’t achieve the desired shape yet, you need to adjust these control parameters precisely – for example, in the supports, prestressing, or loads.
Unfortunately, we cannot offer a fixed recipe for this, as every model is individual. :wrench::slightly_smiling_face:

For inspiration and better understanding, we recommend taking a look at our examples and theses:

There you will find many practical approaches that can help you with your own modeling. :light_bulb:
If you have specific questions about your model, feel free to get in touch again – we are happy to support you! :rocket:

Best regards
Stefan Hoffmann

4

Hello Stefan,

thank you very much for the quick response! All right, then I will take a look and get back to you if necessary.

Best regards and Merry Christmas in advance :christmas_tree:
Fabian Doetsch

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5

Hello Stefan,

I have now looked at the examples and the manual and have chosen an approach for the model based on the relative bar length and additionally included the structural self-weight (without finishing loads) in the load case (as recommended in the manual). I found one example where the relative bar length was simply set to 100% and the shape of the cable already closely resembles a parabola. I adopted this approach in my model but am now unsure whether the results are actually correct.
I have attached my model. Many thanks in advance!

INPL - Projekt_grobe Geometrie.rf6 (2.0 MB)

Best regards
Fabian Doetsch

6

Hi fdoetsch,

unfortunately, we cannot directly tell you from your inputs whether the results are correct.

Form-finding is the process by which you find your geometry. If you are satisfied with that and the loads are derived, I think you are on a good path.
We cannot offer you an analysis on this topic from our side in this context.

Best regards
Stefan Hoffmann

7

Hello Stefan,
all clear, thank you very much for the feedback!
Best regards
Fabian Doetsch

2 Likes