Hello,
I modeled a steel bridge in Grasshopper and I’m currently working on creating shop drawings and NC files. The polybeams are being unfolded in two directions, which is not useful. I converted them to lofted plates using a Grasshopper script, that part works fine.
However, generating unfolded drawings and NC files for most of these plates does not work, see message in the sreenshots. The shapes are not unusual or overly complex. I’ve tested this in both TS2021 and TS2025, but the result is the same. I also tried rebuilding the input curves for the lofted plates, etc.
I have attached a custom component (only parts) of a part of the bridge and the GH-script to convert the polybeams in to Lofted plates. The UEL Test-LoftedPlates-02.uel is the problem. The plates in Test-LoftedPlates-ThesePlatesAreFine.uel works fine.
What is the reason for this issue, and how can I fix it?
Kind regards,
Jan Van Loy
Test-LoftedPlates-ThesePlatesAreFine UEL.zip (11.2 KB)
Test-LoftedPlates-02-UEL.zip (262.6 KB)
ConvertPolybeams2LoftedPlates.gh (211.1 KB)
Hi Jan,
I think this is just down to lofted plates not being a very stable object type. They can easily become invalid and I suspect the same underlying instability is at play here. Unfortunately they’re not getting much love from the devs at the moment.
I’m not sure how to fix this directly other than tweaking the input curves or points through trial and error until you get something that works.
You could send the plates to your local support and see if they have any best practices for how they should be modeled, maybe that can be carried over to Grasshopper.
There are some potential workarounds though.
First, you could split the plate geometry up into triangular plates by using the Triangles Generation (19) component in Tekla and then unfold them with the Unfold Surface (21) component. These can both be controlled from Grasshopper.
Alternatively, you can create the unfolded geometry directly in Grasshopper by using e.g. the Unroll Brep component from the LunchBox plugin, or the Unroll component from the OpenNest plugin. Both seem to be able to handle this geometry. Then you use that to create unfolded versions of your plates in Tekla for fabrication output.
Whether this suits your workflow will probably at least depend on what further modifications you want to do to the geometry.
Cheers,
Sebastian
Hi Sebastian,
Thank you very much for the tips. For the main girders of the bridge, I managed to use lofted plates. I replaced the curves with arcs where possible and placed the welds where the double-curved plates begin. Grasshopper helped me a lot to convert the lofted plates.
It seems that when the radius of the lofted plates is too small, they are not unfolded. I did a test with two 100x100mm plates, bent. At 3mm bend 178°, they are unfolded, below that they are not. It’s strange, because there is no radius visible on the drawing, but it is shown on the drawing. Where does this radius come from and can I change the value? I played with the values in the unfold_corner_ratios.inp but without success.
https://support.tekla.com/video/how_to_correctly_unfold_parts_in_tekla_structures
For the deck plates, I will definitely take a look at your other suggestions: Triangles Generation (19) + Unfold Surface (21) and LunchBox.
Thanks again for the information and tips!
Kind regards,
Jan Van Loy
nice findings 1 mm shows no bend and 3 mm and above are considered as bend plates
is it any issue within the tolerance limit ???
That’s interesting, I’ll add this info to the tracking system. There’s a bunch of tickets similar to this one but they aren’t getting resolved at the moment - maybe this case helps pushing things along.
Here’s a definition to get you started with this approach, using the two edge curves as input to create triangles and unfold them:
