Joint Plane not forming: Issue or not?

Hi! Happy Holiday. I have a problem with regards to the formation of joint plane for my 3DEC model. So the pipeline of the block generation is as follows:

  1. Create an arch model using Grasshopper+Rhino so that I can alter the arch parameters easily.
  2. Bake the Grasshopper solids into extrusions.
  3. Import the extrusions as vrml separately. There were three layers of arches in my model and I imported them separately so that I could group each of the components easily.

Now, the block generation was done nicely (there were no concave shapes). However, when I checked the joint plane:

The connection between the arch and the 1st voussoir was not perfect, although when I used the “block contact gen-sub” command, the sub-contacts formed nicely (i.e, the contacts were forming where interactions were supposed to happen).

My question is: will this imperfect joint plane cause further problem to the mechanical calculation? I know that 3DEC define all of the contact properties to the subcontacts as well as the contact forces application, but I don’t know what would happen if I proceed with these imperfect joint-planes…


my guesses based on your images:

  1. yes, this could potentially lead to problems such as unrealistic stress concentrations and overlaps.

  2. I would guess that this happens since your blocks are not perfectly fitting to each other and/or still have slightly curved surfaces. This can lead to problems especially in you lowest row, since there also the grid spacing is mismatched. 3DEC has internal tolerances for what is “planar enough” and which planes are “close enough” to each other in order to create contacts. You could try to play around with those tolerances and make your model work.
    However, since you mentioned your workflow was designed for different shapes etc. I would much more suggest to modify your workflow to create perfectly planar and fitting blocks from the start. Otherwise you might have to fiddle around with tolerances for each model separately.

Hi Markus,

Thank you for your swift reply.
When you say “tolerances” did you mean altering the global tolerances using “block tolerance” command?

I think modifying workflow is the best solution for now…

There used to be different tolerances in 3DEC5.2 (atol,btol etc.), but I guess currently you can only adjust the global tolerance, e.g. increase it in your case. But maybe someone from Itasca can clarify better.

There are still different tolerances (see block tolerance command — 3DEC 7.0 documentation and block contact tolerance command — 3DEC 7.0 documentation). You might also check the number of significant digits in your output from Rhino. If you only have a few decimal places of accuracy, then you might have problems.

Markus and Jim,

Thank you so much for your answers. I will try altering the tolerances whilst modifying the workflow.

Have a nice holiday!