Understanding self-weight and reactions


I’m sure I’m missing something simple but I can’t see it. I’m trying to understand how to change the self-weight and what units this is in?

I’m also trying to see the reaction forces in terms of their numerical quantity and their units. Is there a method to see the resultant force, say in kN?

Thanks in advance

I think I’m close to finding the answer in the ‘Modify Form/Force Diagram’, but I’m not sure on the definitions for the titles, i.e. Imax, Imin, q, a, etc

Any advice is appreciated

Hi @Ewan. The selfweight of the shell at each vertex is computed by using the vertex attribute t (thickness, which is 1.0 by default, and it can be modified in DiagramAttributes of FormDiagram or ThrustDiagram), multiplied by its tributary area and the density (default value is 1.0, but this currently cannot be modified).

As you have already alluded to in your post, this selfweight value is unitless. In graphic statics, the scale or unit of form and force diagrams can be defined freely by the user. For example, if the unit of your Rhino model is in meters, you could define the scale of your work session or drawings as 1m = 1kN.

At the moment, we do not have a visualisation feature to display the reaction force magnitudes. However, this information can be accessed in the “vertices” tab of the DiagramAttributes of either the FormDiagram or the ThrustDiagram. The vertices marked in red are the supports, where external reaction forces are present; attributes rx, ry, and rz as (rx, ry, rz) reprsent the resultant vector that corresponds to the reaction force at that support vertex.

Hello @juney.

Ah okay, I see now, thank you for the explanation.