topic Re: How to set the moment signs for circular shells in Robot Structural Analysis Forum

How to set the moment signs for circular shells

araj6G9PY — Tue, 24 Jan 2023 17:13:16 GMT

Hello,

I am looking at modelling a tunnel section with openings as can be seen in the image (Image 1). It is currently a circular shell with spring supports and point loading.

How can I set the sign convention for the moments in "Maps" such that if the Mxx or Myy is sagging inwards into the tunnel, then it is positive and if it is hogging out of the tunnel, set it as negative.

When I do a panel cut then you can see at the bench (x-x axis = 0), the tunnel is sagging inwards; however, in the maps the sign convention goes from positive for sagging for the positive x axis and negative for sagging in the negative x axis (Image 2). How do I set it to be either positive or negative, no matter where the shell sits relative to the x axis. I did also create the geometry such that the local axis point in the same directions (Image 3). Please could you help me with this. Thank you.

Re: How to set the moment signs for circular shells

Rafacascudo — Tue, 24 Jan 2023 22:05:36 GMT

The panel local Z axis dictates the moment signal.It means that if map gives a positive value ,then the panel face on the side of the panel positive Z local axis is being tensioned.

So ,if you want maps with inversed signals just invert the panel local Z axi on Geometry/Properties/Local panel direction

Re: How to set the moment signs for circular shells

araj6G9PY — Wed, 25 Jan 2023 09:33:03 GMT

I have also done this check with the local z axis (red) pointing inwards for the bottom half but still the moments sign conventions do not align around the x axis (Figure 6). As you can see, now "Maps" is showing sagging as negative above the global x axis and then sagging as positive below the global x axis (Figure 4). The cross-section confirms that the tunnel is sagging around the global x axis, not sagging and hogging.

I want "Maps" to show the moments as either positive or negative (whichever) both sides of the global x axis. I want the output to be consistent. Please could you help me with this. Thank you.

Re: How to set the moment signs for circular shells

Rafacascudo — Wed, 25 Jan 2023 11:36:46 GMT

Please zip and attach the model

Re: How to set the moment signs for circular shells

araj6G9PY — Wed, 25 Jan 2023 14:01:36 GMT

Please find attached the zipped folder with both the models. Thank you

Re: How to set the moment signs for circular shells

Rafacascudo — Wed, 25 Jan 2023 19:27:24 GMT

In fact,maps displayed obbey to the FEs local system which generally agree with the parent panel local system . But ,strangely for me , that is not what happens in your model. FEs local system of Botton part agrees with the panel local Z(outwards) while in the upper part FEs local Z is pointing inwards.And yes , I am talking about the model where it points outwards all around.

Tried to fix it but I was not able to.

I noticed you used the solid modeler , which I never use. Maybe official autodesk support can help you further

Re: How to set the moment signs for circular shells

araj6G9PY — Thu, 26 Jan 2023 09:14:21 GMT

Thank you for checking the model. I'll go ahead and seek official autodesk support.

Re: How to set the moment signs for circular shells

araj6G9PY — Thu, 26 Jan 2023 10:58:26 GMT

For a solution to this problem, please refer to this video:

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