Modelling Surface (Shell) in AutoCAD - Then Prepomax

General Questions
1

Hello Everyone,

Apologies if this is a basic question.

I am currently trying to model a beam-to-column flange connection with an end plate using shell elements (not solids). The geometry is being created in AutoCAD using surfaces. Since surfaces do not inherently carry thickness information, I am unsure how much gap I should leave between the flange surface and the end plate surface before importing into PrePoMax, as I intend to define a contact interaction between them.

In my initial attempt, I placed both surfaces directly on top of each other, but I believe this approach is incorrect. I am now following the principle that shell elements are modeled at the mid-surface of the actual thickness. Based on this, if the end plate is 19.05 mm thick and the column flange is 11 mm thick, the gap between the two surfaces should be 15.025 mm, calculated as [(19.05 / 2) + (11 / 2)].

My question is, will this gap affect the contact definition in PrePoMax? Is this the correct approach, or is there a better way to handle this situation when working with shell elements?

Thanks in advance :slight_smile:

2

There are two ways to avoid overlapping:

  1. Leave a gap equal to (t1 / 2) + (t2 / 2) where t1 and t2 are thicknesses of both plates. This way, when they are expanded to solids from midsurfaces, they will lie exactly on each other.
  2. Use the Offset parameter when defining shell section - then you don’t need a gap. Offset is defined as a fraction of the shell section thickness and considers normal direction when evaluating the sign.

To visualize the expanded shells, you can right-click on the analysis and select Check Model.

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Thanks alot! @FEAnalyst . Besides your hlep here, I learned alot from your YT channel :slight_smile:

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