How to output section forces for a beam element (B31)?

General Questions
1

Hello everyone,

I am trying to get internal section forces (forces and bending moments) for a beam element (B31) in PrePoMax. I am using this beam element to model a bolt in my assembly.

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2

Check this thread on the FreeCAD forum: https://forum.freecad.org/viewtopic.php?t=102723#p868955

Basically, for reaction forces (where BCs are applied) you can use:

*NODE PRINT, NSET=nset_name
RF

while for section forces and moments you need something else like *SECTION PRINT or *EL FILE, SECTION FORCES.

The syntax for section forces is:

*EL FILE, SECTION FORCES, OUTPUT=2D
S, NOE

Section print needs a surface and for beams it can be tricky.

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3

Thank you for your answer. I need some help with the following issue. When I apply a horizontal load, the upper plate moves by several kilometers (flies away). The beam element is defined between two Reference Points, which are connected to the hole surfaces using a Rigid Body constraint. What could be causing this rigid body motion/instability?

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4

Check this thread: Beam Element connections between Two plates (2D)

And this: Simplified bolt connection with beam element and rigid constraints - #100 by FEAnalyst

Modeling bolts with beams in CalculiX is rather problematic. You may actually need 3 beams per bolt to avoid the hinge effect. And rigid body constraints may not work well with them.

Alternatively, you could use spring elements, but there can be similar issues with them.

In fact, it’s usually best to just model the bolts as simplified solids - just cylinders.

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