What is the "fixed" boundary condition mean compared to 0mm?

General Questions
1

Very new to ProPoMax and FEA in general. I’ve seen in other threads that Fixed is often used when you have multi-step analysis, but I’m not sure what it actual causes.

2

Do you mean Fixed boundary condition type where you don’t select the degrees of freedom or Fixed setting for individual DOFs available in the Displacement/Rotation boundary condition type?

3

Type “Fixed” create boundary conditions, all degrees are fix: x, y, z, rx, ry, rz. In PrePoMax you can see keywords, Menu: Model - Edit Calxulix Keywords:
*Boundary
Node-set-fix, 1, 6, 0.0
…
here 1=x; 6=rz. Or do you mean something different?

4

Fixed setting for DOF in the Displacement/Rotation BC is what I meant, apologies. I’m not sure how that is connected to multi-step analysis, or how it differs from just setting any particular DOF to 0mm

5

Then this is explained here (point 3): Understanding multistep analyses

It’s often used for bolt modeling to freeze pre-tension in the second step with actual loading applied.