A boundary condition, also known as supports, defines how a structure is restrained from rigid body motion under the influence of external loads. You define supports using the six degrees of freedom; X, Y, Z, RX, RY, and RZ; applied in the global coordinate system.
This software displays supports using a unique indicator that appears at the member end. Indicators for fully fixed and RX, RY, and RZ fixed supports look like this:
Indicators for supports where RX, RY, RZ, or a combination of the three moment directions are released look like this:
You can pause over the support for a tool tip that displays the fixed/released directions of that support.
When you split a member system (using Place Split in the Structure task) that has boundary conditions defined, the boundary conditions remain on the ends for which they were defined. For example, if end 1 of the original member was fully supported (X, Y, Z, RX, RY, RZ) and end 2 was supported only in RX, and RZ. Then end 1 of new member 1 gets fully supported and end 2 of new member 2 gets the RX and RZ support. The new interior ends (end 2 for member 1 and end 1 for member 2) do not have any supports defined.
Releases define the type of connection; rigid, released, or elastic; between two member-part ends. Releases are defined using the six degrees of freedom: X, Y, Z, RX, RY, and RZ; applied in the local coordinate system of the member part.
A rigid connection does not allow the member part end to move in the specified direction at the connection.
A released connection does allow the member part end to move freely in the specified direction at the connection.
Releases are defined using the End Releases category on the Member Part tab of the Member Part Prismatic Properties dialog box.
When you split a member system (using Place Split in the Structure task) that has end releases defined for one of its member parts, the member end releases of the original member part are copied to the two new member parts.