Force Peregrin to create Truss not Moment Frame?


During optimisation Peregrin sometimes converts the truss into a moment frame i.e. the elements are no longer pinned at their end points. Is it possible to force the optimiser to only consider solutions with pinned elements?


Hi Leo,

Peregrine does not currently have an option to turn the frame optimization component off.

However, it’s worth considering that the moment frame representation is an intermediate step within the stability restoration process. This step occurs when elements are removed and the structure is no longer in equilibrium. The optimizer then assumes a frame in order to provide a valid structure, while also attempting to restore stability for the reduced complexity pin-jointed situation. In most cases, the joints will still be pinned when the optimization is complete.

If a very large volume increase is seen to occur after the optimization process, then this is an indication that rigid joints may still exist in the structure after restoration, as bending moments will need to be resisted and require additional material.

Thanks for your quick response Tom!

Does Peregrin assume that the point supports resist rotations as well as translations? Currently I just want a point support that takes no moments. (60.4 KB)

Hi Leo,

When the frame representation is active, both rotations and translations are restrained to some degree. However, as mentioned, the software will try to push the structure back to a pin-jointed configuration during the restoration process and, in the majority of cases, the solution will end up as pin-jointed.