When moving part of a frame it is sometimes necessary to disconnect that part of the frame from the rest of the structure. To disconnect members from a model

§    Select the members to be disconnected from the rest of the frame

§    Choose Disconnect Members from the Advanced submenu in the Geometry menu

The command creates new joints at all the joints that connect the selection to the rest of the model. These new joints are then used to define the topology of the disconnected parts of the frame.