Mechanism Generation for Limit Analysis of Frames

A method is presented for the automatic generation of the required basic mechanisms for use in a limit (collapse) analysis of a planar structure. Constraint equations are written to ensure rigid body motion of all members and at the same time releases are introduced in a systematic fashion. The set of equations thus generated may be solved resulting in a set of basic mechanisms. These mechanisms are expressed in terms of the assembled structure's external degrees-of-freedom so that some additional modification is necessary to put them in the usual form of relative deformations for each member. The procedure only requires the joint geometry of the structure and the member connectivity. The method is therefore ideal for programming and removes the necessity for hand generation of the basic mechanisms in a limit analysis.