Zero stiffness elastic structures

In the paper, examples of neutral states of equilibrium, rare in the theory of elastic stability, are presented where the magnitude of the load maintaining equilibrium of the structure does not change even in the case of large displacements. The structures are able to change their shape without any additional external load. They behave like mechanisms. The first example is related to bifurcation of equilibrium paths, and the second is related to the snap-through type loss of stability of unloaded structures having a state of self-stress.