ABSTRACT
Let us consider the rigid bar shown in Fig. 1-la, supported at its lower end by a hinge and against rotation by a spring with the spring constant c. The spring be unstressed when the bar is vertical.
Loading the bar by a force P and rotating it by the angle <p we can write the equilibrium of the moments around point A:
A possible solution of Eq. (1-1) is ip = 0. The corresponding 'first equilibrium path' is to be seen in Fig. 1-lb, denoted by p\. The second possibility is tp ^ 0. In this case P is unequivocally determined by <p:
The corresponding 'second equilibrium path' p^ is shown by the upwards curved symmetric curve in Fig. 1-lb.
