2. Types of elastic instability

When loading a structure – it will often be an elastic – structural element, and its behavior can be examined by means of a load-displacement diagram. The load is obviously that applied to the structure. The displacement is the displacement of a reference point, chosen a priori as arbitrary. In practice, this point is chosen because a significant displacement value is expected there.

When the load is applied in an increasing manner from a zero value, the load-displacement relationship described constitutes an equilibrium trajectory. The instability of the structure corresponds to the transition, on this trajectory, between the respectively stable and unstable equilibrium configurations. This instability occurs through the appearance of :

• of a bifurcation of equilibrium (figure