4. Methods for determining instability loads

The most frequently used methods for stability analysis of conservative systems are :

• adjacent-state equilibrium method ;

• energy method.

• The adjacent-state equilibrium method is used to study bifurcation instability. Its implementation is equivalent to a linear instability analysis. With this method, we examine whether, along a fundamental loading trajectory, there exists, for the same loading level, a possible adjacent deformed configuration in equilibrium, i.e. a configuration infinitely close to the fundamental configuration under consideration.

  Remember that the value of the load for which such an adjacent equilibrium configuration exists is called the bifurcation load, or elastic critical...