Stability of columns and strings under periodically varying forces

1 Numbers in square brackets refer to the bibliography at the end. 2 A special case of this problem has been treated by I. Utida and K. Sezawa [16].8 Analogous problems for plates under loads in the plane of the plate have been considered by R. Einaudi [l ].4 We consider always that the applied forces are simple harmonic functions of the time-otherwise we should have to deal with the more general Hill's equation.