Analisi del meccanismo del flutter per impalcati da ponte: sensibilità rispetto ai parametri dinamici della struttura

In this paper a simplified approach to flutter is discussed, based on the modification of a pair of formulas previously proposed by the writers. The validity of such equations was the object of a careful analysis, whose a few exemplary results are reported herein. Their limits of applicability are also clearly highlighted. The proposed method works fine both in case of classical and torsional flutter. In particular, it is possible to rearrange these equations in such a way that the critical condition for the two-degree-of-freedom instability is written in analogy to that for single-degree-of-freedom torsional flutter. The simplification of the problem allows an easier analytical investigation of the mechanism which leads to the instability onset and this made it possible to explain the origin of the distinction between hard- and soft-type flutter. In particular, it is explained under which conditions the structural damping relative to the torsional mode plays a significant role in delaying the occurrence of the aeroelastic instability. Finally, the simplified analysis of the flutter mechanism allows to draw some qualitative considerations concerning the way to tailor the dynamic parameters of a bridge structure in order to obtain a significant increase of the critical wind speed.