Abstract
Since flutter phenomenon is catastrophic oscillation, its stabilization is very important subject in the design of long span bridge girders. Authors reported that flutter characteristics obtained by step-by-step analysis and Complex-Eigen-Value analysis showed perfect agreement. In this study, by using step-by-step analysis, three kinds of torsional divergence instability are clarified, and physical meanings of flutter branch are discussed in relation to fundamental flutter modes. Then, basing on step-by-step analysis in torsional branch characteristics, similar form of Selberg's formula, which evaluates flutter onset velocity, is described.
