Characterization of vibration amplitude of nonlinear bridge flutter from section model test to full bridge estimation

Abstract This paper presents a comprehensive study of nonlinear flutter characteristics of a bridge deck section through free vibration wind tunnel testing and theoretical analysis. The section model is spring-supported in a single degree of freedom (SDOF) in torsion and 2DOFs in both vertical direction and torsion, respectively. The amplitude-dependent aerodynamic damping and other response characteristics are determined through use of Hilbert Transform of response time histories at different wind speed of smooth flow. An approach is proposed to extract flutter derivatives as nonlinear functions of amplitude of torsional motion at various reduced wind speeds. The flutter derivatives are then used to estimate the nonlinear flutter response of bridge section and a prototype suspension bridge with a main span length of 1700 ​m. The results showed that the magnitude of negative aerodynamic damping increases with increasing wind speed but decreases with vibration amplitude. The flutter of this bridge example is initialed from torsion but the coupled vertical motion further generates negative damping, thus reduces the flutter onset wind speed and increase the vibration amplitude. The estimation using three-dimensional bridge model with coupled vertical and torsional modal responses leads to increase in flutter onset wind speed and decrease in flutter amplitude as compared to section model estimation.