Post-critical behavior of galloping for main cables of suspension bridges in construction phases

Abstract

The main cables of suspension bridges show various cross-sectional shapes with the evolution of construction phases, and they may suffer from severe galloping at certain conditions. The aim of this work is to provide a convenient tool for predicting the critical condition and galloping amplitude of main cables, and to explore the in-depth driving mechanism of nonlinear galloping. Firstly, a numerical scheme of fluid–structure interaction (FSI) was developed to predict the galloping performance of main cables, and the numerical results of both critical conditions and vibration amplitude of galloping were compared to those of wind tunnel tests. The validated computational scheme was then used to investigate the driving mechanism of nonlinear galloping from the perspectives of nonlinear aerodynamic damping and work of aerodynamic lift. Moreover, the amplitude dependencies of unsteady and nonlinear aerodynamic lift were studied. It is found that the hysteresis of the flow with respect to the motion of the main cable is an important reason responsible for the nonnegligible unsteadiness in aerodynamic lift. Remarkable multiple-frequency components of aerodynamic lift emerged at large vibration amplitude, which were caused by the variation of instantaneous relative wind incidence angle for main cable in oscillation. Low-order harmonic components of aerodynamic lift at small vibration amplitude were the trigger of galloping, while the high-order components which contribute negative work at large vibration amplitude were responsible for the nonlinear aerodynamic damping and limited cycle oscillation. Unsteady characteristics of aerodynamic lift were the main cause for the variation of work proportions between different order harmonic components.