Influence of structural nonlinearities and along-span wind coherence on suspension bridge aerodynamics: numerical simulations on simplified structures

The response of suspension bridges to wind excitation is studied by means of numerical simulations with a specifically developed finite element program implementing full structural nonlinearities. A pure time-domain load model, linearized around the average configuration, is considered. The self-excited effects are included by means of the indicial function formulation, whereas the buffeting is considered according to the quasi-steady model. The response to turbulent wind, both fully and par-tially correlated, is evaluated through a Monte Carlo approach. In order to reduce the computational costs of the simulations, a simplified structural model is considered, where only two cross-sections are modeled. This allows a high reduction of the number of degrees of freedom (DoFs), maintaining however many characteristics of the true bridge, precluded to the classical 2-DoF sectional-model (e.g. considering more than two modes at the same time, including geometrical nonlinearities and hanger uni-lateral behavior, introducing along-span wind coherence). The case study of a long-span suspension bridge is analyzed. It is observed that structural nonlinearities deemphasize the presence of a critical flutter wind velocity, as they limit the oscillation amplitudes. On the other hand, fully correlated flow may produce an important underestimation of the structural response.