Higher-order self-excited drag forces on bridge decks

Nonlinear features concerning self-excited drag forces induced by the vertical and torsional motions for typical deck sections are investigated comprehensively in this study. The self-excited drag forces are calculated using computational fluid dynamics (CFD)-based numerical simulations. In a conventional analysis framework, the self-excited drag force is modeled as a linear function of the structural motions. However, the simulation results from CFD indicate that in many instances, the second-order (nonlinear) component of the self-excited drag force is more significant than the first-order (linear) component. To enhance the modeling fidelity of a conventional aeroelastic analysis framework on the basis of the semiempirical flutter derivative concept, a nonlinear mathematical model for characterizing both the first- and second-order components is developed to better quantify the self-excited forces and more accurately extract the flutter derivatives. Its efficacy and superiority compared with the traditional linear model is verified using different deck sections. For asymmetric bluff sections, the first-order self-excited drag force components are more significant than the higher-order ones. However, for streamlined plate-like sections and symmetric deck sections, i.e., streamlined and bluff, the second-order self-excited drag force components are predominant. For such cases, the proposed nonlinear model is more appropriate. The proposed nonlinear mathematical model can help to serve as a building block for developing an overall nonlinear analysis framework for accurately simulating nonlinear aerodynamics and the aeroelasticity of long-span bridges.