Time-domain state-space model formulation of motion-induced aerodynamic forces on bridge decks

Motion-induced aerodynamic forces play a fundamental role in the stability and buffeting analysis of long-span bridges, which are traditionally performed in the frequency domain adopting the well-known approach based on flutter derivatives and aerodynamic admittance functions. However, the increase in span of newly designed bridges currently raises concerns regarding the role of nonlinear aerodynamic effects, the response to non-stationary winds and the aerodynamic coupling in multi-modal vibrations. Addressing these issues requires to calculate aerodynamic forces induced by arbitrary motions and, possibly, consider large variations in the incoming flow orientation, a task better suited for time-domain approaches. In this study, we introduce a time-domain state-space model formulation for motion-induced aerodynamic forces, which systematizes and generalizes previous models, while keeping a simple structure and ease of calibration. We tailor the model formulation to allow for a clear distinction between quasi-static and purely transient aerodynamic contributions and investigate the relations between the proposed model and other available models, highlighting their common underlying framework. The model is finally calibrated for a selection of bridge decks, showing a very good ability to reproduce motion-induced aerodynamic forces.