Improvement of Scanlan’s Nonlinear Model based on Residual Analysis

Scanlan’s semi-empirical nonlinear model has been widely applied in bridge engineering because of its simplicity. However, it is based on the oscillation displacement, and thus it fails to describe the Vortex-induce Vertical Force (VIVF) on a flat closed-box bridge deck. In the study, in order to better depict VIVFs, a new improved model was proposed. First, the residual of the Vortexinduced Vertical Force (VIVF) is regular and maintains the significant quadratic relation with the VIVF reconstructed by Scanlan’s model, which means Scanlan’s model needs to be improved by adding quadratic terms. Second, an appropriate quadratic term was a dot product of dimensionless displacement and velocity, because this term has a significant linear relation with the reconstructed VIVF in the residual plot, and is independent of the other terms in Scanlan’s model. Furthermore, in lock-in range, the maximum oscillation displacement of a blunt body at different wind speeds was predicted by the proposed model. Simulation results showed that the proposed model is suitable for describing the nonlinearity of the VIVF and well fit the measured data. Due to simplicity, validity, and parameters to be easily identified, the proposed model has potential application in engineering.