Three degrees-of-freedom forced vibration method for identifying eighteen flutter derivatives of bridge decks

A three degrees-of-freedom (3-DOFs) identification method was developed to extract 18 flutter derivatives of bridge decks by utilizing the digitally-controlled forced vibration device. The developed forced vibration device consisted of servo motors, digital drivers and a special coupled motion mechanism. The frequency of motions and the motion patterns in terms of single DOF vibration or coupled multi-DOFs vibration were simply controlled by computers. Based on the measured model displacements and the aerodynamic forces exerted on the model, the flutter derivatives of a thin-plate section with a thickness to width ratio of 1/22.5 and other two typical bridge deck sections were identified in time domain. The effect of motion patterns on identification results was discussed. The results show that the identified flutter derivatives of the thin-plate section agree rather well with the theoretical values of thin airfoil given by Theodorsen. The identified major flutter derivatives of the two typical bridge decks demonstrate regular variation patterns with the reduced wind speed. Moreover, the flutter derivatives associated with drag forces generally show good trends, and the motion pattern of the models has little effect on the flutter derivatives of bridge decks.