Dynamic response of suspension bridge decks during construction

The dynamic response of suspension bridge decks during construction is analyzed. The risk of coupled flutter vibrations during the early erection stages is determined by combining natural vibrations of the structure with aerodynamic derivatives describing the motion-induced wind load acting on the bridge deck. The natural vibrations of the structure are determined using an analytical model derived in the paper as well as by a finite element model of the structure. The results obtained by the two methods are found to be in good agreement. This indicates that the analytical model could be used in connection with initial estimates of dynamic response of suspension bridge decks during construction and as independent check of finite element models, which often are very complex and difficult to quality assure. Furthermore, the use of the analytical model gives a physical understanding of the main aspects governing the dynamic behavior of the structure. For the Great Belt Suspension Bridge used as an example describing the fundamental aspects presented, the vertical vibrations are governed by negligible bending stiffness of pylons and bridgedeck. For the torsional vibrations, the pylon stiffness is very large due to the crossbeams, and the reduced torsional stiffness originating from the erection joints is important to include in the model in order to estimate realistic critical flutter wind velocities during construction.