Nonlinear Computer Model for the Simulation of Lock-in Vibration on Long-Span Bridges

The susceptibility of modern bridges to vortex-shedding-induced vibration is a major concern for researchers and designers. The relevance of this phenomenon is associated with the onset of large-amplitude aeroelastic vibration at moderate wind-velocity regimes due to synchronization, that is, lock-in, of the vortex-shedding frequencies with those corresponding to the natural modes of the structure. Recent observations, either recorded during the monitoring of full-scale bridges or during experimental tests of deck models in wind tunnels, confirm the importance of these aspects during the operational life of the structure. In this article, a computer model for the simulation of the aeroelastic loading associated with vortex shedding in lock-in regime is presented, for a direct application to dynamic analysis of long-span bridges. This approach is based on earlier work focused on the response of slender vertical cylindrical chimneys to vortex-shedding excitation, which is here extended to noncircular cross sections. The numerical model was employed in conjunction with a finite-element code for time-domain nonlinear simulation of the structural dynamic response. The validation of the procedure is performed through numerical simulation, conducted on two specific bridge examples.