Towards Optimization of Tuned Mass Dampers in Suspended Bridges by Accounting for Non-Linear Behaviour

This master thesis investigates the dynamic behaviour of suspended pedestrian bridges, with a focus on the non-linearities resulting from the quadratic dependency of cables stiffness to displacement, using the Victor-Neels bridge as a case study. A detailed numerical model was developed in the software Finelg, and was validated by an experimental campaign involving pedestrian induced vibrations. The results from the modal identification using COV-SSI method and the tension measurement in hangers provided meaningful information to refine the numerical model to replicate the real-life behaviour of the bridge as closely as possible. Non-linear dynamic analyses, performed with sine sweep of varying amplitude, revealed a significant increase in structural stiffness beyond a certain excitation threshold, resulting in reduced displacement amplitude compared to the linear predictions as well as a frequency shift in the resonant frequency peak.
Even though a linear analysis is conservative, it can lead to excessive displacement estimations, potentially resulting in unnecessary Tuned Mass Damper (TMD) installations or structural oversizing. This work investigates the effectiveness of linear TMDs in linear and non-linear analyses. While TMDs tuned to the frequency resulting from the modal analysis were effective, their efficiency was increased by taking into account the frequency shift from the non-linear dynamic analyses. The results also showed that a comparable damping efficiency could be achieved with a lower-mass TMD, offering interesting perspective in terms of possible optimization. Other perspectives include the implementation of a non-linear TMD with an exponential damping force depending on the speed, to enhance performance to reduce the amplitudes of the peak response.