Vibration control of a slender footbridge using passive and semiactive tuned mass dampers

This paper describes the work involving the implementation of a control system aimed at reducing vibrations in a slender footbridge located at FEUP campus. This structure was extensively studied in the past, mainly due to the clear exhibition of very perceptible vibrations induced by pedestrian loads. For that reason, a passive tuned mass damper (TMD) was installed in one of the spans of the structure for research purposes. Because the structure has several critical vibration modes with natural frequencies close to 2Hz, only one device cannot act efficiently on all of them, which limits the control efficiency. In these cases, the option for a semiactive TMD seems to be appropriate, given the self-tuning capabilities of these devices and even the possibility of performing multimode control. In this context, this document summarizes the work developed in studying, testing, and installing the passive TMD in the footbridge, as well as its migration to a semiactive system. Taking advantage of a continuous dynamic monitoring system installed in 2009, it was possible to evaluate the vibration levels of the structure measured over the past years, including the periods previous to and after the installation of the control solutions. A tendency was noted in the reduction of the peak accelerations of some sections of the deck after the installation of the passive TMD, which were even more attenuated with the activation of the semiactive system.