RESEARCH ARTICLE Vibration control of a slender footbridge using passive and semiactive tuned mass dampers C. Moutinho 1 | Á. Cunha 1 | E. Caetano 1 | J.M. de Carvalho 2 1 CONSTRUCT, Faculty of Engineering, University of Porto, R. Dr. Roberto Frias, 4200‐465 Porto, Portugal 2 SYSTEC, Faculty of Engineering, University of Porto, R. Dr. Roberto Frias, 4200‐465 Porto, Portugal Correspondence Carlos Moutinho, CONSTRUCT, Faculty of Engineering, University of Porto, R. Dr. Roberto Frias, 4200‐465 Porto, Portugal. Email: moutinho@fe.up.pt Funding information Fundação para a Ciência e a Tecnologia, Grant/Award Number: PTDC/ECM‐EST/ 0535/2012; FEDER, Grant/Award Num- ber: Project POCI‐01‐0145‐FEDER‐007457 Summary This paper describes the work involving the implementation of a control sys- tem aimed at reducing vibrations in a slender footbridge located at FEUP cam- pus. 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 2 Hz, 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 ten- dency 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. KEYWORDS dynamic monitoring system, footbridges, magneto‐rheological damper, passive and semiactive control, tuned mass damper 1 | INTRODUCTION Many civil engineering structures have vibration problems in terms of serviceability limit states due to several transient or periodic dynamic loads, for example, footbridges subjected to pedestrian actions, road and railway bridges excited by traffic loads, and tall buildings exposed to wind forces. In these situations, the implementation of control systems can improve the structural performance by reducing the vibration levels to acceptable values, which are established for each case. To achieve this, several passive, active, semiactive, or hybrid control schemes can be adopted. 1-3 The most popular techniques are those that involve passive systems because, compared with other cases, they are more reliable, more robust, and more economical and require low maintenance. When controlling harmonic vibrations, one of the most interesting devices is the vibration absorber, also known as tuned mass damper (TMD). However, these devices may have some functioning problems common to Received: 4 November 2017 Revised: 18 April 2018 Accepted: 20 April 2018 DOI: 10.1002/stc.2208 Struct Control Health Monit. 2018;e2208. https://doi.org/10.1002/stc.2208 Copyright © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/stc 1 of 22