The application of semi-active control systems in lightweight civil engineering structures is still limited even though several studies have shown an improvement in mitigating vibrations under uncertainty scenarios. In comparison with passive systems, a smart device is employed in a Semi-active Tuned Mass Damper (STMD) system to modify its response in real time, usually the damping force. Based on a control law, a degree of adaptability can be achieved in the smart device, leading to the desired tuning between the structure and the STMD to mitigate the vibration induced by the external force, especially when a detuned response between the structure and the control system is caused by external uncertainties. The magneto-rheological (MR) damper is the most common device used for this purpose. Thus, the practical implementation of an STMD in lightweight structures subjected to human-induced vibrations is presented in this paper. An STMD equipped with two sponge MR dampers is developed, modeled, and installed in a fiber-reinforced polymer footbridge, which fulfills the state requirements but exhibits excessive vibrations when its first vertical vibration mode is excited. Numerical simulations are also carried out considering human-structure-STMD interaction. For the analyses, a Mass-Spring-Damper system is used to depict a pedestrian, and the functioning of the MR dampers is represented through a hyperbolic tangent model. Additionally, three different phase control laws are considered for the numerical and experimental implementation of the STMD, namely: (i) an On-Off controller, (ii) a fixed gain controller, and (iii) a variable gain controller. The comparison of the numerical and test results shows that the model used for the MR damper and the STMD are adequate.
Barrera-Vargas et al. (Fri,) studied this question.