In this paper, which is derived from a MSc. thesis work joinlty developed at Politecnico di Milano and TU-Wien, new design strategies for a new incarnation of the well known Tuned Mass Dampers (TMD) passive structural control devices will be presented.

The proposed "NextGenTMD" is a hysteretic-behaviour version of the linear tuned mass damper (LTMD), a device that, if properly calibrated on the natural frequency of the main building, is able to oscillate in resonance with it, adsorbing part of the seismic energy that could otherwise cause structural damage.

As it is well known LTMDs need to stay properly tuned to the principal structure in order to be effective. The newly proposed incarnation of TMDs aims at overcoming the loss of tuning, and effectiveness, which would occur on normal buildings characterized by a nonlinear dynamic response during severe earthquakes. This allows for broadening the use of TMDs beyond applications to high-rise buildings, which behave in a relatively flexible and elastic way under seismic loading. Indeed, if effective, the simplicity of the installation of such an instrument could allow for a large scale diffusion and a wider reduction of the seismic vulnerability of the built environment.

The tuning problem can be overcome by implementing a hysteretic version of the dynamic absorber, able to remain tuned despite the hysteretic response of the primary structure itself, which can be roughly represented by literature relations for each type of building. The proposed design method was applied on a simplified model of a four story building of which full scale pseudo-dynamic test results were available, and the response was assessed with a set of spectrum compatible time histories according to the Eurocode 8.

The usage of evolutionary algorithms (genetic algorithms) introduced in the design process of the TMD is at the basis of the proposed design method. The approach was suggested by the successful employment of these numerical optimization strategies in the development of high end technologies and provides flexibility in the choice of the quantity of the dynamic structural response to be controlled. Within this context, both the calibration of the hysteretic model of the building and the following design phase of the TMD are presented as a multi-objective minimization problem.

The vey promising results, obtained so far from numerical simulations, show that TMDs can be effective in a seismic setting, differently from what has been deemed as possible in some literature sources, and encourage for a further extension of the research efforts towards physical tests.

fig.  1 comparison of the controlled and non-controlled displacement responses of the model structure