A continuum-based mechanical model describing the nonlinear response of long-span suspension bridges (SB) subjected to wind-induced dynamic forces and including the presence of a novel passive control system is developed to predict and mitigate large-amplitude oscillations arising from aerodynamic instability phenomena. A nonlinear parametric model developed in the past by the Proponent of this project to study aeroelastic instabilities in SB will be the starting point of the proposed research activity. Such mechanical model will be enhanced by including an innovative vibration control system based on tuned mass dampers possessing negative stiffness and hysteretic damping provided by parts made of shape memory alloy (SMA).
This research will lead to an advance in several aspects concerning the control of wind-induced instabilities in long-span suspension bridges and the project will pave the way for the use of novel, non-conventional, control devices based on smart materials possessing strongly nonlinear features.
A parametric tool will be first developed to study the bifurcation scenarios, arising in SB from the wind-structure interaction, by means of advanced analytical and numerical techniques, such as perturbation analyses and numerical continuation. Then, the project will focus on the fine tuning of a novel approach for the control of large-amplitude oscillations in SB through nonlinear passive control devices based on SMA material and possessing negative stiffness. Such unconventional mechanical property will be the key-feature for the control optimization of the SB dynamic response which, as known, is characterized by a strongly nonlinearity of hardening type. Lastly, detailed studies devoted to demonstrate the feasibility of the here proposed novel control system will be carried out after an accurate numerical validation of the model and of the numerical codes; this, will be the starting point for the actual realization of the device in the next future.
Nowadays, the most common applications of SMA wire-ropes can be found in mini-scale mechanical components adopted in the automotive engineering for moving parts. However, the advances in the manufacturing technologies, driven by the increasing number of novel applications making use of SMA wire-ropes for assembling dissipative devices at the meso- and large-scale (such as tuned mass dampers) [1], makes today possible the manufacturing of large-diameter, long wires having also limited costs of production. With respect to classical TMDs, having the limitations of being heavy for the suspension bridge to be controlled, and effective only in narrow frequency operational bandwidths, the hysteretic TMDs here proposed are conceived with a novel design based on the unusual characteristic of possessing negative stiffness which strategically uses nonlinearities to bypass the above mentioned limitations.
The Proponent of this research project is confident in the fact that the use of arrays of TMDs made of innovative SMA wire-ropes and possessing negative stiffness and hysteretic damping to mitigate large-amplitude oscillations in SB is novel and not yet explored in the literature. Therefore, in the present project it will be developed a research activity which will be new and, for sure, innovative in the field. Moreover, the experience acquired by the Proponent in the field of nonlinear modeling of dynamical systems and their bifurcative analyses through asymptotic approaches, together with his expertise in the context of characterization of SMA cables learnt as a Component of a past research project, will facilitate the possibility to achieve a definite goal in the present project.
Then, this research will produce an advance in the state of the art not only at the level of the nonlinear dynamics but also at a general engineering level. In particular:
i. a novel, sophisticated, nonlinear continuum model of suspension bridges will be developed, and this will represent a suitable parametric framework for general bifurcative analyses and control of the instability scenarios arising from the most severe aerodynamic load conditions in SB;
ii. a new oscillations control technique in suspension bridges will be conceived by means of passive nonlinear vibration absorbers characterized by hysteretic damping and negative stiffness and whose disposition will be optimized along the structure;
iii. the parametric studies, corroborated by optimization analyses based on genetic algorithms, will be performed to demonstrate the efficiency, as well as the feasibility, of the conceived new control system. Therefore, this will pave the way to new challenges in the application of smart materials in large-scale mechanical systems.
[1] Lacarbonara, Carboni, Sapienza. A multi-purpose nonlinear rheological device made of shape memory-steel strands. Patent RM2015A000075 (20.2.2015), PCT30259