A parametric nonlinear model of suspension bridges including the presence of Shape Memory Alloy (SMA) hangers will be developed to study and suppress instability phenomena induced by self-excited aerodynamic loads and vortex-induced parametric forces. The starting point of the proposed research will be the nonlinear model developed by the Proponent of this research project (and his co-workers) to study flutter in suspension bridges and its control via hysteretic tuned mass dampers. The project will lead to an advance of the state of the art in several aspects pertaining to various topics. First, it will be developed a parametric tool able to investigate the nonlinear dynamic behavior of suspension bridges and to study the bifurcative scenarios (Hopf instability and parametric instability) arising from the wind-structure interaction by means of advanced analytical and numerical techniques, such as asymptotic and continuation analyses. Second, the project will propose a novel approach for the vibrations control in suspension bridges based on the actuation, via temperature variation, of suspension elements made of smart materials (SMA). Finally, after an accurate numerical validation of the model, a detailed study on the feasibility of the proposed control system will pave the way for the development of the technology suitable for its effective realization.
Nowadays, SMA are typically adopted in micro-mechanical systems where micro-wires made of SMA are used as actuators, for instance, in biomedical tools. Applications of SMA wire-ropes can be also found in mini-scale mechanical components adopted in the automotive engineering for moving parts such as rear-view mirrors. However, the development in the manufacturing technologies, pushed by the novel applications conceived for SMA wire-ropes for creating dissipative devices at the meso- and large-scale (such as tuned mass dampers) [17], makes now possible to manufacture large-diameter, long wire-ropes with limited production costs. To the best of knowledge of the Proponent of this research, the use of suspension hangers made of innovative SMA wire-ropes to control and suppress oscillations in SB is novel and not yet investigated in the literature. For this reason, in the present project will be developed a topic which is new in the field. The experience gained by the Proponent in the modeling and in the bifurcative analyses of nonlinear systems, together with his expertise in the context of characterization of SMA cables acquired 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 active elements whose disposition will be optimized along the structure. Moreover, the control system will be itself a structural part of the bridge and no extra-masses or deck attachments will need to be installed for further control purposes;
iii. the parametric studies, corroborated by optimization analyses based on genetic algorithms, will be performed in order 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.