COMPDYN 2015 5 th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering M. Papadrakakis, V. Papadopoulos, V. Plevris (eds.) Crete Island, Greece, 25–27 May 2015 INTERNAL PARAMETRIC RESONANCE AND AEROELASTIC EFFECTS FOR LONG-SPAN SUSPENSION BRIDGES Raffaele Ardito 1 , Antonio Capsoni 2 , and Andrea Guerrieri 1,2 1 Dept. of Civil and Environmental Engineering, Politecnico di Milano Piazza Leonardo da Vinci 32, Milan, Italy raffaele.ardito@polimi.it 2 Dept. of Architecture, Built Environment and Construction Engineering, Politecnico di Milano Piazza Leonardo da Vinci 32, Milan, Italy antonio.capsoni@polimi.it, andrea.guerrieri@mail.polimi.it Keywords: Suspension Bridges, Non-linear Dynamics, Aeroelasticity, Stability, Parametric Resonance, Floquet Theory. Abstract. The potential occurrence of internal parametric resonance phenomena has been recently indicated as a possible cause of failure for long-span suspension bridges. At the same time, suspension bridges, in view of their flexibility, are prone to aeroelasticity driven response, such as vortex shedding, torsional divergence and flutter. In this paper, a non- linear dynamic model of a suspension bridge is devised, with the purpose of providing a uni- fied framework for the study of aeroelastic and internal resonance instabilities. Inspired by the pioneering work of Herrmann and Hauger, the analyses have been based on a linearized formulation that is able to represent the main structural non-linear effects and the coupling given by aerodynamic forces. The results confirm that the interaction between aeroelastic ef- fects and non-linear internal resonance leads to unstable phenomena for wind speeds which are by far lower than the critical threshold for standard aeroelasticity. 4508