The aim of this thesis is to analyze the behavior of suspension bridges under wind loads, in particular the George Washington bridge has been chosen as a case study, in both original and latest stiffened versions respectively of 1931 and 1962. The goal is to determine the critic wind velocity that leads the bridge to the well-known phenomenon of flutter instability adopting a commercial finite element software and to find a simplified approach for the estimation of the motion-related wind loads. The research is also focused on the study of the computational fluid dynamic models aimed at determining the aerodynamic parameters on which the approach mentioned before is based.