FLUTTER DERIVATIVES IDENTIFICATION THROUGH FULL BRIDGE AEROELASTIC MODEL TRANSFER-FUNCTION ANALYSIS

A full bridge 1:250 scale 13 m long aeroelastic model of the proposed Messina Suspension Bridge has been built and tested at the Danish Mari time Institute wind tunnel. This experimental exercise was undertaken as a check at the conclusion of the design, having already defined the optimised deck section and measured its aerodynamic characteristics t hrough 1 :87 and 1:30 section model tests. In addition to the usual te sts always performed on a full bridge aeroelastic model(i.e. static an d dynamic response to smooth and turbulent flow excitation and flutter speed limit), a specific measure set-up and test program has been rea lised, aimed at defining the modal characteristics of the structure an d their modifications due to the wind effects. In the present paper a modal approach for identifying the aerodynamic terms, usually mentione d as flutter derivatives, from the measure of the aeroelastically modi fied full bridge transfer functions is presented. The analytical formu lation of the transfer functions for a two mode structure description have been obtained as a function of all the modal and aerodynamic para meters. A least squares iterative procedure was then applied allowing to evaluate a best estimate of the parameters minimising the distance between the experimental and the numerical transfer functions. Given t he generality of the identification method, both the structural and ae rodynamic parameters can be addressed, and due to the two DoF approach also the coupling terms can be taken into account. The opportunity of extending the method at least to a three mode structure description w as clearly suggested by this first experience.