Instrumentation, Measurements and Numerical Analysis of Bridges: An Example of the Cable-Stayed Bridge on Evripos Channel, Greece

The instrumentation of special structures such as large bridges, tunnels, monuments etc., contributes towards a better understanding of their dynamic performance, as well as a more accurate and reliable prediction of the earthquake resistance of such large-scale structures. In experimental analysis the classical ways to estimate the modal parameters of the whole structural system, as well as of its structural elements, is either to excite the structure artificially (using, e.g. vibrators, heavy vehicles) or to evaluate the recordings obtained from a weak or strong ground motion. In modeling the behaviour of a civil engineering structure in a realistic way, among the important parameters to be defined are the mass distribution, the damping characteristics, the stiffness of the main load resisting system, the influence of secondary elements and interaction phenomena. Large vibration tests provide reliable data for the evaluation of the influence of such modal parameters. The effective analytical evaluation of the bridge through reliable and effective numerical models is necessary in order to verify the experimental data. By comparing the results of both experimental and analytical approaches and adequately updating the analytical model, a more realistic modeling of the bridge can be obtained. Changes in the modal parameters during the time-life of the bridge can contribute towards detection of damages, such as crackings or any other reasons reducing the stiffness of the structural system. The cable-stayed bridge in Evripos channel (Greece) was selected to apply the aforementioned methodology. The main ambient vibrations recorded are due to traffic, wind and moderate earthquakes at small distances from the bridge. Three-dimensional finite element models of the bridge were created and the dynamic behaviour of the bridge was analysed for both a small and a strong earthquake with high frequency content. Results of the experimental estimation of eigenvalues of the vibration modes are also presented. Finally, comparisons between experimental and analytical values have been performed,