Modal analysis of the Jalon Viaduct using FE updating

Due to differences in stiffness, mass, damping, internal connections, external boundary conditions between a real structure and a FE model, differences will exist in the vibration characteristics including natural frequencies and mode shapes. To solve this discrepancy, FE updating has been widely used in civil engineering. The uncertain parameters in the FE model are adapted to minimize the differences. The Jalon Viaduct along the high-speed railway line between Madrid and Barcelona is selected as a case study. The viaduct is a continuous box girder supported on high piers. From ambient vibration, mode shapes have been derived in vertical, lateral and longitudinal direction. For the updating the natural frequencies and the three- dimensional mode shapes of the first five lateral and first five vertical modes of the viaduct are used. For this calibration, 14 updating parameters including 12 spring stiffnesses and 2 Young's moduli are selected. The fact that also longitudinal components of the mode shapes are considered helped the updating process. Due to the existence of some local minima of the objective function induced by interfering modes, a Multistart Solver is used to obtain the global solution. It is shown that the relative weight of some residuals has to be adjusted in order to have better results for the longitudinal components of the vertical modes. The updating results in a much better agreement between the measured and the predicted natural frequencies and mode shapes.