Structure modal parameter identification based on moving load excitation

The identification of the modal parameters of the structure is the object of experimental modal analysis. For large structures, for which it is generally difficult to apply appropriate dynamic loads, output only measurements are normally used, giving less accurate estimates of damping ratios and from which the generalised masses cannot be directly found. This paper presents an alternative method, using static loading and moving load excitation, which could easily be implemented on bridges loaded by a single vehicle. The generalised stiffness of each mode is found from the static tests, then the natural frequencies and damping ratios are obtained using the logarithmic decrement method on the free decay after the vehicle has passed. Combining the generalised stiffnesses and natural frequencies, the generalised masses are found. The method is demonstrated using simulated data for a simply supported Euler-Bernoulli beam, for which the modal parameters are well known. It is shown that the modal parameters of the first five modes identified from the simulated data are quite consistent with the known theoretical values, even in the presence of noise. In particular, the errors in the estimated generalised masses are less than 4%.