Modal Analysis Based on the Random Decrement Technique: application to civil engineering structures

The thesis describes and develops the theoretical foundations of the Random Decrement technique, while giving several examples of modal analysis of large building constructions (bridges). The connection between modal parameters and Random Decrement functions is described theoretically. The efficiency of the Random Decrement technique for the estimation of correlation functions is compared to other equivalent methods (FFT, Direct method). It is shown that the Random Decrement technique can be as much as a hundred times faster than other methods. The theory behind the Random Decrement technique is expanded to include both a vector formulation that increases speed considerably, and a new method for the prediction of the variance of the estimated Random Decrement functions. The thesis closes with a number of examples of modal analysis of bridges exposed to natural (ambient) load.