Multiscale modeling and model updating of a cable-stayed bridge. II: Model updating using modal frequencies and influence lines

To facilitate an effective assessment of stress-related bridge performance and safety, a baseline multiscale finite-element (FE) model and a corresponding model-updating technique are required so that the FE model can best represent the prototype and can be used to well predict both global and local responses. The companion paper demonstrates that considering modal frequencies alone as updating objectives cannot ensure the updated multiscale FE model being able to predict local (stress) responses accurately. This paper presents a new updating method that uses both modal frequencies and multiscale (displacement and stress) static influence lines as updating objectives. The paper first explains the relationship between displacement influence lines and mode shapes and the relationship between strain influence lines and strain mode shapes. The formulation of the multiscale objective functions and the selection of updating parameters are then presented. As a case study, the proposed model-updating method is finally applied to the multiscale FE model of the Stonecutters Bridge. In light of the large number of degrees of freedom of the multiscale model, the response surface method is adopted in the optimization process to reduce computation time. The updated results show that the proposed model-updating technique can reduce the differences not only between measured and computed modal frequencies but also between measured and computed influence lines.