Operational Modal Parameter Identification from Power Spectrum Density Transmissibility

The article will discuss how operational modal analysis subjected to ambient or natural excitation under operational conditions has recently drawn great attention. The power spectrum density transmissibility (PSDT) is proposed in this article to extract the operational modal parameters of a structure. It is proven that the PSDT is independent of the applied excitations and transferring outputs at the system poles. As a result, the modal frequencies and mode shapes can be extracted by combing the PSDTs with different transferring outputs instead of different load conditions where the outputs from only one load condition are needed. A five-story shear building subjected to a set of uncorrelated forces at different floors is adopted in this study to verify the property of PSDTs and illustrate the accuracy of the proposed method. Furthermore, a concrete-filled steel tubular half-through arch bridge tested in the field under operational conditions is used as a real case study. The identification results obtained from the currently developed method have been compared with those extracted from peak-picking method, stochastic subspace identification, and finite element analysis. This article demonstrated that the operational modal parameters identified by the current technique agree with other independent methods. The real application to the field operational vibration measurements of a full-sized bridge has shown that the proposed PSDTs are capable of identifying the operational modal parameters (natural frequencies and mode shapes) of a structure.