Use of Continuous-Wavelet Transmissibility for Structural Operational Modal Analysis

Abstract

Operational modal analysis is a challenging task to deal with output-only vibration measurements contaminated by noise. This paper proposes a new method for operational modal identification of a linear system using continuous-wavelet transmissibility (CWTR) to make full use of the advantages of operational transmissibility measurements and wavelet transform. A new theorem on limits is mathematically proved, for which the proposed CWTR at different scales are independent of stationary excitations acting on the structure at the system poles. With such a unique feature, the operational modal frequencies and mode shapes can be extracted by combing different CWTRs at numerous wavelet scales with different transferring outputs. The applicability of the method is numerically verified by a 4-story frame subjected to random forces. The effects of wavelet functions and scale discretion step have been investigated. The real case application of a concrete-filled steel tubular arch bridge tested in the field under operational conditions further illustrates that the operational modal parameters, identified by the present technique, agree well with those obtained from the existing identification methods and calculated by finite-element analysis. It is demonstrated that the proposed CWTRs are capable of identifying the operational modal parameters of full-sized structures.