Structural scaling factor identification from output-only data by a moving mass technique

Ambient vibration testing is a convenient and cost-effective alternative to impact testing as it doesn't require artificial excitation devices and traffic control. The lack of input force measurement in ambient vibration testing, however, does impede the identification of structural scaling factors, which are extremely important for Frequency Response Functions (FRFs) estimation and flexibility identification. A moving mass technique of identifying structural scaling factors from output-only data is proposed in this article. By this method, a vehicle passing over a bridge is regarded as a moving mass with spatial and time variation on the structure, inducing a vehicle-bridge system with time-varying modal properties. Theoretical derivation will be performed to identify scaling factors from the measured vibration responses of the bridge with and without the moving vehicle. Magnitudes of FRFs and the structural flexibility matrix can be obtained once the scaling factors are identified. The proposed method delivers comparable results to impact testing but is considerably more convenient. Numerical and experimental examples are studied to verify the effectiveness of proposed method. The effects of vehicle speed, mass value and measurement noise are also investigated.