Practical guidelines for the natural excitation technique (NExT) and the eigensystem realization algorithm (ERA) for modal identification using ambient vibration

摘要

The use of the natural excitation technique (NExT) and the ERA for output-only modal identification of civil infrastructure is defined, providing guidance on the parameter selection for NExT-ERA. Best practices to perform modal identification using NExT-ERA, including guidelines to select these parameters appropriately, are also described. The acceleration records recorded with the fully braced system under ambient excitation only are considered. A reference channel with high amplitude, low noise-to-signal ratio, and far from a node of vibration of the modes of interest, is chosen. It is found that the record length, number of points for the fast fourier transform (FFT) and the record sampling frequency directly affect the calculations of the cross-correlation function. Six natural frequencies, including two closely spaced modes are successfully detected.