  In most cases, structural health monitoring depends on the determination of
the modal parameters of the first few modes of a structure. The data that are
used to identify these modes by output-only methods include the structure
response together with noise. The presence of noise in the structure response
affects the modal parameters. The current study was undertaken to examine the
possibility and accuracy of identifying the modal parameters of beams in the
presence of noise. For this purpose, the modal parameters of the different
modes of single-span beams were obtained using output data with different
signal-to-noise ratios. The acceleration signals were obtained by transient
analysis and then different powers of noise were generated and added to the
signals. The modal parameters of the beams were obtained using output-only
methods. Parameters having signal-to-noise ratios of greater than 13.98 dB for
all modes considered were identified. At a signal-to-noise ratio of -6.02 to
13.98 dB (higher noise level), it was not possible to identify the modal
parameters of the first mode of beams, but the parameters of the higher modes
were identified with good accuracy.
