Modal strain identification from low-amplitude FBG data using an improved wavelength detection algorithm

Vibration-based damage identification of existing infrastructure suffers from a low sensitivity of natural frequencies to certain types of damage while the sensitivity to environmental influences may be sufficiently high to completely mask the effect of severe damage. Modal strains are much more sensitive to local damage, but their direct monitoring is not possible with current measurement techniques due to the very small strain levels occurring during ambient, or operational excitation. The present work explores a novel optical signal processing technique that enables to obtain sub-microstrain accuracy with Fiber Bragg Grating (FBG) strain sensors. The novel technique is validated in an experimental modal analysis test on a steel beam. The quality of the raw strain data and the strain mode shapes as obtained by using the novel optical processing technique and a conventional one are compared. The obtained modal characteristics are also compared with results of an experimental modal analysis in which accelerometers are used as sensors.