LONG GAGE LENGTH INTERFEROMETRIC FIBER OPTIC SENSOR FOR STRUCTURAL DAMAGE DETECTION

Abstract

Two areas of research are brought together in the present study to develop a nondestructive damage detection system and methodology: long gage length interferometric fiber optic sensors and modal analysis. Using modal analysis techniques, the physical state of a concrete beam and steel beam is assessed by monitoring its vibratory signature, i.e. resonant frequencies, mode shapes, or damping. Traditionally, modal analysis has been performed using data from point sensors such as accelerometers, seismometers, LVDTs, or electric strain gages with limited success. A long gage length optical sensor has been developed in the present study for modal analysis on civil structures. Because modal analysis involves monitoring global attributes, a long gage length sensor is used to allow a larger portion of a structure to affect the sensor output. The present study uses a long gage length interferometric fiber optic sensor on a steel beam and a concrete beam to monitor induced physical changes, or damage, of the beams using modal analysis. The frequency response spectrum of the incremental damaged states is evaluated and correlated to a baseline frequency response spectrum to identify patterns of degradation.