Real-time girder deflection reconstruction using a fiber bragg grating system

Fiber Bragg grating (FBG) optical sensor systems have been shown to provide excellent multi-point strain measurements in civil and marine structures. Their ability to be multiplexed easily allows useful population of the structure such that important spatio-temporal information, e.g., vibration modes, can be obtained. In this paper, the application of a multi-channel FBG system to monitor the dynamic strain response of an in-service interstate (1-10) bridge near Las Cruces, New Mexico, is described. Specifically, a linear array of sensors was placed along one girder to obtain local bending strain data during the passage of traffic, and the data were incorporated, in real time, into a shape reconstruction algorithm based on a shear-corrected Euler strain-to-displacement transformation. Preliminary results from the field test reported here indicate that the data may be useful for a number of bridge-related applications, including bending mode reconstruction, transient traffic loadings, weigh in motion, possible vehicle identificalion, vehicle speed, and other dynamic characteristics of the structure.