Use of Long-Gage Fiber Optics Sensors For Earthquake Response Monitoring and Non-Destructive Evaluation of Structures

The objective of this study is to investigate, through numerical simulation, the feasibility and potential benefits of using newly emerging and very promising long-gage length fiber optic deformation sensors for monitoring directly the internal "macroscopic" deformation response of structures to earthquake ground motions and for non-destructive post-earthquake evaluation. Two important types of such sensors are the long-gage length low-coherence interferometric fiber optic sensor and the fiber Bragg grating strain sensor. These sensors are able to measure with a resolution of 2 microns for the interferometric sensors and less than 1 micro-strain (1 ) for the fiber Bragg sensors the change in distance separation between two material points of the structure. Fiber optic sensors (FOS's) can be either embedded inside reinforced concrete and composite structures or bonded to the surface of any structure (steel, reinforced concrete, composite).

When compared to conventional sensors used in earthquake structural engineering such as accelerometers, potentiometers, linear variable displacement transducers (LVDT's), and resistive foil strain gages, the above mentioned fiber optic sensors present numerous significant advantages, including immunity to electromagnetic interferences, high sensitivity and dynamic range, high resolution, extremely high bandwidth capability, long term stability, small size, light weight, and environmental ruggedness. Furthermore, the cost of fiber optic sensor components is driven by the multi-billion dollars commercial telecommunication and optoelectronics market. Experts say that fiber optic sensors have the potential to replace most existing sensors in the next decade due to higher performance and lower cost.

To achieve the objective of this study, a numerical platform is developed in Matlab (high performance language for technical computing) consisting of three modules: (1) earthquake response analysis of 2-D linear elastic frame structures and embedded/attached long-gage FOS's, (2) modal identification using earthquake input excitation and outputs from fiber optic sensors, and (3) damage identification using data from fiber optic sensors.