Dynamic displacement monitoring of flexural structures with distributed long-gage macro-strain sensors

A new method is proposed to monitor dynamic displacement for flexural structures especially. In this method, the distributed macro-strain is first obtained using long-gage fiber Bragg grating sensors. Then, the conjugated beam theory is applied to calculate the displacement. To verify the method, a cantilever beam, installed with the proposed sensors, is subjected to free vibrations. The results from the proposed method agree well with those measured by the traditional displacement transducer as the error for the first three peak values is less than 5%. A finite element model of a simply supported multi-girder bridge is also simulated with a truck load. The results show that the proposed method can evaluate dynamic displacement accurately as the error for the maximum displacement is less than 3% in all the cases. Finally, the method is verified using simply supported beam models subjected to random dynamic loads. However, the sensor gage length shows some influence on the results. To ensure exact measurements, the sensor gage length should be limited to be smaller than 1/20 of the beam length. Considering other advantages of fiber optic sensing, the proposed method shows promise in the field of long-term structural health monitoring.