An Improved Conjugated Beam Method for Deformation Monitoring with a Distributed Sensitive Fiber Optic Sensor

Based on the distributed fiber optic sensing technique of pulse-prepump Brillouin Optical Time Domain Analysis, this paper proposes an improved conjugated beam method (ICBM) for distributed structural deformation monitoring. Because ICBM is suitable for the combined actions of loads, support settlements and temperature variations, it extends the application of the classical conjugated beam method. Other advantages include the linear and explicit relationship between structural deformation and strain and the fact that all calculation parameters can be easily determined free from random load or section stiffness distribution. Theoretical and experimental investigations are carried out to confirm that the accuracy of deformation monitoring with ICBM in one span of a continuous structure is related only to the accuracy of strain measurements for the same span. This characteristic is used to avoid the influence of strain measurement error accumulation from a series of strain measurement data on other spans. Such accumulation can result in uncontrolled deviation of monitoring deformation with the classical double integration method. In order to further increase the accuracy of deformation monitoring, a new distributed sensitive fiber optic sensor (DSFOS) is proposed to improve the accuracy of strain measurement with good designability according to detailed sensing requirements. The results of a uniaxial tensile experiment show that the strain measurements from DSFOSs agree well with the true values, and the measuring standard deviations appear to be lower than those obtained from UV coating fiber optic sensor. The flexural experimental results from reinforced concrete beams show that the obtained structural deflection data agree with the values observed from digital indicators. Relative to common fiber optic sensors, DSFOSs can obtain deformation and strain with higher accuracy to show applicability for daily monitoring.