Evaluation of thermal-drift effect on strain measurement of energy pile

Abstract

Fiber Bragg grating (FBG) strain sensors and electrical resistance strain (ERS) gauges are typically utilized to monitor the internal deformation of structures. However, a common problem inherent in these sensors is the unwanted thermal drift in the measurement results. This study first investigated factors influencing the thermal strain measurements of FBG strain sensors and ERS gauges through a series of calibration experiments. The results demonstrate that the relative error caused by the thermal output of the heated connection cables was as high as 90 %. Then a correction method for the thermal drift of the strain measurement was proposed. This correction method reduced the relative difference between the strain readings of bonded ERS gauges and FBG sensors from 82.6 % to around 10–20 %. Finally, FBG strain sensors and ERS gauges were employed to monitor the strain of the energy piles under cooling and heating cycles. The difference between the corrected readings from FBG strain sensors and ERS gauges was less than ± 10 %. The experimental results also reveal that the monitoring reliability of the FBG strain sensors was higher than the ERS gauges.