Fiber Optic Sensors and Digital Image Correlation for Measuring Deformations in Reinforced Concrete Beams

Abstract

Digital image correlation (DIC) and fiber optic strain sensors (FOSs) are two structural health monitoring (SHM) techniques that are reasonably well developed, but temperature effects remain a difficulty in interpreting the data. In this study, DIC and FOS were used to measure crack widths, deflections, and strains for eight large-scale RC beams tested under static and fatigue loading at room and low temperature. In addition, to evaluate the accuracy and precision of these technologies with temperature variations, calibration tests were conducted to measure the temperature-related strains induced in these systems. The results show that both DIC and FOS were affected by temperature changes, and thus their measurements need to be corrected for temperature when they are used for measuring strains. This study also shows that the DIC technique is capable of measuring crack widths and deflections with high accuracy, and external FOSs can measure strains in concrete in compression with reasonable accuracy. Based on the results of calibration tests, a methodology is proposed to determine the coefficient of thermal expansion (CTE) of the optical fibers to aid in interpreting fiber optic measurements under varying temperature conditions.