Performance and Accuracy of Fibre Optic Sensors and the Digital Image Correlation in Measuring the Strains and Crack Widths of Concrete Structures

A significant proportion of North America’s aging infrastructure has surpassed its intended design life. This includes a large number of concrete structures that are located in Canada or northern parts of the US with prolonged freezing seasons and high temperature fluctuations. One potential solution to assess the condition and performance of a structure and ensure its resilience is to use structural health monitoring (SHM) techniques. Fibre optic strain sensors (FOS) and digital image correlation (DIC) are two SHM breakthrough techniques providing more comprehensive performance data than conventional techniques. Although these SHM techniques are reasonably well developed, there is still a gap between the monitoring data and serviceability and reliability indicators due to uncertainty of measurements caused by parameters varying with time, e.g. temperature. In this work, FOS and DIC were used to measure strains and crack widths for eight large-scale reinforced concrete beams tested under static and fatigue loading at 15°C and -25°C. In addition, to evaluate the accuracy and precision of these technologies with temperature variations, calibration tests were conducted to measure temperature related strain errors that are induced in these systems. The results showed that both FOS and DIC are affected by temperature changes, and their measurements need to be corrected for temperature when they are used for measuring strains. This study also showed that DIC technique is capable of measuring crack widths with a very high accuracy, and external fibres can measure the strains in the concrete in compression with a reasonable accuracy, and can give an indication of the strains in the tensile reinforcement prior to reaching the cracking load of the reinforced concrete.