###### Abstract  
This study aims to develop a prestressed concrete steel (PC) strand with an embedded optical Fiber Bragg Grating (FBG) sensor, which has been developed by the Korea Institute of Civil Engineering and Building Technology since 2013. This new strand is manufactured by replacing the steel core of the normal PC strand with a carbon-fiber-reinforced polymer (CFRP) rod with excellent tensile strength and durability. Because this new strand is manufactured using the pultrusion method, which is a composite material manufacturing process, with an optical fiber sensor embedded in the inner center of the CFRP Rod, it ensures full composite action as well as proper function of the sensor. In this study, a creep test for maintaining a constant load and a relaxation test for maintaining a constant displacement were performed on the proposed sensor-type PC strand. Each of the two tests was conducted for more than 1000 h, and the long-term performance verification of the sensor-type PC strand was only completed by comparing the performance with that of a normal PC strand. The test specimens were fabricated by applying an optical fiber sensor-embedded PC strand, which had undergone long-term performance verification tests, to a reinforced concrete beam. Depending on whether grout was injected in the duct, the specimens were classified into composite and non-composite specimens. A hydraulic jack was used to prestress the fabricated beam specimens, and the long-term change in the prestress force was observed for more than 1600 days using the embedded optical fiber sensor. The experimental results were compared with the analytical results to determine the long-term prestress loss obtained through finite-element analysis based on various international standards. b 24 November 2021 2021 14 December 2021 2021 20 December In general, when introducing a prestress force into a structure using a PC strand, the prestress force is calculated based on the hydraulic change and the extension of the hydraulic jack, as shown in Figure 1. Therefore, a separate measurement method is required to examine the residual prestress force after removing the hydraulic jack. The lift-off test is often used [1; 2; 3] and is a method that is employed to install a load cell, a displacement meter, and a hydraulic jack on the strand and to calculate the prestress force of the strand using the relationship between the force applied to the load cell and the displacement measured with the displacement meter. Although the process is simple and accurate, it is difficult to apply this method to structures in service, as it involves separate hydraulic equipment and excessive hydraulic pressure may, thus, be introduced. After examining the prestress force in the above manner and then removing the hydraulic jack, there are not many ways to manage the prestress force. Therefore, the maintenance of the prestress force tends to be neglected in PC bridges in the absence of a means to check the prestress force, and leakage may occur, owing to voids in the grout in the duct and cracks in the concrete around the installed strands, leading to the corrosion of the strands and even to the collapse of bridges in severe cases. Table 1 below shows examples of bridges showing severe corrosion of prestressed members and anchorages, as well as bridge collapse accidents that have occurred since 2000. The conventional methods used for measuring prestress force include traditional methods such as attaching a gauge directly to the outside of a strand and installing a load cell at the end. There has also been a recent approach to estimating the prestress force based on the relationship between the magnitude of the tension force and the magnetic field variation rate, which is calculated using an electromagnetic (EM) sensor or a magnetic flux leakage (MFL) sensor [7; 8]. In addition, methods for measuring the prestress force or tracking damaged areas by applying an acoustic emission (AE) sensor using acoustic effects are being developed [9; 10].