## 1 Introduction  
Reinforced concrete (RC) is a common material that is used in constructing civil infrastructure, such as buildings and bridges. To resist loading by wind or earthquakes [1], RC shear walls are widely used in newly constructed building structures to improve their lateral strength, stiffness and energy dissipation capacity. RC structures that are designed according to old standards would be damaged during earthquakes owing to a lack of shear reinforcement and/or insufficient lap-splice length. Such structures may exhibit brittle failure modes and so should be retrofitted to satisfy current standards and survive in future earthquakes. Owing to the high lateral strength and stiffness capacity of RC wall members, post-installed RC infill walls for non-ductile frames is are widely used in seismic retrofitting, especially of low-rise building structures. After a large earthquake event, diagnosing the structural health and/or locating damage to an RC structure are very important to providing early warning information. Large-scale civil infrastructure must have structural health monitoring (SHM) systems for this purpose. The structural safety or serviceability of the civil structures may be able to be assessed by visual inspection and nondestructive evaluation (NDE) for local monitoring, which can be carried out by qualified engineers. Some NDE methods for local evaluation include the use of ultrasonic and acoustic emissions. The main limitation of visual inspection and some of the traditional approaches is that they require access to potentially damaged regions in a structure, which may be dangerous or impossible. Experience of disasters indicates that despite the best efforts of inspection officials, the prediction of structural failure by inspection remains a difficult task and the detection of structural components in a critical condition is very difficult. These shortcomings have motivated the development of structural health monitoring over recent decades. SHM is the process of using information that is continuously obtained from an array of sensors that are deployed in a structural system to infer its state of structural integrity (damage diagnosis) and estimate its remaining capacity (damage status) ([PERSON] and [PERSON] [2], [PERSON] and [PERSON] [3]). Numerous important issues concerning the safe operation of a concrete structure arise over its life cycle. The aging and deterioration of concrete structures require improvements in their sustainability and resiliency, as well as their ongoing maintenance. In addition to deterioration from long-term use, extreme events (such as earthquakes) pose a threat that may result in sudden drops in performance or safety. Additionally, using a quantifiable method to determine whether a damaged building is safe for reoccupation and whether structures can continue to serve their required functions is difficult. Therefore, the SHM of an RC structure must be performed to detect its damage or determine its health after an earthquake during its service life. Many investigations of changes in structural vibration properties to detect structural damage to RC structures damage have been performed. [PERSON] et al. [4] reviewed the literature in this field. Damage changes the vibration properties of RC structures, including their fundamental frequencies, structural damping ratios and corresponding mode shapes. However, the natural frequencies and mode shapes are not necessarily favorable indices of damage because structural frequencies are frequently not sensitive to minor damage and many measurements must be made to characterize mode shapes accurately. In the last three decades, sensing systems that are based on optical fiber sensors have been used to detect damage and to monitor the health of RC structures, owing to their smallness, immunity to corrosion and ability to be embedded. Many optical fiber sensor-based monitoring systems have been developed for making continuous measurements and real-time assessments of a wide range of structures. [PERSON] et al.