A Comparative Study of the Data-Driven Stochastic Subspace Methods for Health Monitoring of Structures: A Bridge Case Study  
[PERSON]  
1 School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Skudai 81310, Malaysia; [EMAIL_ADDRESS]  
[PERSON]  
2 Department of Civil Engineering, Islamic Azad University, Tabriz 5157944533, Iran; [EMAIL_ADDRESS]  
[PERSON]  
1 School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Skudai 81310, Malaysia; [EMAIL_ADDRESS]  
Establishing calculation model and identifying dynamic parameters of a vibrating system is the key issue to these methods [4; 5]. VDD has been subject of extensive research in recent years due to accurate results and the reliable damage identification [6; 7; 8]. [PERSON] and [PERSON] [9] conducted a comprehensive review on modal parameter based VDD methods. It was stated that in these VDD methods, damage can be identified by variation in natural frequency, mode shape, curvature mode shape, and both frequencies and mode shapes. The potential and drawbacks of each method is discussed. It is stated that natural frequency is suitable for damage detection whereas mode shape and curvature mode shape is generally used for damage localization. [PERSON] and [PERSON] [10] provided a review of current developments in VDD techniques for small to medium span bridges. It was determined that output-only approaches that use non-modal models offer significant advantage due to ease of application, higher sensitivity and robustness. [PERSON] et al. [11] conducted a comparative study to evaluate different VDD methods. In the paper four different categories of VDD methods including local diagnostic fundamental modal examination, non-probabilistic, and time domain methods were compared. It was stated that time-domain methods proved more successful damage identification than the rest of the methods. [PERSON] [12] provided a comprehensive review on operational modal analysis using vibration response of structures. In the study the system identification methods are revealed. Then, some powerful system identification algorithms are discussed and different algorithms and approaches are compared. Moreover, [PERSON] et al. [13] discussed about economic aspect of VDD using a bridge case study. System identification methods provide a powerful tool to construct analytical model of a dynamic system [14]. These methods rely on the hypothesis that changes in physical parameters of a structure changes its dynamic behavior [15; 16]. System identification is one the powerful methods to extract dynamic parameters of structures. These methods utilize approximate solutions for estimating system parameters and for exploiting possible damage-related variations in structures [17; 18]. Based on the used measurement data system identification methods can be categorized into two input-output and output-only classes [5; 19]. Output-only methods use the structural response of operational and environmental excitation forces for identification of system parameters. Output-only methods are more favorable choice due to ease of setup less-intrusive nature, and lower maintenance cost [6]. Acceleration, velocity and displacement signals are the measures that can be used for system identification in vibrating structures [20]. However, acceleration response is the most frequently used measure for VDD due to relatively superior signal-to-noise ratio at high spectral range, high sensitivity, cost-effectiveness of acceleration transducers, and Installation convenience of acceleration transducers [20; 21]. Several studies have used acceleration response as their input data which among them [PERSON] and [PERSON] [22], [PERSON] et al. [23], and [PERSON] et al., [24] can be mentioned. [PERSON] et al. [25] studied the performance of input-output and output-only algorithms in an offshore platform under three different excitation signals of step relaxation, impact, and ground motion. All procedures had good agreement with estimated modal frequencies of stronger modes.