###### Abstract  
This paper presents advancements in structural health monitoring (SHM) techniques, with a particular focus on wave-screening methods for assessing prestress loss in a large-scale prestressed concrete (PC) bridge model under outdoor conditions. The wave-screening process utilizes low-frequency wave propagation obtained from seismic interferometry of structural free vibrations and high-frequency wave propagation obtained through ultrasonic transducers embedded in the structure. An adjustable post-tensioning system was employed in a series of experiments to simulate prestress loss. By comparing bridge vibrations under varying post-tensioning forces, the study investigated prestress loss and examined temperature-related effects using the coda wave interferometry (CWI) method. Local structural alterations were analyzed through wave velocity variations, demonstrating sensitivity to bridge temperature changes. The findings indicate that wave-based methods are more effective than traditional modal analysis for damage detection, highlighting the dual impacts of prestress loss and temperature, as well as damage localization. This study underscores the need for long-term measurements to account for temperature fluctuations when analyzing vibration measurements to investigate changes in prestressing force in PC structures. c 2025 15 6005 2025 1  
bridges [11], with no single method emerging as definitive. Additionally, factors like tendon relaxation, creep, and shrinkage of concrete significantly influence vibration responses. To address these issues, this paper aims to develop robust and sensitive damage detection methods based on on-site vibration measurements. Many vibration-based damage identification methods are founded on the premise that structural damage reduces stiffness, altering global vibration responses and natural frequencies [12; 13]. The natural frequency of full-scale civil structures is a significant dynamic characteristic and is consequently widely used in civil engineering [14]. Modal analysis, therefore, plays a crucial role in SHM [15]. Recent advancements in active vibration techniques [16; 17] have enabled high-frequency excitations, which are more sensitive to minor damage. [PERSON] et al. outlined two main types of ultrasonic pulse velocity (UPV) systems: through-transmission and pulse-echo methods [18]. While pulse-echo techniques are commonly used in homogeneous materials, their effectiveness in concrete is limited due to the material's inherent heterogeneity [19]. Consequently, surface-mounted piezoelectric transducers have been widely used in SHM. More recently, attention has shifted towards embedded piezoelectric transducers, which can be used in monitoring the hydration process and enabling early-age concrete assessment [20]. Ultrasonic testing has been employed for over three decades to evaluate bridge conditions due to its sensitivity to micro-damage and material inconsistencies [21]. However, high-energy transitions are limited in extensive measurements, and ultrasonics are highly sensitive to environmental temperature changes [22]. In parallel, Lamb waves have been extensively used in SHM applications, particularly due to recent advancements in sensor technology [23]. These waves are highly effective for detecting surface-level damage. However, as noted by [PERSON] et al., Lamb wave-based systems are also significantly influenced by environmental and operational conditions, necessitating the implementation of temperature compensation strategies [24]. While Lamb waves are powerful for surface crack detection, our study focuses on internal structural phenomena--specifically, prestress loss and temperature-induced effects--that extend beyond the primary application domain of Lamb wave techniques. A comprehensive PC bridge model with a post-tensioning system was investigated under outdoor conditions. Various prestressing forces were applied to simulate prestress loss and induce potential damage conditions.