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This study presents a method for on-site assessment of prestress losses in prestressed concrete structures. The study is motivated by the increased use of prestressed concrete, the importance of prestressing force levels as a parameter, and the lack of formalized methods for its on-site assessment. The proposed method uses strain measurements from long-gauge fiber optic sensors to study strain changes at the centroid of stiffness (i.e. centroid of composite section) of the cross-sections. Its advantages include (1) robustness to operational load on the structure caused by seasonal and daily temperature variations, in addition to loading; (2) rigorous quantification of uncertainties associated with measurements and parameters; and (3) applicability to a wide range of beam-like structures. The application of the method is illustrated through application to measurements collected over a 7-year period from strain sensors embedded in Streicker Bridge, a post-tensioned concrete pedestrian bridge on the Princeton University campus. Application of the method indicates that prestress losses measured by sensors are of comparable magnitude to design estimates, which implies that estimates are not necessarily overly conservative. [ABSTRACT FROM AUTHOR]

Summary: This paper presents an overview of currently available methods for monitoring prestressing forces in prestressed concrete structure. Structural health monitoring has become an increasingly important tool for assessment of structural performance. Additionally, the value of the prestressing force represents an important parameter in prestressed concrete structures. Thus, several methods for monitoring prestress forces have emerged. This paper aims to consolidate the work performed in the area of prestressing force monitoring by presenting the most important advances and the directions for future research. The methods presented in this paper are based on indirect monitoring of the prestressing force through monitoring of another relevant parameter. They are divided into five general classes based on the relevant parameter they monitor: (a) vibration‐based methods (based on acceleration), (b) impedance‐based methods (based on electrical impedance), (c) acoustoelastic methods (based on wave velocity), (d) elasto‐magnetic methods (based on magnetic permeability), and (e) strain‐based methods (based on strain). The paper presents a table summarizing the comparison between the methods based on defined criteria. [ABSTRACT FROM AUTHOR]

In civil structures and infrastructure, assessing true performance and characterizing unusual structural behaviors can help avoid severe structural problems. To further refine or validate the conclusions from structural health monitoring (SHM) analyses, nondestructive evaluation or techniques (NDE or NDT) can be applied in conjunction with SHM approaches. Ground penetrating radar (GPR) is an NDT that has been used to investigate defects and internal features in concrete structures, but is not commonly used to assess mechanical properties for the purposes of SHM. As a preliminary investigation of the effectiveness of attribute analysis techniques, a GPR survey was conducted on Streicker Bridge (a pedestrian bridge on Princeton University campus with embedded fiber-optic strain and temperature sensors). The bridge was constructed in two phases, where different curing conditions produced different material properties (compressive strength of 51 MPa and 59 MPa). Both standard processing techniques and attribute analysis techniques were employed to interpret GPR reflections in each phase of construction to identify construction elements and to compare the attribute signatures of different strength concretes.Though this study presents primarily relative differences, the sensitivity of these attributes to material property differences is confirmed. This validates SHM studies of the bridge and indicates the potential of the attribute analysis method for material characterization, especially as a compliment to other SHM and NDE techniques. [ABSTRACT FROM AUTHOR]