Abstract
The proper distribution of prestressing force (PF) is the basis for the design of prestressed concrete (PSC) structures. However, the PF distribution obtained by predictive equations of prestress losses has not been sufficiently validated by comparison with measured data due to the poor reliability and durability of conventional sensing technologies. Therefore, the Smart Strand with embedded fiber optic sensors was developed and applied to PSC structures to investigate the long-term characteristics of PF distribution as affected by concrete creep and shrinkage. The data measured in a 20 m-long full-scale specimen and a 60 m-long PSC girder bridge were analyzed by comparing them with the theoretical estimation obtained from several design equations. Although the long-term decreasing trend of the PF distribution was similar in the measurement and theory, the equation of Eurocode 2 for estimating the long-term prestress losses showed better agreement with the measurement than ACI 209R and ACI 423.10R did. This can be attributed to the more refined form of the predictive equation of Eurocode 2 in dealing with the time-dependency of the PF. The study results also confirmed the need to compensate for the temperature variation in the long-term monitoring to derive the actual mechanical strain related to the PF. We expect our developed Smart Strand to be applied practically in PF measurement for the reasonable safety assessment and maintenance of PSC structures by improving several of the existing drawbacks of conventional sensors.
Highlights
Prestressing tendons, such as seven-wire strands in prestressed concrete (PSC) structures, are used to introduce compressive stress in concrete to overcome its low tensile strength against the tensile stresses imposed in service
The measured data were compared with the theoretical values obtained by the predictive equations for long-term prestress losses that are specified in several design provisions
The prestress losses closely related to the prestressing force (PF) distribution have generally been estimated using predictive equations specified in design codes or manuals, which were mostly derived from small-scale experiments
Summary
Prestressing tendons, such as seven-wire strands in prestressed concrete (PSC) structures, are used to introduce compressive stress in concrete to overcome its low tensile strength against the tensile stresses imposed in service. Garber et al [8] used vibrating wire gauges to measure the prestress loss in full-scale girder specimens Their calculated loss may have been less accurate because the strand strains were derived from the concrete strains obtained from the vibrating wire gauges embedded in concrete at mid-span. Shing and Kottari [10] compared several predictive equations and field data in terms of the long-term prestress losses in some PSC box girder bridges. The Smart Strands were applied to a 20 m-long full-scale specimen and a 60 m-long PSC girder bridge to investigate the long-term characteristics of the PF distribution affected by long-term prestress losses. The measured data were compared with the theoretical values obtained by the predictive equations for long-term prestress losses that are specified in several design provisions
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