One of the most important aspects of a prestressed concrete structure is the distribution of the prestressing force along the structure, both at transfer and in the long term. Time-dependent prestress losses are expected to occur in prestressed concrete due to both strand relaxation and dimensional changes in the concrete caused by creep and shrinkage. Thus, these losses are accounted for in the design based on guidelines set by design codes. However, prestress losses larger than predicted by design can have adverse effects on the structure, where stresses exceed the capacity of the structure at a lower load than predicted. Thus, monitoring of prestress losses will indicate valuable information regarding the performance and health condition of the structure.

However, long-term monitoring of the prestress loss is challenging due to:

1. variable on-site conditions, in particular (but not only) temperature, that affect both the structure and the monitoring system
2. rheological effects in the concrete and prestressing strands, such as creep, shrinkage, and relaxation, that interfere with mechanical effects and affect data analysis
3. presence of pre-release cracks that affects the distribution of the strain in the structure, and also affects the data analysis
4. inherent uncertainties related to the reliability and accuracy of the monitoring system and the estimation of mechanical and geometrical parameters of concrete

The outcomes of the project will be the methodology for determining long-term prestress loss using long-gauge fiber optic sensors; and validation method for long-term temperature and strain measurements used for the analysis.