Evaluation of Post-tensioned Concrete Structures by Fiber Sensors: A study to develop sensor driven methods for evaluation of PRC elements, determine remaining prestressing force and assess key performance indicators.

Abstract

Prestressed concrete structures have numerous advantages over conventionally re inforced concrete, though the usage of post-tensioned structures has declined over the last decades. Structural health monitoring (SHM) have potential to change thistrend and by implementing this technique in civil structures the knowledge about the structural response over time will increase. By constructing two beams and im plement distributed optical fiber sensors (DOFS), key performance indicators of thepost-tensioned concrete specimens were monitored and evaluated. One specimenwas post-tensioned, while the other one served as a reference specimen, built the same apart from being prestressed.Initial losses, as well as long term effects affecting prestressing force, deflections andcracks were tracked and compared to theoretical calculation methods. Later, the specimens were pre-cracked and tested in a four-point bending test. It was found that the theoretical calculation methods mostly agreed well with results from the distributed optic fiber sensors. The loss of prestressing force due to creep and re laxation differed 0.8 %, while the loss due to friction differed 0.6 %. Regardingdeflections, the relative error ranged up to 3.3 % for the reference specimen, while the post-tensioned reinforced concrete specimen ranged up to 2.9 %. The crack onset was traced using both Digital image correlation (DIC) and DOFS. Due to the low strain values, it was only the DOFS that were able to capture the crack onset. Comparisons were made to previous research to verify the assumptionthat certain strain peaks could be correlated to crack onset. The results and conclusions are a foundation for larger scale use of structural health monitoring systems implemented in civil engineering structures, that could con tribute to safer, sustainable, and more resilient infrastructure.