High stress monitoring of prestressing tendons in nuclear concrete vessels using fibre-optic sensors

Abstract

Maintaining the structural health of prestressed concrete nuclear containments is a key element in ensuring nuclear reactors are capable of meeting their safety requirements. This paper discusses the attachment, fabrication and characterisation of optical fibre strain sensors suitable for the prestress mon-itoring of irradiated steel prestressing tendons. The all-metal fabrication and welding process allowed the instrumented strand to simultaneously monitor and apply stresses up to 1300 MPa (80% of steel's ulti-mate tensile strength). There were no adverse effects to the strand's mechanical properties or integrity. After sensor relaxation through cyclic stress treatment, strain transfer between the optical fibre sen-sors and the strand remained at 69%. The fibre strain sensors could also withstand the non-axial forces induced as the strand was deflected around a 4.5 m bend radius. Further development of this technology has the potential to augment current prestress monitoring practices, allowing distributed measurements of short-and long-term prestress losses in nuclear prestressed-concrete vessels.

Deformation monitoring in prestressing tendons using fibre Bragg gratings encapsulated in metallic packages

“…The resultant joints performance was proven at high temperature (350 °C) and high pressure (15 kpsi) conditions 14,15 . We also showed experimentally that by selecting proper materials, such as kovar, brazing standard FBGs into metallic ferrules can be possible without any significant deterioration in the grating reflection 16 . Our recent work related to the high stress monitoring of prestressing tendons 17 employing the developed technology demonstrated an improved performance over the epoxy-based strain monitoring systems 17,18 .…”

Estimation of Tendon Force Distribution in Prestressed Concrete Girders Using Smart Strand

“…Since such steel strands are the most important member of the PSC structure, their rupture is likely to degrade structural health. It is noteworthy that, despite its primary role, it has been challenging to directly measure the prestress distribution within the structure prior to the development of the smart strand [1][2][3][4][5]. The prestress force was estimated indirectly by a formula calculating the loss of prestress using the hydraulic pressure measured externally at the jacked end of the structure and the change in the length of the tendon before and after prestressing [6][7][8].…”

“…The smart strand can be fabricated by attaching the optical fiber between the neighboring helical wires [4,5] or by replacing the steel core wire with a core wire in which the optical fiber is embedded. In such case, the core wire is made by inserting the optical fiber inside a hollow steel tube [2] or by pultruding a carbon fiber reinforced polymer (CFRP) rod [1] or a glass fiber reinforced polymer (GFRP) rod [3] with the optical fiber monolithically.…”

Identifying fabrication defects of metal packaged fibre Bragg grating sensors for smart pre-stressing strands

“…The metal packaging also provides increased structural and chemical protection making them suitable for remote sensing in harsh environments such as those in the nuclear and oil and gas industries [4], [5]. As a consequence, metal packaged FBGs meet many of the requirements for structural health monitoring (SHM) within pre-stressed concrete containment vessels (PCCVs) [6]. PCCVs rely on pre-stressed steel tendons to provide additional concrete compression to compensate against expansion due to increased pressure within the structure.…”