A Sensor-Type PC Strand with an Embedded FBG Sensor for Monitoring Prestress Forces

Abstract

Prestressed Concrete Wire and Strand (PC) strands are the most used materials to introduce prestress in a Pre-Stressed Concrete (PSC) structure. However, it is difficult to evaluate the final prestress force of the PC strand after prestressing or its residual prestress force after completion of the structure on site. This impossibility to assess eventual loss of prestress of the PC strand has resulted in a number of serious accidents and even in the collapse of several structures. This situation stresses the necessity to maintain the prestress force residual or after prestressing for the evaluation of the health of the concrete structure throughout its lifespan. Recently, several researchers have studied methods enabling one to verify the prestress force by inserting an optical fiber sensor inside the strand but failed to provide simple techniques for the fabrication of these devices to fulfill measurement performance from the design prestress to failure. Moreover, these methods require the additional installation of electrical resistance strain gages, displacement sensors and load cells on the outer surface of the structure for long-term precise measurement. This paper proposes a method enabling one to evaluate precisely and effectively the prestress force of the PC strand and intends to verify the applicability of the proposed method on actual concrete structures. To that end, an innovative PC strand is developed by embedding a Fiber Bragg Grating (FBG) sensor in the core wire of the PC strand so as to enable short term as well as long term monitoring. The measurement performance of the developed strand is then evaluated experimentally and the reliability of the monitoring data is assessed.

Estimation of Friction Coefficient Using Smart Strand

“…2b to accurately measure the strain and prestressing force along the strand (KICT 2013(KICT , 2014Kim 2015;Kim et al 2015). In the Smart Strand, the steel core wire of a general strand is replaced with carbon fiber reinforced polymer (CFRP) to contain the optical fiber and Bragg grating sensors at the center of the core wire section.…”

“…In order to overcome these drawbacks of the existing measurement system, the Smart Strand with the embedded fiber Bragg grating sensors was developed in this study to accurately measure the strain and prestressing force along the strand (KICT 2013;Kim et al 2015). As one of the applications of the Smart Strand, friction coefficients were evaluated using a full-scale test of a 20 m long beam.…”

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. Moreover, the strain can be measured at the locations at which the fiber Bragg grating (FBG) is engraved in the optical fiber [1,2] or all along the optical fiber using the Brillouin wave [9].…”

“…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. Moreover, the strain can be measured at the locations at which the fiber Bragg grating (FBG) is engraved in the optical fiber [1,2] or all along the optical fiber using the Brillouin wave [9]. Figure 1 presents a typical configuration of the smart strand in which the steel core wire is replaced by a core wire with sensing function.…”