A sensor-type PC strand with an embedded FBG sensor for monitoring prestress forces.

Sung Kim,Younghwan Park,Sung Park,Keunhee Cho,Jeong-Rae Cho

doi:10.3390/s150101060

Sung Kim, Younghwan Park + Show 3 more

Open Access

https://doi.org/10.3390/s150101060

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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.

Highlights

The introduction of prestress in a concrete structure improves its ultimate strength and its deflection and cracking characteristics
Electrical resistance strain gauges are bonded on the surface of the core wire for further comparison of the measured data with the optical fiber sensor embedded in the core wire
Since the sensing-strand developed in this study is planned to replace a traditional PC strand, it must possess sufficient structural performance apart from its sensing performance

Summary

Introduction

The introduction of prestress in a concrete structure improves its ultimate strength and its deflection and cracking characteristics. Kim et al [3] and Kim et al [4] proposed a method enabling one to assess the prestress force by inserting an optical fiber sensor inside a tube installed in the core wire of the strand. Since previous studies used a tube or glass fiber as core wire, it was impossible to prestress the strand Form all this it follows that most advantageous material satisfying all these requirements in terms of performance, fabricability and economy is carbon fiber. The emerging FBG sensor, which has started to be applied extensively for the monitoring of recent structures, satisfies these conditions Since this sensor presents a thin diameter of about 0.15 to 0.25 μm and can be fabricated with the desired length, it is the most suitable for being embedded during the manufacture of the carbon core wire. The measured data are analyzed to examine their reliability, and the applicability of the new PC strand on real PSC structures is validated

Fabrication of Sensor-Type PC Strand

Performance Test of the Sensing Strand

Core Wire Specimens

Strand Specimens

Discussion

Conclusions