Quasi-distributed optical fibre extensometers for continuous embedding into concrete: design and realization

Abstract

This paper reports on the design and realization of a new optical fibre sensor for continuous measurement of concrete strain over very long distances.We propose a composite-made wave-like sensor body that enables continuous bonding between optical fibre and concrete. Finite element analysis shows that the stiffness of the optical fibre can be adapted to that of the concrete, reducing the strain concentrations and the need for a theoretical calibration factor. Moreover, unlike the body of traditional I-shaped sensors, a wave-like sensor body enables a symmetrical response in tensile and compressive loadings whatever the contact conditions may be.We have realized optical fibre extensometers based on this technique and on a low-coherence interferometry method for the measurements. Despite its wave-shape, the proposed sensor body does not introduce any losses or strain that would result from fibre microbending. The process of realization is adapted to distributed sensors and sensors with a very long gauge length. Furthermore, several sensors were multiplexed, demonstrating the ability to perform quasi-distributed measurements. Once embedded into concrete cylinders, the optical fibre sensors were tested under compressive and tensile loading, and compared with traditional sensors. The allocation of one of the multiplexed sensors as a dummy gauge provides self-compensation for thermal effects and ambient fluctuations. As a result, and without any calibration factor, optical sensor measurements perfectly agreed with external linear variable differential transducer measurements.

Smart Sensing Technologies for Structural Health Monitoring of Civil Engineering Structures

“…The sensors survived the 4 million loading cycles at a strain amplitude of 2000 με, and showed good response to dynamic loading. Delepine-lesoille et al [11] designed a kind of composite-made wave-like sensor body, which could make the stiffness of optical fiber and concrete match to one another. Thus, strain concentrations were reduced, and no theoretical calibration factor had to be taken into account.…”

Qualification of a truly distributed fiber optic technique for strain and temperature measurements in concrete structures

“…In this experimental campaign, a wave-like composite sensing cable, made of fiber reinforced epoxy resin, with an average diameter of 5 mm [10] (Figure 3(a)), was embedded into the centre of a concrete cylinder of height 100 cm and diameter 16 cm. Distributed measurements were performed using an OBR device.…”

Multiplexed Long-Base Flexible Optical Fiber Extensometers and Temperature Bragg Sensors Interrogated by Low-Coherence Interferometry

“…Recently, the SMARTape [25] has been proposed. For embedding into concrete, we developed an original composite-wave-like fiber sheath [26] which is able to transfer the concrete strain field to the optical fiber without being sensitive to the bounding conditions, even if slipping occurs at the interface between the sensor and the host material.…”

“…1. The fiber is enclosed in a packaging whose primary function is to guarantee a continuous and optimal transfer of the strain from the host material to the fiber [26]. The cavities are sensitive to the elongation, and to the temperature.…”

“…A wave-like fiber sheath has been developed and validated separately [26], leading to long-base flexible sensors enabling quasi-distributed strain measurements (see Fig. 3).…”