Application of Distributed Fibre Optical Sensing in Reinforced Concrete Elements Subjected to Monotonic and Cyclic Loading

Yasmin Lemcherreq,Jaime Mata-Falcón,Tena Galkovski,Walter Kaufmann

doi:10.3390/s22052023

Abstract

Distributed fibre optical sensing (DFOS) is increasingly used in civil engineering research. For reinforced concrete structures, almost continuous information concerning the deformations of embedded reinforcing bars can be obtained. This information enables the validation of basic and conventional assumptions in the design and modelling of reinforced concrete, particularly regarding the interaction of concrete and reinforcing bars. However, this relatively new technology conceals some difficulties, which may lead to erroneous interpretations. This paper (i) discusses the selection of sensing fibres for reinforced concrete instrumentation, accounting for strain gradients and local anomalies caused by stress concentrations due to the reinforcing bar ribs; (ii) describes suitable methods for sensor installation, strain acquisition and post-processing of the data, as well as determining and validating structurally relevant entities; and (iii) presents the results obtained by applying DFOS with these methods in a variety of experiments. The analysed experiments comprise a reinforced concrete tie, a pull-out test under cyclic load, and a flexural member in which the following mechanical relevant quantities are assessed: the initial strain state in reinforcing bars, normal and bond shear stresses, deflections as well as forces. These applications confirm the benefit of DFOS to better understand the bond behaviour, but also demonstrate that its application is intricate and the results may lead to erroneous conclusions unless evaluated meticulously.

Highlights

Received: 22 January 2022The response of structural concrete members is governed by the interaction between the reinforcement and the surrounding concrete
The results confirm the observations reported in the companion paper [28]: at the start and end of the length of interest, the polyimide coated fibres measured a sharp strain increase, while the strains measured by the acrylate-coated fibres showed a gradual increase to the same level as the other two fibres
The slip between fibre and coating causes this variance in the activation length and is the reason why the acrylate coated fibre is unable to reproduce sharp changes in the strain profile: unlike both polyimide-coated fibre types (PG and PS), the acrylate-coated fibre could not reproduce the plateau in the strain profile and measured lower maximum strains

Summary

Introduction

Received: 22 January 2022The response of structural concrete members is governed by the interaction between the reinforcement and the surrounding concrete. Since the first use of reinforced concrete structures, researchers have been concerned with the understanding and proper modelling of this interaction. It was hardly possible to investigate the stress transfer between concrete and reinforcement experimentally due to limitations of the measurement technology available and the fact that the interface remains difficult to access without influencing its structural behaviour. Under the assumption of nominal bond shear stresses of constant magnitude over the bonded area, these simple tests allow the deriving of bond stress–slip relationships, which can be used to model the stress transfer between concrete and reinforcement. The traditional experimental setup remains controversial, as it does not represent the stress conditions in an actual structure: for instance, compression fields are generated by the bearing plate used in the tests, and the concrete cover exceeds practical values.

Methods

Results

Conclusion