PSI - Issue 17

Kristýna Čápová et al. / Procedia Structural Integrity 17 (2019) 726 – 733 Kristýna Čápová et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Fibre Bragg grating (FBG) is an in-fibre component, which consists of a periodic modulation of the refractive index along the fibre core. Due to the advantages given by the basic properties of an optical fibre (immunity to electromagnetic interference, low loss transmission, etc.), the intrinsic grating can be conveniently utilized in sensing, Othonos and Kyriacos (1999) and Kersey (1996). This paper introduces the utilization of FBG sensors for monitoring glued laminated timber (GLT) and concrete structures. At first, a sequence of environmental tests is presented. The environmental testing in the first phase (2016) included the testing of the “interrogator – fibre optic sensors” system. This specific system is planned to be used for structural health monitoring of glued laminated timber beams; bare optical fibres, surface strain sensors attached by anchor points and temperature sensors were tested. The attention in this phase was mainly focused on the technical aspects of testing, such as positioning and interconnection of interrogators and sensors, and in particular testing of the behaviour of the entire measuring chain. In the second phase (2017) the impact of temperature change was tested on small GLT beams with laminated FBG sensors. The third phase (2018) was performed in order to verify the behaviour of FBG sensors incorporated in GLT and concrete beams under normal operating conditions. The paper shortly describes the mechanical loading tests of a full size GLT beam equipped with FBG sensors performed in the same arrangement in 2016, 2017 and 2018; year-on-year changes are presented and commented. 2. Environmental testing 2.1. Parameters of the test equipment The parameters used for the test equipment (climate chambers) define the technical conditions for designing the test cycles for the tested measuring equipment and sensors. Concerning the need of testing the interrogators and sensors in separate chambers with separately controllable environmental parameters, these facts are particularly important: • internal dimensions of the climate chamber (width x height x depth): 1000 x 1000 x 600 mm, see Fig. 1 (a) • possibility of horizontal partition: wire baskets, shelves • holes for cabling, 100 mm in diameter (sealable with cork / plastic plug) in the side walls of both climate chambers

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Fig. 1. (a) The internal space of the climate chamber; (b) Humidity diagram, A – temperature, °C, B – relative humidity, %

The boundary conditions of testing with regard to the technical capabilities of the used climate chambers were specified according to the technical documentation of the chambers. The parameters for climate chambers A and B are listed in Table 1. The relevant ranges of the working areas are presented in the humidity diagram (Fig. 1 (b) –