PSI - Issue 64

Ivan Markovic et al. / Procedia Structural Integrity 64 (2024) 1621–1627 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction 1.1. Research significance and main research objective

Aged and overburdened infrastructure, increased loads on the transport network as well as increasing natural disasters require intelligent and reliable monitoring systems that allows to control and monitor structural properties of an object. Fibre optic sensors make in general possible to detect dangers more quickly and thus to take necessary actions in time. Through the commercialization of measuring devices, these technologies could find their way into the engineering practice, where the measurement of strains is generally of importance. Related to existing concrete structures, the detection and monitoring of bending and shear cracking are of great importance for the general estimation of the structural behaviour, as well as for the behaviour of structure in service state and in terms of durability of the structures. Although the Distributed Fibre Optic Measurement Systems (DFOS) are in application in lab conditions for about two decades, their use on real existing concrete structures on site is still very modest. The reasons for this could be the time-consuming installation and evaluation of the results and specific expertise which is required to achieve this. The main objective of this work is to prove the feasibility of the DFOS measuring technique for structural monitoring of existing concrete structures in the future by means of laboratory tests. The laboratory tests should be performed in such a way and in an accuracy, which correspond to the real situation and possibilities in the monitoring of existing concrete structures. 1.2. Previous studies In this sub-chapter, a short literature study is given. In the scope of the applications of crack detection and crack control, most of the existing studies have been investigated tensile and flexural loading state (e.g. (Villalba und Casas 2013), (Henault et al. 2012), (Barrias et al., 2016), (Galkovski et al. 2021), (Winkler et al. 2019)). In (Villalba und Casas 2013) bending tests were performed on a plate, which was simply supported at both ends and loading was applied in the middle of the plate. The DFOS were glued on the concrete surface using a commercial glue. In (Henault et al. 2012), a reinforced concrete beam was tested in four point bending, where fibre optic cables were subsequently bonded on the beam surface as well as pre concrete pouring. The pre concrete pouring fibre optic cables were installed at three levels of the formwork. Different investigations were performed in (Galkovski et al. 2021) on strain sensing on reinforcing steel and concrete. 2. Research Methodology Within the scope of this work, a total of 8 beam specimens are tested in the laboratory and subsequently evaluated, within two test series (Table 1). In the laboratory tests, a bending failure is targeted for the first four specimens and for the last four specimens, a shear failure is targeted.

Table 1. Overview of the performed bending and shear tests on beams in lab conditions

Test Series

Arrangement of external DFOS bottom surf., longitudinal bottom surf., longitudinal bottom surf., longitudinal bottom surf., longitudinal side surface, perpendicular side surface, perpendicular side surface, diagonal side surface, diagonal

Beam Specimen Nr.

Loading

Load scenario

Targeted failure type

continuous stepwise stepwise continuous stepwise stepwise stepwise stepwise

Bending fracture Bending fracture Bending fracture Bending fracture

1 2 3 4 5 6 7 8

4 point 3 point 4 point 4 point 4 point 4 point 4 point 4 point

First test series

Shear fracture, beam with stirrups Shear fracture, beam without stirrups Shear fracture, beam without stirrups Shear fracture, beam without stirrups

Second test series