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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cracks develop in large critical shear crack (or cracks) due to the load increase, which may lead to the sudden shear collapse of the whole reinforced concrete structure. Already after the 15 th load level (at the loading force of 59 kN, being approx. 30% of the maximum applied load in this test), a clear strain peak appears in specimen 5 in the lower horizontal DFOS cable (Figure 4, point C2), which corresponds to the first visible crack in the experiment. From the 16 th load level (loading force of 66 kN and further), the shear crack on the left-hand side of the beam progresses further upwards and is already visible in the middle part of the DFOS cable (Figure 4: points B1 and B2). The upper part of the beam is almost strain-free until the load level of appr. 120 kN (appr. 60% of the maximum applied load), after which tensile strains occur in the vicinity of the diagonal cracks. For the specimen Nr. 5, the loading had to be stopped at the load of about 178 kN, because the maximum loading capacity of the testing machine was reached. The specimen was however very extensively cracked at this load level, with clear diagonal crack pattern. Although the test was stopped, the feasibility of utilization of DFOS for the detection of shear cracks, especially at the critical early cracking stages, was clearly proved. Strangely, no strain peaks at middle horizontal optical glass fiber occurs on the right-hand side of the beam specimen Nr. 5 during the entire test, which is not plausible at the first sight. A possible source of this error could be the missing bond between the fibre optic cable and the beam. This shows, that similarly as any other measuring system, a proper installation is of a tremendous importance for the correct result. The results of shear tests are in further evaluation during writing of this short paper.

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Fig. 4. Left, from top to bottom: DFOS arrangement at left-hand side of the beam specimen Nr. 5, with typical shear cracking pattern at maximum load (178 kN) and with mapping of the measurement zones in upper, middle and lower part of beam; Right, top to bottom: measured strains at measurement zones (upper part, middle part and lower part of the beam), with precise position of cracks and corresponding peak strains at points B1, B2, i.e. C1 and C2