PSI - Issue 59

Serhii Drobyshynets et al. / Procedia Structural Integrity 59 (2024) 601–608 Serhii Drobyshynets et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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weight) was made in the factory. The mixture was compacted using a hand vibrator. The samples were opened after three days and then stored in a humid environment for 28 days. A total of 30 prisms and 12 cubes were made of steel fibre-reinforced concrete. The prismatic strength of the matrix at the age of 270 days was 26.9 MPa. The prisms were tested in compression in a press with a division price of 2 kN. The prisms were centred along the physical axis with a load of approximately 10 % of the destructive load. The prisms were loaded in a mild mode in stages, the values of which were 5 % of the destructive force. At each loading stage, the prisms were held for 3 to 4 minutes to take readings on the instruments. Complete unloading was performed in the same steps when testing the prisms with repeated (cyclic) loads. The deformations of the prisms were measured by clock-type indicators with a division price of 0.001 mm on a 300 mm base. The indicators were attached to the prisms on their four faces using holders glued with epoxy glue. 4. Research results and discussion Before cyclic prism testing, the performance of steel fibre-reinforced concrete under a single monotonic load of three prisms was investigated until failure. Based on these studies, the main parameters of elastic-plastic deformation of steel fibre-reinforced concrete, which are necessary to determine its low-cycle fatigue, i.e. to implement equation (4), were determined. When loaded from the natural state, the average prismatic strength of steel fibre-reinforced concrete was R fb = 31.3 MPa, i.e., it exceeded the strength of the matrix by 16.4 %. Fig. 1 shows a graph of prism deformation (average data for three prisms) and the nature of the change in the modulus of elastic-plastic deformation of steel fibre reinforced concrete E fb depending on the applied load R fb /    fb .

a

b

1

30

0.8

25

0.6

0.4

20

0.2

15

0

0.2

0.6

0.8

1

0.4

0

50

100

150

200

0

Fig. 1. The dependence between stresses  fb and longitudinal relative strains  fb at a single load to failure ( а ) and the elastic-plastic modulus E fb on the load level  (b) .

From Fig. 1a, 1b shows that almost from the beginning of loading, the prisms deformed elastic-plastically, the dependence between stresses and deflections is curvilinear, which indicates that low-cycle fatigue may occur in steel fibre reinforced concrete at high levels of compressive loads. The correlation between the modulus of elastic-plastic deformation E fb and the stress level  for the tested concrete is linear (1 0,31 ) ,0    fb fb E E (6)