PSI - Issue 72

Oleksandr Chapiuk et al. / Procedia Structural Integrity 72 (2025) 308–314

312

(2)

s m an kl  0 

The stress distribution in the reinfo rcing rods σs at a displacement δu of 0.2 mm from the anchoring length lan is illustrated in Fig. 4.

σ s , МPа

500

400

300

2

200

1

100

l an , cm

0

0

5

10

15

20

25

30

Fig. 4. Dependency of the stress in reinforcing rods σ s at δ u = 0.2 mm on the length of its anchorage l an : 1 - experimental data; 2 - according to formula (2)

The standard tensile strength of reinforcement A500C is Rsn =500 MPa, while the calculated tensile strength is Rs=400 MPa. According to formula (2), to ensure equal strength in terms of cohesion with B25 class concrete, the minimum anchoring length must be at least 30.3 cm. To achieve the calculated resistance in the reinforcement, a minimum anchoring length of 24.2 cm, or at least 15d, is required. These findings are supported by both preliminary and main experiments. It is important to note that the coefficient k should be determined for each class of concrete. The tangential adhesion stresses τum in specimens P -1 with an anchoring length of 8 cm were calculated using formula (1), resulting in τum = 6.7 MPa at stresses σs0m = 135.1 MPa. In specimen P -2, with an anchoring length of 16 cm, τum = 6.2 MPa at a stress of σs0m = 248.8 MPa. For specimen P -3, with an anchoring length of 24 cm, τum = 6.6 MPa at a stress of σs0m = 398.0 MPa. These results indicate that tangential adhesion stresses in the limit state τum are largely independent of the rods’ anchoring length lan. Let us analyze the performance of specimens P-4, P-5, and P-6 under repeated low-cycle loads. In the first cycle for prism P-4, the average displacements of the reinforcement relative to the concrete at the maximum level of repeated loads, Pcyc= 79.6 MPa, were 0.015 mm, and the value of residual slippage after the first cycle was 0.003mm (Fig. 5). During the second loading-unloading cycle, the maximum slip was recorded at 0.017 mm, and the residual slip increased to 0.004 mm (23.5% of the maximum). As the cycles continued, both the maximum and residual slip increased slightly, and after the fifth cycle, they stabilized at the same level: the maximum slip was 0.02 mm, and the residual slip was 0.006 mm. On the 11th cycle, the displacement of the free end of the rod relative to the end of the prism reached 0.2 mm at a stress of σs0m = 134.3 MPa, and the sample collapsed under this load.