PSI - Issue 72

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

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fcube = 30.5 MPa, while the prism strength at 57 days of age (the age of concrete when testing the main specimens began) was fprism = 21.3 MPa. Since the tests of this series of specimens were carried out over 6 days, it is reasonable to assume that the concrete strength remained unchanged during this period (see Fig. 1a). The scope of experimental studies is presented in Table 1.

Table 1. The scope of experimental studies

Sample number

Concrete class

Rod diameter d , mm

Anchoring length, cm

Number of samples

Type of load

P-1 P-2 P-3 P-4 P-5 P-6

В25 В25 В25 В25 В25 В25

16 16 16 16 16 16

8

3 3 3 3 3 3

One-time load One-time load One-time load Low-cycle load Low-cycle load Low-cycle load

16 24

8

16 24

The study of reinforcement adhesion to concrete was conducted by extracting the rod from the concrete prism using a specialized tensioning device in a hydraulic tensile machine (Fig. 1b). The load was applied to the rod in increments of P=0.5 to 1.0 kN. During loading, the slip (displacement) of the free end of the rod relative to the end of the prism was measured using a dial indicator with a graduated scale of 0.001 mm, and the deformation of the rod on the loading side was monitored with a Guggenberger strain gauge on a 20 mm base, also with a precision of 0.001 mm.

a)

b)

Fig. 1. (a) general view of the test samples; (b) testing of the samples.

Specimens P-1, P-2, and P-3 were tested using a single load until failure, while specimens P-4, P-5, and P-6 were subjected to repeated low-cycle loading and unloading (10 cycles) at the level o f ηcyc=0.6. On the eleventh cycle, these prisms were loaded to their limit state, characterized by a total slip of δu=0.2 mm. The limiting state of reinforcement adhesion to concrete is defined as the condition when the slip (displacement) of the free end of the rod relative to the end of the prisms reaches δu = 0.2 mm. For our purposes, we assume that this value of δu corresponds to the stress in the reinforcement, σs0. 3. Results and discussion The test results confirmed adequate homogeneity of concrete in the twin specimens P-1. In these specimens, a value of δu =0.2 mm was achieved at an average rod stress of σs0m =135.1 MPa (coefficient of variation υ=0.0107). In all P- 1 specimens, slippage began at a stress of σs=9.95 MPa, with a displacement of δ=0.001 mm.