PSI - Issue 81

Serhii Drobyshynets et al. / Procedia Structural Integrity 81 (2026) 406–410

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a hydraulic jack. At each loading stage, a holding time of 5 minutes was maintained, which ensured stabilization of deformations and allowed the readings to be recorded. The magnitude of the applied force was monitored using a dynamometer, while beam deflections were measured using deflectometers installed at characteristic sections. The obtained experimental data were used to analyze the stress – strain state and to perform a comparative assessment of the load-bearing capacity and deformability of beams with different types of reinforcement. The failure criterion of the beams was defined as the condition under which the reinforcement strains in the normal cross-section

of the beams reached their ultimate values (yield limit). All beams were tested under low-cycle loading (Fig. 1). 3. Results and discussion

Based on the conducted tests, graphical relationships of the variation in the maximum and residual midspan deflections of the tested beams were constructed (Fig. 2). The obtained curves make it possible to analyze the deflection development for each individual beam as a function of the upper level of cyclic loading and the number of applied cycles.

a

b

Fig. 2. Deflections of the investigated beams: (a) maximum, (b) residual

For beam B- 2 (η=0.6/0), the values of total deflections determined in the first cycle were 7.93 mm, while the residual deflections were 1.65 mm (20.8% of the total). Up to the fifth cycle, a gradual increase in total deflections to 8.56 mm and residual deflections to 1.82 mm was observed. During cycles 5 to 6, the deflection values showed partial stabilization, although no distinct stabilization limit was identified. Subsequently, the beam operated in a nearly stable mode, with deflections increasing in each subsequent cycle by 1 to 1.5% for total deflections and by about 6% for residual deflections. Prior to failure in the eleventh cycle, the total deflections increased to 16.08 mm and the residual deflections to 2.01 mm, corresponding to an increase of 103% and 22%, respectively, compared with the first loading cycle. Beam B-3, which was tested under the same loading regime as beam B-2, exhibited a total deflection of 7.89 mm in the first cycle, while the residual deflections were 1.57 mm, which is 4.85% lower than those of the reinforced concrete beam. Thereafter, the beam operated in a stable mode, with a minor increase in deflections of 2 to 5.5%. During the fifth to sixth loading – unloading cycles, stabilization occurred, and the total deflections reached 8.8 mm, while the residual deflections were 2.13 mm. With an increase in the number of cycles to ten, a slight increase in deflections was again observed, amounting to 0.5 to 1.5% for total deflections and 2 to 4.5% for residual deflections. Prior to forced failure in the eleventh cycle, the total deflections increased to 15.96 mm and the residual deflections to 2.27 mm. Compared with the first cycle, the total deflections at failure increased by 102%, while the residual deflections increased by 44.6%. It should be noted that the deflections of the reinforced concrete and reinforced concrete with rebar and steel fibers beams developed in a nearly identical manner and amounted to 16.08 mm and 15.96 mm, respectively, before failure. The total deflections of beam B- 1 (η=0.6/0) determined in the first cycle were 0.92 mm, while the residual deflections were 0.30 mm (33% of the total). Such low deflection values can be explained by the fact that, according to the experimental program, the beam was manufactured without longitudinal main reinforcement. Similar to the previous beams, up to the fifth cycle a gradual increase in total deflections to 1.07 mm and residual deflections to 0.40 mm was observed. In the subsequent cycles, almost up to the tenth cycle, a stabilization process of beam deflections can be assumed, with only a slight increase in their values. In the tenth