PSI - Issue 72

Yuriy Panchuk et al. / Procedia Structural Integrity 72 (2025) 216–221

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(2016); Datsiuk et al. (2024); Roshchuk et al. (2024)). Such stresses can be constant, variable, and long-term (Aleksiievets et al. (2024); Homon et al. (2024)). Variable once include repeated cyclic (Drobyshynets et al. (2024)), alternating (Korniychuk et al. (2024)) and others. Very often in the construction of residential, public and industrial buildings, load-bearing reinforced concrete structures (Kovalchuk et al. (2022); Borysiuk et al. (2019); Iskhakov et al. (2023) Mel'nyk (2019); Kos et al. (2022)) made of fine-grained and coarse-grained concrete (Chapiuk et al. (2023), Dvorkin et al. (2021), Dovbenko et al. (2024)) are used.

Nomenclature f b

concrete strength

number of cycles until failure

n cyc М кр η cyc

fineness modulus

loading level

During operation, building structures are subjected to low cyclic loads at various levels (DBN B.1.2-14-2018; DSTU B V.2.6-156:2010; Eurocode 2 (2004)). The impact of these cyclic loads can lead to a specific type of failure characterized by an unlimited increase in the deformation of the structural material, even when the repeated loads do not exceed the maximum single load. Consequently, one of the key priorities when calculating the strength of structures under low-cycle loads is to identify the level and number of repeated load cycles at which deformation stabilization occurs. In practice, building structures and their components may face overloading, wherein the repeated cyclic loads surpass the design limits. Such scenarios, after a certain number of load cycles, can result in a significant escalation of plastic deformations within the structure, ultimately leading to a limit state under the influence of repeated cyclic loads, commonly referred to as low-cycle fatigue. The objective of this study is to conduct both experimental and theoretical investigations into the behavior of fine and coarse-grained concrete under high levels of low-cycle loading and unloading, as well as to determine the low cycle fatigue limits for each type of concrete. 2. Methods of experimental research To conduct a more comprehensive study on low-cycle fatigue in concrete, two types of specimens were manufactured and tested: coarse-grained concrete (CGC-1 and CGC-2) made with traditional aggregates, and fine grained concrete (FGC), which utilized only sand as an aggregate. It was hypothesized that the fine-grained concrete specimens would exhibit greater homogeneity, resulting in more reliable test results. The concrete specimens were produced using slag Portland cement. For the cement-sand concrete (FGC), quartz sand with a particle size modulus of Mkr = 1.8 to 2.2 was used, displaying a bulk density of 1410 to 1460 kg/m³. The sand was thoroughly washed to remove clay and dust impurities and was subsequently dried. The fine aggregate utilized in the CGC-2 concrete specimens was quartz sand, characterized by a particle size modulus of Mkr = 1.18, a bulk density of 1320 kg/m³, and a specific gravity of 2590 kg/m³. In the SGC-1 samples, granite crushed stone with a grain size ranging from 5 to 20 mm was employed as the coarse aggregate. This crushed stone exhibited a crushability of 10.7%, a density of 33.7%, and a specific gravity ranging from 1310 to 1410 kg/m³. For the CGC-2 concrete specimens, crushed stone with minimum and maximum grain sizes of 5 mm and 20 mm, respectively, was utilized. The bulk weight for this aggregate was 1350 kg/m³, with a specific gravity of 2700 kg/m³ and a moisture content of 0.8%. Modified Dophen was added as an additive in the production of the coarse-grained concrete specimens. Table 1 provides the composition of the concrete used for manufacturing the prism specimens. The concrete mix (FGC) was prepared in the laboratory. First, the dry components of cement and sand were mixed, and then the required amount of water was gradually added to achieve cone shrinkage of 7 to 8 cm. The concrete mix (CGC-1) was produced in a 1500-liter concrete mixer at a concrete shop, while the concrete mix (CGC-2) was made at a reinforced concrete plant.