PSI - Issue 59

Mykola Roshchuk et al. / Procedia Structural Integrity 59 (2024) 718–723 Mykola Roshchuk et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Sobczak-Piastka et al. (2023)), and modified wood (Huang et al. (2006); Thygesen et al. (2010); Yasniy et al. (2022)). This is because wood is used in many industries, including the construction and reconstruction of bridges and bridge crossings, hydrotechnical and other engineering structures located in the territories of the city, load bearing structures of water sports complexes, and many other things (Sobczak-Piastka et al. (2020); Gomon et al. (2022); Bosak et al. (2021); Nsouami et al. (2022)). Wood-based materials, components, and structures are strong, reliable (Green and Kretschmann et al. (1992); Bojok and Vintoniv et al. (1992); Gomon et al. (2023)), and successfully compete with composite materials based on concrete (Dvorkin et al. (2021)), and other composites (Imbirovych et al. (2023). In many criteria, wood-based products have the advantage.

Nomenclature σ с

compressive stress of wood along the fibers

relative compression deformations of wood along the fibers

u c Е

elasticity modulus of wood

ultimate compressive strength of wood along the fibers relative critical compressive deformations of wood along the fibers

f c,0,d u c,0,d

Wood can be exposed to the influence of active, aggressive environments, such as aqueous (Báder and Németh (2019); Madsen (1982); Vasic and Stanzl-Tschegg et al. (2007); Wang et al. (2003)), alkaline, acidic (Homon et al. (2023)), etc. The change in the mechanical properties of different wood types during drying at a moisture content of 30% to 12% under axial compression along the fibers (Homon et al. (2023); Janiak et al. (2023)) has been previously investigated. In contrast, this article will focus on the impact of the water environment on the physical and mechanical properties of pine, spruce, and oak wood after prolonged moistening with river and seawater. Examples of such work can include load-bearing structures of bridges, bridge crossings, and piers, as well as shore-protecting engineering structures. Under these operating conditions, wood is constantly moistened and, under certain conditions, may operate in a supercritical stage of work. Therefore, the aim of this study is to conduct experimental studies of pine, birch, and oak wood after prolonged moistening with fresh and seawater under compression along the fibers, establish the basic mechanical characteristics in the pre-critical and supercritical stages of material operation, and compare the results with indicators at the standard moisture content of 12%. 2. Methods of experimental research To address the main objectives, 54 samples of first-grade wood (spruce, pine, oak) with dimensions of 30x30x120 mm and no visible defects were prepared. Prisms were manufactured from pre-prepared timber and dried in special drying chambers to a standard moisture content of 12%. Subsequently, the samples were immersed in fresh and saltwater for 180 days. Freshwater was taken from the Ustia River (Rivne region, Ukraine), and saltwater from the Black Sea (Odesa region, Ukraine). Immediately before testing, the prisms were removed from the containers with the aqueous medium. The wood samples were subjected to a rigorous loading regime on the STM 100 testing machine, applying a single short-term load under axial compression along the fibers (ASTM D 143-14: 2014; DSTU 3129: 2015; DSTU EN 38). The deformation rate was set at 2 mm/min. To investigate changes in the mechanical properties of wood parallel to the testing of prisms long-soaked in water, an experimental study of samples at the standard moisture content of 12% was conducted simultaneously. The scope of experimental wood research under the influence of different aqueous environments is presented in Table 1.