PSI - Issue 59

Svyatoslav Gomon et al. / Procedia Structural Integrity 59 (2024) 559–565 Svyatoslav Gomon et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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researchers focus on investigating its physical and mechanical properties (Green and Kretschmann (1992); Landis et al. (2002); Gomon et al. (2022); Huang et al. (2006); Galicki and Czech (2005)). Wooden structures are widely used in the construction of objects for various purposes (Zhao et al. (2020), Bosak et al. (2021), Gomon (2022), Sobczak Piastka et al. (2020); Zhou et al. (2018)). They can easily compete with structures based on metal (Wang et al. (2018); Romaniuk and Supruniuk (2021)), concrete (Dvorkin et al. (2021); Babych et al. (2019); Konkol (2019); Iskhakov et al. (2022); Solodkyy et al. (2017)), and other composite materials (Imbirovych et al. (2023)).

Nomenclature M max

maximum bending moment due to external loading calculated area of the cross-section of the bending element (beam) distance from the neutral axis to any point in the compressed and tension zones

A f md

z с b

width of the cross-section of the bending element (beam) calculated value of wood strength in bending height of the cross-section of the bending element (beam).

f т,d

h

W у resistance moment of the cross-section of the bending element (beam) with respect to the y-y axis σ normal stress Е modulus of wood elasticity и deformation of wood fibers k 1 , k 2 polynomial coefficients u c,d relative wood compression deformations u t,d relative wood tensile deformations f c,0,d calculated value of compression along the fibers u c,fin,d total compression deformations of wood along the fibers σ с,d compression stress under single loading f m,z,d calculated strength values for bending relative to the z-z axis f m,y,d calculated strength values for bending relative to the y-y axis f t,0,d calculated value of tension along the fibers σ t,d tensile stress The European and Ukrainian national standards (Eurocode 5:2004, DBN B.2.6-161:2017) accept the axioms that wood behaves elastically under longitudinal tension, compression, and lateral bending up to the limit of proportional conditions. However, incomplete treatment of wood anisotropy has led to certain questionable decisions regarding the establishment of material strength for lateral bending and the determination of the load-bearing capacity of normal cross-sections by the formula: ( ) ( ) . (1) Since wood behaves elastically under longitudinal tension, nonlinear deformation occurs under the slightest load applied to the wood under longitudinal compression, with an increase in elastic and plastic relative deformations (Janiak et al. (2023), Homon et al. (2023); Yasniy et al. (2022); Madsen (1975)). Therefore, even with the same relative deformations in wood in the cross-section of the bending element, different compression and tension stresses arise (Fig. 1). At the destruction stage of the bending element, tensile stresses in the outer fibers of the wood may be twice the compression stresses. With the onset of loading, the neutral force line of the cross-section shifts towards the stretched zone. In this case, the value of the cross-section resistance moment cannot be determined:

(2)