CONCERNING THE NEED TO USE THE DEFORMATION MODEL IN THE CALCULATION OF WOODEN STRUCTURES

Abstract

Over the course of many years of research, it has been established that edge stresses are approximately equal, but with opposite signs, only at the initial stage of the operation of wooden bending elements that work under transverse bending. This is also confirmed by the works of many domestic and foreign scientists. Given that the position of the neutral axis in the calculated cross-section changes from the start of loading until failure, the calculation of normal sections of bending elements according to current standards is unreliable due to the assumption taken as an axiom that wood behaves elastically under longitudinal tension, compression, and transverse bending. In a wooden bending element, the material works simultaneously under both compression and tension, meaning they function together. It has been established that the failure of wooden bending elements in their ultimate state predominantly occurs due to the rupture of the outer layers of the tensioned zone. However, the tensile strength of wood along the grain is almost twice as high as its compressive strength. Such a paradox cannot be explained by current standards. These standards rely on determining physical and mechanical properties according to DSTU EN 408:2007, which does not use the force distribution of the cross-sectional area into compressed and tensioned zones but instead uses the geometric distribution through the center of gravity. Determining the layer-by-layer development of relative deformations across the height of the calculated cross-section for unreinforced or reinforced wooden beams in the pure bending zone at all stages of operation during loading provides an exceptional opportunity to track changes in the position of the neutral axis and stresses at these points. The conditions created for the use of the deformation model for calculating unreinforced and reinforced wooden bending elements, based on the elastic-plastic behavior of the material, completely eliminates these shortcomings. It is proposed to adopt and introduce a deformation model for the calculation of unreinforced and reinforced wooden bending elements based on the elastic-plastic behavior of the material into current standards.