SIMULATION OF WORK OF A REINFORCED PRE-STRESSED WOODEN ELEMENT
Authors:   National University of Water and Environmental Engineering, Homon Petro 
Published: August 2023

An undeniable disadvantage of wood when using it in construction is its excessive flexibility. One of the ways to increase the stiffness of wooden elements is to use prestressing and reinforcement with stiffer elements. The manufacturing process of pre-stressed bending elements proposed by us is simple. However, determining the necessary effort, the necessary bending of the beam to ensure reliable operation, preventing the destruction of the element is quite difficult. One of the methods of prestressing is described, namely, the method by which the beam receives internal stresses due to the release of the bending element after the action of the external load by gluing reinforced elements. The principle of such tension can be described in the following sequence: 1. We create a bend in the bending element by applying an external load to the element. 2. We reinforce the lower zone of the bending element. At the same time, we need to know under which stress-strained state the reinforced element was installed, so that its operation can be predicted. 3. We remove the applied force with which we created the bend in the flexible wooden element, while the element wants to acquire its original shape, but this will be prevented by the armature, which will absorb part of the load and leave a small bend. It was established that the level of prestressing, namely the curvature acquired by the bending element after prestressing, depends on the initial curvature of the wooden element, as well as on the area and physical and mechanical characteristics of the materials reinforcing the beam zones. To determine the prestress, it is necessary to establish the stress-deformed states of the bending element, which occur after gluing and release of the external force. At the same time, 3 levels of the stress-strain state can be distinguished. 1. At the first stage, the compressed zone is more than the stretched zone. The relative deformations of the compressed lower zone, where the material is to be attached, is the initial start for the work of the reinforced element. 2. At the second stage, the external bending moment decreases, the internal redistribution of forces takes place, in addition to the moment perceived by the compressed and stretched zone, a moment also occurs in the stretched reinforced element. 3. The third stage is characterized by the absence of an external load, and this causes a balance between the internal forces of the bending prestressed element. The equilibrium equation for three stages was obtained. When using the element as a load-bearing structure, the cross-section in the element can be with both positive and negative curvature. The peculiarities of these two stress-strain states are manifested in the change in the position of the compressed and stretched zones. In the first case, the compressed zone is located in the lower part of the element and the upper part is occupied by the stretched zone. After the curvature changes its sign from negative to positive, the upper part becomes compressed, and the lower part becomes stretched. As a result of the simulation, it is possible to conclude that the cross-section of a bending wooden element undergoes 3 main stress-deformed states during prestressing and two during its operation