DETERMINATION OF TANGENTIAL STRESSES IN WOODEN BEAMS TAKING INTO ACCOUNT NONLINEAR DEFORMATION OF WOOD

Abstract

Wood structures have a number of advantages. It is less weight, resistance to chemically aggressive environment, high fire resistance when properly processed (even compared to reinforced concrete), as well as aesthetic appeal, which is also very importantly. Various methods of reinforcing wooden structures have been proposed and investigated to improve the performance of wood elements, increase load-bearing  strength and decrease flexibility. This made it possible to reduce the overall dimensions of the cross section of the reinforced element of wood and increase the spans. A new design of combined reinforcement of glued wood beams was proposed, in which steel rod reinforcement of periodic profile was arranged in the grooves of the compressed zone, and the stretched zone was reinforced with external composite tape. These reinforcements of the compressed and stretched zone had a positive effect on the overall strength and reduced deflections of such beams, but the destruction of some beams was due to chipping of wood along the fibers. Nowadays, the definition of tangential stresses is reduced to the definition of tangential stresses using the "Zhuravsky" formula, which can be used to determine stresses in elastic elements. However, wood is not an elastic element. Therefore, the task was to determine the tangential stresses in the cross section taking into account the nonlinear deformation of wood. We have built three plots of tangential stresses for wooden beams, which are supported on two supports. The first diagram is for a beam on which a uniformly distributed load acts, the second beam with a concentrated force acting in the center of the beam and also with two concentrated forces and a section of pure bending. As can be seen from the figures, the plot of tangential stresses is not rectilinear, there are maxima of tangential stresses in the areas, and therefore there are dangerous sections where destruction can begin. It should also be noted that the maximum tangential stresses are not in the center of the section, they are just below the center. This fact is confirmed by the destruction of beams by cutting between the compressed and stretched area, namely the cut below the cross-sectional center of the wooden beam. The article describes a method for determining tangential stresses along the entire length and height of a wooden beam, taking into account the nonlinear operation of wood. The diagram of the maximum tangential stresses, which we obtain when calculating wood using classical methods, namely the theories of elasticity does not correspond to the actual diagram. Tangential stresses should be determined taking into account the elastic-plasticity of wood.