Stress-strain condition of reinforced timber structures with artificially created weakenings

Abstract

About 20% of the world’s timber grows in Russia, but the huge forest-raw material potential is used inefficiently. The forest industry is modestly represented and the Russian economy brings minimal income. In recent decades, more serious requirements have been placed on building structures, but the quality of lumber has been steadily declining throughout the world. The modern woodworking industry improves the quality of lumber by removing unacceptable wood defects, followed by end gluing of boards to a “mustache” or “toothed joint”. Of all types of joints of wooden elements, the notched adhesive or “toothed joint” provides the best use of their bearing capacity, since it causes less weakening of the cross-section of the elements, which is characteristic of other methods of joining (nailing, bolting, etc.). But along with this, the results of numerous tests showed that in conditions of mass production, the main place of destruction is the “toothed joint” or gear joints (about 50%) in the layers of the structures of the stretched zone. The presence in the most stressed layers of the stretched zone of the bent glued elements of the gear joints leads, as a rule, to the destruction of the elements precisely because of these weaknesses. As a result, there is a need for a more detailed and indepth study of the effect of artificially created weakenings on the work of wooden structures. One of the methods for improving the performance of structures made of low-grade wood is their reinforcement. The purpose of the research is to determine the degree of influence of some artificially created types of attenuation on the stress-strain state of reinforced wooden beams. The main research methods: mathematical calculations, computer modeling in the PC “COSMOS / M”, experiment. The experimental design technique is given [27]. The results are presented in the form of graphs and tables. The main conclusions made after the work: deformability in reinforced beams is 15-20% lower than in unreinforced ones; the destruction of reinforced beams with a weakened cross section occurs without a sharp collapse, due to the supporting effect of the reinforcement in the stretched zone and the reliable connection of the reinforcement with the wood, which provides an adhesive joint up to the destruction of the wood. The safety factor of reinforced wooden structures varies from 3.00 to 5.00.