Load Bearing Capacity of Wooden Bending Elements

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UDС

UDK 624.011

DOI:

DOI: 10.17238/issn0536-1036.2016.1.115

Abstract

The paper presents the increasing possibility of load bearing capacity of bending wood structures through some special methods of wood modification or stratified reinforcement. Wood as a natural polymer is composed of cellulose in the form of hollow fibers. The cellulose chains in the walls of hollow fibers are grouped in the form of crystalline particles of micelles, where the chains are oriented parallel and held firmly by intermolecular forces. The rest of the so-called amorphous cellulose is composed of the unoriented regions. There is no complete chain intersaturability, and the interaction of cellulose with other materials can easily occur. As for the plastic nature of timber behavior in compression the loss of sta-bility of one fiber causes the additional loading of adjacent fibers, and this process increases the compressed zone cross-sectional height along. The amorphous part of cellulose provides the plastic nature of deformation of compression, and causes the decrease the deformation zone of compression and the tensile deformation. This leads to the overloading of extended fibers and their rupture. This is the scheme of normal stresses of compression and tensile in a wooden beam under transverse bending. In case of reinforcement of only compressed tim-ber zone by modifying the amorphous part of cellulose there occurs the volume filling be-tween the bundles of fibrils and engaging it into the mechanical work. There are a lot of methods of wood modification. They are used to increase the wood strength and stiffness. Pine wood modified by phenolic alcohols in compression strengthens at close range to the tensile strength of unmodified pine wood. This means that their proportional limits are al-most identical; the normal stresses in a beam with a modified compressed layer increase essentially. Another method is a stratified reinforcement. However, the known method of wood reinforcing by the separate rods is efficient from a technological point of view, but rather cost-based. In the process of manufacturing of glued board beams of stratified rein-forcement the metal meshes or carbon fiber webs of high modulus materials are installed between the layers of boards. In order to increase the bending strength and rigidity of a beam, it is necessary to increase its geometrical characteristics. In this regard, the modulus of elasticity of high modulus materials (metal or CFRP) should be not less than 21 times greater than the modulus of wood elasticity. The metal mesh is very convenient to use. Its thickness should be in the range of 1 mm, which provides the indentation of the mesh into the adherend boards with minimal pressure.

Authors

V.V. Stoyanov, Doctor of Engineering Sciences, Professor Sh. Zhgalli, Postgraduate Student

Affiliation

Odessa State Academy of Civil Engineering and Architecture, Didrihsona str., 4, Odessa, 65029, Ukraine; е-mail: mdipk@yandex.ru

Keywords

wood structure, wood modification, transverse crack, high modulus materials.

References

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Received on May 22, 2015