Defects are always an undesirable element in construction elements. They occur in all types of trees. We should pay special attention to them during the construction of the facility we are implementing. They can significantly change the properties and strength of the material to be built-in. Defects may later cause damage that is difficult to repair. Disadvantages given wood we define them by comparing them with the ideal wood pattern, that is, the one with the shape of a cylinder, with parallel fibers, with even grain distribution and without knots. We treat any deviation from the ideal as a disadvantage. Defects play an important role in the construction of wooden structures, which cause that the wood does not meet the safety and quality conditions. We distinguish different types of wood defects, which are described below.
Knots it is the most common wood defect. They damage the homogeneous structure of the wood. Knots reduce the tensile strength of a given material. Keep this in mind, in order to avoid knots in places where structural elements are connected. There are several ways to classify this disadvantage. They are divided e.g.. on Open i closed; on fused, partially fused and falling out. Knots are distinguished: healthy (no decomposition of the wood), nadpsute, broken, tinted, unlucky (debris of decomposed wood stuck with resin) and the so-called. tobacco, which lead to the decomposition of the surrounding material. Undoubtedly, knots reduce the strength of the wood. The degree of material weakening depends on the size of the defect, its location and type.
The curvature of the trunk in wood is caused by improper care of the material during drying or poor abrasion. This defect may also be present in the tree, it causes damage to the tops of growing trees and the action of winds in one direction.
Cracks are a defect often found in wood and trees. They are found in trees frost cracks, these are the gaps which narrow from the outside towards the core. Radial core cracks also appear, circular, arched and so-called. circular between annual rings. These cracks have a significant impact on the strength of a given construction material. Differences in humidity and shrinkage of the wood layers cause internal stresses, the result of which is the appearance of cracks in a given material. They destroy the wood from the forehead and on its surface. This can be seen on the cross-sections of the wood.
Convergence it is a changed shape of the trunk. It is the decreasing diameter of a round timber. After sawing the wood with this defect, the fibers are not parallel to the axis of the element, the so-called. twist of fibers. As a result, the strength of the lumber is reduced. Other significant defects of the trunk shape are the eccentricity of the core and the double core (two trunks fused together).
The last one, however, is equally important the disadvantage of wood is its unnatural color. It may be caused by blue stain, which increases the hygroscopicity of the material. The discoloration of the wood is also caused by rot – development of the fungus. Hard rot is the initial stage of development which causes a pink color change. Soft rot is the further development of the fungus, causes more damage. Infested wood has a lower strength and becomes softer. This material deforms much more than the material not infected with the fungus.
Wood defects have a significant impact on the performance properties of this material, therefore we should know them and be aware of the dangers, to be able to face them in the implementation of wooden structures.