Wood properties, grades, protection

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Overview:

(1) Characteristics of wood: light weight, high strength; good elasticity and toughness; low thermal conductivity; good decorative; good durability; soft material. Disadvantages are: anisotropy, large deformation, perishable, flammable and so on.

(2) Properties of wood: mainly including water content, swelling, shrinkage, strength and other properties.

Moisture content: There are three main types of moisture in wood, namely free water, adsorbed water and combined water. When there is no free water in the wood and the adsorbed water in the cell wall reaches saturation, the moisture content of the wood at this time is called the fiber saturation point. The fiber saturation point is the turning point in the change in the properties of wood. The moisture contained in the wood changes with the temperature and humidity of the environment. When the wood is in a certain temperature and humidity environment for a long time, the water content in the wood will eventually reach equilibrium with the surrounding environment, and the moisture content of the wood is called the equilibrium moisture content.

Swelling and shrinkage deformation: When the moisture content of wood is below the fiber saturation point, the volume of wood expands as the moisture content increases. When the moisture content of the wood is above the fiber saturation point, the volume of the wood does not change when only the free water increases or decreases.

Wood strength: The strengths commonly used in wood are tensile strength, compressive strength, flexural strength and shear strength. The strength of the wood is divided into the strength of the grain and the strength of the grain. The strength of the grain of the wood is much greater than the strength of the grain, and the strength of the grain of the wood is fully utilized in engineering. In theory, the tensile strength of the wood is the largest, followed by the flexural strength and the tensile strength.

The main influencing factors of wood strength: water content, load time, temperature and rickets.

(3) Grade and protection of wood

Wood is usually divided into one, two, three, four, etc., depending on the defect of the wood. Wood for structural and decorative use generally uses a higher grade of wood.

According to the force requirements of the load-bearing structure, the wood is classified into three levels: I, II and III. Generally, the I grade material is used for the tensioned or bent member; the II grade material is used for the bent or pressed member; the III grade material is used for the pressed member and the secondary bent member.

Preservation of wood: First, destroy the living conditions of fungi, and second, apply chemical preservatives. Chemical preservatives are classified into water-soluble preservatives, oily preservatives, and paste preservatives.

Fire protection of wood: mainly surface coating method and solution infusion method.

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